Stability of the Einstein static universe in f(R, T) gravity

International Nuclear Information System (INIS)

Shabani, Hamid; Ziaie, Amir Hadi

2017-01-01

The Einstein static (ES) universe has played a major role in various emergent scenarios recently proposed in order to cure the problem of the initial singularity of the standard model of cosmology. In the model we address, we study the existence and stability of an ES universe in the context of f(R, T) modified theories of gravity. Considering specific forms of the f(R, T) function, we seek for the existence of solutions representing ES state. Using dynamical system techniques along with numerical analysis, we find two classes of solutions: the first one is always unstable of the saddle type, while the second is always stable so that its dynamical behavior corresponds to a center equilibrium point. The importance of the second class of solutions is due to the significant role they play in constructing non-singular emergent models in which the universe could have experienced past-eternally a series of infinite oscillations about such an initial static state after which it enters, through a suitable physical mechanism, to an inflationary era. Considering specific forms for the functionality of f(R, T), we show that this theory is capable of providing cosmological solutions which admit emergent universe (EU) scenarios. We also investigate homogeneous scalar perturbations for the mentioned models. The stability regions of the solutions are parametrized by a linear equation of state (EoS) parameter and other free parameters that will be introduced for the models. Our results suggest that modifications in f(R, T) gravity would lead to stable solutions which are unstable in f(R) gravity model. (orig.)

Design strategies for the International Space University's variable gravity research facility

Science.gov (United States)

Bailey, Sheila G.; Chiaramonte, Francis P.; Davidian, Kenneth J.

1990-01-01

A variable gravity research facility named 'Newton' was designed by 58 students from 13 countries at the International Space University's 1989 summer session at the Universite Louis Pasteur, Strasbourge, France. The project was comprehensive in scope, including a political and legal foundation for international cooperation, development and financing; technical, science and engineering issues; architectural design; plausible schedules; and operations, crew issues and maintenance. Since log-term exposure to zero gravity is known to be harmful to the human body, the main goal was to design a unique variable gravity research facility which would find a practical solution to this problem, permitting a manned mission to Mars. The facility would not duplicate other space-based facilities and would provide the flexibility for examining a number of gravity levels, including lunar and Martian gravities. Major design alternatives included a truss versus a tether based system which also involved the question of docking while spinning or despinning to dock. These design issues are described. The relative advantages or disadvantages are discussed, including comments on the necessary research and technology development required for each.

Emergence of a classical Universe from quantum gravity and cosmology.

Science.gov (United States)

Kiefer, Claus

2012-09-28

I describe how we can understand the classical appearance of our world from a universal quantum theory. The essential ingredient is the process of decoherence. I start with a general discussion in ordinary quantum theory and then turn to quantum gravity and quantum cosmology. There is a whole hierarchy of classicality from the global gravitational field to the fluctuations in the cosmic microwave background, which serve as the seeds for the structure in the Universe.

Universal aspects of gravity localized on thick branes

International Nuclear Information System (INIS)

Csaki, Csaba; Erlich, Joshua; Hollowood, Timothy J.; Shirman, Yuri

2000-01-01

We study gravity in backgrounds that are smooth generalizations of the Randall-Sundrum model, with and without scalar fields. These generalizations include three-branes in higher dimensional spaces which are not necessarily anti-de Sitter far from the branes, intersecting brane configurations and configurations involving negative tension branes. We show that under certain mild assumptions there is a universal equation for the gravitational fluctuations. We study both the graviton ground state and the continuum of Kaluza-Klein modes and we find that the four-dimensional gravitational mode is localized precisely when the effects of the continuum modes decouple at distances larger than the fundamental Planck scale. The decoupling is contingent only on the long-range behaviour of the metric from the brane and we find a universal form for the corrections to Newton's law. We also comment on the possible contribution of resonant modes. Given this, we find general classes of metrics which maintain localized four-dimensional gravity. We find that three-brane metrics in five dimensions can arise from a single scalar field source, and we rederive the BPS type conditions without any a priori assumptions regarding the form of the scalar potential. We also show that a single scalar field cannot produce conformally-flat locally intersecting brane configurations or a p-brane in greater than (p+2)-dimensions

Self-accelerated Universe Induced by Repulsive Effects as an Alternative to Dark Energy and Modified Gravities

Science.gov (United States)

Luongo, Orlando; Quevedo, Hernando

2018-01-01

The existence of current-time universe's acceleration is usually modeled by means of two main strategies. The first makes use of a dark energy barotropic fluid entering by hand the energy-momentum tensor of Einstein's theory. The second lies on extending the Hilbert-Einstein action giving rise to the class of extended theories of gravity. In this work, we propose a third approach, derived as an intrinsic geometrical effect of space-time, which provides repulsive regions under certain circumstances. We demonstrate that the effects of repulsive gravity naturally emerge in the field of a homogeneous and isotropic universe. To this end, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. Moreover, we show that repulsive gravity counterbalances the standard gravitational attraction influencing both late and early times of the universe evolution. This phenomenon leads to the present speed up and to the fast expansion due to the inflationary epoch. In so doing, we are able to unify both dark energy and inflation in a single scheme, showing that the universe changes its dynamics when {\\ddot{H}\\over H}=-2 \\dot{H}, at the repulsion onset time where this condition is satisfied. Further, we argue that the spatial scalar curvature can be taken as vanishing because it does not affect at all the emergence of repulsive gravity. We check the goodness of our approach through two cosmological fits involving the most recent union 2.1 supernova compilation.

Universality of isothermal fluid spheres in Lovelock gravity

Science.gov (United States)

Dadhich, Naresh; Hansraj, Sudan; Maharaj, Sunil D.

2016-02-01

We show universality of isothermal fluid spheres in pure Lovelock gravity where the equation of motion has only one N th order term coming from the corresponding Lovelock polynomial action of degree N . Isothermality is characterized by the equation of state, p =α ρ and the property, ρ ˜1 /r2 N . Then the solution describing isothermal spheres, which exist only for the pure Lovelock equation, is of the same form for the general Lovelock degree N in all dimensions d ≥2 N +2 . We further prove that the necessary and sufficient condition for the isothermal sphere is that its metric is conformal to the massless global monopole or the solid angle deficit metric, and this feature is also universal.

Evolution of universes in quadratic theories of gravity

International Nuclear Information System (INIS)

Barrow, John D.; Hervik, Sigbjoern

2006-01-01

We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Because of the complicated nature of the equations of motion we focus on the stability of exact solutions and find that there exists an isotropic Friedmann-Robertson-Walker (FRW) universe acting as a past attractor. This may indicate that there is an isotropization mechanism at early times for these kind of theories. We also discuss the Kasner universes, elucidate the associated center manifold structure, and show that there exists a set of nonzero measure which has the Kasner solutions as a past attractor. Regarding the late-time behavior, the stability shows a dependence of the parameters of the theory. We give the conditions under which the de Sitter solution is stable and also show that for certain values of the parameters there is a possible late-time behavior with phantomlike behavior. New types of anisotropic inflationary behavior are found which do not have counterparts in general relativity

Stability of Einstein static universe in gravity theory with a non-minimal derivative coupling

Energy Technology Data Exchange (ETDEWEB)

Huang, Qihong [Hunan Normal University, Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications, Changsha, Hunan (China); Zunyi Normal College, School of Physics and Electronic Science, Zunyi (China); Wu, Puxun [Hunan Normal University, Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications, Changsha, Hunan (China); Peking University, Center for High Energy Physics, Beijing (China); Yu, Hongwei [Hunan Normal University, Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications, Changsha, Hunan (China)

2018-01-15

The emergent mechanism provides a possible way to resolve the big-bang singularity problem by assuming that our universe originates from the Einstein static (ES) state. Thus, the existence of a stable ES solution becomes a very crucial prerequisite for the emergent scenario. In this paper, we study the stability of an ES universe in gravity theory with a non-minimal coupling between the kinetic term of a scalar field and the Einstein tensor. We find that the ES solution is stable under both scalar and tensor perturbations when the model parameters satisfy certain conditions, which indicates that the big-bang singularity can be avoided successfully by the emergent mechanism in the non-minimally kinetic coupled gravity. (orig.)

Stability of Einstein static universe in gravity theory with a non-minimal derivative coupling

Science.gov (United States)

Huang, Qihong; Wu, Puxun; Yu, Hongwei

2018-01-01

The emergent mechanism provides a possible way to resolve the big-bang singularity problem by assuming that our universe originates from the Einstein static (ES) state. Thus, the existence of a stable ES solution becomes a very crucial prerequisite for the emergent scenario. In this paper, we study the stability of an ES universe in gravity theory with a non-minimal coupling between the kinetic term of a scalar field and the Einstein tensor. We find that the ES solution is stable under both scalar and tensor perturbations when the model parameters satisfy certain conditions, which indicates that the big-bang singularity can be avoided successfully by the emergent mechanism in the non-minimally kinetic coupled gravity.

Universality of quantum gravity corrections.

Science.gov (United States)

Das, Saurya; Vagenas, Elias C

2008-11-28

We show that the existence of a minimum measurable length and the related generalized uncertainty principle (GUP), predicted by theories of quantum gravity, influence all quantum Hamiltonians. Thus, they predict quantum gravity corrections to various quantum phenomena. We compute such corrections to the Lamb shift, the Landau levels, and the tunneling current in a scanning tunneling microscope. We show that these corrections can be interpreted in two ways: (a) either that they are exceedingly small, beyond the reach of current experiments, or (b) that they predict upper bounds on the quantum gravity parameter in the GUP, compatible with experiments at the electroweak scale. Thus, more accurate measurements in the future should either be able to test these predictions, or further tighten the above bounds and predict an intermediate length scale between the electroweak and the Planck scale.

Cosmic acceleration in a dust only universe via energy-momentum powered gravity

Science.gov (United States)

Akarsu, Özgür; Katırcı, Nihan; Kumar, Suresh

2018-01-01

We propose a modified theory of gravitation constructed by the addition of the term f (Tμ νTμ ν) to the Einstein-Hilbert action, and elaborate a particular case f (Tμ νTμ ν)=α (Tμ νTμ ν)η, where α and η are real constants, dubbed energy-momentum powered gravity (EMPG). We search for viable cosmologies arising from EMPG, especially in the context of the late-time accelerated expansion of the Universe. We investigate the ranges of the EMPG parameters (α ,η ) on theoretical as well as observational grounds leading to the late-time acceleration of the Universe with pressureless matter only, while keeping the successes of standard general relativity at early times. We find that η =0 corresponds to the Λ CDM model, whereas η ≠0 leads to a w CDM -type model. However, the underlying physics of the EMPG model is entirely different in the sense that the energy in the EMPG Universe is sourced by pressureless matter only. Moreover, the energy of the pressureless matter is not conserved, namely, in general it does not dilute as ρ ∝a-3 with the expansion of the Universe. Finally, we constrain the parameters of an EMPG-based cosmology with a recent compilation of 28 Hubble parameter measurements, and find that this model describes an evolution of the Universe similar to that in the Λ CDM model. We briefly discuss that EMPG can be unified with Starobinsky gravity to describe the complete history of the Universe including the inflationary era.

Astrophysical tests of modified gravity: Constraints from distance indicators in the nearby universe

Energy Technology Data Exchange (ETDEWEB)

Jain, Bhuvnesh; Vikram, Vinu [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Sakstein, Jeremy [Department of Applied Mathematics and Theoretical Physics, Cambridge CB3 0WA (United Kingdom)

2013-12-10

We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators—cepheids, tip of the red giant branch (TRGB) stars, and water masers—operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered (in opposite directions) over a range of chameleon gravity theory parameters well below the sensitivity of cosmological probes. Using published data, we have compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. We use a comparable set of screened galaxies as a control sample. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background field value), we obtain constraints on both the chameleon and symmetron screening scenarios. In particular we show that f(R) models with background field values f {sub R0} above 5 × 10{sup –7} are ruled out at the 95% confidence level. We also compare TRGB and maser distances to the galaxy NGC 4258 as a second test for larger field values. While there are several approximations and caveats in our study, our analysis demonstrates the power of gravity tests in the local universe. We discuss the prospects for additional improved tests with future observations.

Astrophysical tests of modified gravity: Constraints from distance indicators in the nearby universe

International Nuclear Information System (INIS)

Jain, Bhuvnesh; Vikram, Vinu; Sakstein, Jeremy

2013-01-01

We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators—cepheids, tip of the red giant branch (TRGB) stars, and water masers—operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered (in opposite directions) over a range of chameleon gravity theory parameters well below the sensitivity of cosmological probes. Using published data, we have compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. We use a comparable set of screened galaxies as a control sample. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background field value), we obtain constraints on both the chameleon and symmetron screening scenarios. In particular we show that f(R) models with background field values f R0 above 5 × 10 –7 are ruled out at the 95% confidence level. We also compare TRGB and maser distances to the galaxy NGC 4258 as a second test for larger field values. While there are several approximations and caveats in our study, our analysis demonstrates the power of gravity tests in the local universe. We discuss the prospects for additional improved tests with future observations.

Radiation perturbation theory in gravity and quantum universe as a hydrogen atom

International Nuclear Information System (INIS)

Pervushin, V.N.

1992-01-01

In quantum theory of gravity of the (n+1)-dimensional space-time the Faddeev-Popov functional integral is constructed for radiation perturbation theory. In this version the Universe expansion looks as the collective superfluid motion of quantum space, and the vacuum energy density plays the role of the hidden mass. 6 refs

f(R,T,R{sub μν}T{sup μν}) gravity phenomenology and ΛCDM universe

Energy Technology Data Exchange (ETDEWEB)

Odintsov, Sergei D., E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain); Institut de Ciències de l' Espai ICE (CSIC-IEEC), Campus UAB Facultat de Ciències, Torre C5-Parell-2a pl, E-08193 Bellaterra (Barcelona) (Spain); Sáez-Gómez, Diego, E-mail: diego.saezgomez@uct.ac.za [Astrophysics, Cosmology and Gravity Centre (ACGC) and Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town (South Africa); Fisika Teorikoaren eta Zientziaren Historia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, 644 Posta Kutxatila, 48080 Bilbao (Spain)

2013-10-01

We propose general f(R,T,R{sub μν}T{sup μν}) theory as generalization of covariant Hořava-like gravity with dynamical Lorentz symmetry breaking. FRLW cosmological dynamics for several versions of such theory is considered. The reconstruction of the above action is explicitly done, including the numerical reconstruction for the occurrence of ΛCDM universe. De Sitter universe solutions in the presence of non-constant fluid are also presented. The problem of matter instability in f(R,T,R{sub μν}T{sup μν}) gravity is discussed.

Stability of the Kasner universe in f (T ) gravity

Science.gov (United States)

Paliathanasis, Andronikos; Said, Jackson Levi; Barrow, John D.

2018-02-01

f (T ) gravity theory offers an alternative context in which to consider gravitational interactions where torsion, rather than curvature, is the mechanism by which gravitation is communicated. We investigate the stability of the Kasner solution with several forms of the arbitrary Lagrangian function examined within the f (T ) context. This is a Bianchi type-I vacuum solution with anisotropic expansion factors. In the f (T ) gravity setting, the solution must conform to a set of conditions in order to continue to be a vacuum solution of the generalized field equations. With this solution in hand, the perturbed field equations are determined for power-law and exponential forms of the f (T ) function. We find that the point which describes the Kasner solution is a saddle point which means that the singular solution is unstable. However, we find the de Sitter universe is a late-time attractor. In general relativity, the cosmological constant drives the isotropization of the spacetime while in this setting the extra f (T ) contributions now provide this impetus.

Accelerated Expansion of the Universe: Dark Energy or modifications to the theory of gravity to Einstein?

International Nuclear Information System (INIS)

Quiros, I.

2008-01-01

Full text: An overview of the state of the art in modern astrophysics and cosmology is given, emphasizing the 'Dark Energy Problem', one of the fundamental problems of theoretical physics at present. In particular is analyzed the possibility that the universe could be a three-dimensional membrane embedded in a higher dimensional space. These models known as 'brane worlds' can explain the present accelerated expansion of the Universe as dissipation due to gravity at cosmological scales extra or limit space infrared (IR). However there are many other problems to solve, including the problem of 'ghost' modes that are inevitable in any IR modification of gravity. (author)

Astrophysical tests of gravity: a screening map of the nearby universe

Energy Technology Data Exchange (ETDEWEB)

Cabré, Anna; Vikram, Vinu; Jain, Bhuvnesh [Center for Particle Cosmology, Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104-6396 (United States); Zhao, Gong-Bo; Koyama, Kazuya, E-mail: annanusca@gmail.com, E-mail: vinu@sas.upenn.edu, E-mail: gong-bo.zhao@port.ac.uk, E-mail: bjain@physics.upenn.edu, E-mail: Kazuya.Koyama@port.ac.uk [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth, PO1 3FX (United Kingdom)

2012-07-01

Astrophysical tests of modified gravity theories in the nearby universe have been emphasized recently by Hui 2009 and Jain 2011. A key element of such tests is the screening mechanism whereby general relativity is restored in massive halos or high density environments like the Milky Way. In chameleon theories of gravity, including all f(R) models, field dwarf galaxies may be unscreened and therefore feel an extra force, as opposed to screened galaxies. The first step to study differences between screened and unscreened galaxies is to create a 3D screening map. We use N-body simulations to test and calibrate simple approximations to determine the level of screening in galaxy catalogs. Sources of systematic errors in the screening map due to observational inaccuracies are modeled and their contamination is estimated. We then apply our methods to create a map out to 200 Mpc in the Sloan Digital Sky Survey footprint using data from the Sloan survey and other sources. In two companion papers this map will be used to carry out new tests of gravity using distance indicators and the disks of dwarf galaxies. We also make our screening map publicly available.

Is higher-derivative gravity a good therapy to the causal pathologies of Goedel-type universes

International Nuclear Information System (INIS)

Accioly, A.J.

1988-01-01

The possibility of considering higher-derivative gravity as a therapy to the causal pathologies of Goedel-type universes is investigated. As a consequence an unusual cosmological solution is obtained. (author) [pt

Open FRW universes and self-acceleration from nonlinear massive gravity

International Nuclear Information System (INIS)

Gümrükçüoğlu, A. Emir; Lin, Chunshan; Mukohyama, Shinji

2011-01-01

In the context of a recently proposed nonlinear massive gravity with Lorentz-invariant mass terms, we investigate open Friedmann-Robertson-Walker (FRW) universes driven by arbitrary matter source. While the flat FRW solutions were recently shown to be absent, the proof does not extend to the open universes. We find three independent branches of solutions to the equations of motion for the Stückelberg scalars. One of the branches does not allow any nontrivial FRW cosmologies, as in the previous no-go result. On the other hand, both of the other two branches allow general open FRW universes governed by the Friedmann equation with the matter source, the standard curvature term and an effective cosmological constant Λ ± = c ± m g 2 . Here, m g is the graviton mass, + and - represent the two branches, and c ± are constants determined by the two dimensionless parameters of the theory. Since an open FRW universe with a sufficiently small curvature constant can approximate a flat FRW universe but there is no exactly flat FRW solution, the theory exhibits a discontinuity at the flat FRW limit

Anamorphic quasiperiodic universes in modified and Einstein gravity with loop quantum gravity corrections

Science.gov (United States)

Amaral, Marcelo M.; Aschheim, Raymond; Bubuianu, Laurenţiu; Irwin, Klee; Vacaru, Sergiu I.; Woolridge, Daniel

2017-09-01

The goal of this work is to elaborate on new geometric methods of constructing exact and parametric quasiperiodic solutions for anamorphic cosmology models in modified gravity theories, MGTs, and general relativity, GR. There exist previously studied generic off-diagonal and diagonalizable cosmological metrics encoding gravitational and matter fields with quasicrystal like structures, QC, and holonomy corrections from loop quantum gravity, LQG. We apply the anholonomic frame deformation method, AFDM, in order to decouple the (modified) gravitational and matter field equations in general form. This allows us to find integral varieties of cosmological solutions determined by generating functions, effective sources, integration functions and constants. The coefficients of metrics and connections for such cosmological configurations depend, in general, on all spacetime coordinates and can be chosen to generate observable (quasi)-periodic/aperiodic/fractal/stochastic/(super) cluster/filament/polymer like (continuous, stochastic, fractal and/or discrete structures) in MGTs and/or GR. In this work, we study new classes of solutions for anamorphic cosmology with LQG holonomy corrections. Such solutions are characterized by nonlinear symmetries of generating functions for generic off-diagonal cosmological metrics and generalized connections, with possible nonholonomic constraints to Levi-Civita configurations and diagonalizable metrics depending only on a time like coordinate. We argue that anamorphic quasiperiodic cosmological models integrate the concept of quantum discrete spacetime, with certain gravitational QC-like vacuum and nonvacuum structures. And, that of a contracting universe that homogenizes, isotropizes and flattens without introducing initial conditions or multiverse problems.

UNIVERSE IN A BLACK HOLE IN EINSTEIN–CARTAN GRAVITY

Energy Technology Data Exchange (ETDEWEB)

Popławski, Nikodem, E-mail: NPoplawski@newhaven.edu [Department of Mathematics and Physics, University of New Haven, 300 Boston Post Road, West Haven, CT 06516 (United States)

2016-12-01

The conservation law for the angular momentum in curved spacetime, consistent with relativistic quantum mechanics, requires that the antisymmetric part of the affine connection (torsion tensor) is a variable in the principle of least action. The coupling between the spin of elementary particles and torsion in the Einstein–Cartan theory of gravity generates gravitational repulsion at extremely high densities in fermionic matter, approximated as a spin fluid, and thus avoids the formation of singularities in black holes. The collapsing matter in a black hole should therefore bounce at a finite density and then expand into a new region of space on the other side of the event horizon, which may be regarded as a nonsingular, closed universe. We show that quantum particle production caused by an extremely high curvature near a bounce can create enormous amounts of matter, produce entropy, and generate a finite period of exponential expansion (inflation) of this universe. This scenario can thus explain inflation without a scalar field and reheating. We show that, depending on the particle production rate, such a universe may undergo several nonsingular bounces until it has enough matter to reach a size at which the cosmological constant starts cosmic acceleration. The last bounce can be regarded as the big bang of this universe.

Universe in a Black Hole in Einstein-Cartan Gravity

Science.gov (United States)

Popławski, Nikodem

2016-12-01

The conservation law for the angular momentum in curved spacetime, consistent with relativistic quantum mechanics, requires that the antisymmetric part of the affine connection (torsion tensor) is a variable in the principle of least action. The coupling between the spin of elementary particles and torsion in the Einstein-Cartan theory of gravity generates gravitational repulsion at extremely high densities in fermionic matter, approximated as a spin fluid, and thus avoids the formation of singularities in black holes. The collapsing matter in a black hole should therefore bounce at a finite density and then expand into a new region of space on the other side of the event horizon, which may be regarded as a nonsingular, closed universe. We show that quantum particle production caused by an extremely high curvature near a bounce can create enormous amounts of matter, produce entropy, and generate a finite period of exponential expansion (inflation) of this universe. This scenario can thus explain inflation without a scalar field and reheating. We show that, depending on the particle production rate, such a universe may undergo several nonsingular bounces until it has enough matter to reach a size at which the cosmological constant starts cosmic acceleration. The last bounce can be regarded as the big bang of this universe.

Cosmological tests of modified gravity.

Science.gov (United States)

Koyama, Kazuya

2016-04-01

We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.

Gravity, Magnetism, and "Down": Non-Physics College Students' Conceptions of Gravity

Science.gov (United States)

Asghar, Anila; Libarkin, Julie C.

2010-01-01

This study investigates how students enrolled in entry-level geology, most of whom would graduate from college without university-level physics courses, thought about and applied the concept of gravity while solving problems concerning gravity. The repercussions of students' gravity concepts are then considered in the context of non-physics…

Gravity a very short introduction

CERN Document Server

Clifton, Timothy

2017-01-01

Gravity is one of the four fundamental interactions that exist in nature. It also has the distinction of being the oldest, weakest, and most difficult force to quantize. Understanding gravity is not only essential for understanding the motion of objects on Earth, but also the motion of all celestial objects, and even the expansion of the Universe itself. It was the study of gravity that led Einstein to his profound realizations about the nature of space and time. Gravity is not only universal, it is also essential for understanding the behavior of the Universe, and all astrophysical bodies within it. In this Very Short Introduction Timothy Clifton looks at the development of our understanding of gravity since the early observations of Kepler and Newtonian theory. He discusses Einstein's theory of gravity, which now supplants Newton's, showing how it allows us to understand why the frequency of light changes as it passes through a gravitational field, why GPS satellites need their clocks corrected as they orbi...

Gravity how the weakest force in the universe shaped our lives

CERN Document Server

Clegg, Brian

2012-01-01

Gravity is one of the most accepted laws of science. Drop an object and it falls to earth because of the attraction between the earth and the object. What alerts the earth and the object to act? Is there a sort of communication between them? Theoretical physicists have struggled to explain gravitational attraction over distance since Einstein posed his theories of special and general relativity. Quantum theory, string theory, M theory, and other theoretical inquiries have failed to solve the riddle. In his history of gravity from the Big Bang to the present, popular science author Clegg recounts international efforts to understand what is thought to be the weakest yet most essential force holding the universe together. Black holes, warps in space and time, and antimatter are featured in this wide-ranging account, which will be of interest to science students and readers of science fiction.

Late time acceleration of the universe in f(R) gravity model

International Nuclear Information System (INIS)

Mukherjee, Ankan

2014-01-01

In this work, a new way to look at the nature of late time dynamics of the universe for f(R) gravity models using the contracted Bianchi Identity has been proposed. As the Einstein field equations contain derivatives of the curvature scalar R, the contracted Bianchi identity yields a second order nonlinear differential equation in H, the Hubble parameter. This equation is studied for two particular forms of f(R), and the late time behaviour of the model is discussed. (author)

Gravity

CERN Document Server

Gamow, George

2003-01-01

A distinguished physicist and teacher, George Gamow also possessed a special gift for making the intricacies of science accessible to a wide audience. In Gravity, he takes an enlightening look at three of the towering figures of science who unlocked many of the mysteries behind the laws of physics: Galileo, the first to take a close look at the process of free and restricted fall; Newton, originator of the concept of gravity as a universal force; and Einstein, who proposed that gravity is no more than the curvature of the four-dimensional space-time continuum.Graced with the author's own draw

Anisotropic perturbations and stability of a static universe in f(G,T) gravity

Science.gov (United States)

Sharif, M.; Ikram, Ayesha

2017-12-01

The aim of this paper is to analyze the stability of the Einstein universe against anisotropic homogeneous perturbations in f(G,T) gravity ( G and T represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, respectively). The corresponding field equations are constructed for static as well as perturbed configurations in the presence of a perfect fluid. We consider two specific forms of generic function f(G,T) associated with zero as well as non-zero covariant divergence of the energy-momentum tensor and explore the stability regions of the Einstein universe parameterized by the equation of state parameter. It is concluded that a stable Einstein universe exists for an appropriate choice of model parameters.

A Possible Universe in Pulsation by Using a Hydro-Dynamical Model for Gravity

Directory of Open Access Journals (Sweden)

Corneliu BERBENTE

2016-12-01

Full Text Available By using a hydro-dynamical model for gravity previously given by the author, a pulsating universe is possible to describe. This is possible because two hydro-dynamical sources are in attraction both when they are emitting and absorbing fluid. In our model, bodies (matter and energy are interacting via an incompressible fluid made of gravitons (photon-like particles having a wave length of the order of magnitude of the radius of universe. One considers the universe uniform at large scale, the effects of general relativity type being local and negligible at global scale. An “elastic sphere” model for the universe is suggested to describe the possible inversion. The expansion of the universe stops when the “elastic energy” overcomes the kinetic one; this takes place near the point of maximal emission speed of the fluid of gravitons. The differential equation for the universe in expansion is adapted to contraction. Analytical solutions are given.

Generalized Gödel universes in higher dimensions and pure Lovelock gravity

Science.gov (United States)

Dadhich, Naresh; Molina, Alfred; Pons, Josep M.

2017-10-01

The Gödel universe is a homogeneous rotating dust with negative Λ which is a direct product of a three-dimensional pure rotation metric with a line. We would generalize it to higher dimensions for Einstein and pure Lovelock gravity with only one N th-order term. For higher-dimensional generalization, we have to include more rotations in the metric, and hence we shall begin with the corresponding pure rotation odd (d =2 n +1 )-dimensional metric involving n rotations, which eventually can be extended by a direct product with a line or a space of constant curvature for yielding a higher-dimensional Gödel universe. The considerations of n rotations and also of constant curvature spaces is a new line of generalization and is being considered for the first time.

76 FR 44506 - Petition Requesting Non-See-Through Packaging for Torch Fuel and Lamp Oil

Science.gov (United States)

2011-07-26

... weight of petroleum distillates and have a viscosity of less than 100 Saybolt universal seconds at 100... attractive'' to children. Petitioner asserts that certain petroleum distillates, including torch fuel and... taste of juice and are accustomed to drinking it regularly, packaging petroleum distillates in clear...

Emergent Gravity and the Dark Universe

Directory of Open Access Journals (Sweden)

Erik P. Verlinde

2017-05-01

Full Text Available Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional 'dark' gravitational force describing the 'elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a_0 =cH_0, and provide evidence for the fact that this additional `dark gravity~force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.

Towards a Gravity Dual for the Large Scale Structure of the Universe

CERN Document Server

Kehagias, A.

2016-01-01

The dynamics of the large-scale structure of the universe enjoys at all scales, even in the highly non-linear regime, a Lifshitz symmetry during the matter-dominated period. In this paper we propose a general class of six-dimensional spacetimes which could be a gravity dual to the four-dimensional large-scale structure of the universe. In this set-up, the Lifshitz symmetry manifests itself as an isometry in the bulk and our universe is a four-dimensional brane moving in such six-dimensional bulk. After finding the correspondence between the bulk and the brane dynamical Lifshitz exponents, we find the intriguing result that the preferred value of the dynamical Lifshitz exponent of our observed universe, at both linear and non-linear scales, corresponds to a fixed point of the RGE flow of the dynamical Lifshitz exponent in the dual system where the symmetry is enhanced to the Schrodinger group containing a non-relativistic conformal symmetry. We also investigate the RGE flow between fixed points of the Lifshitz...

76 FR 64042 - Petition Requesting Non-See-Through Packaging for Torch Fuel and Lamp Oil

Science.gov (United States)

2011-10-17

... percent or more by weight of petroleum distillates and have a viscosity of less than 100 Saybolt universal... distillates, including torch fuel and lamp oil, as currently packaged, resemble juice. The petitioner notes..., packaging petroleum distillates in clear plastic bottles causes needless danger, as children may mistake it...

Gravity, black holes and the very early Universe an introduction to general relativity and cosmology

CERN Document Server

Chow, Tai L

2008-01-01

In the early 1900s, Albert Einstein formulated two theories that would forever change the landscape of physics: the Special Theory of Relativity and the General Theory of Relativity. By 1925, quantum mechanics had been born out of the dissection of these two theories, and shortly after that, relativistic quantum field theory. We now had in place some important ties between the laws of physics and the types of particle interactions the new physics was uncovering. Gravity is one of the four types of forces that are found throughout the universe. In fact, although it is a relatively weak force, it operates at huge distances, and so must be accounted for in any cosmological system. Unfortunately, gravity continues to defy our neat categorization of how all the forces in nature work together. Professor Tai Chow, from the California State University at Stanislaus in Turlock, lays out for us the basic ideas of Einstein, including his law of gravitation, explains the physics behind black holes, and weaves into this a...

Can the causal pathologies of Goedel-type universes be avoided in higher-derivative gravity

International Nuclear Information System (INIS)

Accioly, A.J.; Goncalves, A.T.

1986-10-01

A completely causal rotating Goedel-type universe is obtained in the context of higher-derivative gravity. The solution is such that it has no similar in the framework of standard general relativity. The aforementioned solution presents the interesting feature of relating the mass of the nontachyonic spin-O particle, concerning the linearized higher-derivative theory, with the velocity of rigid rotation of matter. (Author) [pt

Quantum gravity

International Nuclear Information System (INIS)

Markov, M.A.; West, P.C.

1984-01-01

This book discusses the state of the art of quantum gravity, quantum effects in cosmology, quantum black-hole physics, recent developments in supergravity, and quantum gauge theories. Topics considered include the problems of general relativity, pregeometry, complete cosmological theories, quantum fluctuations in cosmology and galaxy formation, a new inflationary universe scenario, grand unified phase transitions and the early Universe, the generalized second law of thermodynamics, vacuum polarization near black holes, the relativity of vacuum, black hole evaporations and their cosmological consequences, currents in supersymmetric theories, the Kaluza-Klein theories, gauge algebra and quantization, and twistor theory. This volume constitutes the proceedings of the Second Seminar on Quantum Gravity held in Moscow in 1981

Bianchi type-I universe in f(R, T) modified gravity with quark matter and Λ

Science.gov (United States)

Ćaǧlar, Halife; Aygün, Sezgin

2017-02-01

In this study, we investigate homogeneous and anisotropic Bianchi type I universe in the presence of quark matter source in f(R, T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011) with cosmological constant Λ (where R is the Ricci scalar and T is the trace of the energy momentum tensor). For this aim we have used the anisotropy feature of Bianchi type I universe and equation of states (EoS) of quark matter. We explore the exact solution f(R,T)=R+2f(T) model for Bianchi type I universe model. When t→∞, we get very small cosmological constant value, this result agrees with recent observations.

Gravity Data for South America

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National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (152,624 records) were compiled by the University of Texas at Dallas. This data base was received in June 1992. Principal gravity parameters...

Constraining inverse curvature gravity with supernovae

Energy Technology Data Exchange (ETDEWEB)

Mena, Olga; Santiago, Jose; /Fermilab; Weller, Jochen; /University Coll., London /Fermilab

2005-10-01

We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.

Hořava–Lifshitz gravity inspired Bianchi-II cosmology and the mixmaster universe

International Nuclear Information System (INIS)

Giani, Leonardo; Kamenshchik, Alexander Y

2017-01-01

We study different aspects of the Hořava-Lifshitz inspired Bianchi-II cosmology and its relations with the mixmaster universe model. First, we present exact solutions for a toy model, where only the cubic in spatial curvature terms are present in the action; then we briefly discuss some exotic singularities, which can appear in this toy model. We study also the toy model where only the quadratic in spatial curvature terms are present in the action. We establish relations between our results and those obtained by using the Hamiltonian formalism. Finally, we apply the results obtained by studying Bianchi-II cosmology to describe the evolution of the mixmaster universe in terms of the Belinsky–Khalatnikov–Lifshitz formalism. Generally, our analysis gives some arguments in favour of the existence of the oscillatory approach to the singularity in a universe governed by the Hořava–Lifshitz type gravity. (paper)

Cosmology of Horava-Lifshitz f(R) gravity

International Nuclear Information System (INIS)

Chakrabarti, Sayan K.; Sen, Anjan A.

2011-08-01

We discuss the cosmology of recently proposed Horava-Lifshitz f(R) gravity. In particular, we derive the modified Hubble equation that reduces to the standard HL gravity case in appropriate limit. We show how the bounce solutions in this theory are modified due to nonlinear effect of f(R) gravity. In addition we find that the solutions exist when the Universe can make turn around for large scale-factor. Therefore, in principle, the Universe in this set-up can show cyclic behavior. (orig.)

Cosmology of Horava-Lifshitz f(R) gravity

Energy Technology Data Exchange (ETDEWEB)

Chakrabarti, Sayan K. [Univ. Tecnica de Lisboa (Portugal). Inst. Superior Tecnico; Dutta, Koushik [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Sen, Anjan A. [Centre of Theoretical Physics, Jamia Millia Islamia, New Dehli (India)

2011-08-15

We discuss the cosmology of recently proposed Horava-Lifshitz f(R) gravity. In particular, we derive the modified Hubble equation that reduces to the standard HL gravity case in appropriate limit. We show how the bounce solutions in this theory are modified due to nonlinear effect of f(R) gravity. In addition we find that the solutions exist when the Universe can make turn around for large scale-factor. Therefore, in principle, the Universe in this set-up can show cyclic behavior. (orig.)

Light fermions in quantum gravity

International Nuclear Information System (INIS)

Eichhorn, Astrid; Gies, Holger

2011-01-01

We study the impact of quantum gravity, formulated as a quantum field theory of the metric, on chiral symmetry in a fermionic matter sector. Specifically we address the question of whether metric fluctuations can induce chiral symmetry breaking and bound state formation. Our results based on the functional renormalization group indicate that chiral symmetry is left intact even at strong gravitational coupling. In particular, we found that asymptotically safe quantum gravity where the gravitational couplings approach a non-Gaußian fixed point generically admits universes with light fermions. Our results thus further support quantum gravity theories built on fluctuations of the metric field such as the asymptotic-safety scenario. A study of chiral symmetry breaking through gravitational quantum effects may also serve as a significant benchmark test for other quantum gravity scenarios, since a completely broken chiral symmetry at the Planck scale would not be in accordance with the observation of light fermions in our universe. We demonstrate that this elementary observation already imposes constraints on a generic UV completion of gravity. (paper)

Does time exist in quantum gravity?

Directory of Open Access Journals (Sweden)

Claus Kiefer

2015-12-01

Full Text Available Time is absolute in standard quantum theory and dynamical in general relativity. The combination of both theories into a theory of quantum gravity leads therefore to a “problem of time”. In my essay, I investigate those consequences for the concept of time that may be drawn without a detailed knowledge of quantum gravity. The only assumptions are the experimentally supported universality of the linear structure of quantum theory and the recovery of general relativity in the classical limit. Among the consequences are the fundamental timelessness of quantum gravity, the approximate nature of a semiclassical time, and the correlation of entropy with the size of the Universe.

The generalized second law of thermodynamics in generalized gravity theories

International Nuclear Information System (INIS)

Wu Shaofeng; Yang Guohong; Wang Bin; Zhang Pengming

2008-01-01

We investigate the generalized second law of thermodynamics (GSL) in generalized theories of gravity. We examine the total entropy evolution with time including the horizon entropy, the non-equilibrium entropy production, and the entropy of all matter, field and energy components. We derive a universal condition to protect the generalized second law and study its validity in different gravity theories. In Einstein gravity (even in the phantom-dominated universe with a Schwarzschild black hole), Lovelock gravity and braneworld gravity, we show that the condition to keep the GSL can always be satisfied. In f(R) gravity and scalar-tensor gravity, the condition to protect the GSL can also hold because the temperature should be positive, gravity is always attractive and the effective Newton constant should be an approximate constant satisfying the experimental bounds

Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

Science.gov (United States)

Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

2005-01-01

Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

Universal regularization prescription for Lovelock AdS gravity

International Nuclear Information System (INIS)

Kofinas, Georgios; Olea, Rodrigo

2007-01-01

A definite form for the boundary term that produces the finiteness of both the conserved quantities and Euclidean action for any Lovelock gravity with AdS asymptotics is presented. This prescription merely tells even from odd bulk dimensions, regardless the particular theory considered, what is valid even for Einstein-Hilbert and Einstein-Gauss-Bonnet AdS gravity. The boundary term is a given polynomial of the boundary extrinsic and intrinsic curvatures (also referred to as Kounterterms series). Only the coupling constant of the boundary term changes accordingly, such that it always preserves a well-posed variational principle for boundary conditions suitable for asymptotically AdS spaces. The background-independent conserved charges associated to asymptotic symmetries are found. In odd bulk dimensions, this regularization produces a generalized formula for the vacuum energy in Lovelock AdS gravity. The standard entropy for asymptotically AdS black holes is recovered directly from the regularization of the Euclidean action, and not only from the first law of thermodynamics associated to the conserved quantities

Study on Inertia as a Gravity Induced Property of Mass, in an Infinite Hubble Expanding Universe

Directory of Open Access Journals (Sweden)

Jeroen van Engelshoven

2013-01-01

Full Text Available Mass is experienced to have two intrinsic properties: inertia (resistance to acceleration and gravity (attraction to other masses. In this paper we evaluate the gravitational effect of all masses of the universe on an accelerated mass, starting from linearized general relativity. The gravitational interaction of all masses in a finite static universe model is shown to create a finite resistance to acceleration, which is inertia. Then, we propose a generalization of the linearized theory and evaluate the Hubble expanding universe. It is shown that the gravitational impact of an infinite expanding universe creates finite inertia, according to . The Friedmann critical mass density is found to be valid. The Mach principle is made explicit. The value and sign of the gravitational constant G are found to be of no consequence on an astronomical scale.

Towards a quantum gravity

International Nuclear Information System (INIS)

Romney, B.; Barrau, A.; Vidotto, F.; Le Meur, H.; Noui, K.

2011-01-01

The loop quantum gravity is the only theory that proposes a quantum description of space-time and therefore of gravitation. This theory predicts that space is not infinitely divisible but that is has a granular structure at the Planck scale (10 -35 m). Another feature of loop quantum gravity is that it gets rid of the Big-Bang singularity: our expanding universe may come from the bouncing of a previous contracting universe, in this theory the Big-Bang is replaced with a big bounce. The loop quantum theory predicts also the huge number of quantum states that accounts for the entropy of large black holes. (A.C.)

Gravity Data for Indiana (300 records compiled)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The gravity data (300 records) were compiled by Purdue University. This data base was received in February 1993. Principal gravity parameters include Free-air...

Gravity Data for the Greater Portland Area

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National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (1,522 records) were compiled by the Portland State University. This data base was received in August 1990. Principal gravity parameters...

Scaling in quantum gravity

Directory of Open Access Journals (Sweden)

J. Ambjørn

1995-07-01

Full Text Available The 2-point function is the natural object in quantum gravity for extracting critical behavior: The exponential falloff of the 2-point function with geodesic distance determines the fractal dimension dH of space-time. The integral of the 2-point function determines the entropy exponent γ, i.e. the fractal structure related to baby universes, while the short distance behavior of the 2-point function connects γ and dH by a quantum gravity version of Fisher's scaling relation. We verify this behavior in the case of 2d gravity by explicit calculation.

Cosmological dynamics of mimetic gravity

Science.gov (United States)

Dutta, Jibitesh; Khyllep, Wompherdeiki; Saridakis, Emmanuel N.; Tamanini, Nicola; Vagnozzi, Sunny

2018-02-01

We present a detailed investigation of the dynamical behavior of mimetic gravity with a general potential for the mimetic scalar field. Performing a phase-space and stability analysis, we show that the scenario at hand can successfully describe the thermal history of the universe, namely the successive sequence of radiation, matter, and dark-energy eras. Additionally, at late times the universe can either approach a de Sitter solution, or a scaling accelerated attractor where the dark-matter and dark-energy density parameters are of the same order, thus offering an alleviation of the cosmic coincidence problem. Applying our general analysis to various specific potential choices, including the power-law and the exponential ones, we show that mimetic gravity can be brought into good agreement with the observed behavior of the universe. Moreover, with an inverse square potential we find that mimetic gravity offers an appealing unified cosmological scenario where both dark energy and dark matter are characterized by a single scalar field, and where the cosmic coincidence problem is alleviated.

BOOK REVIEW: Canonical Gravity and Applications: Cosmology, Black Holes, and Quantum Gravity Canonical Gravity and Applications: Cosmology, Black Holes, and Quantum Gravity

Science.gov (United States)

Husain, Viqar

2012-03-01

researchers in other areas who wish to learn about the canonical approach to gravity. However, given the brief chapter on quantization, the book would go well with a review paper, or parts of the other three quantum gravity books cited above. References [1] Kiefer C 2006 Quantum Gravity 2nd ed. (Oxford University Press) [2] Rovelli C 2007 Quantum Gravity (Cambridge University Press) [3] Thiemann T 2008 Modern Canonical Quantum Gravity (Cambridge University Press) [4] Posson E 2004 A Relativist's Toolkit: The Mathematics of Black-Hole Mechanics (Cambridge University Press) [5] Ryan M P and Shepley L C 1975 Homogeneous Relativistic Cosmology (Princeton University Press)

Colossal creations of gravity

DEFF Research Database (Denmark)

Skielboe, Andreas

Gravity governs the evolution of the universe on the largest scales, and powers some of the most extreme objects at the centers of galaxies. Determining the masses and kinematics of galaxy clusters provides essential constraints on the large-scale structure of the universe, and act as direct probes...

Measuring wood specific gravity, correctly

Science.gov (United States)

G. Bruce Williamson; Michael C. Wiemann

2010-01-01

The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a forester’s variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these...

Fractal universe and quantum gravity.

Science.gov (United States)

Calcagni, Gianluca

2010-06-25

We propose a field theory which lives in fractal spacetime and is argued to be Lorentz invariant, power-counting renormalizable, ultraviolet finite, and causal. The system flows from an ultraviolet fixed point, where spacetime has Hausdorff dimension 2, to an infrared limit coinciding with a standard four-dimensional field theory. Classically, the fractal world where fields live exchanges energy momentum with the bulk with integer topological dimension. However, the total energy momentum is conserved. We consider the dynamics and the propagator of a scalar field. Implications for quantum gravity, cosmology, and the cosmological constant are discussed.

Vacuum stability in the early universe and the backreaction of classical gravity.

Science.gov (United States)

Markkanen, Tommi

2018-03-06

In the case of a metastable electroweak vacuum, the quantum corrected effective potential plays a crucial role in the potential instability of the standard model. In the early universe, in particular during inflation and reheating, this instability can be triggered leading to catastrophic vacuum decay. We discuss how the large space-time curvature of the early universe can be incorporated in the calculation and in many cases significantly modify the flat space prediction. The two key new elements are the unavoidable generation of the non-minimal coupling between the Higgs field and the scalar curvature of gravity and a curvature induced contribution to the running of the constants. For the minimal set up of the standard model and a decoupled inflation sector we show how a metastable vacuum can lead to very tight bounds for the non-minimal coupling. We also discuss a novel and very much related dark matter generation mechanism.This article is part of the Theo Murphy meeting issue 'Higgs cosmology'. © 2018 The Author(s).

On higher derivative gravity

International Nuclear Information System (INIS)

Accioly, A.J.

1987-01-01

A possible classical route conducting towards a general relativity theory with higher-derivatives starting, in a sense, from first principles, is analysed. A completely causal vacuum solution with the symmetries of the Goedel universe is obtained in the framework of this higher-derivative gravity. This very peculiar and rare result is the first known vcuum solution of the fourth-order gravity theory that is not a solution of the corresponding Einstein's equations.(Author) [pt

Cosmological footprints of loop quantum gravity.

Science.gov (United States)

Grain, J; Barrau, A

2009-02-27

The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated corrections should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity.

Stochastic quantum gravity-(2+1)-dimensional case

International Nuclear Information System (INIS)

Hosoya, Akio

1991-01-01

At first the amazing coincidences are pointed out in quantum field theory in curved space-time and quantum gravity, when they exhibit stochasticity. To explore the origin of them, the (2+1)-dimensional quantum gravity is considered as a toy model. It is shown that the torus universe in the (2+1)-dimensional quantum gravity is a quantum chaos in a rigorous sense. (author). 15 refs

Hairs of discrete symmetries and gravity

Energy Technology Data Exchange (ETDEWEB)

Choi, Kang Sin [Scranton Honors Program, Ewha Womans University, Seodaemun-Gu, Seoul 03760 (Korea, Republic of); Center for Fields, Gravity and Strings, CTPU, Institute for Basic Sciences, Yuseong-Gu, Daejeon 34047 (Korea, Republic of); Kim, Jihn E., E-mail: jihnekim@gmail.com [Department of Physics, Kyung Hee University, 26 Gyungheedaero, Dongdaemun-Gu, Seoul 02447 (Korea, Republic of); Center for Axion and Precision Physics Research (IBS), 291 Daehakro, Yuseong-Gu, Daejeon 34141 (Korea, Republic of); Kyae, Bumseok [Department of Physics, Pusan National University, 2 Busandaehakro-63-Gil, Geumjeong-Gu, Busan 46241 (Korea, Republic of); Nam, Soonkeon [Department of Physics, Kyung Hee University, 26 Gyungheedaero, Dongdaemun-Gu, Seoul 02447 (Korea, Republic of)

2017-06-10

Gauge symmetries are known to be respected by gravity because gauge charges carry flux lines, but global charges do not carry flux lines and are not conserved by gravitational interaction. For discrete symmetries, they are spontaneously broken in the Universe, forming domain walls. Since the realization of discrete symmetries in the Universe must involve the vacuum expectation values of Higgs fields, a string-like configuration (hair) at the intersection of domain walls in the Higgs vacua can be realized. Therefore, we argue that discrete charges are also respected by gravity.

Hairs of discrete symmetries and gravity

Directory of Open Access Journals (Sweden)

Kang Sin Choi

2017-06-01

Full Text Available Gauge symmetries are known to be respected by gravity because gauge charges carry flux lines, but global charges do not carry flux lines and are not conserved by gravitational interaction. For discrete symmetries, they are spontaneously broken in the Universe, forming domain walls. Since the realization of discrete symmetries in the Universe must involve the vacuum expectation values of Higgs fields, a string-like configuration (hair at the intersection of domain walls in the Higgs vacua can be realized. Therefore, we argue that discrete charges are also respected by gravity.

Gravity Data for Indiana-over 10,000 records

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The gravity data (10,629 records) were compiled by Purdue University. This data base was received in December 1989. Principal gravity parameters include Free-air...

Cosmological acceleration. Dark energy or modified gravity?

International Nuclear Information System (INIS)

Bludman, S.

2006-05-01

We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model ΛCDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)

Cosmological acceleration. Dark energy or modified gravity?

Energy Technology Data Exchange (ETDEWEB)

Bludman, S

2006-05-15

We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)

New View on Quantum Gravity:. Micro-Structure of Spacetime and Origin of the Universe

Science.gov (United States)

Hu, B. L.

2008-04-01

It is generally agreed that the primary goal of quantum gravity is to find the microscopic structure of spacetime. However, for the last half a century the cardinal principle upheld by most general relativists has been to find ways to quantize Einstein's general theory of relativity, a theory which has proven to be highly successful in describing the macroscopic structure of spacetime we live in today. A tacit assumption in this existing paradigm is that doing so will yield the micro-structures of spacetime. We challenge this supposition and present a different view. If general relativity is an effective theory valid only at the long wavelength and low energy limits, and the metric and connection forms are collective variables, then quantizing a classical theory such as general relativity valid in the macroscopic domain is unlikely to yield a theory of the microscopic structures of spacetime. To uncover the microscopic structures one needs to find ways to unravel the underlying microscopic structures from observed macroscopic phenomena rather than naively quantizing the macroscopic variables, two very different paradigms. This task is similar to deducing the molecular constituents or even their quantum features from hydrodynamics or universalities of microscopic theories from critical phenomena. The macro to micro road poses a new and perhaps more difficult challenge to the next generation of theorists, phenomenologists and experimentalists in quantum gravity. Here we need to address issues at the quantum-classical and micro-macro interfaces familiar in mesoscopic physics, focusing on quantum fluctuations and correlations, coarse-graining and backreaction, and adopt ideas of nonequilibrium statistical mechanics and techniques from quantum field theory to explore theories built upon general relativity in a `bottom-up' approach or a `grass-root' road to quantum gravity. This view also provides us with a natural resolution towards the `Origin of the Universe' issue

Wuhan University Deep-space Orbit Determination and Gravity Recovery System(WUDOGS and Its Application Analysis

Directory of Open Access Journals (Sweden)

YE Mao

2017-03-01

Full Text Available WUDOGS(Wuhan University deep-space orbit determination and gravity recovery system is a software system designed for deep spacecraft precise orbit determination and planetary gravity recovery, developed independently at Wuhan University. WUDOGS now has the function for Lunar and Mars spacecraft precision orbit determination. Its design pattern and main function are briefly introduced. The cross verification test(CVT between WUDOGS and state of the art planetary precise orbit determination software GEODYN-Ⅱ are elaborated. The results show that:①for orbit propagation, with all the same forces and other configuration, the predicted orbit difference in R,T,N directions are less than 0.3 mm for one month arc, 5×10-3 mm for 2 days arc, compared with GEODYN-Ⅱ;②the difference RMS of computed values of observables for two-way range and two-way range rate is at levels of 0.06 mm and 0.002 mm/s respectively;③for Chinese Chang'E-1 POD, the reconstructed orbit difference between WUDOGS and GEODYN-Ⅱ is at 2 cm level, for ESA MEX POD, the reconstructed orbit difference between WUDOGS and ESA is at 25 m level. Current developing situation of WUDOGS and comparison with international research level show that WUDOGS has a good application prospect, which will be important for meeting the demand of Chinese future planetary exploration and the development of deep space spacecraft POD software.

Gravity Data for the State of New Mexico

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (21,242 records) were compiled by the University of Texas at El Paso. This data base was received in October 1984. Principal gravity...

Natural inflation and quantum gravity.

Science.gov (United States)

de la Fuente, Anton; Saraswat, Prashant; Sundrum, Raman

2015-04-17

Cosmic inflation provides an attractive framework for understanding the early Universe and the cosmic microwave background. It can readily involve energies close to the scale at which quantum gravity effects become important. General considerations of black hole quantum mechanics suggest nontrivial constraints on any effective field theory model of inflation that emerges as a low-energy limit of quantum gravity, in particular, the constraint of the weak gravity conjecture. We show that higher-dimensional gauge and gravitational dynamics can elegantly satisfy these constraints and lead to a viable, theoretically controlled and predictive class of natural inflation models.

Early universe with modified scalar-tensor theory of gravity

Science.gov (United States)

Mandal, Ranajit; Sarkar, Chandramouli; Sanyal, Abhik Kumar

2018-05-01

Scalar-tensor theory of gravity with non-minimal coupling is a fairly good candidate for dark energy, required to explain late-time cosmic evolution. Here we study the very early stage of evolution of the universe with a modified version of the theory, which includes scalar curvature squared term. One of the key aspects of the present study is that, the quantum dynamics of the action under consideration ends up generically with de-Sitter expansion under semiclassical approximation, rather than power-law. This justifies the analysis of inflationary regime with de-Sitter expansion. The other key aspect is that, while studying gravitational perturbation, the perturbed generalized scalar field equation obtained from the perturbed action, when matched with the perturbed form of the background scalar field equation, relates the coupling parameter and the potential exactly in the same manner as the solution of classical field equations does, assuming de-Sitter expansion. The study also reveals that the quantum theory is well behaved, inflationary parameters fall well within the observational limit and quantum perturbation analysis shows that the power-spectrum does not deviate considerably from the standard one obtained from minimally coupled theory.

Cosmology and modifications of gravity at large distances

International Nuclear Information System (INIS)

Ziour, R.

2010-01-01

In the framework of General Relativity, the observed current acceleration of the expansion of the Universe requires the presence of a Dark Energy component, whose nature is not well understood. In order to explain the acceleration of the Universe without introducing such a tantalizing source of energy, other gravitation theories have been designed. This thesis is devoted to the study of some of these modified gravity theories, as well as to the observation methods that could constrain them. The first part of this thesis presents a review of modified gravity theories and their motivations. The second part is devoted to the study of the massive gravity theories and of the so-called Vainshtein's mechanism, which allows some of the solutions of Massive Gravity to strongly differ from General Relativity at cosmological scales while satisfying the experimental constraints inside the solar system. For the first time, the validity of the Vainshtein's mechanism is demonstrated, through the study of specific spherically symmetric solutions. The third part deals with scalar modification of gravity; a new model of this sort is presented, inspired by the Vainshtein's mechanism in Massive Gravity. Finally, the fourth part discusses local, astrophysical and cosmological observations that might constrain modified gravity theories. (author)

2D higher spin gravity and the multimatrix models

International Nuclear Information System (INIS)

Awada, M.; Qiu Zongan

1990-01-01

We quantize W-gravity coupled to matter fields in the conformal gauge and obtain the critical exponents. We demonstrate explicitly how the generators of the W-algebra are described by an infinite set of conserved charges of the KdV hierarchy. We obtain the generalized hamiltonian equation of motion and show that it contains the class of universal differential equations of the matrix models. Thus we propose that these models describe pure W-gravity theories of the A-type. Consequently we give a new set of universal equations that correspond to other types of W-gravity theories. (orig.)

FRW cosmology in F(R,T) gravity

International Nuclear Information System (INIS)

Myrzakulov, Ratbay

2012-01-01

In this paper, we consider a theory of gravity with a metric-dependent torsion namely the F(R,T) gravity, where R is the curvature scalar and T is the torsion scalar. We study the geometric root of such theory. In particular we give the derivation of the model from the geometrical point of view. Then we present the more general form of F(R,T) gravity with two arbitrary functions and give some of its particular cases. In particular, the usual F(R) and F(T) gravity theories are particular cases of the F(R,T) gravity. In the cosmological context, we find that our new gravitational theory can describe the accelerated expansion of the Universe. (orig.)

Gravity Defied From Potato Asteroids to Magnetised Neutron Stars

Indian Academy of Sciences (India)

Left to itself, gravity wouldpull everything together, and the Universe would be nothingbut a gigantic black hole. Nature throws almost every bit ofphysics – rotation, magnetic field, heat, quantum effects andso on, at gravity to escape such a fate. In this series of articles,we shall explore systems where the eternal pull of gravity ...

Logamediate Inflation in f ( T ) Teleparallel Gravity

Energy Technology Data Exchange (ETDEWEB)

Rezazadeh, Kazem; Karami, Kayoomars [Department of Physics, University of Kurdistan, Pasdaran Street, P.O. Box 66177-15175, Sanandaj (Iran, Islamic Republic of); Abdolmaleki, Asrin, E-mail: rezazadeh86@gmail.com [Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), P.O. Box 55134-441, Maragha (Iran, Islamic Republic of)

2017-02-20

We study logamediate inflation in the context of f ( T ) teleparallel gravity. f ( T )-gravity is a generalization of the teleparallel gravity which is formulated on the Weitzenbock spacetime, characterized by the vanishing curvature tensor (absolute parallelism) and the non-vanishing torsion tensor. We consider an f ( T )-gravity model which is sourced by a canonical scalar field. Assuming a power-law f ( T ) function in the action, we investigate an inflationary universe with a logamediate scale factor. Our results show that, although logamediate inflation is completely ruled out by observational data in the standard inflationary scenario based on Einstein gravity, it can be compatible with the 68% confidence limit joint region of Planck 2015 TT,TE,EE+lowP data in the framework of f ( T )-gravity.

Dark-energy cosmological models in f(G) gravity

Energy Technology Data Exchange (ETDEWEB)

Shamir, M. F., E-mail: farasat.shamir@nu.edu.pk [National University of Computer and Emerging Sciences Lahore Campus, Department of Sciences and Humanities (Pakistan)

2016-10-15

We discuss dark-energy cosmological models in f(G) gravity. For this purpose, a locally rotationally symmetric Bianchi type I cosmological model is considered. First, exact solutions with a well-known form of the f(G) model are explored. One general solution is discussed using a power-law f(G) gravity model and physical quantities are calculated. In particular, Kasner’s universe is recovered and the corresponding f(G) gravity models are reported. Second, the energy conditions for the model under consideration are discussed using graphical analysis. It is concluded that solutions with f(G) = G{sup 5/6} support expansion of universe while those with f(G) = G{sup 1/2} do not favor the current expansion.

Cosmological and black hole brane-world universes in higher derivative gravity

International Nuclear Information System (INIS)

Nojiri, Shin'ichi; Odintsov, Sergei D.; Ogushi, Sachiko

2002-01-01

A general model of multidimensional R 2 gravity including a Riemann tensor square term (nonzero c case) is considered. The number of brane-worlds in such a model is constructed (mainly in five dimensions) and their properties are discussed. The thermodynamics of a Schwarzschild-anti-deSitter (S-AdS) BH (with boundary) is presented when perturbation on c is used. The entropy, free energy, and energy are calculated. For a nonzero c the entropy (energy) is not proportional to the area (mass). The equation of motion of the brane in a BH background is presented as a FRW equation. Using a dual CFT description it is shown that the dual field theory is not a conformal one when c is not zero. In this case the holographic entropy does not coincide with the BH entropy (they coincide for Einstein gravity or c=0 HD gravity where the AdS/CFT description is well applied). An asymmetrically warped background (an analogue of a charged AdS BH) where Lorentz invariance violation occurs is found. The cosmological 4D dS brane connecting two dS bulk spaces is formulated in terms of the parameters of R 2 gravity. Within the proposed dS/CFT correspondence the holographic conformal anomaly from five-dimensional higher derivative gravity in a de Sitter background is evaluated

And what if gravity is intrinsically quantic?

International Nuclear Information System (INIS)

Ziaeepour, Houri

2009-01-01

Since the early days of search for a quantum theory of gravity the attempts have been mostly concentrated on the quantization of an otherwise classical system. The two most contentious candidate theories of gravity, string theory and quantum loop gravity are based on a quantum field theory - the latter is a quantum field theory of connections on a SU(2) group manifold and the former is a quantum field theory in two dimensional spaces. Here we argue that there is a very close relation between quantum mechanics (QM) and gravity. Without gravity, QM becomes ambiguous. We consider this observation as the evidence for an intrinsic relation between these fundamental laws of nature. We suggest a quantum role and definition for gravity in the context of a quantum Universe, and present a preliminary formulation for gravity in a system with a finite number of particles.

QCD ghost f(T)-gravity model

Energy Technology Data Exchange (ETDEWEB)

Karami, K.; Abdolmaleki, A.; Asadzadeh, S. [University of Kurdistan, Department of Physics, Sanandaj (Iran, Islamic Republic of); Safari, Z. [Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of)

2013-09-15

Within the framework of modified teleparallel gravity, we reconstruct a f(T) model corresponding to the QCD ghost dark energy scenario. For a spatially flat FRW universe containing only the pressureless matter, we obtain the time evolution of the torsion scalar T (or the Hubble parameter). Then, we calculate the effective torsion equation of state parameter of the QCD ghost f(T)-gravity model as well as the deceleration parameter of the universe. Furthermore, we fit the model parameters by using the latest observational data including SNeIa, CMB and BAO data. We also check the viability of our model using a cosmographic analysis approach. Moreover, we investigate the validity of the generalized second law (GSL) of gravitational thermodynamics for our model. Finally, we point out the growth rate of matter density perturbation. We conclude that in QCD ghost f(T)-gravity model, the universe begins a matter dominated phase and approaches a de Sitter regime at late times, as expected. Also this model is consistent with current data, passes the cosmographic test, satisfies the GSL and fits the data of the growth factor well as the {Lambda}CDM model. (orig.)

Focus on quantum Einstein gravity Focus on quantum Einstein gravity

Science.gov (United States)

Ambjorn, Jan; Reuter, Martin; Saueressig, Frank

2012-09-01

time cosmology and the big bang, as well as TeV-scale gravity models testable at the Large Hadron Collider. On different grounds, Monte-Carlo studies of the gravitational partition function based on the discrete causal dynamical triangulations approach provide an a priori independent avenue towards unveiling the non-perturbative features of gravity. As a highlight, detailed simulations established that the phase diagram underlying causal dynamical triangulations contains a phase where the triangulations naturally give rise to four-dimensional, macroscopic universes. Moreover, there are indications for a second-order phase transition that naturally forms the discrete analog of the non-Gaussian fixed point seen in the continuum computations. Thus there is a good chance that the discrete and continuum computations will converge to the same fundamental physics. This focus issue collects a series of papers that outline the current frontiers of the gravitational asymptotic safety program. We hope that readers get an impression of the depth and variety of this research area as well as our excitement about the new and ongoing developments. References [1] Weinberg S 1979 General Relativity, an Einstein Centenary Survey ed S W Hawking and W Israel (Cambridge: Cambridge University Press)

Universal power law of the gravity wave manifestation in the AIM CIPS polar mesospheric cloud images

Science.gov (United States)

Rong, Pingping; Yue, Jia; Russell, James M., III; Siskind, David E.; Randall, Cora E.

2018-01-01

We aim to extract a universal law that governs the gravity wave manifestation in polar mesospheric clouds (PMCs). Gravity wave morphology and the clarity level of display vary throughout the wave population manifested by the PMC albedo data. Higher clarity refers to more distinct exhibition of the features, which often correspond to larger variances and a better-organized nature. A gravity wave tracking algorithm based on the continuous Morlet wavelet transform is applied to the PMC albedo data at 83 km altitude taken by the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument to obtain a large ensemble of the gravity wave detections. The horizontal wavelengths in the range of ˜ 20-60 km are the focus of the study. It shows that the albedo (wave) power statistically increases as the background gets brighter. We resample the wave detections to conform to a normal distribution to examine the wave morphology and display clarity beyond the cloud brightness impact. Sample cases are selected at the two tails and the peak of the normal distribution to represent the full set of wave detections. For these cases the albedo power spectra follow exponential decay toward smaller scales. The high-albedo-power category has the most rapid decay (i.e., exponent = -3.2) and corresponds to the most distinct wave display. The wave display becomes increasingly blurrier for the medium- and low-power categories, which hold the monotonically decreasing spectral exponents of -2.9 and -2.5, respectively. The majority of waves are straight waves whose clarity levels can collapse between the different brightness levels, but in the brighter background the wave signatures seem to exhibit mildly turbulent-like behavior.

Gravity as Quantum Entanglement Force

OpenAIRE

Lee, Jae-Weon; Kim, Hyeong-Chan; Lee, Jungjai

2010-01-01

We conjecture that the total quantum entanglement of matter and vacuum in the universe tends to increase with time, like entropy, and that an effective force is associated with this tendency. We also suggest that gravity and dark energy are types of quantum entanglement forces, similar to Verlinde's entropic force, and give holographic dark energy with an equation of state comparable to current observational data. This connection between quantum entanglement and gravity could give some new in...

Noether symmetry approach in f(G,T) gravity

Energy Technology Data Exchange (ETDEWEB)

Shamir, M.F.; Ahmad, Mushtaq [National University of Computer and Emerging Sciences, Lahore Campus (Pakistan)

2017-01-15

We explore the recently introduced modified Gauss-Bonnet gravity (Sharif and Ikram in Eur Phys J C 76:640, 2016), f(G,T) pragmatic with G, the Gauss-Bonnet term, and T, the trace of the energy-momentum tensor. Noether symmetry approach has been used to develop some cosmologically viable f(G,T) gravity models. The Noether equations of modified gravity are reported for flat FRW universe. Two specific models have been studied to determine the conserved quantities and exact solutions. In particular, the well known deSitter solution is reconstructed for some specific choice of f(G,T) gravity model. (orig.)

A Universal Velocity Dispersion Profile for Pressure Supported Systems: Evidence for MONDian Gravity across Seven Orders of Magnitude in Mass

Energy Technology Data Exchange (ETDEWEB)

Durazo, R.; Hernandez, X.; Sánchez, S. F. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 70-264 C.P. 04510 México D.F., México (Mexico); Sodi, B. Cervantes [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Campus Morelia, A.P. 3-72, C.P. 58089 Michoacán, México (Mexico)

2017-03-10

For any MONDian extended theory of gravity where the rotation curves of spiral galaxies are explained through a change in physics rather than the hypothesis of dark matter, a generic dynamical behavior is expected for pressure supported systems: an outer flattening of the velocity dispersion profile occurring at a characteristic radius, where both the amplitude of this flat velocity dispersion and the radius at which it appears are predicted to show distinct scalings with the total mass of the system. By carefully analyzing the dynamics of globular clusters and elliptical galaxies, we are able to significantly extend the astronomical diversity of objects in which MONDian gravity has been tested, from spiral galaxies to the much larger mass range covered by pressure supported systems. We show that a universal projected velocity dispersion profile accurately describes various classes of pressure supported systems, and further, that the expectations of extended gravity are met across seven orders of magnitude in mass. These observed scalings are not expected under dark matter cosmology, and would require particular explanations tuned at the scales of each distinct astrophysical system.

Can dark energy be a bonus in Horava gravity?

International Nuclear Information System (INIS)

Park, Mu-In

2010-01-01

Recently, Horava proposed a renormalizable gravity theory with higher spatial derivatives in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors. Here, I consider a non-trivial test of the new gravity theory in a Friedmann-Robertson-Walker (FRW) universe by considering an IR modification which breaks 'softly' the detailed balance condition in the original Horava model. I separate the dark energy parts from the usual Einstein gravity parts in the Friedman equations and obtain the formula of the equations of the state parameters. The IR-modified Horava gravity seems to be consistent with the current observational data, but we need some more refined data sets to see whether the theory is really consistent with our universe. From the consistency of our theory, I obtain some constraints on the allowed values of w 0 and w a in Chevallier, Polarski, and Linder's parametrization, and this may be tested in the near future, by sharpening the data sets.

Spectral dimension of the universe in quantum gravity at a lifshitz point.

Science.gov (United States)

Horava, Petr

2009-04-24

We extend the definition of "spectral dimension" d_{s} (usually defined for fractal and lattice geometries) to theories in spacetimes with anisotropic scaling. We show that in gravity with dynamical critical exponent z in D+1 dimensions, the spectral dimension of spacetime is d_{s}=1+D/z. In the case of gravity in 3+1 dimensions with z=3 in the UV which flows to z=1 in the IR, the spectral dimension changes from d_{s}=4 at large scales to d_{s}=2 at short distances. Remarkably, this is the behavior found numerically by Ambjørn et al. in their causal dynamical triangulations approach to quantum gravity.

Quantum gravity and quantum cosmology

CERN Document Server

Papantonopoulos, Lefteris; Siopsis, George; Tsamis, Nikos

2013-01-01

Quantum gravity has developed into a fast-growing subject in physics and it is expected that probing the high-energy and high-curvature regimes of gravitating systems will shed some light on how to eventually achieve an ultraviolet complete quantum theory of gravity. Such a theory would provide the much needed information about fundamental problems of classical gravity, such as the initial big-bang singularity, the cosmological constant problem, Planck scale physics and the early-time inflationary evolution of our Universe.   While in the first part of this book concepts of quantum gravity are introduced and approached from different angles, the second part discusses these theories in connection with cosmological models and observations, thereby exploring which types of signatures of modern and mathematically rigorous frameworks can be detected by experiments. The third and final part briefly reviews the observational status of dark matter and dark energy, and introduces alternative cosmological models.   ...

Compact Stars in Eddington-inspired Born-Infeld Gravity and General Relativity

Science.gov (United States)

Sham, Yu Hin

In this thesis we apply the Eddington inspired Born-Infeld (EiBI) gravity to study the structure and the properties of compact stars. The hydrostatic equilibrium structure of compact stars characterized by different equations of state (EOSs) is considered and it is found that EiBI gravity can lead to different new features that are not found in standard general relativity (GR). A unified framework to study radial perturbations and the stability of compact stars in this theory is also developed. As in the GR case, the frequency- square of the fundamental oscillation mode vanishes for the maximum mass stellar configuration. Also, the oscillation modes depend on the parameter kappa introduced in EiBI gravity and the dependence is stronger for higher-order modes. We also discover that EiBI gravity imposes certain constraints on the EOSs that allow physical stable equilibrium states of compact stars to exist. However, such constraints are unphysical as the validity of an EOS should be independent of the theory of gravity, hinting that EiBI gravity needs to be modified. On the other hand, we demonstrate that two universal relations of compact stars, namely the I-Love-Q relation, which relates the moment of intertia, the tidal Love number and the quadrupole moment of compact stars, and the f-I relation, which links the f-mode oscillation frequency and the moment of inertia of compact stars together, still hold in EiBI gravity within the observational bounds of kappa. The origin of the two universal relations is then studied and it is found that a stiff EOS at the core of the compact star guarantees the universality. The two universal relations are further extended and universal relations relating the multipolar f-mode oscillation frequency and the corresponding multipolar tidal Love number, which can be derived analytically in the Newtonian limit for stars with sufficiently stiff EOSs, are found.

The Lighter Side of Gravity

Science.gov (United States)

Narlikar, Jayant Vishnu

1996-10-01

From the drop of an apple to the stately dance of the galaxies, gravity is omnipresent in the Cosmos. Even with its high profile, gravity is the most enigmatic of all the known basic forces in nature. The Lighter Side of Gravity presents a beautifully clear and completely nontechnical introduction to the phenomenon of this force in all its manifestations. Astrophysicist Jayant Narlikar begins with an historical background to the discovery of the law of gravitation by Isaac Newton in the seventeenth century. Using familiar analogies, interesting anecdotes, and numerous illustrations to get across subtle effects and difficult points to readers, he goes on to describe the general theory of relativity and some of its strange and unfamiliar ideas such as curved spacetime, the bending of light, and black holes. Since first publication in 1982 (W.H. Freeman), Dr. Narlikar has brought his book completely up to date and expanded it to include the discovery of gigantic gravitational lenses in space, the findings of the Cosmic Background Explorer (COBE) satellite, the detection of dark matter in galaxies, the investigation of the very early Universe, and other new ideas in cosmology. This lucid and stimulating book presents a clear approach to the intriguing phenomenon of gravity for everyone who has ever felt caught in its grip. Jayant Narlikar is the winner of many astronomical prizes and the author of Introduction to Cosmology (Cambridge University Press, 1993).

Generalized Noether symmetry in f(T) gravity

International Nuclear Information System (INIS)

Mohseni Sadjadi, H.

2012-01-01

We consider modified teleparallel gravity (f(T) gravity), as a framework to explain the present accelerated expansion of the universe. The matter component is assumed to be cold dark matter. To find the explicit form of the function f, we utilize generalized Noether theorem and use generalized vector fields as variational symmetries of the corresponding Lagrangian. We study the cosmological consequences of the obtained results.

Quantum Gravity corrections and entropy at the Planck time

International Nuclear Information System (INIS)

Basilakos, Spyros; Vagenas, Elias C.; Das, Saurya

2010-01-01

We investigate the effects of Quantum Gravity on the Planck era of the universe. In particular, using different versions of the Generalized Uncertainty Principle and under specific conditions we find that the main Planck quantities such as the Planck time, length, mass and energy become larger by a factor of order 10−10 4 compared to those quantities which result from the Heisenberg Uncertainty Principle. However, we prove that the dimensionless entropy enclosed in the cosmological horizon at the Planck time remains unchanged. These results, though preliminary, indicate that we should anticipate modifications in the set-up of cosmology since changes in the Planck era will be inherited even to the late universe through the framework of Quantum Gravity (or Quantum Field Theory) which utilizes the Planck scale as a fundamental one. More importantly, these corrections will not affect the entropic content of the universe at the Planck time which is a crucial element for one of the basic principles of Quantum Gravity named Holographic Principle

Acceleration of the universe dark energy or modified

International Nuclear Information System (INIS)

Cardenas, Rolando; Leyva, Yoelsy

2007-01-01

We present a composite model of dark energy, motivated in string and quantum field theory considerations. Then we speak on gravity theories in which the gravity Lagrangian is modified, resulting in a modification of General Relativity. We outline a methodology allowing a mapping between these two theories, i. e., both dark energy models and modified gravity can give the same cosmological dynamics. We apply aforementioned methodology to obtain the mapping composite dark energy-modified gravity for a particular case. Cosmic expansion history takes into account very large scales, the homogeneous Universe, and can not discriminate between above two theories. However, cosmic growth history takes into consideration intermediate cluster and galactic scales, the inhomogeneous Universe, and there might be the clue to discriminate whether the current acceleration of the Universe is because it is filled with a new fluid having repulsive gravity (dark energy) or it is just that gravity gets weaker and long scales (modified gravity). (Author)

Breeze Gravity Current in a Uniform Flow of Air

Directory of Open Access Journals (Sweden)

M.V. Shokurov

2017-02-01

Full Text Available Breeze circulation is often observed nearby the water basin coasts and usually accompanied by a background synoptic wind. One of the basic dynamically important components of the breeze circulation is gravity current. In the present paper the latter is used as the breeze simplified model. The theory of interaction of gravity current and a uniform synoptic wind are developed. The gravity current in the domain of infinite height in a stationary environment and environment with background flow was considered. To solve this problem the law of conservation of mass and universal property of the Froude number was used, which is true in the steady state. It is shown that increase of a tail-wind is followed by growth of the gravity current velocity and decrease of its height. The opposite situation is observed at increase of a head wind: the current velocity reduces and its height increases. Using a Taylor series expansion for small values of the background flow velocity a linear dependence of gravity current velocity on background flow velocity can be obtained. The factor determining the slope of the velocity of gravity current propagation on the background wind speed, which is equal 2/3, is a universal constant. The theory explains the results of numerical simulation previously obtained by numerous authors. A physical interpretation of dependence of the height and velocity of the gravity current on the background flow velocity is presented.

Issues concerning gravity waves from first-order phase transitions

International Nuclear Information System (INIS)

Kosowsky, A.

1993-01-01

The stochastic background of gravitational radiation is a unique and potentially valuable source of information about the early universe. Photons thermally decoupled when the universe was around 100,000 years old; electromagnetic radiation cannot directly provide information about the epoch earlier than this. In contrast, gravitons presumably decoupled around the Planck time, when the universe was only 10 -44 seconds old. Since gravity wave propagate virtually unimpeded, any energetic event in the evolution of the universe will leave an imprint on the gravity wave background. Turner and Wilczek first suggested that first-order phase transitions, and particularly transitions which occur via the nucleation, expansion, and percolation of vacuum bubbles, will be a particularly efficient source of gravitational radiation. Detailed calculations with scalar-field vacuum bubbles confirm this conjecture and show that strongly first-order phase transitions are probably the strongest stochastic gravity-wave source yet conjectured. In this work the author first reviews the vacuum bubble calculations, stressing their physical assumptions. The author then discusses realistic scenarios for first-order phase transitions and describes how the calculations must be modified and extended to produce reliable results. 11 refs

Massive gravity from bimetric gravity

International Nuclear Information System (INIS)

Baccetti, Valentina; Martín-Moruno, Prado; Visser, Matt

2013-01-01

We discuss the subtle relationship between massive gravity and bimetric gravity, focusing particularly on the manner in which massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure is more delicate than currently appreciated. Specifically, this limiting procedure should not unnecessarily constrain the background metric, which must be externally specified by the theory of massive gravity itself. The fact that in bimetric theories one always has two sets of metric equations of motion continues to have an effect even in the massive gravity limit, leading to additional constraints besides the one set of equations of motion naively expected. Thus, since solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statement is not necessarily true, there is no complete continuity in the parameter space of the theory. In particular, we study the massive cosmological solutions which are continuous in the parameter space, showing that many interesting cosmologies belong to this class. (paper)

Atom-Interferometry Tests of the Isotropy of Post-Newtonian Gravity

International Nuclear Information System (INIS)

Mueller, Holger; Chiow, Sheng-wey; Herrmann, Sven; Chu, Steven; Chung, Keng-Yeow

2008-01-01

We present a test of the local Lorentz invariance of post-Newtonian gravity by monitoring Earth's gravity with a Mach-Zehnder atom interferometer that features a resolution of up to 8x10 -9 g/√(Hz), the highest reported thus far. Expressed within the standard model extension (SME) or Nordtvedt's anisotropic universe model, the analysis limits four coefficients describing anisotropic gravity at the ppb level and three others, for the first time, at the 10 ppm level. Using the SME we explicitly demonstrate how the experiment actually compares the isotropy of gravity and electromagnetism

Late time acceleration of the 3-space in a higher dimensional steady state universe in dilaton gravity

International Nuclear Information System (INIS)

Akarsu, Özgür; Dereli, Tekin

2013-01-01

We present cosmological solutions for (1+3+n)-dimensional steady state universe in dilaton gravity with an arbitrary dilaton coupling constant w and exponential dilaton self-interaction potentials in the string frame. We focus particularly on the class in which the 3-space expands with a time varying deceleration parameter. We discuss the number of the internal dimensions and the value of the dilaton coupling constant to determine the cases that are consistent with the observed universe and the primordial nucleosynthesis. The 3-space starts with a decelerated expansion rate and evolves into accelerated expansion phase subject to the values of w and n, but ends with a Big Rip in all cases. We discuss the cosmological evolution in further detail for the cases w = 1 and w = ½ that permit exact solutions. We also comment on how the universe would be conceived by an observer in four dimensions who is unaware of the internal dimensions and thinks that the conventional general relativity is valid at cosmological scales

Late time acceleration of the 3-space in a higher dimensional steady state universe in dilaton gravity

Science.gov (United States)

Akarsu, Özgür; Dereli, Tekin

2013-02-01

We present cosmological solutions for (1+3+n)-dimensional steady state universe in dilaton gravity with an arbitrary dilaton coupling constant w and exponential dilaton self-interaction potentials in the string frame. We focus particularly on the class in which the 3-space expands with a time varying deceleration parameter. We discuss the number of the internal dimensions and the value of the dilaton coupling constant to determine the cases that are consistent with the observed universe and the primordial nucleosynthesis. The 3-space starts with a decelerated expansion rate and evolves into accelerated expansion phase subject to the values of w and n, but ends with a Big Rip in all cases. We discuss the cosmological evolution in further detail for the cases w = 1 and w = ½ that permit exact solutions. We also comment on how the universe would be conceived by an observer in four dimensions who is unaware of the internal dimensions and thinks that the conventional general relativity is valid at cosmological scales.

f(R) gravity: scalar perturbations in the late Universe

Czech Academy of Sciences Publication Activity Database

Eingorn, M.; Novák, Jan; Zhuk, A.

2014-01-01

Roč. 74, č. 8 (2014), s. 3005 ISSN 1434-6044 Institutional support: RVO:67985840 Keywords : nonlinear f(R) gravity * scalar cosmological perturbations * scalaron Subject RIV: BA - General Mathematics Impact factor: 5.084, year: 2014 http://link.springer.com/article/10.1140/epjc/s10052-014-3005-1

The relation between Euclidean and Lorentzian 2D quantum gravity

NARCIS (Netherlands)

Ambjørn, J.; Correia, J.; Kristjansen, C.; Loll, R.

1999-01-01

Starting from 2D Euclidean quantum gravity, we show that one recovers 2D Lorentzian quantum gravity by removing all baby universes. Using a peeling procedure to decompose the discrete, triangulated geometries along a one-dimensional path, we explicitly associate with each Euclidean space-time a

Ghost quintessence in fractal gravity

Indian Academy of Sciences (India)

In this study, using the time-like fractal theory of gravity, we mainly focus on the ghost ... Here a(t) is the cosmic scale factor and it measures the expansion of the Universe. ..... effectively appear as self-conserved dark energy, with a non-trivial ...

Black holes, strings and quantum gravity

International Nuclear Information System (INIS)

Maldacena, Juan

2001-01-01

Most physical phenomena can be explained by 'Quantum Mechanics' and 'Einstein Theory of Gravity'. Quantum mechanics is needed for descriptions involving small objects (atoms, nuclei, molecules, etc.) whereas gravity is required for understanding big objects (planets, galaxies). Since, usually small objects are light while big ones are heavy, when one theory is called for, the other is not relevant. Interestingly enough, if we pretend to use both theories simultaneously, for instance when small and very heavy objects are considered (as those in the beginning of our universe), we find that they are mutually inconsistent. Thus, a new theory, so called 'Quantum Gravity', is needed. This works comments on above inconsistencies and indicates how the string theory, rather than a pointlike particle theory, could provide us with a quantum theory of gravity. Though a discussion of black holes it shows us how a string theory on certain space, ca be equivalently described by a particle theory on its boundary, like a sort of hologram. (author)

Conformal Gravity

International Nuclear Information System (INIS)

Hooft, G.

2012-01-01

The dynamical degree of freedom for the gravitational force is the metric tensor, having 10 locally independent degrees of freedom (of which 4 can be used to fix the coordinate choice). In conformal gravity, we split this field into an overall scalar factor and a nine-component remainder. All unrenormalizable infinities are in this remainder, while the scalar component can be handled like any other scalar field such as the Higgs field. In this formalism, conformal symmetry is spontaneously broken. An imperative demand on any healthy quantum gravity theory is that black holes should be described as quantum systems with micro-states as dictated by the Hawking-Bekenstein theory. This requires conformal symmetry that may be broken spontaneously but not explicitly, and this means that all conformal anomalies must cancel out. Cancellation of conformal anomalies yields constraints on the matter sector as described by some universal field theory. Thus black hole physics may eventually be of help in the construction of unified field theories. (author)

What energy does gravity unite with grand unified theories in the early universe

International Nuclear Information System (INIS)

Sivaram, C.

1987-01-01

Unification of gravity with GUTs is usually expected at the Planck energy E/sub PI/ ∼ 10 19 GeV. However, the vastly different values of the two couplings at E/sub PI/ (α/sub GUT/ E/sub PI/ with a single dimensionless coupling constant (α/sub U/ << 1) and described by a scale-invariant action quadratic in the Weyl curvature (with Yang-Mills fields). Breaking of scale invariance at E/sub PI/ then separates the interactions into gravity, now described by a Hilbert action with a dimensional G and GUTs with a dimensionless α/sub GUT/ and YM action. Problems with Klein-Kaluza unification of gravity with GUTs are also discussed in this context

Algorithmic Complexity in Cosmology and Quantum Gravity

Directory of Open Access Journals (Sweden)

D. Singleton

2002-01-01

Full Text Available Abstract: In this article we use the idea of algorithmic complexity (AC to study various cosmological scenarios, and as a means of quantizing the ravitational interaction. We look at 5D and 7D cosmological models where the Universe begins as a higher dimensional Planck size spacetime which fluctuates between Euclidean and Lorentzian signatures. These fluctuations are overned by the AC of the two different signatures. At some point a transition to a 4D Lorentzian signature Universe occurs, with the extra dimensions becoming "frozen" or non-dynamical. We also apply the idea of algorithmic complexity to study composite wormholes, the entropy of black holes, and the path integral for quantum gravity. Some of the physical consequences of the idea presented here are:the birth of the Universe with a fluctuating metric signature; the transition from a fluctuating metric signature to Lorentzian one; "frozen" extra dimensions as a consequence of this transition; quantum handles in the spacetime foam as regions with multidimensional gravity.

Gravity's dark side: Doing without dark matte

International Nuclear Information System (INIS)

Chalmers, M.

2006-01-01

Despite decades of searching, the 'dark matter' thought to hold galaxies together is still nowhere to be found. Matthew Chalmers describes how some physicists think it makes more sense to change our theory of gravity instead. Einstein's general theory of relativity is part of the bedrock of modern physics. It describes in elegant mathematical terms how matter causes space-time to curve, and therefore how objects move in a gravitational field. Since it was published in 1916, general relativity has passed every test asked of it with flying colours, and to many physicists the notion that it is wrong is sacrilege. But the motivation for developing an alternative theory of gravity is compelling. Over the last few years cosmologists have arrived at a simple yet extraordinarily successful model of universe. The trouble is that it requires most of the cosmos to be filled with mysterious stuff that we cannot see. In particular, general relativity - or rather its non-relativistic limit otherwise known as Newtonian gravity - can only correctly describe the dynamics of galaxies if we invoke huge quantities of 'dark matter'. Furthermore, an exotic entity called dark energy is necessary to account for the recent discovery that the expansion of the universe is accelerating. Indeed, in the standard model of cosmology, visible matter such as stars, planets and physics textbooks accounts for just 4% of the total universe. (U.K.)

Matter Loops Corrected Modified Gravity in Palatini Formulation

International Nuclear Information System (INIS)

Meng Xinhe; Wang Peng

2008-01-01

Recently, corrections to the standard Einstein-Hilbert action were proposed to explain the current cosmic acceleration in stead of introducing dark energy. In the Palatini formulation of those modified gravity models, there is an important observation due to Arkani-Hamed: matter loops will give rise to a correction to the modified gravity action proportional to the Ricci scalar of the metric. In the presence of such a term, we show that the current forms of modified gravity models in Palatini formulation, specifically, the 1/R gravity and ln R gravity, will have phantoms. Then we study the possible instabilities due to the presence of phantom fields. We show that the strong instability in the metric formulation of 1/R gravity indicated by Dolgov and Kawasaki will not appear and the decay timescales for the phantom fields may be long enough for the theories to make sense as effective field theory. On the other hand, if we change the sign of the modification terms to eliminate the phantoms, some other inconsistencies will arise for the various versions of the modified gravity models. Finally, we comment on the universal property of the Palatini formulation of the matter loops corrected modified gravity models and its implications

Discussion of entanglement entropy in quantum gravity

International Nuclear Information System (INIS)

Ma, Chen-Te

2018-01-01

We study entanglement entropy in gravity theory with quantum effects. A simplest model is a two dimensional Einstein gravity theory. We use an n-sheet manifold to obtain an area term of entanglement entropy by summing over all background fields. Based on AdS/CFT correspondence, strongly coupled conformal field theory is expected to describe perturbative quantum gravity theory. An ultraviolet complete quantum gravity theory should not depend on a choice of an entangling surface. To analysis the problem explicitly, we analyze two dimensional conformal field theory. We find that a coefficient of a universal term of entanglement entropy is independent of a choice of an entangling surface in two dimensional conformal field theory for one interval to show a tentative evidence. Finally, we discuss that translational invariance in a quantum system at zero temperature, size goes to infinity and no mass scales, except for cut-off, possibly be a necessary condition in quantum gravity theory by ruing out a volume law of entanglement entropy. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Constraining inverse-curvature gravity with supernovae.

Science.gov (United States)

Mena, Olga; Santiago, José; Weller, Jochen

2006-02-03

We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07baryonic matter component.

Insight into the baryon-gravity relation in galaxies

International Nuclear Information System (INIS)

Famaey, Benoit; Gentile, Gianfranco; Bruneton, Jean-Philippe; Zhao Hongsheng

2007-01-01

Observations of spiral galaxies strongly support a one-to-one analytical relation between the inferred gravity of dark matter at any radius and the enclosed baryonic mass. It is baffling that baryons manage to settle the dark matter gravitational potential in such a precise way, leaving no 'messy' fingerprints of the merging events and 'gastrophysical' feedbacks expected in the history of a galaxy in a concordance Universe. This correlation of gravity with baryonic mass can be interpreted from several nonstandard angles, especially as a modification of gravity called TeVeS, in which no galactic dark matter is needed. In this theory, the baryon-gravity relation is captured by the dieletric-like function μ of modified Newtonian dynamics (MOND), controlling the transition from 1/r 2 attraction in the strong gravity regime to 1/r attraction in the weak regime. Here, we study this μ-function in detail. We investigate the observational constraints upon it from fitting galaxy rotation curves, unveiling the degeneracy between the stellar mass-to-light ratio and the μ-function as well as the importance of the sharpness of transition from the strong to weak gravity regimes. We also numerically address the effects of nonspherical baryon geometry in the framework of nonlinear TeVeS, and exhaustively examine how the μ-function connects with the free function of that theory. In that regard, we exhibit the subtle effects and wide implications of renormalizing the gravitational constant. We finally present a discontinuity-free transition between quasistatic galaxies and the evolving Universe for the free function of TeVeS, inevitably leading to a return to 1/r 2 attraction at very low accelerations in isolated galaxies

How to distinguish dark energy and modified gravity?

International Nuclear Information System (INIS)

Wei Hao; Zhang Shuangnan

2008-01-01

The current accelerated expansion of our universe could be due to an unknown energy component (dark energy) or a modification of general relativity (modified gravity). In the literature it has been proposed that combining the probes of the cosmic expansion history and growth history can distinguish between dark energy and modified gravity. In this work, without invoking nontrivial dark energy clustering, we show that the possible interaction between dark energy and dark matter could make the interacting dark model and the modified gravity model indistinguishable. An explicit example is also given. Therefore, it is required to seek some complementary probes beyond the ones of cosmic expansion history and growth history.

Scalar-tensor theory of fourth-order gravity

International Nuclear Information System (INIS)

Accioly, A.J.; Goncalves, A.T.

1986-04-01

A scalar-tensor theory of fourth-order gravity is considered. Some cosmological consequences, due to the presence of the scalar field, as well as of metric derivatives higher than second order, are analysed. In particular, upperbpunds are obtained for the coupling constant α and for the scale factor of the universe, respectively. The discussion is restricted to Robertson-Walker universes. (Author) [pt

f(R)-theories of gravity and gravitational baryogenesis

Energy Technology Data Exchange (ETDEWEB)

Lambiase, G; Scarpetta, G [Dipartimento di Fisica ' E.R. Caianiello' Universita di Salerno, 84081 Baronissi (Italy); INFN - Gruppo Collegato di Salerno (Italy)

2007-05-15

The mechanism for generating the baryon asymmetry in the Universe is discussed in the framework of f(R)-theories of gravity. The gravitational baryogenesis, based on the coupling between the Ricci scalar curvature R and the baryon current, allows to determine the form of gravity Lagrangian, i.e. L(R) {approx} R{sup n}. The current bound on the observed matter-antimatter asymmetry and Big Bang Nucleosynthesis data lead to n = 0.97.

In search of fundamental discreteness in (2 + 1)-dimensional quantum gravity

NARCIS (Netherlands)

Budd, T.G.; Loll, R.

2009-01-01

Inspired by previous work in (2 + 1)-dimensional quantum gravity, which found evidence for a discretization of time in the quantum theory, we reexamine the issue for the case of pure Lorentzian gravity with vanishing cosmological constant and spatially compact universes of genus g ≥ 2. Taking the

Gravity Probe B Inspection

Science.gov (United States)

2000-01-01

The space vehicle Gravity Probe B (GP-B) is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at a 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies that are already enlivening other branches of science and engineering. In this photograph, engineer Gary Reynolds is inspecting the inside of the probe neck during probe thermal repairs. GP-B is scheduled for launch in April 2004 and managed for NASA by the Marshall Space Flight Center. Development of the GP-B is the responsibility of Stanford University along with major subcontractor Lockheed Martin Corporation. (Image credit to Russ Leese, Gravity Probe B, Stanford University)

Observational tests of modified gravity

International Nuclear Information System (INIS)

Jain, Bhuvnesh; Zhang Pengjie

2008-01-01

Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the Universe. Modified gravity theories have richer observational consequences for large-scale structures than conventional dark energy models, in that different observables are not described by a single growth factor even in the linear regime. We examine the relationships between perturbations in the metric potentials, density and velocity fields, and discuss strategies for measuring them using gravitational lensing, galaxy cluster abundances, galaxy clustering/dynamics, and the integrated Sachs-Wolfe effect. We show how a broad class of gravity theories can be tested by combining these probes. A robust way to interpret observations is by constraining two key functions: the ratio of the two metric potentials, and the ratio of the gravitational 'constant' in the Poisson equation to Newton's constant. We also discuss quasilinear effects that carry signatures of gravity, such as through induced three-point correlations. Clustering of dark energy can mimic features of modified gravity theories and thus confuse the search for distinct signatures of such theories. It can produce pressure perturbations and anisotropic stresses, which break the equality between the two metric potentials even in general relativity. With these two extra degrees of freedom, can a clustered dark energy model mimic modified gravity models in all observational tests? We show with specific examples that observational constraints on both the metric potentials and density perturbations can in principle distinguish modifications of gravity from dark energy models. We compare our result with other recent studies that have slightly different assumptions (and apparently contradictory conclusions).

Relic gravity waves from braneworld inflation

International Nuclear Information System (INIS)

Sahni, Varun; Sami, M.; Souradeep, Tarun

2002-01-01

We discuss a scenario in which extra dimensional effects allow a scalar field with a steep potential to play the dual role of the inflaton as well as dark energy (quintessence). The post-inflationary evolution of the universe in this scenario is generically characterized by a 'kinetic regime' during which the kinetic energy of the scalar field greatly exceeds its potential energy resulting in a 'stiff' equation of state for scalar field matter P φ ≅ρ φ . The kinetic regime precedes the radiation dominated epoch and introduces an important new feature into the spectrum of relic gravity waves created quantum mechanically during inflation. The amplitude of the gravity wave spectrum increases with the wave number for wavelengths shorter than the comoving horizon scale at the commencement of the radiative regime. This 'blue tilt' is a generic feature of models with steep potentials and imposes strong constraints on a class of inflationary braneworld models. Prospects for detection of the gravity wave background by terrestrial and space-borne gravity wave observatories such as LIGO II and LISA are discussed

PREFACE: Conceptual and Technical Challenges for Quantum Gravity 2014 - Parallel session: Noncommutative Geometry and Quantum Gravity

Science.gov (United States)

Martinetti, P.; Wallet, J.-C.; Amelino-Camelia, G.

2015-08-01

The conference Conceptual and Technical Challenges for Quantum Gravity at Sapienza University of Rome, from 8 to 12 September 2014, has provided a beautiful opportunity for an encounter between different approaches and different perspectives on the quantum-gravity problem. It contributed to a higher level of shared knowledge among the quantum-gravity communities pursuing each specific research program. There were plenary talks on many different approaches, including in particular string theory, loop quantum gravity, spacetime noncommutativity, causal dynamical triangulations, asymptotic safety and causal sets. Contributions from the perspective of philosophy of science were also welcomed. In addition several parallel sessions were organized. The present volume collects contributions from the Noncommutative Geometry and Quantum Gravity parallel session4, with additional invited contributions from specialists in the field. Noncommutative geometry in its many incarnations appears at the crossroad of many researches in theoretical and mathematical physics: • from models of quantum space-time (with or without breaking of Lorentz symmetry) to loop gravity and string theory, • from early considerations on UV-divergencies in quantum field theory to recent models of gauge theories on noncommutative spacetime, • from Connes description of the standard model of elementary particles to recent Pati-Salam like extensions. This volume provides an overview of these various topics, interesting for the specialist as well as accessible to the newcomer. 4partially funded by CNRS PEPS /PTI ''Metric aspect of noncommutative geometry: from Monge to Higgs''

I-Love-Q relations for neutron stars in dynamical Chern Simons gravity

Science.gov (United States)

Gupta, Toral; Majumder, Barun; Yagi, Kent; Yunes, Nicolás

2018-01-01

Neutron stars are ideal to probe, not only nuclear physics, but also strong-field gravity. Approximate universal relations insensitive to the star’s internal structure exist among certain observables and are useful in testing general relativity, as they project out the uncertainties in the equation of state. One such set of universal relations between the moment of inertia (I), the tidal Love number and the quadrupole moment (Q) has been studied both in general relativity and in modified theories. In this paper, we study the relations in dynamical Chern–Simons gravity, a well-motivated, parity-violating effective field theory, extending previous work in various ways. First, we study how projected constraints on the theory using the I-Love relation depend on the measurement accuracy of I with radio observations and that of the Love number with gravitational-wave observations. Provided these quantities can be measured with future observations, we find that the latter could place bounds on dynamical Chern–Simons gravity that are six orders of magnitude stronger than current bounds. Second, we study the I–Q and Q-Love relations in this theory by constructing slowly-rotating neutron star solutions to quadratic order in spin. We find that the approximate universality continues to hold in dynamical Chern–Simons gravity, and in fact, it becomes stronger than in general relativity, although its existence depends on the normalization of the dimensional coupling constant of the theory. Finally, we study the variation of the eccentricity of isodensity contours inside a star and its relation to the degree of universality. We find that, in most cases, the eccentricity variation is smaller in dynamical Chern–Simons gravity than in general relativity, providing further support to the idea that the approximate self-similarity of isodensity contours is responsible for universality.

Secular effects on inflation from one-loop quantum gravity

International Nuclear Information System (INIS)

Cabrer, J.A.; Espriu, D.

2008-01-01

In this Letter we revisit and extend a previous analysis where the possible relevance of quantum gravity effects in a cosmological setup was studied. The object of interest are non-local (logarithmic) terms generated in the effective action of gravity due to the exchange in loops of massless modes (such as photons or the gravitons themselves). We correct one mistake existing in the previous work and discuss the issue in a more general setting in different cosmological scenarios. We obtain the one-loop quantum-corrected evolution equations for the cosmological scale factor up to a given order in a derivative expansion in two particular cases: a matter dominated universe with vanishing cosmological constant, and in a de Sitter universe. We show that the quantum corrections, albeit tiny, may have a secular effect that eventually modifies the expansion rate. For a de Sitter universe they tend to slow down the rate of the expansion, while the effect may be the opposite in a matter dominated universe

Gauge/gravity duality. Exploring universal features in quantum matter

Energy Technology Data Exchange (ETDEWEB)

Klug, Steffen

2013-07-09

In this dissertation strongly correlated quantum states of matter are explored with the help of the gauge/gravity duality, relating strongly coupled gauge theories to weakly curved gravitational theories. The main focus of the present work is on applications to condensed matter systems, in particular high temperature superconductors and quantum matter close to criticality at zero temperature. The gauge/gravity duality originates from string theory and is a particular realization of the holographic principle. Therefore, a brief overview of the conceptual ideas behind string theory and the ramifications of the holographic principle are given. Along the way, supersymmetry and supersymmetric field theories needed to understand the low energy effective field theories of superstring theory will be discussed. Armed with the string theory background, the double life of D-branes, extended object where open strings end, is explained as massive solitonic solutions to the type II supergravity equations of motion and their role in generating supersymmetric Yang-Mills theories. Connecting these two different pictures of D-branes will give an explicit construction of a gauge/gravity duality, the AdS{sub 5}/CFT{sub 4} correspondence between N=4 supersymmetric SU(N{sub c}) Yang-Mills theory in four dimensions with vanishing β-function to all orders, describing a true CFT, and type IIB supergravity in ten-dimensional AdS{sub 5} x S{sup 5} spacetime. Furthermore, the precise dictionary relating operators of the conformal field theory to fields in the gravitational theory is established. More precisely, the partitions functions of the strongly coupled N=4 supersymmetric Yang-Mills theory in the large N{sub c} limit is equal to the on-shell supergravity partition evaluated at the boundary of the AdS space. Applying the knowledge of perturbative quantum field theory and its relation to the quantum partition function the dictionary may be extended to finite temperature and finite

Gauge/gravity duality. Exploring universal features in quantum matter

International Nuclear Information System (INIS)

Klug, Steffen

2013-01-01

In this dissertation strongly correlated quantum states of matter are explored with the help of the gauge/gravity duality, relating strongly coupled gauge theories to weakly curved gravitational theories. The main focus of the present work is on applications to condensed matter systems, in particular high temperature superconductors and quantum matter close to criticality at zero temperature. The gauge/gravity duality originates from string theory and is a particular realization of the holographic principle. Therefore, a brief overview of the conceptual ideas behind string theory and the ramifications of the holographic principle are given. Along the way, supersymmetry and supersymmetric field theories needed to understand the low energy effective field theories of superstring theory will be discussed. Armed with the string theory background, the double life of D-branes, extended object where open strings end, is explained as massive solitonic solutions to the type II supergravity equations of motion and their role in generating supersymmetric Yang-Mills theories. Connecting these two different pictures of D-branes will give an explicit construction of a gauge/gravity duality, the AdS 5 /CFT 4 correspondence between N=4 supersymmetric SU(N c ) Yang-Mills theory in four dimensions with vanishing β-function to all orders, describing a true CFT, and type IIB supergravity in ten-dimensional AdS 5 x S 5 spacetime. Furthermore, the precise dictionary relating operators of the conformal field theory to fields in the gravitational theory is established. More precisely, the partitions functions of the strongly coupled N=4 supersymmetric Yang-Mills theory in the large N c limit is equal to the on-shell supergravity partition evaluated at the boundary of the AdS space. Applying the knowledge of perturbative quantum field theory and its relation to the quantum partition function the dictionary may be extended to finite temperature and finite density states. Thus, all aspects

Loop Quantum Gravity.

Science.gov (United States)

Rovelli, Carlo

2008-01-01

The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime , is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i) The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii) A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler's "spacetime foam" intuition. (iii) Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv) A derivation of the Bekenstein-Hawking black-hole entropy. (v) Low-energy calculations, yielding n -point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.

A Combined Gravity Compensation Method for INS Using the Simplified Gravity Model and Gravity Database.

Science.gov (United States)

Zhou, Xiao; Yang, Gongliu; Wang, Jing; Wen, Zeyang

2018-05-14

In recent decades, gravity compensation has become an important way to reduce the position error of an inertial navigation system (INS), especially for a high-precision INS, because of the extensive application of high precision inertial sensors (accelerometers and gyros). This paper first deducts the INS's solution error considering gravity disturbance and simulates the results. Meanwhile, this paper proposes a combined gravity compensation method using a simplified gravity model and gravity database. This new combined method consists of two steps all together. Step 1 subtracts the normal gravity using a simplified gravity model. Step 2 first obtains the gravity disturbance on the trajectory of the carrier with the help of ELM training based on the measured gravity data (provided by Institute of Geodesy and Geophysics; Chinese Academy of sciences), and then compensates it into the error equations of the INS, considering the gravity disturbance, to further improve the navigation accuracy. The effectiveness and feasibility of this new gravity compensation method for the INS are verified through vehicle tests in two different regions; one is in flat terrain with mild gravity variation and the other is in complex terrain with fierce gravity variation. During 2 h vehicle tests, the positioning accuracy of two tests can improve by 20% and 38% respectively, after the gravity is compensated by the proposed method.

Beyond Einstein Gravity A Survey of Gravitational Theories for Cosmology and Astrophysics

CERN Document Server

Faraoni, Valerio

2011-01-01

Beyond Einstein’s Gravity is a graduate level introduction to extended theories of gravity and cosmology, including variational principles, the weak-field limit, gravitational waves, mathematical tools, exact solutions, as well as cosmological and astrophysical applications. The book provides a critical overview of the research in this area and unifies the existing literature using a consistent notation. Although the results apply in principle to all alternative gravities, a special emphasis is on scalar-tensor and f(R) theories. They were studied by theoretical physicists from early on, and in the 1980s they appeared in attempts to renormalize General Relativity and in models of the early universe. Recently, these theories have seen a new lease of life, in both their metric and metric-affine versions, as models of the present acceleration of the universe without introducing the mysterious and exotic dark energy. The dark matter problem can also be addressed in extended gravity. These applications are contr...

Asymptomatic freedom in renormalisable gravity and supergravity

International Nuclear Information System (INIS)

Fradkin, E.S.; Tseytlin, A.A.

1984-01-01

This chapter demonstrates that renormalizable supergravity, which is a superextension of renormalizable quantum gravity, can be the basis for a natural ''induced supergravity'' theory. A perturbatively operational unified theory is needed for a description of the early stages of the Universe, and renormalizable quantum gravity is well suited for unification with the renormalizable Grand Unified Models of matter. Topics considered include one-loop counter-terms and renormalization group (RG) equations for pure renormalizable gravity; the consequences of asymptotic freedom; the inclusion of matter; conformal supergravities; and renormalizable supergravity models. It is concluded that the presented lagrangian, which contains a locally superconformal extension of the Yang-Mills and massless spinor lagrangians and the conformal supergravity term, shows that conformal supergravity may play an important role in a fundamental theory

Clustering of galaxies with f(R) gravity

Science.gov (United States)

Capozziello, Salvatore; Faizal, Mir; Hameeda, Mir; Pourhassan, Behnam; Salzano, Vincenzo; Upadhyay, Sudhaker

2018-02-01

Based on thermodynamics, we discuss the galactic clustering of expanding Universe by assuming the gravitational interaction through the modified Newton's potential given by f(R) gravity. We compute the corrected N-particle partition function analytically. The corrected partition function leads to more exact equations of state of the system. By assuming that the system follows quasi-equilibrium, we derive the exact distribution function that exhibits the f(R) correction. Moreover, we evaluate the critical temperature and discuss the stability of the system. We observe the effects of correction of f(R) gravity on the power-law behaviour of particle-particle correlation function also. In order to check the feasibility of an f(R) gravity approach to the clustering of galaxies, we compare our results with an observational galaxy cluster catalogue.

Gauge/gravity duality. A road towards reality

International Nuclear Information System (INIS)

Kerner, Patrick

2012-01-01

an Abelian symmetry spontaneously. Since the broken symmetry is global, the condensed phase describes a superfluid. At large magnetic field, we expect that the instability can be cured in a similar way. The gravity description of these superfluids is in the main focus of this thesis. Especially, we concentrate on systems in which, in addition to the Abelian symmetry, the rotational symmetry SO(3) is spontaneously broken down to SO(2). These systems are named holographic p-wave superfluids. We construct these in a bottom-up gravity model as well as in a top-down string theory model. The former allows us to describe the back-reaction of the superfluid condensate on the energy-momentum tensor while the latter has the great advantage that we know the dual field theory explicitly. This string theory model is the first description of a holographic superfluid embedded in string theory. In these holographic models, we study the thermodynamics which allows us to identify the phase transition to the superfluid phase as well as some transport properties. In the bottom-up gravity model, we find a non-universal ratio of shear viscosity to entropy density. This is the first example for a non-universal value of this ratio in large N gauge theories at infinite 't Hooft coupling.

Gauge/gravity duality. A road towards reality

Energy Technology Data Exchange (ETDEWEB)

Kerner, Patrick

2012-02-23

breaks an Abelian symmetry spontaneously. Since the broken symmetry is global, the condensed phase describes a superfluid. At large magnetic field, we expect that the instability can be cured in a similar way. The gravity description of these superfluids is in the main focus of this thesis. Especially, we concentrate on systems in which, in addition to the Abelian symmetry, the rotational symmetry SO(3) is spontaneously broken down to SO(2). These systems are named holographic p-wave superfluids. We construct these in a bottom-up gravity model as well as in a top-down string theory model. The former allows us to describe the back-reaction of the superfluid condensate on the energy-momentum tensor while the latter has the great advantage that we know the dual field theory explicitly. This string theory model is the first description of a holographic superfluid embedded in string theory. In these holographic models, we study the thermodynamics which allows us to identify the phase transition to the superfluid phase as well as some transport properties. In the bottom-up gravity model, we find a non-universal ratio of shear viscosity to entropy density. This is the first example for a non-universal value of this ratio in large N gauge theories at infinite 't Hooft coupling.

Unveiling the Dynamics of the Universe

Directory of Open Access Journals (Sweden)

Pedro Avelino

2016-07-01

Full Text Available We explore the dynamics and evolution of the Universe at early and late times, focusing on both dark energy and extended gravity models and their astrophysical and cosmological consequences. Modified theories of gravity not only provide an alternative explanation for the recent expansion history of the universe, but they also offer a paradigm fundamentally distinct from the simplest dark energy models of cosmic acceleration. In this review, we perform a detailed theoretical and phenomenological analysis of different modified gravity models and investigate their consistency. We also consider the cosmological implications of well motivated physical models of the early universe with a particular emphasis on inflation and topological defects. Astrophysical and cosmological tests over a wide range of scales, from the solar system to the observable horizon, severely restrict the allowed models of the Universe. Here, we review several observational probes—including gravitational lensing, galaxy clusters, cosmic microwave background temperature and polarization, supernova and baryon acoustic oscillations measurements—and their relevance in constraining our cosmological description of the Universe.

In the Beginning Was Quantum Gravity.

Science.gov (United States)

Thomsen, Dietrick E.

1983-01-01

Cosmology is the theory by which the structure and history of the universe is described. Discusses the relationship between cosmology, gravity, and quantum mechanics, and whether the relationship can be formulated through Einstein's theory or a modification of it. Also discusses progress made in these scientific areas. (JN)

Weak lensing: Dark Matter, Dark Energy and Dark Gravity

International Nuclear Information System (INIS)

Heavens, Alan

2009-01-01

In this non-specialist review I look at how weak lensing can provide information on the dark sector of the Universe. The review concentrates on what can be learned about Dark Matter, Dark Energy and Dark Gravity, and why. On Dark Matter, results on the confrontation of theoretical profiles with observation are reviewed, and measurements of neutrino masses discussed. On Dark Energy, the interest is whether this could be Einstein's cosmological constant, and prospects for high-precision studies of the equation of state are considered. On Dark Gravity, we consider the exciting prospects for future weak lensing surveys to distinguish General Relativity from extra-dimensional or other gravity theories.

The New Era of Precision Cosmology: Testing Gravity at Large Scales

Science.gov (United States)

Prescod-Weinstein, Chanda

2011-01-01

Cosmic acceleration may be the biggest phenomenological mystery in cosmology today. Various explanations for its cause have been proposed, including the cosmological constant, dark energy and modified gravities. Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy ore modified gravity implement the Press & Schechter formalism (PGF). However, does the PGF apply in all cosmologies? The search is on for a better understanding of universality in the PGF In this talk, I explore the potential for universality and talk about what dark matter haloes may be able to tell us about cosmology. I will also discuss the implications of this and new cosmological experiments for better understanding our theory of gravity.

PREFACE: Loops 11: Non-Perturbative / Background Independent Quantum Gravity

Science.gov (United States)

Mena Marugán, Guillermo A.; Barbero G, J. Fernando; Garay, Luis J.; Villaseñor, Eduardo J. S.; Olmedo, Javier

2012-05-01

only was it a showroom for the research currently being carried out by many groups throughout the world, but there was also a permanent look towards the future. During these days, the CSIC Campus witnessed many scientific conversations triggered by the interaction amongst the people and groups that participated in LOOPS'11 Madrid and which, in many cases, will crystallise into new results and advances in the field. The conference would not have been possible without the generous help of a number of national and international institutions. The organizers would like to acknowledge the financial support provided by the Spanish Ministry of Science and Innovation (Ministerio de Ciencia e Innovación), the Spanish Research Council, CSIC (Consejo Superior de Investigaciones Cientĺficas), The BBVA Foundation (Fundación BBVA), The CONSOLIDER-CPAN project, the Spanish Society for Gravitation and Relativity (SEGRE), The Universidad Carlos III of Madrid (UC3M), and the European Science Foundation (ESF). The ESF, through the Quantum Gravity and Quantum Geometry network, provided full support for a number of young participants that have contributed to these proceedings: Dario Benedetti (Albert Einstein Institute, Potsdam, Germany), Norbert Bodendorfer (Institute for Theoretical Physics III, FAU Erlangen Nürnberg, Germany), Mariam Bouhmadi López (CENTRA, Centro Multidisciplinar de Astrofĺsica, Lisbon), Timothy Budd (Institute for Theoretical Physics, Utrecht University, The Netherlands), Miguel Campiglia (Institute for Gravitation and the Cosmos, Penn State University, USA), Gianluca Delfino (School of Mathematical Sciences, University of Nottingham, UK), Maite Dupuis (Institute for Theoretical Physics III, FAU Erlangen Nürnberg, Germany), Michał Dziendzikowski (Institute of Theoretical Physics, Warsaw University, Poland), Muxin Han (Centre de Physique Théorique de Luminy, Marseille, France), Philipp Höhn (Institute for Theoretical Physics, Utrecht University, The

Cosmic history of chameleonic dark matter in F (R ) gravity

Science.gov (United States)

Katsuragawa, Taishi; Matsuzaki, Shinya

2018-03-01

We study the cosmic history of the scalaron in F (R ) gravity with constructing the time evolution of the cosmic environment and discuss the chameleonic dark matter based on the chameleon mechanism in the early and current Universe. We then find that the scalaron can be a dark matter. We also propose an interesting possibility that the F (R ) gravity can address the coincidence problem.

Newtonian gravity in loop quantum gravity

OpenAIRE

Smolin, Lee

2010-01-01

We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime.

Cosmological Tests of Gravity

CERN Multimedia

CERN. Geneva

2017-01-01

Extensions of Einstein’s theory of General Relativity are under investigation as a potential explanation of the accelerating expansion rate of the universe. I’ll present a cosmologist’s overview of attempts to test these ideas in an efficient and unbiased manner. I’ll start by introducing the bestiary of alternative gravity theories that have been put forwards. This proliferation of models motivates us to develop model-independent, agnostic tools for comparing the theory space to cosmological data. I’ll introduce the effective field theory for cosmological perturbations, a framework designed to unify modified gravity theories in terms of a manageable set of parameters. Having outlined the formalism, I’ll talk about the current constraints on this framework, and the improvements expected from the next generation of large galaxy clustering, weak lensing and intensity mapping experiments.

Loop Quantum Gravity

Directory of Open Access Journals (Sweden)

Rovelli Carlo

2008-07-01

Full Text Available The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime, is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler’s “spacetime foam” intuition. (iii Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv A derivation of the Bekenstein–Hawking black-hole entropy. (v Low-energy calculations, yielding n-point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.

Cosmography in f(T) gravity

International Nuclear Information System (INIS)

Capozziello, S.; Cardone, V. F.; Farajollahi, H.; Ravanpak, A.

2011-01-01

Based only on the assumption that the Universe is homogenous and isotropic on large scales, cosmography is an ideal tool to investigate the cosmic expansion history in an almost model-independent way. Fitting the data on the luminosity distance and baryon acoustic oscillations allows to determine the confidence ranges for the cosmographic parameters hence giving some quantitative constraints that at whatever theory has to fulfill. As an application, we consider here the case of teleparallel gravity also referred to as f(T) gravity. To this end, we first work out analytical expressions to express the present day values of f(T) derivatives as a function of the cosmographic parameters, which hold under quite general and physically motivated conditions. We then use the constraints coming from cosmography to find out the confidence ranges for f(T) derivatives up to the fifth order and show how these can be used to check the viability of given teleparallel gravity models without the need to explicitly solve the second order dynamic equations.

Chiral gravity, log gravity, and extremal CFT

International Nuclear Information System (INIS)

Maloney, Alexander; Song Wei; Strominger, Andrew

2010-01-01

We show that the linearization of all exact solutions of classical chiral gravity around the AdS 3 vacuum have positive energy. Nonchiral and negative-energy solutions of the linearized equations are infrared divergent at second order, and so are removed from the spectrum. In other words, chirality is confined and the equations of motion have linearization instabilities. We prove that the only stationary, axially symmetric solutions of chiral gravity are BTZ black holes, which have positive energy. It is further shown that classical log gravity--the theory with logarithmically relaxed boundary conditions--has finite asymptotic symmetry generators but is not chiral and hence may be dual at the quantum level to a logarithmic conformal field theories (CFT). Moreover we show that log gravity contains chiral gravity within it as a decoupled charge superselection sector. We formally evaluate the Euclidean sum over geometries of chiral gravity and show that it gives precisely the holomorphic extremal CFT partition function. The modular invariance and integrality of the expansion coefficients of this partition function are consistent with the existence of an exact quantum theory of chiral gravity. We argue that the problem of quantizing chiral gravity is the holographic dual of the problem of constructing an extremal CFT, while quantizing log gravity is dual to the problem of constructing a logarithmic extremal CFT.

The coincidence problem in holographic f(R) gravity

Energy Technology Data Exchange (ETDEWEB)

Bisabr, Yousef, E-mail: y-bisabr@srttu.edu [Department of Physics, Shahid Rajaee Teacher Training University, Lavizan, Tehran 16788 (Iran, Islamic Republic of)

2011-09-15

It is well known that f(R) gravity models formulated in the Einstein conformal frame are equivalent to Einstein gravity together with a minimally coupled scalar field. In this case, the scalar field couples with the matter sector and the coupling term is given by the conformal factor. We apply the holographic principle to such interacting models. In a spatially flat universe, we show that the Einstein frame representation of f(R) models leads to a constant ratio of energy densities of dark matter to dark energy.

Gravity Does it: Redshift of Light from the Galaxies Yes, Expanding Universe NO!

Science.gov (United States)

Malhotra, Satish

2018-04-01

In the history of physics, ideas on space and time have changed the course of physics a number of times; this is another such event. We postulate 'space and time' as a flow of quantum gravity energy, having the absolute velocity c (same as velocity of light), where time is the delay in the spread of space (delay from infinite velocity flow, when there would be no time), such a flow has to have a reverse cycle, as energy creating it (howsoever large it might be has to be limited and limited energy can only create a limited space and time energy spread) and the reverse cycle is that of the creation of fundamental particles. This explanation of the universe tells us that the idea of an expanding universe is only an appearance, the argument, in brief, is as follows: One, the universe is so large that we cannot see the edges, light from the edges, the reality is non-observable. Two, the process is dark, it is beyond observation, the process of creation of charge (the reflection of light starts with it), the space energy flow process is in the range of invisible (before charge emerged); it is the elusive dark energy of the universe; we never connected space and time to flow of energy, and so did not find its connection either to its limitedness or to its dark nature (dark energy). Three, the space energy flow has a reverse process which leads to the formation of fundamental particles we have not included it in the totality of the processes of the universe, the former is the dark energy and the initial part of the reverse process—till it reaches the state of ionisation-- is dark matter. In the continuity of the cycle of space flow and its reversal to matter forms, ionisation happens at a particular point and visibility comes through along with; ionisation here is a later event (which is a part of the reverse process, enters visibility).It is this reverse process which creates fundamental particles (no big bang creation. With no idea of space as energy flow and no idea

Covariant generalized holographic dark energy and accelerating universe

Energy Technology Data Exchange (ETDEWEB)

Nojiri, Shin' ichi [Nagoya University, Department of Physics, Nagoya (Japan); Nagoya University, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya (Japan); Odintsov, S.D. [ICREA, Barcelona (Spain); Institute of Space Sciences (IEEC-CSIC), Barcelona (Spain); National Research Tomsk State University, Tomsk (Russian Federation); Tomsk State Pedagogical University, Tomsk (Russian Federation)

2017-08-15

We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F(R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy. (orig.)

Covariant generalized holographic dark energy and accelerating universe

International Nuclear Information System (INIS)

Nojiri, Shin'ichi; Odintsov, S.D.

2017-01-01

We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F(R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy. (orig.)

Covariant generalized holographic dark energy and accelerating universe

Science.gov (United States)

Nojiri, Shin'ichi; Odintsov, S. D.

2017-08-01

We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F( R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy.

Modified gravity in Arnowitt-Deser-Misner formalism

Science.gov (United States)

Gao, Changjun

2010-02-01

Motivated by Hořava-Lifshitz gravity theory, we propose and investigate two kinds of modified gravity theories, the f(R) kind and the K-essence kind, in the Arnowitt-Deser-Misner (ADM) formalism. The f(R) kind includes one ultraviolet (UV) term and one infrared (IR) term together with the Einstein-Hilbert action. We find that these two terms naturally present the ultraviolet and infrared modifications to the Friedmann equation. The UV and IR modifications can avoid the past Big-Bang singularity and the future Big-Rip singularity, respectively. Furthermore, the IR modification can naturally account for the current acceleration of the Universe. The Lagrangian of K-essence kind modified gravity is made up of the three-dimensional Ricci scalar and an arbitrary function of the extrinsic curvature term. We find the cosmic acceleration can also be naturally interpreted without invoking any kind of dark energy. The static, spherically symmetry and vacuum solutions of both theories are Schwarzschild or Schwarzschild-de Sitter solution. Thus these modified gravity theories are viable for solar system tests.

Modified gravity in Arnowitt-Deser-Misner formalism

International Nuclear Information System (INIS)

Gao Changjun

2010-01-01

Motivated by Horava-Lifshitz gravity theory, we propose and investigate two kinds of modified gravity theories, the f(R) kind and the K-essence kind, in the Arnowitt-Deser-Misner (ADM) formalism. The f(R) kind includes one ultraviolet (UV) term and one infrared (IR) term together with the Einstein-Hilbert action. We find that these two terms naturally present the ultraviolet and infrared modifications to the Friedmann equation. The UV and IR modifications can avoid the past Big-Bang singularity and the future Big-Rip singularity, respectively. Furthermore, the IR modification can naturally account for the current acceleration of the Universe. The Lagrangian of K-essence kind modified gravity is made up of the three-dimensional Ricci scalar and an arbitrary function of the extrinsic curvature term. We find the cosmic acceleration can also be naturally interpreted without invoking any kind of dark energy. The static, spherically symmetry and vacuum solutions of both theories are Schwarzschild or Schwarzschild-de Sitter solution. Thus these modified gravity theories are viable for solar system tests.

McVittie solution in f(T) gravity

Energy Technology Data Exchange (ETDEWEB)

Bejarano, Cecilia; Jose Guzman, Maria [Instituto de Astronomia y Fisica del Espacio (IAFE, CONICET-UBA), Buenos Aires (Argentina); Ferraro, Rafael [Instituto de Astronomia y Fisica del Espacio (IAFE, CONICET-UBA), Buenos Aires (Argentina); Universidad de Buenos Aires, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina)

2017-12-15

We show that McVittie geometry, which describes a black hole embedded in a FLRW universe, not only solves the Einstein equations but also remains as a non-deformable solution of f(T) gravity. This search for GR solutions that survive in f(T) gravity is facilitated by a null tetrad approach. We also show that flat FLRW geometry is a consistent solution of f(T) dynamical equations not only for T = -6H{sup 2} but also for T = 0, which could be a manifestation of the additional degrees of freedom involved in f(T) theories. (orig.)

McVittie solution in f(T) gravity

International Nuclear Information System (INIS)

Bejarano, Cecilia; Jose Guzman, Maria; Ferraro, Rafael

2017-01-01

We show that McVittie geometry, which describes a black hole embedded in a FLRW universe, not only solves the Einstein equations but also remains as a non-deformable solution of f(T) gravity. This search for GR solutions that survive in f(T) gravity is facilitated by a null tetrad approach. We also show that flat FLRW geometry is a consistent solution of f(T) dynamical equations not only for T = -6H 2 but also for T = 0, which could be a manifestation of the additional degrees of freedom involved in f(T) theories. (orig.)

f(T) teleparallel gravity and cosmology.

Science.gov (United States)

Cai, Yi-Fu; Capozziello, Salvatore; De Laurentis, Mariafelicia; Saridakis, Emmanuel N

2016-10-01

Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations-or, alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to illuminate the subject of which formulation, or combination of formulations, might be more suitable

Principles of astrophysics using gravity and stellar physics to explore the cosmos

CERN Document Server

Keeton, Charles

2014-01-01

This book gives a survey of astrophysics at the advanced undergraduate level.  It originates from a two-semester course sequence at Rutgers University that is meant to appeal not only to astrophysics students but also more broadly to physics and engineering students.  The organization is driven more by physics than by astronomy; in other words, topics are first developed in physics and then applied to astronomical systems that can be investigated, rather than the other way around. The first half of the book focuses on gravity.  Gravity is the dominant force in many astronomical systems, so a tremendous amount can be learned by studying gravity, motion and mass.  The theme in this part of the book, as well as throughout astrophysics, is using motion to investigate mass.  The goal of Chapters 2-11 is to develop a progressively richer understanding of gravity as it applies to objects ranging from planets and moons to galaxies and the universe as a whole. The second half uses other aspects of physics to addr...

Dynamics of Mixed Dark Energy Domination in Teleparallel Gravity and Phase-Space Analysis

Directory of Open Access Journals (Sweden)

Emre Dil

2015-01-01

Full Text Available We consider a novel dark energy model to investigate whether it will provide an expanding universe phase. Here we propose a mixed dark energy domination which is constituted by tachyon, quintessence, and phantom scalar fields nonminimally coupled to gravity, in the absence of background dark matter and baryonic matter, in the framework of teleparallel gravity. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions implying the acceleration phase of universe.

Palatini actions and quantum gravity phenomenology

International Nuclear Information System (INIS)

Olmo, Gonzalo J.

2011-01-01

We show that an invariant an universal length scale can be consistently introduced in a generally covariant theory through the gravitational sector using the Palatini approach. The resulting theory is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, it is found that in this theory field excitations propagating with different energy-densities perceive different background metrics, which is a fundamental characteristic of the DSR and Rainbow Gravity approaches. We illustrate these properties with a particular gravitational model and explicitly show how the soccer ball problem is avoided in this framework. The isotropic and anisotropic cosmologies of this model also avoid the big bang singularity by means of a big bounce

Palatini actions and quantum gravity phenomenology

Energy Technology Data Exchange (ETDEWEB)

Olmo, Gonzalo J., E-mail: gonzalo.olmo@csic.es [Departamento de Física Teórica and IFIC, Centro Mixto Universidad de Valencia - CSIC, Facultad de Física, Universidad de Valencia, Burjassot-46100, Valencia (Spain)

2011-10-01

We show that an invariant an universal length scale can be consistently introduced in a generally covariant theory through the gravitational sector using the Palatini approach. The resulting theory is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, it is found that in this theory field excitations propagating with different energy-densities perceive different background metrics, which is a fundamental characteristic of the DSR and Rainbow Gravity approaches. We illustrate these properties with a particular gravitational model and explicitly show how the soccer ball problem is avoided in this framework. The isotropic and anisotropic cosmologies of this model also avoid the big bang singularity by means of a big bounce.

Gravity mediated preheating

International Nuclear Information System (INIS)

Maity, Debaprasad

2015-01-01

In this work we propose a mechanism of natural preheating of our universe induced by the inflation field dependent effective mass term for the gravitational wave. For any single field inflationary model, the inflation must go through the oscillatory phase after the end of inflation. As has recently been shown, if the gravitational fluctuation has inflation dependent mass term, there will be a resonant amplification of the amplitude of the gravitational wave during the oscillatory phase of inflation though parametric resonance. Because of this large enhancement of the amplitude of the gravitational wave, we show that universe can be naturally pre-heated through a minimally coupled matter field with gravity. Therefore, during the pre-heating phase, there is no need to introduce any arbitrary coupling between the matter field and the inflation. (author)

Correspondence of f(R,∇R) Modified Gravity with Scalar Field Models

International Nuclear Information System (INIS)

Jawad, Abdul; Debnath, Ujjal

2014-01-01

This paper is devoted to study the scalar field dark energy models by taking its different aspects in the framework of f(R,∇R) gravity. We consider flat FRW universe to construct the equation of state parameter governed by f(R,∇R) gravity. The stability of the model is discussed with the help of squared speed of sound parameter. It is found that models show quintessence behavior of the universe in stable as well as unstable modes. We also develop the correspondence of f(R,∇R) model with some scalar field dark energy models like quintessence, tachyonic field, k-essence, dilaton, hessence, and DBI-essence. The nature of scalar fields and corresponding scalar potentials is being analyzed in f(R,∇R) gravity graphically which show consistency with the present day observations about accelerated phenomenon

On the universal hydrodynamics of strongly coupled CFTs with gravity duals

International Nuclear Information System (INIS)

Gupta, Rajesh Kumar; Mukhopadhyay, Ayan

2009-01-01

It is known that the solutions of pure classical 5D gravity with AdS 5 asymptotics can describe strongly coupled large N dynamics in a universal sector of 4D conformal gauge theories. We show that when the boundary metric is flat we can uniquely specify the solution by the boundary stress tensor. We also show that in the Fefferman-Graham coordinates all these solutions have an integer Taylor series expansion in the radial coordinate (i.e. no log terms). Specifying an arbitrary stress tensor can lead to two types of pathologies, it can either destroy the asymptotic AdS boundary condition or it can produce naked singularities. We show that when solutions have no net angular momentum, all hydrodynamic stress tensors preserve the asymptotic AdS boundary condition, though they may produce naked singularities. We construct solutions corresponding to arbitrary hydrodynamic stress tensors in Fefferman-Graham coordinates using a derivative expansion. In contrast to Eddington-Finkelstein coordinates here the constraint equations simplify and at each order it is manifestly Lorentz covariant. The regularity analysis, becomes more elaborate, but we can show that there is a unique hydrodynamic stress tensor which gives us solutions free of naked singularities. In the process we write down explicit first order solutions in both Fefferman-Graham and Eddington-Finkelstein coordinates for hydrodynamic stress tensors with arbitrary η/s. Our solutions can describe arbitrary (slowly varying) velocity configurations. We point out some field-theoretic implications of our general results.

Testing a Dilaton Gravity Model Using Nucleosynthesis

International Nuclear Information System (INIS)

Boran, S.; Kahya, E. O.

2014-01-01

Big bang nucleosynthesis (BBN) offers one of the most strict evidences for the Λ-CDM cosmology at present, as well as the cosmic microwave background (CMB) radiation. In this work, our main aim is to present the outcomes of our calculations related to primordial abundances of light elements, in the context of higher dimensional steady-state universe model in the dilaton gravity. Our results show that abundances of light elements (primordial D, 3 He, 4 He, T, and 7 Li) are significantly different for some cases, and a comparison is given between a particular dilaton gravity model and Λ-CDM in the light of the astrophysical observations

Eddington's theory of gravity and its progeny.

Science.gov (United States)

Bañados, Máximo; Ferreira, Pedro G

2010-07-02

We resurrect Eddington's proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the big bang. We thus argue that the modern formulation of Eddington's theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe.

Geometric constructions for repulsive gravity and quantization

International Nuclear Information System (INIS)

Hohmann, Manuel

2010-11-01

In this thesis we present two geometric theories designed to extend general relativity. It can be seen as one of the aims of such theories to model the observed accelerating expansion of the universe as a gravitational phenomenon, or to provide a mathematical structure for the formulation of quantum field theories on curved spacetimes and quantum gravity. This thesis splits into two parts: In the first part we consider multimetric gravity theories containing N>1 standard model copies which interact only gravitationally and repel each other in the Newtonian limit. The dynamics of each of the standard model copies is governed by its own metric tensor. We show that the antisymmetric case, in which the mutual repulsion between the different matter sectors is of equal strength compared to the attractive gravitational force within each sector, is prohibited by a no-go theorem for N=2. We further show that this theorem does not hold for N>2 by explicitly constructing an antisymmetric multimetric repulsive gravity theory. We then examine several properties of this theory. Most notably, we derive a simple cosmological model and show that the accelerating expansion of the late universe can indeed be explained by the mutual repulsion between the different matter sectors. We further present a simple model for structure formation and show that our model leads to the formation of filament-like structures and voids. Finally, we show that multimetric repulsive gravity is compatible with high-precision solar system data using the parametrized post-Newtonian formalism. In the second part of the thesis we propose a mathematical model of quantum spacetime as an infinite-dimensional manifold locally homeomorphic to an appropriate Schwartz space. This extends and unifies both the standard function space construction of quantum mechanics and the differentiable manifold structure of classical spacetime. In this picture we demonstrate that classical spacetime emerges as a finite

Geometric constructions for repulsive gravity and quantization

Energy Technology Data Exchange (ETDEWEB)

Hohmann, Manuel

2010-11-15

In this thesis we present two geometric theories designed to extend general relativity. It can be seen as one of the aims of such theories to model the observed accelerating expansion of the universe as a gravitational phenomenon, or to provide a mathematical structure for the formulation of quantum field theories on curved spacetimes and quantum gravity. This thesis splits into two parts: In the first part we consider multimetric gravity theories containing N>1 standard model copies which interact only gravitationally and repel each other in the Newtonian limit. The dynamics of each of the standard model copies is governed by its own metric tensor. We show that the antisymmetric case, in which the mutual repulsion between the different matter sectors is of equal strength compared to the attractive gravitational force within each sector, is prohibited by a no-go theorem for N=2. We further show that this theorem does not hold for N>2 by explicitly constructing an antisymmetric multimetric repulsive gravity theory. We then examine several properties of this theory. Most notably, we derive a simple cosmological model and show that the accelerating expansion of the late universe can indeed be explained by the mutual repulsion between the different matter sectors. We further present a simple model for structure formation and show that our model leads to the formation of filament-like structures and voids. Finally, we show that multimetric repulsive gravity is compatible with high-precision solar system data using the parametrized post-Newtonian formalism. In the second part of the thesis we propose a mathematical model of quantum spacetime as an infinite-dimensional manifold locally homeomorphic to an appropriate Schwartz space. This extends and unifies both the standard function space construction of quantum mechanics and the differentiable manifold structure of classical spacetime. In this picture we demonstrate that classical spacetime emerges as a finite

Even-dimensional topological gravity from Chern-Simons gravity

International Nuclear Information System (INIS)

Merino, N.; Perez, A.; Salgado, P.

2009-01-01

It is shown that the topological action for gravity in 2n-dimensions can be obtained from the (2n+1)-dimensional Chern-Simons gravity genuinely invariant under the Poincare group. The 2n-dimensional topological gravity is described by the dynamics of the boundary of a (2n+1)-dimensional Chern-Simons gravity theory with suitable boundary conditions. The field φ a , which is necessary to construct this type of topological gravity in even dimensions, is identified with the coset field associated with the non-linear realizations of the Poincare group ISO(d-1,1).

Gravity effects on endogenous movements

Science.gov (United States)

Johnsson, Anders; Antonsen, Frank

Gravity effects on endogenous movements A. Johnsson * and F. Antonsen *+ * Department of Physics, Norwegian University of Science and Technology,NO-7491, Trond-heim, Norway, E-mail: anders.johnsson@ntnu.no + Present address: Statoil Research Center Trondheim, NO-7005, Trondheim, Norway Circumnutations in stems/shoots exist in many plants and often consists of more or less regular helical movements around the plumb line under Earth conditions. Recent results on circumnu-tations of Arabidopsis in space (Johnsson et al. 2009) showed that minute amplitude oscilla-tions exist in weightlessness, but that centripetal acceleration (mimicking the gravity) amplified and/or created large amplitude oscillations. Fundamental mechanisms underlying these results will be discussed by modeling the plant tissue as a cylinder of cells coupled together. As a starting point we have modeled (Antonsen 1998) standing waves on a ring of biological cells, as first discussed in a classical paper (Turing 1952). If the coupled cells can change their water content, an `extension' wave could move around the ring. We have studied several, stacked rings of cells coupled into a cylinder that together represent a cylindrical plant tissue. Waves of extensions travelling around the cylinder could then represent the observable circumnutations. The coupling between cells can be due to cell-to-cell diffusion, or to transport via channels, and the coupling can be modeled to vary in both longitudinal and transversal direction of the cylinder. The results from ISS experiments indicate that this cylindrical model of coupled cells should be able to 1) show self-sustained oscillations without the impact of gravity (being en-dogenous) and 2) show how an environmental factor like gravity can amplify or generate the oscillatory movements. Gravity has been introduced in the model by a negative, time-delayed feed-back transport across the cylinder. This represents the physiological reactions to acceler

Corrected entropy of Friedmann-Robertson-Walker universe in tunneling method

International Nuclear Information System (INIS)

Zhu, Tao; Ren, Ji-Rong; Li, Ming-Fan

2009-01-01

In this paper, we study the thermodynamic quantities of Friedmann-Robertson-Walker (FRW) universe by using the tunneling formalism beyond semiclassical approximation developed by Banerjee and Majhi [25]. For this we first calculate the corrected Hawking-like temperature on apparent horizon by considering both scalar particle and fermion tunneling. With this corrected Hawking-like temperature, the explicit expressions of the corrected entropy of apparent horizon for various gravity theories including Einstein gravity, Gauss-Bonnet gravity, Lovelock gravity, f(R) gravity and scalar-tensor gravity, are computed. Our results show that the corrected entropy formula for different gravity theories can be written into a general expression (4.39) of a same form. It is also shown that this expression is also valid for black holes. This might imply that the expression for the corrected entropy derived from tunneling method is independent of gravity theory, spacetime and dimension of the spacetime. Moreover, it is concluded that the basic thermodynamical property that the corrected entropy on apparent horizon is a state function is satisfied by the FRW universe

Gravity waves as a probe of the Hubble expansion rate during an electroweak scale phase transition

International Nuclear Information System (INIS)

Chung, Daniel J. H.; Zhou Peng

2010-01-01

Just as big bang nucleosynthesis allows us to probe the expansion rate when the temperature of the Universe was around 1 MeV, the measurement of gravity waves from electroweak scale first order phase transitions may allow us to probe the expansion rate when the temperature of the Universe was at the electroweak scale. We compute the simple transformation rule for the gravity wave spectrum under the scaling transformation of the Hubble expansion rate. We then apply this directly to the scenario of quintessence kination domination and show how gravity wave spectra would shift relative to Laser Interferometer Space Antenna and Big Bang Observer projected sensitivities.

Ostrogradski Hamiltonian approach for geodetic brane gravity

International Nuclear Information System (INIS)

Cordero, Ruben; Molgado, Alberto; Rojas, Efrain

2010-01-01

We present an alternative Hamiltonian description of a branelike universe immersed in a flat background spacetime. This model is named geodetic brane gravity. We set up the Regge-Teitelboim model to describe our Universe where such field theory is originally thought as a second order derivative theory. We refer to an Ostrogradski Hamiltonian formalism to prepare the system to its quantization. This approach comprize the manage of both first- and second-class constraints and the counting of degrees of freedom follows accordingly.

Gravity and domain wall problem

International Nuclear Information System (INIS)

Rai, B.; Senjanovic, G.

1992-11-01

It is well known that the spontaneous breaking of discrete symmetries may lead to conflict with big-bang cosmology. This is due to formation of domain walls which give unacceptable contribution to the energy density of the universe. On the other hand, it is expected that gravity breaks global symmetries explicitly. In this work we propose that this could provide a natural solution to the domain-wall problem. (author). 17 refs

A general thermodynamical description of the event horizon in the FRW universe

International Nuclear Information System (INIS)

Tu, Fei-Quan; Chen, Yi-Xin

2016-01-01

The Friedmann equation in the Friedmann-Robertson-Walker (FRW) universe with any spatial curvature is derived from the first law of thermodynamics on the event horizon. The key idea is to redefine a Hawking temperature on the event horizon. Furthermore, we obtain the evolution equations of the universe including the quantum correction and explore the evolution of the universe in f(R) gravity. In addition, we also investigate the generalized second law of thermodynamics in Einstein gravity and f(R) gravity. This perspective also implies that the first law of thermodynamics on the event horizon has a general description in respect of the evolution of the FRW universe. (orig.)

Polar gravity fields from GOCE and airborne gravity

DEFF Research Database (Denmark)

Forsberg, René; Olesen, Arne Vestergaard; Yidiz, Hasan

2011-01-01

Airborne gravity, together with high-quality surface data and ocean satellite altimetric gravity, may supplement GOCE to make consistent, accurate high resolution global gravity field models. In the polar regions, the special challenge of the GOCE polar gap make the error characteristics...... of combination models especially sensitive to the correct merging of satellite and surface data. We outline comparisons of GOCE to recent airborne gravity surveys in both the Arctic and the Antarctic. The comparison is done to new 8-month GOCE solutions, as well as to a collocation prediction from GOCE gradients...... in Antarctica. It is shown how the enhanced gravity field solutions improve the determination of ocean dynamic topography in both the Arctic and in across the Drake Passage. For the interior of Antarctica, major airborne gravity programs are currently being carried out, and there is an urgent need...

Distinguishing modified gravity from dark energy

International Nuclear Information System (INIS)

Bertschinger, Edmund; Zukin, Phillip

2008-01-01

The acceleration of the Universe can be explained either through dark energy or through the modification of gravity on large scales. In this paper we investigate modified gravity models and compare their observable predictions with dark energy models. Modifications of general relativity are expected to be scale independent on superhorizon scales and scale dependent on subhorizon scales. For scale-independent modifications, utilizing the conservation of the curvature scalar and a parametrized post-Newtonian formulation of cosmological perturbations, we derive results for large-scale structure growth, weak gravitational lensing, and cosmic microwave background anisotropy. For scale-dependent modifications, inspired by recent f(R) theories we introduce a parametrization for the gravitational coupling G and the post-Newtonian parameter γ. These parametrizations provide a convenient formalism for testing general relativity. However, we find that if dark energy is generalized to include both entropy and shear stress perturbations, and the dynamics of dark energy is unknown a priori, then modified gravity cannot in general be distinguished from dark energy using cosmological linear perturbations.

Phase space of modified Gauss-Bonnet gravity

Energy Technology Data Exchange (ETDEWEB)

Carloni, Sante [Universidade de Lisboa-UL, Centro Multidisciplinar de Astrofisica-CENTRA, Instituto Superior Tecnico-IST, Lisbon (Portugal); Mimoso, Jose P. [Instituto de Astrofisica e Ciencias do Espaco, Universidade de Lisboa, Departamento de Fisica, Faculdade de Ciencias, Lisbon (Portugal)

2017-08-15

We investigate the evolution of non-vacuum Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetimes with any spatial curvature in the context of Gauss-Bonnet gravity. The analysis employs a new method which enables us to explore the phase space of any specific theory of this class. We consider several examples, discussing the transition from a decelerating into an acceleration universe within these theories. We also deduce from the dynamical equations some general conditions on the form of the action which guarantee the presence of specific behaviours like the emergence of accelerated expansion. As in f(R) gravity, our analysis shows that there is a set of initial conditions for which these models have a finite time singularity which can be an attractor. The presence of this instability also in the Gauss-Bonnet gravity is to be ascribed to the fourth-order derivative in the field equations, i.e., is the direct consequence of the higher order of the equations. (orig.)

Wormholes in higher dimensions with non-linear curvature terms from quantum gravity corrections

Energy Technology Data Exchange (ETDEWEB)

El-Nabulsi, Ahmad Rami [Neijiang Normal University, Neijiang, Sichuan (China)

2011-11-15

In this work, we discuss a 7-dimensional universe in the presence of a static traversable wormhole and a decaying cosmological constant and dominated by higher-order curvature effects expected from quantum gravity corrections. We confirmed the existence of wormhole solutions in the form of the Lovelock gravity. Many interesting and attractive features are discussed in some detail.

Spherically symmetric static spacetimes in vacuum f(T) gravity

International Nuclear Information System (INIS)

Ferraro, Rafael; Fiorini, Franco

2011-01-01

We show that Schwarzschild geometry remains as a vacuum solution for those four-dimensional f(T) gravitational theories behaving as ultraviolet deformations of general relativity. In the gentler context of three-dimensional gravity, we also find that the infrared-deformed f(T) gravities, like the ones used to describe the late cosmic speed up of the Universe, have as the circularly symmetric vacuum solution a Deser-de Sitter or a Banados, Teitelboim and Zanelli-like spacetime with an effective cosmological constant depending on the infrared scale present in the function f(T).

Rotation of Galaxies within Gravity of the Universe

Directory of Open Access Journals (Sweden)

Arto Annila

2016-05-01

Full Text Available Rotation of galaxies is examined by the general principle of least action. This law of nature describes a system in its surroundings, here specifically a galaxy in the surrounding Universe. According to this holistic theory the gravitational potential due to all matter in the expanding Universe relates to the universal curvature which, in turn, manifests itself as the universal acceleration. Then the orbital velocities from the central bulge to distant perimeters are understood to balance both the galactic and universal acceleration. Since the galactic acceleration decreases with distance from the galaxy’s center to its luminous edge, the orbital velocities of ever more distant stars and gas clouds tend toward a value that tallies the universal acceleration. This tiny term has been acknowledged earlier by including it as a parameter in the modified gravitational law, but here the tiny acceleration is understood to result from the gravitational potential that spans across the expanding Universe. This resolution of the galaxy rotation problem is compared with observations and contrasted with models of dark matter. Also, other astronomical observations that have been interpreted as evidence for dark matter are discussed in light of the least-action principle.

Cosmological evolution in vector-tensor theories of gravity

International Nuclear Information System (INIS)

Beltran Jimenez, Jose; Maroto, Antonio L.

2009-01-01

We present a detailed study of the cosmological evolution in general vector-tensor theories of gravity without potential terms. We consider the evolution of the vector field throughout the expansion history of the Universe and carry out a classification of models according to the behavior of the vector field in each cosmological epoch. We also analyze the case in which the Universe is dominated by the vector field, performing a complete analysis of the system phase map and identifying those attracting solutions which give rise to accelerated expansion. Moreover, we consider the evolution in a universe filled with a pressureless fluid in addition to the vector field and study the existence of attractors in which we can have a transition from matter domination to vector domination with accelerated expansion so that the vector field may play the role of dark energy. We find that the existence of solutions with late-time accelerated expansion is a generic prediction of vector-tensor theories and that such solutions typically lead to the presence of future singularities. Finally, limits from local gravity tests are used to get constraints on the value of the vector field at small (Solar System) scales.

Nonsingular cosmology from evolutionary quantum gravity

Science.gov (United States)

Cianfrani, Francesco; Montani, Giovanni; Pittorino, Fabrizio

2014-11-01

We provide a cosmological implementation of the evolutionary quantum gravity, describing an isotropic Universe, in the presence of a negative cosmological constant and a massive (preinflationary) scalar field. We demonstrate that the considered Universe has a nonsingular quantum behavior, associated to a primordial bounce, whose ground state has a high occupation number. Furthermore, in such a vacuum state, the super-Hamiltonian eigenvalue is negative, corresponding to a positive emerging dust energy density. The regularization of the model is performed via a polymer quantum approach to the Universe scale factor and the proper classical limit is then recovered, in agreement with a preinflationary state of the Universe. Since the dust energy density is redshifted by the Universe de Sitter phase and the cosmological constant does not enter the ground state eigenvalue, we get a late-time cosmology, compatible with the present observations, endowed with a turning point in the far future.

Gravity the quest for gravitational wave

CERN Document Server

Binétruy, Pierre

2018-01-01

What force do the Big Bang, the expansion of the Universe, dark matter and dark energy, black holes, and gravitational waves all have in common? This book uncovers gravity as a key to understanding these fascinating phenomena that have so captivated public interest in recent years. Readers will discover the latest findings on how this familiar force in our everyday lives powers the most colossal changes in the Universe. Written by the widely recognized French public scientist and leading astrophysicist Pierre Binetruy, the book also explains the recent experimental confirmation of the existence of gravitational waves.

Superbounce and loop quantum ekpyrotic cosmologies from modified gravity: F(R) , F(G) and F(T) theories

Science.gov (United States)

Odintsov, S. D.; Oikonomou, V. K.; Saridakis, Emmanuel N.

2015-12-01

We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the F(R) , F(G) and F(T) gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of the different effective gravities which realize the above two bouncing cosmologies, indicates that a universality might be lying behind the bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable.

Gravity and isostatic anomaly maps of Greece produced

Science.gov (United States)

Lagios, E.; Chailas, S.; Hipkin, R. G.

A gravity anomaly map of Greece was first compiled in the early 1970s [Makris and Stavrou, 1984] from all available gravity data collected by different Hellenic institutions. However, to compose this map the data had to be smoothed to the point that many of the smaller-wavelength gravity anomalies were lost. New work begun in 1987 has resulted in the publication of an updated map [Lagios et al., 1994] and an isostatic anomaly map derived from it.The gravity data cover the area between east longitudes 19° and 27° and north latitudes 32° and 42°, organized in files of 100-km squares and grouped in 10-km squares using UTM zone 34 coordinates. Most of the data on land come from the gravity observations of Makris and Stavrou [1984] with additional data from the Institute of Geology and Mining Exploration, the Public Oil Corporation of Greece, and Athens University. These data were checked using techniques similar to those used in compiling the gravity anomaly map of the United States, but the horizontal gradient was used as a check rather than the gravity difference. Marine data were digitized from the maps of Morelli et al. [1975a, 1975b]. All gravity anomaly values are referred to the IGSN-71 system, reduced with the standard Bouger density of 2.67 Mg/m3. We estimate the errors of the anomalies in the continental part of Greece to be ±0.9 mGal; this is expected to be smaller over fairly flat regions. For stations whose height has been determined by leveling, the error is only ±0.3 mGal. For the marine areas, the errors are about ±5 mGal [Morelli, 1990].

Gravity's rainbow: A bridge between LQC and DSR

Directory of Open Access Journals (Sweden)

M.A. Gorji

2017-02-01

Full Text Available The doubly special relativity (DSR theories are constructed in order to take into account an observer-independent length scale in special relativity framework. Gravity's rainbow is a simple generalization of DSR theories to incorporate gravity. In this paper, we show that the effective Friedmann equations that are suggested by loop quantum cosmology (LQC can be exactly reobtained in rainbow cosmology setup. The deformed geometry of LQC then fixes the modified dispersion relation and results in a unique DSR model. In comparison with standard LQC scenario where only the geometry is modified, both geometry and matter parts get modified in our setup. In this respect, we show that the total number of microstates for the universe is finite which suggests the statistical origin of the energy and entropy density bounds. These results explicitly show that the DSR theories are appropriate candidates for the flat limit of loop quantum gravity.

On the stability of the cosmological solutions in f(R, G) gravity

International Nuclear Information System (INIS)

De la Cruz-Dombriz, Álvaro; Sáez-Gómez, Diego

2012-01-01

Modified gravity is one of the most promising candidates for explaining the current accelerating expansion of the Universe, and even its unification with the inflationary epoch. Nevertheless, the wide range of models capable of explaining the phenomena of dark energy imposes that current research focuses on a more precise study of the possible effects of modified gravity on both cosmological and local levels. In this paper, we focus on the analysis of a type of modified gravity, the so-called f(R, G) gravity, and we perform a deep analysis on the stability of important cosmological solutions. This not only can help to constrain the form of the gravitational action, but also facilitate a better understanding of the behavior of the perturbations in this class of higher order theories of gravity, which will lead to a more precise analysis of the full spectrum of cosmological perturbations in future. (paper)

Massive gravity wrapped in the cosmic web

International Nuclear Information System (INIS)

Shim, Junsup; Lee, Jounghun; Li, Baojiu

2014-01-01

We study how the filamentary pattern of the cosmic web changes if the true gravity deviates from general relativity (GR) on a large scale. The f(R) gravity, whose strength is controlled to satisfy the current observational constraints on the cluster scale, is adopted as our fiducial model and a large, high-resolution N-body simulation is utilized for this study. By applying the minimal spanning tree algorithm to the halo catalogs from the simulation at various epochs, we identify the main stems of the rich superclusters located in the most prominent filamentary section of the cosmic web and determine their spatial extents per member cluster to be the degree of their straightness. It is found that the f(R) gravity has the effect of significantly bending the superclusters and that the effect becomes stronger as the universe evolves. Even in the case where the deviation from GR is too small to be detectable by any other observables, the degree of the supercluster straightness exhibits a conspicuous difference between the f(R) and the GR models. Our results also imply that the supercluster straightness could be a useful discriminator of f(R) gravity from the coupled dark energy since it is shown to evolve differently between the two models. As a final conclusion, the degree of the straightness of the rich superclusters should provide a powerful cosmological test of large scale gravity.

Massive gravity wrapped in the cosmic web

Energy Technology Data Exchange (ETDEWEB)

Shim, Junsup; Lee, Jounghun [Astronomy Program, Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-747 (Korea, Republic of); Li, Baojiu, E-mail: jsshim@astro.snu.ac.kr, E-mail: jounghun@astro.snu.ac.kr [Institute of Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom)

2014-03-20

We study how the filamentary pattern of the cosmic web changes if the true gravity deviates from general relativity (GR) on a large scale. The f(R) gravity, whose strength is controlled to satisfy the current observational constraints on the cluster scale, is adopted as our fiducial model and a large, high-resolution N-body simulation is utilized for this study. By applying the minimal spanning tree algorithm to the halo catalogs from the simulation at various epochs, we identify the main stems of the rich superclusters located in the most prominent filamentary section of the cosmic web and determine their spatial extents per member cluster to be the degree of their straightness. It is found that the f(R) gravity has the effect of significantly bending the superclusters and that the effect becomes stronger as the universe evolves. Even in the case where the deviation from GR is too small to be detectable by any other observables, the degree of the supercluster straightness exhibits a conspicuous difference between the f(R) and the GR models. Our results also imply that the supercluster straightness could be a useful discriminator of f(R) gravity from the coupled dark energy since it is shown to evolve differently between the two models. As a final conclusion, the degree of the straightness of the rich superclusters should provide a powerful cosmological test of large scale gravity.

Massive Gravity

OpenAIRE

de Rham, Claudia

2014-01-01

We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...

Holographic Superconductivity with Gauss-Bonnet gravity

OpenAIRE

Gregory, Ruth

2010-01-01

I review recent work on holographic superconductivity with Einstein-Gauss-Bonnet gravity, and show how the critical temperature of the superconductor depends on both gravitational backreaction and the Gauss-Bonnet parameter, using both analytic and numerical arguments. I also review computations of the conductivity, finding the energy gap, and demonstrating that there is no universal gap ratio, $\\omega_g/T_c$, for these superconductors.

Gravity does not exist a puzzle for the 21st century

CERN Document Server

Icke, Vincent

2014-01-01

Every scientific fact begins as an opinion about the unknown—a theory—that becomes fact as evidence piles up to support it. But what if two theories exist that correspond perfectly to observed phenomena and they cannot be reconciled with each other? Can theory become fact? Such is the dilemma in contemporary physics. In seeking to understand the mechanisms of the universe, physicists have arrived at two conflicting theories: one explains the mystery of gravity through a precise model of space and time, and the other explains the mystery of matter via the behavior of quantum particles. Each theory reigns in its own domain. But 13.8 billion years ago, when the universe first came into being, gravity and matter belonged to a single realm. Can these theories be united, and if so, what facts will be revealed? This, contends Vincent Icke, is the central puzzle facing physics in our century. Combining Icke’s expertise with a robust argument and intellectual playfulness, Gravity Does Not Exist makes a notorious...

Characterization of the Lovelock gravity by Bianchi derivative

Indian Academy of Sciences (India)

Characterization of the Lovelock gravity by Bianchi derivative. NARESH DADHICH. Inter-University Centre for Astronomy & Astrophysics, Post Bag 4, Pune 411 007, India. E-mail: nkd@iucaa.ernet.in. MS received 30 November 2009; revised 15 February 2010; accepted 19 February 2010. Abstract. We prove the theorem: ...

Scales of gravity

International Nuclear Information System (INIS)

Dvali, Gia; Kolanovic, Marko; Nitti, Francesco; Gabadadze, Gregory

2002-01-01

We propose a framework in which the quantum gravity scale can be as low as 10 -3 eV. The key assumption is that the standard model ultraviolet cutoff is much higher than the quantum gravity scale. This ensures that we observe conventional weak gravity. We construct an explicit brane-world model in which the brane-localized standard model is coupled to strong 5D gravity of infinite-volume flat extra space. Because of the high ultraviolet scale, the standard model fields generate a large graviton kinetic term on the brane. This kinetic term 'shields' the standard model from the strong bulk gravity. As a result, an observer on the brane sees weak 4D gravity up to astronomically large distances beyond which gravity becomes five dimensional. Modeling quantum gravity above its scale by the closed string spectrum we show that the shielding phenomenon protects the standard model from an apparent phenomenological catastrophe due to the exponentially large number of light string states. The collider experiments, astrophysics, cosmology and gravity measurements independently point to the same lower bound on the quantum gravity scale, 10 -3 eV. For this value the model has experimental signatures both for colliders and for submillimeter gravity measurements. Black holes reveal certain interesting properties in this framework

Characterization of diesel oil mixtures with soy oil used for activation of engines of internal combustion; Caracterizacao de misturas de oleo diesel com oleo de soja reutilizado para acionamento de motores de combustao interna

Energy Technology Data Exchange (ETDEWEB)

Siqueira, Wagner da Cunha; Fernandes, Haroldo Carlos; Teixiera, Mauri Martins; Abrahao, Selma Alves; Leite, Daniel Mariano [Universidade de Vicosa, (DEA/UFV), MG (Brazil). Dept. de Engenharia Agricola], Emails: wagner.siqueira@ufv.br, haroldo@ufv.br, mauri@ufv.br, selma.abrahao@ufv.br, daniel.mariano@ufv.br

2011-07-01

Alternative energy sources have been studied in several countries, with emphasis on ways of obtaining and using more efficient. The objective of this work to evaluate and characterize mixtures of diesel oil (DO) with soybean oil reused (OSR), the ratios of 0, 25, 50, 75, and 100% of OSR in relation to specific gravity index viscosity and calorific value. To determine the specific gravity was used beaker, thermometer and a balance for each mixture was adjusted a regression model to estimate the bulk density as a function of temperature (25 to 90 deg C). We analyzed the viscosity of the mixtures using an orifice-type viscometer Saybolt, through regression analysis models were fit to estimate the viscosity as a function of temperature, heating the OSR 100% from 40 to 90 deg C decreased by up 90.4% to its viscosity. The tests were performed calorimetric using a bomb calorimeter determines the calorific value , the variation in calorific value followed a descending order with respect to OD with the increasing content of OSR. The OSR is efficient for use in internal combustion engines in small proportions. (author)

PPN-limit of Fourth Order Gravity inspired by Scalar-Tensor Gravity

OpenAIRE

Capozziello, S.; Troisi, A.

2005-01-01

Based on the {\\it dynamical} equivalence between higher order gravity and scalar-tensor gravity the PPN-limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN-parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled.

Terrestrial gravity data analysis for interim gravity model improvement

Science.gov (United States)

1987-01-01

This is the first status report for the Interim Gravity Model research effort that was started on June 30, 1986. The basic theme of this study is to develop appropriate models and adjustment procedures for estimating potential coefficients from terrestrial gravity data. The plan is to use the latest gravity data sets to produce coefficient estimates as well as to provide normal equations to NASA for use in the TOPEX/POSEIDON gravity field modeling program.

Nonlinear evolution of the matter power spectrum in modified theories of gravity

International Nuclear Information System (INIS)

Koyama, Kazuya; Taruya, Atsushi; Hiramatsu, Takashi

2009-01-01

We present a formalism to calculate the nonlinear matter power spectrum in modified gravity models that explain the late-time acceleration of the Universe without dark energy. Any successful modified gravity models should contain a mechanism to recover general relativity (GR) on small scales in order to avoid the stringent constrains on deviations from GR at solar system scales. Based on our formalism, the quasi-nonlinear power spectrum in the Dvali-Gabadadze-Porratti braneworld models and f(R) gravity models are derived by taking into account the mechanism to recover GR properly. We also extrapolate our predictions to fully nonlinear scales using the parametrized post-Friedmann framework. In the Dvali-Gabadadze-Porratti and f(R) gravity models, the predicted nonlinear power spectrum is shown to reproduce N-body results. We find that the mechanism to recover GR suppresses the difference between the modified gravity models and dark energy models with the same expansion history, but the difference remains large at the weakly nonlinear regime in these models. Our formalism is applicable to a wide variety of modified gravity models and it is ready to use once consistent models for modified gravity are developed.

A new approach for gravity localization in six-dimensional geometries

International Nuclear Information System (INIS)

Santos, Victor Pereira do Nascimento; Almeida, Carlos Alberto Santos de

2011-01-01

Full text: The idea that spacetime may have more than four dimensions is old, originally presented as an attempt to unify Maxwell's theory of Electromagnetism with the brand-new gravitation theory of Einstein. Such extra dimensions are in principle unobservable to the energy scales currently available. However, its effects can be seen in short distance gravity experiments and in observations in cosmology. Also, it is used as a mechanism to explain the difference between the energy scales of the weak force and gravity, which is called the hierarchy problem. The current framework for the extra dimension scenario is consider the four-dimensional known universe as embedded in a higher dimensional space called bulk. The form of this bulk determines how we perceive gravity in our universe; then, the behaviour of gravitational field depends on the geometry of the bulk. Metric solutions were already presented for string-like defect, with and without matter sources, where was shown that the gravity Newtonian potential grows with the inverse cube of distance. Such correction arises from a very particular mass spectrum for the gravitational field, which already contains the orbital angular momentum contributions. In this work we study the behaviour of gravitational field in a extra-dimensional braneworld scenario, using non-factorizable geometries (which preserves Poincare symmetry) and setting suitable matter distributions in order to verify its localization, for several geometries. For such geometries it is possible to find explicit solutions for the tensor fluctuations of the metric. (author)

Signatures of modified gravity on the 21 cm power spectrum at reionisation

Energy Technology Data Exchange (ETDEWEB)

Brax, Philippe [Institut de Physique Théorique, CEA, IPhT, CNRS, URA 2306, F-91191 Gif/Yvette Cedex (France); Clesse, Sébastien; Davis, Anne-Christine, E-mail: philippe.brax@cea.fr, E-mail: s.clesse@damtp.cam.ac.uk, E-mail: a.c.davis@damtp.cam.ac.uk [DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

2013-01-01

Scalar modifications of gravity have an impact on the growth of structure. Baryon and Cold Dark Matter (CDM) perturbations grow anomalously for scales within the Compton wavelength of the scalar field. In the late time Universe when reionisation occurs, the spectrum of the 21 cm brightness temperature is thus affected. We study this effect for chameleon-f(R) models, dilatons and symmetrons. Although the f(R) models are more tightly constrained by solar system bounds, and effects on dilaton models are negligible, we find that symmetrons where the phase transition occurs before z{sub *} ∼ 12 could be detectable for a scalar field range as low as 5kpc. For all these models, the detection prospects of modified gravity effects are higher when considering modes parallel to the line of sight where very small scales can be probed. The study of the 21 cm spectrum thus offers a complementary approach to testing modified gravity with large scale structure surveys. Short scales, which would be highly non-linear in the very late time Universe when structure forms and where modified gravity effects are screened, appear in the linear spectrum of 21 cm physics, hence deviating from General Relativity in a maximal way.

How many 'times' do we have in quantum gravity?

International Nuclear Information System (INIS)

Hosoya, Akio; Soda, Jiro.

1990-07-01

Apparently, there are infinite number of time-like variables in the Wheeler-DeWitt equation in quantum gravity. This gives rise to an obvious conceptual difficulty and further becomes an obstacle if one wants to canonically third quantize the universe. In this paper, adopting York's gauge in the path-integral approach, we formulate quantum geometrodynamics so that it contains only a single time-like variable corresponding to the total volume of the universe. (author)

Thermodynamic laws for generalized f(R) gravity with curvature-matter coupling

International Nuclear Information System (INIS)

Wu Yabo; Zhao Yueyue; Cai Ronggen; Lu Jianbo; Lu Junwang; Gao Xiaojing

2012-01-01

The first law and the generalized second law (GSL) of thermodynamics for the generalized f(R) gravity with curvature-matter coupling are studied in the spatially homogeneous, isotropic FRW universe. The research results show that the field equations of the generalized f(R) gravity with curvature-matter coupling can be cast to the form of the first law of thermodynamics with the so-called the entropy production terms dS ¯ and the GSL can be given by considering the FRW universe filled only with ordinary matter enclosed by the dynamical apparent horizon with the Hawking temperature. Furthermore, as a concrete example, by utilizing the GSL the constraints on the gravitational model with f 1 (R)=R+αR l and f 2 (R)=R m are also discussed. It is worth noting these results given by us are quite general and can degenerate to the ones in Einstein's general relativity and pure f(R) gravity with non-coupling and non-minimal coupling as special cases. Comparing with the case of Einstein's general relativity, the appearance of the entropy production term dS ¯ in the first law of thermodynamics demonstrates that the horizon thermodynamics is non-equilibrium one for generalized f(R) gravity with curvature-matter coupling, which is consistent with the arguments given in Akbar and Cai (2007) [13] and Eling et al. (2006) [18].

Accelerated FRW solutions in Chern-Simons gravity

International Nuclear Information System (INIS)

Cataldo, Mauricio; Crisostomo, Juan; Gomez, Fernando; Salgado, Patricio; Campo, Sergio del; Quinzacara, Cristian C.

2014-01-01

We consider a five-dimensional Einstein-Chern-Simons action which is composed of a gravitational sector and a sector of matter where the gravitational sector is given by a Chern-Simons gravity action instead of the Einstein-Hilbert action and where the matter sector is given by the so-called perfect fluid. It is shown that (i) the Einstein-Chern-Simons (EChS) field equations subject to suitable conditions can be written in a similar way to the Einstein-Maxwell field equations; (ii) these equations have solutions that describe an accelerated expansion for the three possible cosmological models of the universe, namely, spherical expansion, flat expansion, and hyperbolic expansion when α a parameter of the theory, is greater than zero. This result allows us to conjecture that these solutions are compatible with the era of dark energy and that the energy-momentum tensor for the field h a , a bosonic gauge field from the Chern-Simons gravity action, corresponds to a form of positive cosmological constant. It is also shown that the EChS field equations have solutions compatible with the era of matter: (i) In the case of an open universe, the solutions correspond to an accelerated expansion (α > 0) with a minimum scale factor at initial time that, when time goes to infinity, the scale factor behaves as a hyperbolic sine function. (ii) In the case of a flat universe, the solutions describe an accelerated expansion whose scale factor behaves as an exponential function of time. (iii) In the case of a closed universe there is found only one solution for a universe in expansion, which behaves as a hyperbolic cosine function of time. (orig.)

Unified cosmic history in modified gravity: From F(R) theory to Lorentz non-invariant models

Science.gov (United States)

Nojiri, Shin'Ichi; Odintsov, Sergei D.

2011-08-01

The classical generalization of general relativity is considered as the gravitational alternative for a unified description of the early-time inflation with late-time cosmic acceleration. The structure and cosmological properties of a number of modified theories, including traditional F(R) and Hořava-Lifshitz F(R) gravity, scalar-tensor theory, string-inspired and Gauss-Bonnet theory, non-local gravity, non-minimally coupled models, and power-counting renormalizable covariant gravity are discussed. Different representations of and relations between such theories are investigated. It is shown that some versions of the above theories may be consistent with local tests and may provide a qualitatively reasonable unified description of inflation with the dark energy epoch. The cosmological reconstruction of different modified gravities is provided in great detail. It is demonstrated that eventually any given universe evolution may be reconstructed for the theories under consideration, and the explicit reconstruction is applied to an accelerating spatially flat Friedmann-Robertson-Walker (FRW) universe. Special attention is paid to Lagrange multiplier constrained and conventional F(R) gravities, for latter F(R) theory, the effective ΛCDM era and phantom divide crossing acceleration are obtained. The occurrences of the Big Rip and other finite-time future singularities in modified gravity are reviewed along with their solutions via the addition of higher-derivative gravitational invariants.

On the stability of Einstein static universe in doubly general relativity scenario

Energy Technology Data Exchange (ETDEWEB)

Khodadi, M.; Nozari, K. [University of Mazandaran, Department of Physics, Faculty of Basic Sciences, Babolsar (Iran, Islamic Republic of); Heydarzade, Y. [Azarbaijan Shahid Madani University, Department of Physics, Tabriz (Iran, Islamic Republic of); Darabi, F. [Azarbaijan Shahid Madani University, Department of Physics, Tabriz (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of)

2015-12-15

By presenting a relation between the average energy of the ensemble of probe photons and the energy density of the universe, in the context of gravity's rainbow or the doubly general relativity scenario, we introduce a rainbow FRW universe model. By analyzing the fixed points in the flat FRW model modified by two well-known rainbow functions, we find that the finite time singularity avoidance (i.e. Big Bang) may still remain as a problem. Then we follow the ''emergent universe'' scenario in which there is no beginning of time and consequently there is no Big-Bang singularity. Moreover, we study the impact of high energy quantum gravity modifications related to the gravity's rainbow on the stability conditions of an ''Einstein static universe'' (ESU). We find that independent of the particular rainbow function, the positive energy condition dictates a positive spatial curvature for the universe. In fact, without raising a nonphysical energy condition in the quantum gravity regimes, we can observe agreement between gravity's rainbow scenario and the basic assumption of the modern version of the ''emergent universe''. We show that in the absence and presence of an energy-dependent cosmological constant Λ(ε), a stable Einstein static solution is available versus the homogeneous and linear scalar perturbations under the variety of the obtained conditions. Also, we explore the stability of ESU against the vector and tensor perturbations. (orig.)

Gravity mediated supersymmetry breaking in six dimensions

International Nuclear Information System (INIS)

Falkowski, Adam; Lee, Hyun Min; Luedeling, Christoph

2005-01-01

We study gravity mediated supersymmetry breaking in four-dimensional effective theories derived from six-dimensional brane-world supergravity. Using the Noether method we construct a locally supersymmetric action for a bulk-brane system consisting of the minimal six-dimensional supergravity coupled to vector and chiral multiplets located at four-dimensional branes. Couplings of the bulk moduli to the brane are uniquely fixed, in particular, they are flavour universal. We compactify this system on T 2 /Z 2 and derive the four-dimensional effective supergravity. The tree-level effective Kaehler potential is not of the sequestered form, therefore gravity mediation may occur at tree-level. We identify one scenario of moduli stabilization in which the soft scalar masses squared are positive

Superconducting gravity gradiometer for sensitive gravity measurements. I. Theory

International Nuclear Information System (INIS)

Chan, H.A.; Paik, H.J.

1987-01-01

Because of the equivalence principle, a global measurement is necessary to distinguish gravity from acceleration of the reference frame. A gravity gradiometer is therefore an essential instrument needed for precision tests of gravity laws and for applications in gravity survey and inertial navigation. Superconductivity and SQUID (superconducting quantum interference device) technology can be used to obtain a gravity gradiometer with very high sensitivity and stability. A superconducting gravity gradiometer has been developed for a null test of the gravitational inverse-square law and space-borne geodesy. Here we present a complete theoretical model of this instrument. Starting from dynamical equations for the device, we derive transfer functions, a common mode rejection characteristic, and an error model of the superconducting instrument. Since a gradiometer must detect a very weak differential gravity signal in the midst of large platform accelerations and other environmental disturbances, the scale factor and common mode rejection stability of the instrument are extremely important in addition to its immunity to temperature and electromagnetic fluctuations. We show how flux quantization, the Meissner effect, and properties of liquid helium can be utilized to meet these challenges

Dualities and emergent gravity: Gauge/gravity duality

Science.gov (United States)

de Haro, Sebastian

2017-08-01

In this paper I develop a framework for relating dualities and emergence: two notions that are close to each other but also exclude one another. I adopt the conception of duality as 'isomorphism', from the physics literature, cashing it out in terms of three conditions. These three conditions prompt two conceptually different ways in which a duality can be modified to make room for emergence; and I argue that this exhausts the possibilities for combining dualities and emergence (via coarse-graining). I apply this framework to gauge/gravity dualities, considering in detail three examples: AdS/CFT, Verlinde's scheme, and black holes. My main point about gauge/gravity dualities is that the theories involved, qua theories of gravity, must be background-independent. I distinguish two senses of background-independence: (i) minimalistic and (ii) extended. I argue that the former is sufficiently strong to allow for a consistent theory of quantum gravity; and that AdS/CFT is background-independent on this account; while Verlinde's scheme best fits the extended sense of background-independence. I argue that this extended sense should be applied with some caution: on pain of throwing the baby (general relativity) out with the bath-water (extended background-independence). Nevertheless, it is an interesting and potentially fruitful heuristic principle for quantum gravity theory construction. It suggests some directions for possible generalisations of gauge/gravity dualities. The interpretation of dualities is discussed; and the so-called 'internal' vs. 'external' viewpoints are articulated in terms of: (i) epistemic and metaphysical commitments; (ii) parts vs. wholes. I then analyse the emergence of gravity in gauge/gravity dualities in terms of the two available conceptualisations of emergence; and I show how emergence in AdS/CFT and in Verlinde's scenario differ from each other. Finally, I give a novel derivation of the Bekenstein-Hawking black hole entropy formula based on

The ascent of gravity the quest to understand the force that explains everything

CERN Document Server

Chown, Marcus

2017-01-01

Gravity is the weakest force in the everyday world yet it is the strongest force in the universe. It was the first force to be recognised and described yet it is the least understood. It is a 'force' that keeps your feet on the ground yet no such force actually exists. Gravity, to steal the words of Winston Churchill, is 'a riddle, wrapped in a mystery, inside an enigma'. And penetrating that enigma promises to answer the biggest questions in science: what is space? What is time? What is the universe? And where did it all come from? Award-winning writer Marcus Chown takes us on an unforgettable journey from the recognition of the 'force' of gravity in 1666 to the discovery of gravitational waves in 2015. And, as we stand on the brink of a seismic revolution in our worldview, he brings us up to speed on the greatest challenge ever to confront physics.

Contravariant gravity on Poisson manifolds and Einstein gravity

International Nuclear Information System (INIS)

Kaneko, Yukio; Watamura, Satoshi; Muraki, Hisayoshi

2017-01-01

A relation between gravity on Poisson manifolds proposed in Asakawa et al (2015 Fortschr. Phys . 63 683–704) and Einstein gravity is investigated. The compatibility of the Poisson and Riemann structures defines a unique connection, the contravariant Levi-Civita connection, and leads to the idea of the contravariant gravity. The Einstein–Hilbert-type action yields an equation of motion which is written in terms of the analog of the Einstein tensor, and it includes couplings between the metric and the Poisson tensor. The study of the Weyl transformation reveals properties of those interactions. It is argued that this theory can have an equivalent description as a system of Einstein gravity coupled to matter. As an example, it is shown that the contravariant gravity on a two-dimensional Poisson manifold can be described by a real scalar field coupled to the metric in a specific manner. (paper)

Virial Theorem in Nonlocal Newtonian Gravity

Directory of Open Access Journals (Sweden)

Bahram Mashhoon

2016-05-01

Full Text Available Nonlocal gravity is the recent classical nonlocal generalization of Einstein’s theory of gravitation in which the past history of the gravitational field is taken into account. In this theory, nonlocality appears to simulate dark matter. The virial theorem for the Newtonian regime of nonlocal gravity theory is derived and its consequences for “isolated” astronomical systems in virial equilibrium at the present epoch are investigated. In particular, for a sufficiently isolated nearby galaxy in virial equilibrium, the galaxy’s baryonic diameter D 0 —namely, the diameter of the smallest sphere that completely surrounds the baryonic system at the present time—is predicted to be larger than the effective dark matter fraction f D M times a universal length that is the basic nonlocality length scale λ 0 ≈ 3 ± 2 kpc.

New solutions of the Einstein equations for the Mixmaster and Taub Universe models and the anti gravity phenomena

International Nuclear Information System (INIS)

Melendez L, L.

2004-01-01

In the first part of this work, starting from Einstein's equations of the Classical General Relativity, a new kind of solutions for the Mixmaster model are explored. By dispensing with the extension to the complex variable field, which is usual in problems such as the Laplace equation or the harmonic oscillator, in a similar manner to that of Quantum Mechanics, the equations appear to have solutions that belong to the complex General Relativity. A first integral is performed by establishing a separation of the first derivatives. Then a second integral is obtained once the respective equations with separate variables are found and whose integrals provide a family of complex solutions. However, reality conditions do not seem to be easily imposed at this stage. Above all, it is significant that the classical Einstein's equations for the debatably integrable Mixmaster model present complex solutions. In the second part of this work, following a specific strategy in which the cosmological time variables are operated upon, a new family of solutions to the empty Taub universe is found. Among the characteristics of such a family, it stands the positive acceleration provided by the tri-curvature property of this universe to two of the three scale factors of the Taub model. This effect of the tri-curvature results not in a restoring force such as normal gravity but in the conversion of the Taub cosmology into an accelerating universe. (Author)

Einstein gravity 3-point functions from conformal field theory

Science.gov (United States)

Afkhami-Jeddi, Nima; Hartman, Thomas; Kundu, Sandipan; Tajdini, Amirhossein

2017-12-01

We study stress tensor correlation functions in four-dimensional conformal field theories with large N and a sparse spectrum. Theories in this class are expected to have local holographic duals, so effective field theory in anti-de Sitter suggests that the stress tensor sector should exhibit universal, gravity-like behavior. At the linearized level, the hallmark of locality in the emergent geometry is that stress tensor three-point functions 〈 T T T 〉, normally specified by three constants, should approach a universal structure controlled by a single parameter as the gap to higher spin operators is increased. We demonstrate this phenomenon by a direct CFT calculation. Stress tensor exchange, by itself, violates causality and unitarity unless the three-point functions are carefully tuned, and the unique consistent choice exactly matches the prediction of Einstein gravity. Under some assumptions about the other potential contributions, we conclude that this structure is universal, and in particular, that the anomaly coefficients satisfy a ≈ c as conjectured by Camanho et al. The argument is based on causality of a four-point function, with kinematics designed to probe bulk locality, and invokes the chaos bound of Maldacena, Shenker, and Stanford.

Fracture analysis of concrete gravity dam under earthquake induced ...

African Journals Online (AJOL)

Michael Horsfall

Fracture analysis of concrete gravity dam under earthquake induced loads. 1. ABBAS MANSOURI;. 2 ... 1 Civil Engineering, Islamic Azad University (South Branch of Tehran)Tehran, Iran ..... parameter has on the results of numerical calculations. In this analysis ... with the help of Abaqus software (Abaqus theory manual ...

Is nonrelativistic gravity possible?

International Nuclear Information System (INIS)

Kocharyan, A. A.

2009-01-01

We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (anti-)de Sitter black holes of Einstein gravity and IR limit of Horava gravity are locally identical.

Warm inflation in f(G) theory of gravity

Energy Technology Data Exchange (ETDEWEB)

Sharif, M., E-mail: msharif.math@pu.edu.pk; Ikram, A., E-mail: ayeshamaths91@gmail.com [University of the Punjab, Quaid-e-Azam Campus, Department of Mathematics (Pakistan)

2016-07-15

The aim of this paper is to explore warm inflation in the background of f(G) theory of gravity using scalar fields for the FRW universe model. We construct the field equations under slow-roll approximations and evaluate the slow-roll parameters, scalar and tensor power spectra and their corresponding spectral indices using viable power-law model. These parameters are evaluated for a constant as well as variable dissipation factor during intermediate and logamediate inflationary epochs. We also find the number of e-folds and tensor- scalar ratio for each case. The graphical behavior of these parameters proves that the isotropic model in f(G) gravity is compatible with observational Planck data.

Gödel metrics with chronology protection in Horndeski gravities

Science.gov (United States)

Geng, Wei-Jian; Li, Shou-Long; Lü, H.; Wei, Hao

2018-05-01

Gödel universe, one of the most interesting exact solutions predicted by General Relativity, describes a homogeneous rotating universe containing naked closed time-like curves (CTCs). It was shown that such CTCs are the consequence of the null energy condition in General Relativity. In this paper, we show that the Gödel-type metrics with chronology protection can emerge in Einstein-Horndeski gravity. We construct such exact solutions also in Einstein-Horndeski-Maxwell and Einstein-Horndeski-Proca theories.

Gravity-matter entanglement in Regge quantum gravity

International Nuclear Information System (INIS)

Paunković, Nikola; Vojinović, Marko

2016-01-01

We argue that Hartle-Hawking states in the Regge quantum gravity model generically contain non-trivial entanglement between gravity and matter fields. Generic impossibility to talk about “matter in a point of space” is in line with the idea of an emergent spacetime, and as such could be taken as a possible candidate for a criterion for a plausible theory of quantum gravity. Finally, this new entanglement could be seen as an additional “effective interaction”, which could possibly bring corrections to the weak equivalence principle. (paper)

Miniaturised Gravity Sensors for Remote Gravity Surveys.

Science.gov (United States)

Middlemiss, R. P.; Bramsiepe, S. G.; Hough, J.; Paul, D. J.; Rowan, S.; Samarelli, A.; Hammond, G.

2016-12-01

Gravimetry lets us see the world from a completely different perspective. The ability to measure tiny variations in gravitational acceleration (g), allows one to see not just the Earth's gravitational pull, but the influence of smaller objects. The more accurate the gravimeter, the smaller the objects one can see. Gravimetry has applications in many different fields: from tracking magma moving under volcanoes before eruptions; to locating hidden tunnels. The top commercial gravimeters weigh tens of kg and cost at least $100,000, limiting the situations in which they can be used. By contrast, smart phones use a MEMS (microelectromechanical system) accelerometer that can measure the orientation of the device. These are not nearly sensitive or stable enough to be used for the gravimetry but they are cheap, light-weight and mass-producible. At Glasgow University we have developed a MEMS device with both the stability and sensitivity for useful gravimetric measurements. This was demonstrated by a measurement of the Earth tides - the first time this has been achieved with a MEMS sensor. A gravimeter of this size opens up the possiblility for new gravity imaging modalities. Thousands of gravimeters could be networked over a survey site, storing data on an SD card or communicating wirelessly to a remote location. These devices could also be small enough to be carried by a UAVs: airborne gravity surveys could be carried out at low altitude by mulitple UAVs, or UAVs could be used to deliver ground based gravimeters to remote or inaccessible locations.

No-go theorem for bimetric gravity with positive and negative mass

International Nuclear Information System (INIS)

Hohmann, Manuel; Wohlfarth, Mattias N. R.

2009-01-01

We argue that the most conservative geometric extension of Einstein gravity describing both positive and negative mass sources and observers is bimetric gravity and contains two copies of standard model matter which interact only gravitationally. Matter fields related to one of the metrics then appear dark from the point of view of an observer defined by the other metric, and so may provide a potential explanation for the dark universe. In this framework we consider the most general form of linearized field equations compatible with physically and mathematically well-motivated assumptions. Using gauge-invariant linear perturbation theory, we prove a no-go theorem ruling out all bimetric gravity theories that, in the Newtonian limit, lead to precisely opposite forces on positive and negative test masses.

FLRW Cosmology with Horava-Lifshitz Gravity: Impacts of Equations of State

Science.gov (United States)

Tawfik, A.; Abou El Dahab, E.

2017-07-01

Inspired by Lifshitz theory for quantum critical phenomena in condensed matter, Horava proposed a theory for quantum gravity with an anisotropic scaling in ultraviolet. In Horava-Lifshitz gravity (HLG), we have studied the impacts of six types of equations of state on the evolution of various cosmological parameters such as Hubble parameters and scale factor. From the comparison of the general relativity gravity with the HLG with detailed and without with non-detailed balance conditions, remarkable differences are found. Also, a noticeable dependence of singular and non-singular Big Bang on the equations of state is observed. We conclude that HLG explains various epochs in the early universe and might be able to reproduce the entire cosmic history with and without singular Big Bang.

Lovelock gravities from Born-Infeld gravity theory

Science.gov (United States)

Concha, P. K.; Merino, N.; Rodríguez, E. K.

2017-02-01

We present a Born-Infeld gravity theory based on generalizations of Maxwell symmetries denoted as Cm. We analyze different configuration limits allowing to recover diverse Lovelock gravity actions in six dimensions. Further, the generalization to higher even dimensions is also considered.

Euler–Chern–Simons gravity from Lovelock–Born–Infeld gravity

OpenAIRE

Izaurieta, F.; Rodriguez, E.; Salgado, P.

2004-01-01

In the context of a gauge theoretical formulation, higher dimensional gravity invariant under the AdS group is dimensionally reduced to Euler-Chern-Simons gravity. The dimensional reduction procedure of Grignani-Nardelli [Phys. Lett. B 300, 38 (1993)] is generalized so as to permit reducing D-dimensional Lanczos Lovelock gravity to d=D-1 dimensions.

Proposal for testing quantum gravity in the lab

International Nuclear Information System (INIS)

Ali, Ahmed Farag; Das, Saurya; Vagenas, Elias C.

2011-01-01

Attempts to formulate a quantum theory of gravitation are collectively known as quantum gravity. Various approaches to quantum gravity such as string theory and loop quantum gravity, as well as black hole physics and doubly special relativity theories predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called generalized uncertainty principle (GUP). We have proposed a GUP consistent with string theory, black hole physics, and doubly special relativity theories and have showed that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it suggests that the space that confines it must be quantized, and in fact that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this may signal the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale. Because this influences all the quantum Hamiltonians in an universal way, it predicts quantum gravity corrections to various quantum phenomena. Therefore, in the present work we compute these corrections to the Lamb shift, simple harmonic oscillator, Landau levels, and the tunneling current in a scanning tunneling microscope.

Lower dimensional gravity

International Nuclear Information System (INIS)

Brown, J.D.

1988-01-01

This book addresses the subject of gravity theories in two and three spacetime dimensions. The prevailing philosophy is that lower dimensional models of gravity provide a useful arena for developing new ideas and insights, which are applicable to four dimensional gravity. The first chapter consists of a comprehensive introduction to both two and three dimensional gravity, including a discussion of their basic structures. In the second chapter, the asymptotic structure of three dimensional Einstein gravity with a negative cosmological constant is analyzed. The third chapter contains a treatment of the effects of matter sources in classical two dimensional gravity. The fourth chapter gives a complete analysis of particle pair creation by electric and gravitational fields in two dimensions, and the resulting effect on the cosmological constant

Energy conditions in f(G,T) gravity

Energy Technology Data Exchange (ETDEWEB)

Sharif, M.; Ikram, Ayesha [University of the Punjab, Department of Mathematics, Lahore (Pakistan)

2016-11-15

The aim of this paper is to introduce a new modified gravity theory named f(G,T) gravity (G and T are the Gauss-Bonnet invariant and trace of the energy-momentum tensor, respectively) and investigate energy conditions for two reconstructed models in the context of FRW universe. We formulate general field equations, divergence of energy-momentum tensor, equation of motion for test particles as well as corresponding energy conditions. The massive test particles follow non-geodesic lines of geometry due to the presence of an extra force. We express the energy conditions in terms of cosmological parameters like the deceleration, jerk, and snap parameters. The reconstruction technique is applied to this theory using de Sitter and power-law cosmological solutions. We analyze the energy bounds and obtain feasible constraints on the free parameters. (orig.)

Quantum cosmology of classically constrained gravity

International Nuclear Information System (INIS)

Gabadadze, Gregory; Shang Yanwen

2006-01-01

In [G. Gabadadze, Y. Shang, hep-th/0506040] we discussed a classically constrained model of gravity. This theory contains known solutions of General Relativity (GR), and admits solutions that are absent in GR. Here we study cosmological implications of some of these new solutions. We show that a spatially-flat de Sitter universe can be created from 'nothing'. This universe has boundaries, and its total energy equals to zero. Although the probability to create such a universe is exponentially suppressed, it favors initial conditions suitable for inflation. Then we discuss a finite-energy solution with a nonzero cosmological constant and zero space-time curvature. There is no tunneling suppression to fluctuate into this state. We show that for a positive cosmological constant this state is unstable-it can rapidly transition to a de Sitter universe providing a new unsuppressed channel for inflation. For a negative cosmological constant the space-time flat solutions is stable.

The Gravity Probe B Flight Dewar

Science.gov (United States)

2001-01-01

Gravity Probe B (GP-B) is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. This photograph is of the Gravity Probe B flight dewar, a metal container made like a vacuum bottle that is used especially for storing liquefied gases, that will maintain the experiment at a temperature just above absolute zero, staying cold for two years. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies -- technologies that are already enlivening other branches of science and engineering. Launched in 2004 and managed for NASA by the Marshall Space Flight Center, development of the GP-B is the responsibility of Stanford University, with major subcontractor Lockheed Martin Corporation. (Photo Credit: Lockheed Martin Corporation/R. Underwood)

Double universe and the arrow of time

Energy Technology Data Exchange (ETDEWEB)

Alfinito, Eleonora [Dipartimento di Ingegneria dell' Innovazione, Universitta di Lecce, 73100 Lecce and CNISM-Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia. Universita di Lecce (Italy); Vitiello, Giuseppe [Dipartimento di Fisica, Universita di Salerno, and INFN Gruppo Collegato di Salerno, 84100 Salerno (Italy)

2007-05-15

The canonical quantum field theory formalism for the expanding geometry universe leads to the 'Double Universe' scenario envisaged by quantum loop gravity. Thermal properties of inflating universe and the classicality of the time-evolution trajectories in the space of the representations of the canonical commutation relations are also discussed.

Gravity Variations Related to Earthquakes in the BTTZ Region in China

Science.gov (United States)

Zheng, J.; Liu, K.; Lu, H.; Liu, D.; Chen, Y.; Kuo, J. T.

2006-05-01

limited temporally discrete data of gravity variation can be used in forecasting impending earthquakes in the region; 8. Precise measurements of spatially and temporally continuous and discrete gravity variations promise to open a new avenue of monitoring earthquakes, in turn, saving lives in the potentially earthquake prone areas in not only China but also the world. This work has been gratefully supported by the National Science Foundation through the grants to the Lamont-Doherty Earth Observatory, Columbia University and the China Earthquake Administration, formerly China Seismological Bureau.

Lovelock gravities from Born–Infeld gravity theory

Directory of Open Access Journals (Sweden)

P.K. Concha

2017-02-01

Full Text Available We present a Born–Infeld gravity theory based on generalizations of Maxwell symmetries denoted as Cm. We analyze different configuration limits allowing to recover diverse Lovelock gravity actions in six dimensions. Further, the generalization to higher even dimensions is also considered.

Scalar QNMs for higher dimensional black holes surrounded by quintessence in Rastall gravity

Energy Technology Data Exchange (ETDEWEB)

Graca, J.P.M.; Lobo, Iarley P. [Universidade Federal da Paraiba, Departamento de Fisica, Joao Pessoa, PB (Brazil)

2018-02-15

The spacetime solution for a black hole, surrounded by an exotic matter field, in Rastall gravity, is calculated in an arbitrary d-dimensional spacetime. After this, we calculate the scalar quasinormal modes of such solution, and study the shift on the modes caused by the modification of the theory of gravity, i.e., by the introduction of a new term due to Rastall. We conclude that the shift strongly depends on the kind of exotic field one is studying, but for a low density matter that supposedly pervades the universe, it is unlikely that Rastall gravity will cause an instability for the probe field. (orig.)

From quantum cosmology to quantum gravity

International Nuclear Information System (INIS)

Englert, F.

1983-01-01

A theory is proposed which solves the problem of the acausal character of the hot big bang cosmology in general relativity. The initial thermal state is stabilized by constructing a semi-classical solution to the coupled graviation and matter system with zero cosmological constant. This solution is an expanding deSitter in which black holes are created by a quantum process out of the expansion energy. It is argued that the initial nucleation process originates from a quantum metric fluctuation. Universe-like configurations must be added over the path integral metrics. This stabilizes the path integral and saturates it with a ''foam of universes'' where the nonrenormalizability of gravity can be seen as the manifestation of long range interactions within a universe. This description introduces indeterminacy into quantum field theory and suggests that 4-D space-time should be explained by new concepts

Spherical collapse and cluster counts in modified gravity models

International Nuclear Information System (INIS)

Martino, Matthew C.; Stabenau, Hans F.; Sheth, Ravi K.

2009-01-01

Modifications to the gravitational potential affect the nonlinear gravitational evolution of large scale structures in the Universe. To illustrate some generic features of such changes, we study the evolution of spherically symmetric perturbations when the modification is of Yukawa type; this is nontrivial, because we should not and do not assume that Birkhoff's theorem applies. We then show how to estimate the abundance of virialized objects in such models. Comparison with numerical simulations shows reasonable agreement: When normalized to have the same fluctuations at early times, weaker large scale gravity produces fewer massive halos. However, the opposite can be true for models that are normalized to have the same linear theory power spectrum today, so the abundance of rich clusters potentially places interesting constraints on such models. Our analysis also indicates that the formation histories and abundances of sufficiently low mass objects are unchanged from standard gravity. This explains why simulations have found that the nonlinear power spectrum at large k is unaffected by such modifications to the gravitational potential. In addition, the most massive objects in models with normalized cosmic microwave background and weaker gravity are expected to be similar to the high-redshift progenitors of the most massive objects in models with stronger gravity. Thus, the difference between the cluster and field galaxy populations is expected to be larger in models with stronger large scale gravity.

Gravity Defied From Potato Asteroids to Magnetised Neutron Stars 2 ...

Indian Academy of Sciences (India)

Gravitation, the universal attractive force, acts upon all matter(and radiation) relentlessly. Stable extended structurescan exist only when gravity is held off by other forces of nature.This series of articles explores this interplay, looking atobjects that just missed being stars in this particular installment.

A test of Newton's Law of Gravity using the BREN Tower, Nevada

International Nuclear Information System (INIS)

Kasameyer, P.; Thomas, J.; Fackler, O.; Mugge, M.; Kammeraad, J.; Millett, M.; Harris, B.; Felske, D.

1989-01-01

We predicted gravity values on a tower by upward continuing an extensive set of surface data in order to test the 1/r 2 dependence of Newton's Law of Universal Gravitation. We measured gravity at 12 heights up to 454 m on a tower at the Nevada Test Site, and at 91 locations on the surface of the earth within 2.5 kilometers of the tower. These data have been combined with 60,000 surface gravity measurements within 300 kilometers of the tower and have been used to predict the gravitational field on the tower via a solution of Laplace's equation. A discrepancy between the observed gravity values and the prediction could suggest a breakdown of Newtonian Gravity, but we observe none. Our preliminary results are consistent with the Newtonian hypothesis to within 93 +- 95 μgals at the top of the tower, a result which conflicts with the previously reported 500 μgal non-Newtonian signal seen at 562 meters above the earth. 24 refs., 2 figs

Nonlocal gravity

CERN Document Server

Mashhoon, Bahram

2017-01-01

Relativity theory is based on a postulate of locality, which means that the past history of the observer is not directly taken into account. This book argues that the past history should be taken into account. In this way, nonlocality---in the sense of history dependence---is introduced into relativity theory. The deep connection between inertia and gravitation suggests that gravity could be nonlocal, and in nonlocal gravity the fading gravitational memory of past events must then be taken into account. Along this line of thought, a classical nonlocal generalization of Einstein's theory of gravitation has recently been developed. A significant consequence of this theory is that the nonlocal aspect of gravity appears to simulate dark matter. According to nonlocal gravity theory, what astronomers attribute to dark matter should instead be due to the nonlocality of gravitation. Nonlocality dominates on the scale of galaxies and beyond. Memory fades with time; therefore, the nonlocal aspect of gravity becomes wea...

Thermodynamics of the Apparent Horizon in FRW Universe with Massive Gravity

International Nuclear Information System (INIS)

Li Hui; Zhang Yi

2013-01-01

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive gravity model in cosmology proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified Misner-Sharp internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation δQ = T d S, where the heat Bow δQ is the energy-supply of pure matter projecting on the vector ξ tangent to the apparent horizon and should be looked on as the amount of energy crossing the apparent horizon during the time interval dt and the temperature of the apparent horizon for energy crossing during the same interval is 1/(2πr A ), the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit H c → 0, which recovers the Minkowski reference metric solution in the fiat case, the generalized second law of thermodynamics holds if α 3 + 4α 4 3 = α 4 = 0, the generalized second law of thermodynamics could be violated. (general)

One-loop effective action for non-local modified Gauss-Bonnet gravity in de Sitter space

Energy Technology Data Exchange (ETDEWEB)

Cognola, Guido; Zerbini, Sergio [Universita di Trento (Italy); Istituto Nazionale di Fisica Nucleare Gruppo Collegato di Trento, Dipartimento di Fisica, Trento (Italy); Elizalde, Emilio [Consejo Superior de Investigaciones Cientificas (ICE/CSIC) and Institut d' Estudis Espacials de Catalunya (IEEC), Facultat Ciencies, Bellaterra (Barcelona) (Spain); Nojiri, Shin' ichi [Nagoya University, Department of Physics, Nagoya (Japan); Odintsov, Sergei D. [Consejo Superior de Investigaciones Cientificas (ICE/CSIC) and Institut d' Estudis Espacials de Catalunya (IEEC), Facultat Ciencies, Bellaterra (Barcelona) (Spain); ICREA, Barcelona (Spain); TSPU, Center of Theor. Phys., Tomsk (Russian Federation)

2009-12-15

We discuss the classical and quantum properties of non-local modified Gauss-Bonnet gravity in de Sitter space, using its equivalent representation via string-inspired local scalar-Gauss-Bonnet gravity with a scalar potential. A classical, multiple de Sitter universe solution is found where one of the de Sitter phases corresponds to the primordial inflationary epoch, while the other de Sitter space solution - the one with the smallest Hubble rate - describes the late-time acceleration of our universe. A Chameleon scenario for the theory under investigation is developed, and it is successfully used to show that the theory complies with gravitational tests. An explicit expression for the one-loop effective action for this non-local modified Gauss-Bonnet gravity in the de Sitter space is obtained. It is argued that this effective action might be an important step towards the solution of the cosmological constant problem. (orig.)

Topics in quantum gravity

International Nuclear Information System (INIS)

Lamon, Raphael

2010-01-01

Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem. Furthermore, we

The evolution of Brown-York quasilocal energy as due to evolution of Lovelock gravity in a system of M0-branes

Science.gov (United States)

Sepehri, Alireza; Rahaman, Farook; Capozziello, Salvatore; Ali, Ahmed Farag; Pradhan, Anirudh

Recently, it has been suggested in [S. Chakraborty and N. Dadhich, Brown-York quasilocal energy in Lanczos-Lovelock gravity and black hole horizons, J. High Energ. Phys. 12 (2015) 003.] that the Brown-York mechanism can be used to measure the quasilocal energy in Lovelock gravity. We have used this method in a system of M0-branes and show that the Brown-York energy evolves in the process of birth and growth of Lovelock gravity. This can help us to predict phenomenological events which are emerged as due to dynamical structure of Lovelock gravity in our universe. In this model, first, M0-branes join each other and form an M3-brane and an anti-M3-branes connected by an M2-brane. This system is named BIon. Universes and anti-universes live on M3-branes and M2 plays the role of wormhole between them. By passing time, M2 dissolves in M3’s and nonlinear massive gravities like Lovelock massive gravity emerges and grows. By closing M3-branes, BIon evolves and wormhole between branes makes a transition to black hole. During this stage, Brown-York energy increases and shrinks to large values at the colliding points of branes. By approaching M3-branes towards each other, the square energy of their system becomes negative and some tachyonic states are produced. To remove these states, M3-branes compact, the sign of compacted gravity changes, anti-gravity is created which leads to getting away of branes from each other. Also, the Lovelock gravity disappears and its energy forms a new M2 between M3-branes. By getting away of branes from each other, Brown-York energy decreases and shrinks to zero.

Pulsar spin down and cosmologies with varying gravity

International Nuclear Information System (INIS)

Mansfield, V.N.

1976-01-01

Reference is made to the measured spin down of the pulsar JP1953 and it is stated that this conflicts with conclusions concerning cosmologies having weakening gravity. An explanation is also given for the lack of long period pulsars in terms of group theory cosmologies with strengthening gravity. The implications of Dirac's large number hypothesis are considered, including possibilities for the implied continuous creation of matter, both 'additive creation' in which nucleons are created uniformly throughout space and 'multiplicative creation' in which matter is created where it already exists in proportion to the amount existing. Malin's suggestion (Phys. Rev. D9:3228 (1974)) that the mass of all particles varies inversely as the four-dimensional radius of curvature of the universe is also considered. (U.K.)

Acoustic-gravity waves in atmospheric and oceanic waveguides.

Science.gov (United States)

Godin, Oleg A

2012-08-01

A theory of guided propagation of sound in layered, moving fluids is extended to include acoustic-gravity waves (AGWs) in waveguides with piecewise continuous parameters. The orthogonality of AGW normal modes is established in moving and motionless media. A perturbation theory is developed to quantify the relative significance of the gravity and fluid compressibility as well as sensitivity of the normal modes to variations in sound speed, flow velocity, and density profiles and in boundary conditions. Phase and group speeds of the normal modes are found to have certain universal properties which are valid for waveguides with arbitrary stratification. The Lamb wave is shown to be the only AGW normal mode that can propagate without dispersion in a layered medium.

Cosmological reconstruction of realistic modified F(R) gravities

International Nuclear Information System (INIS)

Nojiri, Shin'ichi; Odintsov, Sergei D.; Saez-Gomez, Diego

2009-01-01

The cosmological reconstruction scheme for modified F(R) gravity is developed in terms of e-folding (or, redshift). It is demonstrated how any FRW cosmology may emerge from specific F(R) theory. The specific examples of well-known cosmological evolution are reconstructed, including ΛCDM cosmology, deceleration with transition to phantom superacceleration era which may develop singularity or be transient. The application of this scheme to viable F(R) gravities unifying inflation with dark energy era is proposed. The additional reconstruction of such models leads to non-leading gravitational correction mainly relevant at the early/late universe and helping to pass the cosmological bounds (if necessary). It is also shown how cosmological reconstruction scheme may be generalized in the presence of scalar field.

Geometric Liouville gravity

International Nuclear Information System (INIS)

La, H.

1992-01-01

A new geometric formulation of Liouville gravity based on the area preserving diffeo-morphism is given and a possible alternative to reinterpret Liouville gravity is suggested, namely, a scalar field coupled to two-dimensional gravity with a curvature constraint

Quintessential inflation on the brane and the relic gravity wave background

International Nuclear Information System (INIS)

Sami, M.; Sahni, V.

2004-01-01

Quintessential inflation describes a scenario in which both inflation and dark energy (quintessence) are described by the same scalar field. In conventional braneworld models of quintessential inflation gravitational particle-production is used to reheat the universe. This reheating mechanism is very inefficient and results in an excessive production of gravity waves which violate nucleosynthesis constraints and invalidate the model. We describe a new method of realizing quintessential inflation on the brane in which inflation is followed by 'instant preheating' (Felder, Kofman and Linde 1999). The larger reheating temperature in this model results in a smaller amplitude of relic gravity waves which is consistent with nucleosynthesis bounds. The relic gravity wave background has a 'blue' spectrum at high frequencies and is a generic byproduct of successful quintessential inflation on the brane

Interacting Dark Matter and q-Deformed Dark Energy Nonminimally Coupled to Gravity

Directory of Open Access Journals (Sweden)

Emre Dil

2016-01-01

Full Text Available In this paper, we propose a new approach to study the dark sector of the universe by considering the dark energy as an emerging q-deformed bosonic scalar field which is not only interacting with the dark matter, but also nonminimally coupled to gravity, in the framework of standard Einsteinian gravity. In order to analyze the dynamic of the system, we first give the quantum field theoretical description of the q-deformed scalar field dark energy and then construct the action and the dynamical structure of this interacting and nonminimally coupled dark sector. As a second issue, we perform the phase-space analysis of the model to check the reliability of our proposal by searching the stable attractor solutions implying the late-time accelerating expansion phase of the universe.

A bridge between unified cosmic history by f( R)-gravity and BIonic system

Science.gov (United States)

Sepehri, Alireza; Capozziello, Salvatore; Setare, Mohammad Reza

2016-04-01

Recently, the cosmological deceleration-acceleration transition redshift in f( R) gravity has been considered in order to address consistently the problem of cosmic evolution. It is possible to show that the deceleration parameter changes sign at a given redshift according to observational data. Furthermore, a f( R) gravity cosmological model can be constructed in brane-antibrane system starting from the very early universe and accounting for the cosmological redshift at all phases of cosmic history, from inflation to late time acceleration. Here we propose a f( R) model where transition redshifts correspond to inflation-deceleration and deceleration-late time acceleration transitions starting froma BIon system. At the point where the universe was born, due to the transition of k black fundamental strings to the BIon configuration, the redshift is approximately infinity and decreases with reducing temperature (z˜ T2). The BIon is a configuration in flat space of a universe-brane and a parallel anti-universe-brane connected by a wormhole. This wormhole is a channel for flowing energy from extra dimensions into our universe, occurring at inflation and decreasing with redshift as z˜ T^{4+1/7}. Dynamics consists with the fact that the wormhole misses its energy and vanishes as soon as inflation ends and deceleration begins. Approaching two universe branes together, a tachyon is originated, it grows up and causes the formation of a wormhole. We show that, in the framework of f( R) gravity, the cosmological redshift depends on the tachyonic potential and has a significant decrease at deceleration-late time acceleration transition point (z˜ T^{2/3}). As soon as today acceleration approaches, the redshift tends to zero and the cosmological model reduces to the standard Λ CDM cosmology.

A theory of some gravity

International Nuclear Information System (INIS)

Gribbin, John.

1990-01-01

This paper looks at Einstein's Theory of General Relativity and lists its accomplishments in explaining many problems in gravitation and astrophysics. It was Einstin's genius that led to our present comprehensive theory of gravity. Various ideas central to the theory are explained, such as the bending of space and time by massive objects, geodesics, the origin of the universe. In astrophysics, recent discoveries such as black holes, quasars, gravitational lenses, gravitational radiation, such as that coming from pulsars, can all be explained and understood using Einstein's ideas. (UK)

On gravitational energy in conformal teleparallel gravity

Science.gov (United States)

da Silva, J. G.; Ulhoa, S. C.

2017-07-01

The paper deals with the definition of gravitational energy in conformal teleparallel gravity. The total energy is defined by means of the field equations which allow a local conservation law. Then such an expression is analyzed for a homogeneous and isotropic Universe. This model is implemented by the Friedmann-Robertson-Walker (FRW) line element. The energy of the Universe in the absence of matter is identified with the dark energy, however it can be expanded for curved models defining such an energy as the difference between the total energy and the energy of the perfect fluid which is the matter field in the FRW model.

Cosmological models in energy-momentum-squared gravity

Science.gov (United States)

Board, Charles V. R.; Barrow, John D.

2017-12-01

We study the cosmological effects of adding terms of higher order in the usual energy-momentum tensor to the matter Lagrangian of general relativity. This is in contrast to most studies of higher-order gravity which focus on generalizing the Einstein-Hilbert curvature contribution to the Lagrangian. The resulting cosmological theories give rise to field equations of similar form to several particular theories with different fundamental bases, including bulk viscous cosmology, loop quantum gravity, k -essence, and brane-world cosmologies. We find a range of exact solutions for isotropic universes, discuss their behaviors with reference to the early- and late-time evolution, accelerated expansion, and the occurrence or avoidance of singularities. We briefly discuss extensions to anisotropic cosmologies and delineate the situations where the higher-order matter terms will dominate over anisotropies on approach to cosmological singularities.

Covariant w∞ gravity

NARCIS (Netherlands)

Bergshoeff, E.; Pope, C.N.; Stelle, K.S.

1990-01-01

We discuss the notion of higher-spin covariance in w∞ gravity. We show how a recently proposed covariant w∞ gravity action can be obtained from non-chiral w∞ gravity by making field redefinitions that introduce new gauge-field components with corresponding new gauge transformations.

Evaluation of using digital gravity field models for zoning map creation

Science.gov (United States)

Loginov, Dmitry

2018-05-01

At the present time the digital cartographic models of geophysical fields are taking a special significance into geo-physical mapping. One of the important directions to their application is the creation of zoning maps, which allow taking into account the morphology of geophysical field in the implementation automated choice of contour intervals. The purpose of this work is the comparative evaluation of various digital models in the creation of integrated gravity field zoning map. For comparison were chosen the digital model of gravity field of Russia, created by the analog map with scale of 1 : 2 500 000, and the open global model of gravity field of the Earth - WGM2012. As a result of experimental works the four integrated gravity field zoning maps were obtained with using raw and processed data on each gravity field model. The study demonstrates the possibility of open data use to create integrated zoning maps with the condition to eliminate noise component of model by processing in specialized software systems. In this case, for solving problem of contour intervals automated choice the open digital models aren't inferior to regional models of gravity field, created for individual countries. This fact allows asserting about universality and independence of integrated zoning maps creation regardless of detail of a digital cartographic model of geo-physical fields.

Gravity's rainbow: A bridge between LQC and DSR

Energy Technology Data Exchange (ETDEWEB)

Gorji, M.A., E-mail: m.gorji@stu.umz.ac.ir [Department of Physics, Faculty of Basic Sciences, University of Mazandaran, P.O. Box 47416-95447, Babolsar (Iran, Islamic Republic of); Nozari, K., E-mail: knozari@umz.ac.ir [Department of Physics, Faculty of Basic Sciences, University of Mazandaran, P.O. Box 47416-95447, Babolsar (Iran, Islamic Republic of); Vakili, B., E-mail: b.vakili@iauctb.ac.ir [Department of Physics, Central Tehran Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of)

2017-02-10

The doubly special relativity (DSR) theories are constructed in order to take into account an observer-independent length scale in special relativity framework. Gravity's rainbow is a simple generalization of DSR theories to incorporate gravity. In this paper, we show that the effective Friedmann equations that are suggested by loop quantum cosmology (LQC) can be exactly reobtained in rainbow cosmology setup. The deformed geometry of LQC then fixes the modified dispersion relation and results in a unique DSR model. In comparison with standard LQC scenario where only the geometry is modified, both geometry and matter parts get modified in our setup. In this respect, we show that the total number of microstates for the universe is finite which suggests the statistical origin of the energy and entropy density bounds. These results explicitly show that the DSR theories are appropriate candidates for the flat limit of loop quantum gravity.

Analogue Gravity

Directory of Open Access Journals (Sweden)

Carlos Barceló

2011-05-01

Full Text Available Analogue gravity is a research programme which investigates analogues of general relativistic gravitational fields within other physical systems, typically but not exclusively condensed matter systems, with the aim of gaining new insights into their corresponding problems. Analogue models of (and for gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity.

Light-like scattering in quantum gravity

International Nuclear Information System (INIS)

Bjerrum-Bohr, N.E.J.; Donoghue, John F.; Holstein, Barry R.; Planté, Ludovic; Vanhove, Pierre

2016-01-01

We consider scattering in quantum gravity and derive long-range classical and quantum contributions to the scattering of light-like bosons and fermions (spin-0, spin-(1/2), spin-1) from an external massive scalar field, such as the Sun or a black hole. This is achieved by treating general relativity as an effective field theory and identifying the non-analytic pieces of the one-loop gravitational scattering amplitude. It is emphasized throughout the paper how modern amplitude techniques, involving spinor-helicity variables, unitarity, and squaring relations in gravity enable much simplified computations. We directly verify, as predicted by general relativity, that all classical effects in our computation are universal (in the context of matter type and statistics). Using an eikonal procedure we confirm the post-Newtonian general relativity correction for light-like bending around large stellar objects. We also comment on treating effects from quantum ℏ dependent terms using the same eikonal method.

Light-like scattering in quantum gravity

Energy Technology Data Exchange (ETDEWEB)

Bjerrum-Bohr, N.E.J. [Niels Bohr International Academy & Discovery Center, Niels Bohr Institute,University of Copenhagen, Blegdamsvej 17, Copenhagen Ø, DK-2100 (Denmark); Donoghue, John F. [Department of Physics-LGRT, University of Massachusetts,Amherst, MA, 01003 (United States); Holstein, Barry R. [Department of Physics-LGRT, University of Massachusetts,Amherst, MA, 01003 (United States); Kavli Institute for Theoretical Physics, University of California,Santa Barbara, CA, 93016 (United States); Planté, Ludovic; Vanhove, Pierre [CEA, DSM, Institut de Physique Théorique, IPhT, CNRS MPPU, URA2306,Saclay, Gif-sur-Yvette, F-91191 (France)

2016-11-21

We consider scattering in quantum gravity and derive long-range classical and quantum contributions to the scattering of light-like bosons and fermions (spin-0, spin-(1/2), spin-1) from an external massive scalar field, such as the Sun or a black hole. This is achieved by treating general relativity as an effective field theory and identifying the non-analytic pieces of the one-loop gravitational scattering amplitude. It is emphasized throughout the paper how modern amplitude techniques, involving spinor-helicity variables, unitarity, and squaring relations in gravity enable much simplified computations. We directly verify, as predicted by general relativity, that all classical effects in our computation are universal (in the context of matter type and statistics). Using an eikonal procedure we confirm the post-Newtonian general relativity correction for light-like bending around large stellar objects. We also comment on treating effects from quantum ℏ dependent terms using the same eikonal method.

Quantum Gravity Phenomenology

OpenAIRE

Amelino-Camelia, Giovanni

2003-01-01

Comment: 9 pages, LaTex. These notes were prepared while working on an invited contribution to the November 2003 issue of Physics World, which focused on quantum gravity. They intend to give a non-technical introduction (accessible to readers from outside quantum gravity) to "Quantum Gravity Phenomenology"

Extended DBI massive gravity with generalized fiducial metric

Science.gov (United States)

Chullaphan, Tossaporn; Tannukij, Lunchakorn; Wongjun, Pitayuth

2015-06-01

We consider an extended model of DBI massive gravity by generalizing the fiducial metric to be an induced metric on the brane corresponding to a domain wall moving in five-dimensional Schwarzschild-Anti-de Sitter spacetime. The model admits all solutions of FLRW metric including flat, closed and open geometries while the original one does not. The background solutions can be divided into two branches namely self-accelerating branch and normal branch. For the self-accelerating branch, the graviton mass plays the role of cosmological constant to drive the late-time acceleration of the universe. It is found that the number degrees of freedom of gravitational sector is not correct similar to the original DBI massive gravity. There are only two propagating degrees of freedom from tensor modes. For normal branch, we restrict our attention to a particular class of the solutions which provides an accelerated expansion of the universe. It is found that the number of degrees of freedom in the model is correct. However, at least one of them is ghost degree of freedom which always present at small scale implying that the theory is not stable.

Extended DBI massive gravity with generalized fiducial metric

International Nuclear Information System (INIS)

Chullaphan, Tossaporn; Tannukij, Lunchakorn; Wongjun, Pitayuth

2015-01-01

We consider an extended model of DBI massive gravity by generalizing the fiducial metric to be an induced metric on the brane corresponding to a domain wall moving in five-dimensional Schwarzschild-Anti-de Sitter spacetime. The model admits all solutions of FLRW metric including flat, closed and open geometries while the original one does not. The background solutions can be divided into two branches namely self-accelerating branch and normal branch. For the self-accelerating branch, the graviton mass plays the role of cosmological constant to drive the late-time acceleration of the universe. It is found that the number degrees of freedom of gravitational sector is not correct similar to the original DBI massive gravity. There are only two propagating degrees of freedom from tensor modes. For normal branch, we restrict our attention to a particular class of the solutions which provides an accelerated expansion of the universe. It is found that the number of degrees of freedom in the model is correct. However, at least one of them is ghost degree of freedom which always present at small scale implying that the theory is not stable.

Automated borehole gravity meter system

International Nuclear Information System (INIS)

Lautzenhiser, Th.V.; Wirtz, J.D.

1984-01-01

An automated borehole gravity meter system for measuring gravity within a wellbore. The gravity meter includes leveling devices for leveling the borehole gravity meter, displacement devices for applying forces to a gravity sensing device within the gravity meter to bring the gravity sensing device to a predetermined or null position. Electronic sensing and control devices are provided for (i) activating the displacement devices, (ii) sensing the forces applied to the gravity sensing device, (iii) electronically converting the values of the forces into a representation of the gravity at the location in the wellbore, and (iv) outputting such representation. The system further includes electronic control devices with the capability of correcting the representation of gravity for tidal effects, as well as, calculating and outputting the formation bulk density and/or porosity

Quantum mechanics vs. general covariance in gravity and string models

International Nuclear Information System (INIS)

Martinec, E.J.

1984-01-01

Quantization of simple low-dimensional systems embodying general covariance is studied. Functional methods are employed in the calculation of effective actions for fermionic strings and 1 + 1 dimensional gravity. The author finds that regularization breaks apparent symmetries of the theory, providing new dynamics for the string and non-trivial dynamics for 1 + 1 gravity. The author moves on to consider the quantization of some generally covariant systems with a finite number of physical degrees of freedom, assuming the existence of an invariant cutoff. The author finds that the wavefunction of the universe in these cases is given by the solution to simple quantum mechanics problems

Study of some chaotic inflationary models in f(R) gravity

Science.gov (United States)

Sharif, M.; Nawazish, Iqra

2018-04-01

In this paper, we discuss an inflationary scenario via scalar field and fluid cosmology for an anisotropic homogeneous universe model in f(R) gravity. We consider an equation of state which corresponds to a quasi-de Sitter expansion and investigate the effect of the anisotropy parameter for different values of the deviation parameter. We evaluate potential models like linear, quadratic and quartic models which correspond to chaotic inflation. We construct the observational parameters for a power-law model of f(R) gravity and construct the graphical analysis of tensor-scalar ratio and spectral index which indicates the consistency of these parameters with Planck 2015 data.

Exact solutions for scalar field cosmology in f(R) gravity

Science.gov (United States)

Maharaj, S. D.; Goswami, R.; Chervon, S. V.; Nikolaev, A. V.

2017-09-01

We study scalar field FLRW cosmology in the content of f(R) gravity. Our consideration is restricted to the spatially flat Friedmann universe. We derived the general evolution equations of the model, and showed that the scalar field equation is automatically satisfied for any form of the f(R) function. We also derived representations for kinetic and potential energies, as well as for the acceleration in terms of the Hubble parameter and the form of the f(R) function. Next we found the exact cosmological solutions in modified gravity without specifying the f(R) function. With negligible acceleration of the scalar curvature, we found that the de Sitter inflationary solution is always attained. Also we obtained new solutions with special restrictions on the integration constants. These solutions contain oscillating, accelerating, decelerating and even contracting universes. For further investigation, we selected special cases which can be applied with early or late inflation. We also found exact solutions for the general case for the model with negligible acceleration of the scalar curvature in terms of special Airy functions. Using initial conditions which represent the universe at the present epoch, we determined the constants of integration. This allows for the comparison of the scale factor in the new solutions with that for current stage of the universe evolution in the ΛCDM model.

Gravity is Geometry.

Science.gov (United States)

MacKeown, P. K.

1984-01-01

Clarifies two concepts of gravity--those of a fictitious force and those of how space and time may have geometry. Reviews the position of Newton's theory of gravity in the context of special relativity and considers why gravity (as distinct from electromagnetics) lends itself to Einstein's revolutionary interpretation. (JN)

Gravity inversion code

International Nuclear Information System (INIS)

Burkhard, N.R.

1979-01-01

The gravity inversion code applies stabilized linear inverse theory to determine the topography of a subsurface density anomaly from Bouguer gravity data. The gravity inversion program consists of four source codes: SEARCH, TREND, INVERT, and AVERAGE. TREND and INVERT are used iteratively to converge on a solution. SEARCH forms the input gravity data files for Nevada Test Site data. AVERAGE performs a covariance analysis on the solution. This document describes the necessary input files and the proper operation of the code. 2 figures, 2 tables

Principal facts for about 16,000 gravity stations in the Nevada Test Site and vicinity

International Nuclear Information System (INIS)

Harris, R.N.; Ponce, D.A.; Oliver, H.W.; Healey, D.L.

1989-01-01

The Nevada Test Site (NTS) and vicinity includes portions of the Goldfield, Caliente, Death Valley, and Las Vegas. This report documents and consolidates previously published and recently compiled gravity data to establish a gravity data base of about 16,000 stations for the NTS and vicinity. While compiling data sets, redundant stations and stations having doubtful locations or gravity values were excluded. Details of compiling the gravity data sets are discussed in later sections. Where feasible, an accuracy code has been assigned to each station so that the accuracy or reliability of each station can be evaluated. This data base was used in preparing complete Bouguer and isostatic gravity maps of the NTS and vicinity. Since publication of the complete Bouguer gravity map, additional data were incorporated into the isostatic gravity map. Gravity data were compiled from five sources: 14,183 stations from the US Geological Survey (USGS), 326 stations from Exploration Data Consultants (EDCON) of Denver, Colorado, 906 stations from the Los Alamos National Laboratory (LANL), 212 stations from the University of Texas at Dallas (UTD), and 48 stations from the Defense Mapping Agency (DMA). This investigation is an effort to study several areas for potential storage of high-level radioactive waste. Gravity stations established under YMP are shown. The objective of this gravity survey was to explore for the presence of plutons. This volume contains only compiled data

Principal facts for about 16,000 gravity stations in the Nevada Test Site and vicinity

International Nuclear Information System (INIS)

Harris, R.N.; Ponce, D.A.; Oliver, H.W.; Healey, D.L.

1989-01-01

The Nevada Test Site (NTS) and vicinity includes portions of the Goldfield, Caliente, Death Valley, and Las Vegas. This report documents and consolidates previously published and recently compiled gravity data to establish a gravity data base of about 16,000 stations for the NTS and vicinity. While compiling data sets, redundant stations and stations having doubtful locations or gravity values were excluded. Details of compiling the gravity data sets are discussed in later sections. Where feasible, an accuracy code has been assigned to each station so that the accuracy or reliability of each station can be evaluated. This data base was used in preparing complete Bouguer and isostatic gravity maps of the NTS and vicinity. Since publication of the complete Bouguer gravity map, additional data were incorporated into the isostatic gravity map. Gravity data were compiled from five sources: 14,183 stations from the US Geological Survey (USGS), 326 stations from Exploration Data Consultants (EDCON) of Denver, Colorado, 906 stations from the Los Alamos National Laboratory (LANL), 212 stations from the University of Texas at Dallas (UTD), and 48 stations from the Defense Mapping Agency (DMA). This investigation is an effort to study several areas for potential storage of high-level radioactive waste. Gravity stations established under YMP are shown. The objective of this gravity survey was to explore for the presence of plutons. 33 refs., 24 figs., 9 tabs

Consciousness in the Universe

Directory of Open Access Journals (Sweden)

Khalil Chamcham

2013-07-01

Full Text Available So far we can identify at least three concepts within modern cosmology that bring into debate the question of consciousness in the universe: 1 Fine Tuning; 2 The Anthropic Principle and 3 The Multiverse. This does not exclude the question of the role of observer (i.e. consciousness in cosmology as developed within Quantum Physics: we observe the universe through quanta and any breakthrough in understanding the origin and nature of the universe will come only through a quantum theory of gravity […

Gravity brake

Science.gov (United States)

Lujan, Richard E.

2001-01-01

A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.

The Cause of Gravity

OpenAIRE

Byrne, Michael

1999-01-01

Einstein said that gravity is an acceleration like any other acceleration. But gravity causes relativistic effects at non-relativistic speeds; so gravity could have relativistic origins. And since the strong force is thought to cause most of mass, and mass is proportional to gravity; the strong force is therefore also proportional to gravity. The strong force could thus cause relativistic increases of mass through the creation of virtual gluons; along with a comparable contraction of space ar...

How (not) to use the Palatini formulation of scalar-tensor gravity

International Nuclear Information System (INIS)

Iglesias, Alberto; Kaloper, Nemanja; Park, Minjoon; Padilla, Antonio

2007-01-01

We revisit the problem of defining nonminimal gravity in the first order formalism. Specializing to scalar-tensor theories, which may be disguised as ''higher-derivative'' models with the gravitational Lagrangians that depend only on the Ricci scalar, we show how to recast these theories as Palatini-like gravities. The correct formulation utilizes the Lagrange multiplier method, which preserves the canonical structure of the theory, and yields the conventional metric scalar-tensor gravity. We explain the discrepancies between the naieve Palatini and the Lagrange multiplier approach, showing that the naieve Palatini approach really swaps the theory for another. The differences disappear only in the limit of ordinary general relativity, where an accidental redundancy ensures that the naieve Palatini approach works there. We outline the correct decoupling limits and the strong coupling regimes. As a corollary we find that the so-called ''modified source gravity'' models suffer from strong coupling problems at very low scales, and hence cannot be a realistic approximation of our universe. We also comment on a method to decouple the extra scalar using the chameleon mechanism

Cutoff for extensions of massive gravity and bi-gravity

International Nuclear Information System (INIS)

Matas, Andrew

2016-01-01

Recently there has been interest in extending ghost-free massive gravity, bi-gravity, and multi-gravity by including non-standard kinetic terms and matter couplings. We first review recent proposals for this class of extensions, emphasizing how modifications of the kinetic and potential structure of the graviton and modifications of the coupling to matter are related. We then generalize existing no-go arguments in the metric language to the vielbein language in second-order form. We give an ADM argument to show that the most promising extensions to the kinetic term and matter coupling contain a Boulware–Deser ghost. However, as recently emphasized, we may still be able to view these extensions as effective field theories below some cutoff scale. To address this possibility, we show that there is a decoupling limit where a ghost appears for a wide class of matter couplings and kinetic terms. In particular, we show that there is a decoupling limit where the linear effective vielbein matter coupling contains a ghost. Using the insight we gain from this decoupling limit analysis, we place an upper bound on the cutoff for the linear effective vielbein coupling. This result can be generalized to new kinetic interactions in the vielbein language in second-order form. Combined with recent results, this provides a strong uniqueness argument on the form of ghost-free massive gravity, bi-gravity, and multi-gravity. (paper)

Physical attributes of anisotropic compact stars in f(R, G) gravity

Energy Technology Data Exchange (ETDEWEB)

Shamir, M.F.; Zia, Saeeda [National University of Computer and Emerging Sciences, Department of Sciences and Humanities, Lahore (Pakistan)

2017-07-15

Modified gravity is one of the potential candidates to explain the accelerated expansion of the universe. Current study highlights the materialization of anisotropic compact stars in the context of f(R, G) theory of gravity. In particular, to gain insight in the physical behavior of three stars namely, Her X1, SAX J 1808-3658 and 4U 1820-30, energy density, and radial and tangential pressures are calculated. The f(R, G) gravity model is split into a Starobinsky like f(R) model and a power law f(G) model. The main feature of the work is a 3-dimensional graphical analysis in which, anisotropic measurements, energy conditions and stability attributes of these stars are discussed. It is shown that all three stars behave as usual for positive values of the f(G) model parameter n. (orig.)

Quark–hadron phase transition in massive gravity

Energy Technology Data Exchange (ETDEWEB)

Atazadeh, K., E-mail: atazadeh@azaruniv.ac.ir

2016-11-15

We study the quark–hadron phase transition in the framework of massive gravity. We show that the modification of the FRW cosmological equations leads to the quark–hadron phase transition in the early massive Universe. Using numerical analysis, we consider that a phase transition based on the chiral symmetry breaking after the electroweak transition, occurred at approximately 10 μs after the Big Bang to convert a plasma of free quarks and gluons into hadrons.

Topics in quantum gravity

Energy Technology Data Exchange (ETDEWEB)

Lamon, Raphael

2010-06-29

Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem

Effects of Low Anisotropy on Generalized Ghost Dark Energy in Galileon Gravity

Science.gov (United States)

Hossienkhani, H.; Fayaz, V.; Jafari, A.; Yousefi, H.

2018-04-01

The definition of the Galileon gravity form is extended to the Brans-Dicke theory. Given, the framework of the Galileon theory, the generalized ghost dark energy model in an anisotropic universe is investigated. We study the cosmological implications of this model. In particular, we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy in Bianchi type I model. We also probe observational constraints by using the latest observational data on the generalized ghost dark energy models as the unification of dark matter and dark energy. In order to do so, we focus on observational determinations of the Hubble expansion rate (namely, the expansion history) H(z). As a result, we show the influence of the anisotropy (although low) on the evolution of the universe in the statefinder diagrams for Galileon gravity.

The International Gravity Field Service (IGFS): Present Day Activities And Future Plans

Science.gov (United States)

Barzaghi, R.; Vergos, G. S.

2016-12-01

IGFS is a unified "umbrella" IAG service that coordinates the servicing of the geodetic and geophysical community with gravity field related data, software and information. The combined data of the IGFS entities will include global geopotential models, terrestrial, airborne, satellite and marine gravity observations, Earth tide data, GPS/levelling data, digital models of terrain and bathymetry, as well as ocean gravity field and geoid from satellite altimetry. The IGFS structure is based on the Gravity Services, the "operating arms" of IGFS. These Services related to IGFS are: BGI (Bureau Gravimetrique International), Toulouse, France ISG (International Service for the Geoid), Politecnico di Milano, Milano, Italy IGETS (International Geodynamics and Earth Tides Service), EOST, Strasbourg, France ICGEM (International Center for Global Earth Models), GFZ, Potsdam, Germany IDEMS (International Digital Elevation Model Service), ESRI, Redlands, CA, USA The Central Bureau, hosted at the Aristotle Thessaloniki University, is in charge for all the interactions among the services and the other IAG bodies, particularly GGOS. In this respect, connections with the GGOS Bureaus of Products and Standards and of Networks and Observations have been recently strengthened in order to align the Gravity services to the GGOS standards. IGFS is also strongly involved in the most relevant projects related to the gravity field such as the establishment of the new Global Absolute Gravity Reference System and of the International Height Reference System. These projects, along with the organization of Geoid Schools devoted to methods for gravity and geoid estimate, will play a central role in the IGFS future actions in the framework of GGOS.

Gsolve, a Python computer program with a graphical user interface to transform relative gravity survey measurements to absolute gravity values and gravity anomalies

Science.gov (United States)

McCubbine, Jack; Tontini, Fabio Caratori; Stagpoole, Vaughan; Smith, Euan; O'Brien, Grant

2018-01-01

A Python program (Gsolve) with a graphical user interface has been developed to assist with routine data processing of relative gravity measurements. Gsolve calculates the gravity at each measurement site of a relative gravity survey, which is referenced to at least one known gravity value. The tidal effects of the sun and moon, gravimeter drift and tares in the data are all accounted for during the processing of the survey measurements. The calculation is based on a least squares formulation where the difference between the absolute gravity at each surveyed location and parameters relating to the dynamics of the gravimeter are minimized with respect to the relative gravity observations, and some supplied gravity reference site values. The program additionally allows the user to compute free air gravity anomalies, with respect to the GRS80 and GRS67 reference ellipsoids, from the determined gravity values and calculate terrain corrections at each of the surveyed sites using a prism formula and a user supplied digital elevation model. This paper reviews the mathematical framework used to reduce relative gravimeter survey observations to gravity values. It then goes on to detail how the processing steps can be implemented using the software.

Simultaneous measurement of gravity acceleration and gravity gradient with an atom interferometer

International Nuclear Information System (INIS)

Sorrentino, F.; Lien, Y.-H.; Rosi, G.; Tino, G. M.; Bertoldi, A.; Bodart, Q.; Cacciapuoti, L.; Angelis, M. de; Prevedelli, M.

2012-01-01

We demonstrate a method to measure the gravitational acceleration with a dual cloud atom interferometer; the use of simultaneous atom interferometers reduces the effect of seismic noise on the gravity measurement. At the same time, the apparatus is capable of accurate measurements of the vertical gravity gradient. The ability to determine the gravity acceleration and gravity gradient simultaneously and with the same instrument opens interesting perspectives in geophysical applications.

General proof of the entropy principle for self-gravitating fluid in f(R) gravity

Energy Technology Data Exchange (ETDEWEB)

Fang, Xiongjun [Department of Physics and Key Laboratory of Low Dimensional Quantum Structures andQuantum Control of Ministry of Education, Hunan Normal University,Changsha, Hunan 410081 (China); Guo, Minyong [Department of Physics, Beijing Normal University,Beijing 100875 (China); Jing, Jiliang [Department of Physics and Key Laboratory of Low Dimensional Quantum Structures andQuantum Control of Ministry of Education, Hunan Normal University,Changsha, Hunan 410081 (China)

2016-08-29

The discussions on the connection between gravity and thermodynamics attract much attention recently. We consider a static self-gravitating perfect fluid system in f(R) gravity, which is an important theory could explain the accelerated expansion of the universe. We first show that the Tolman-Oppenheimer-Volkoff equation of f(R) theories can be obtained by thermodynamical method in spherical symmetric spacetime. Then we prove that the maximum entropy principle is also valid for f(R) gravity in general static spacetimes beyond spherical symmetry. The result shows that if the constraint equation is satisfied and the temperature of fluid obeys Tolmans law, the extrema of total entropy implies other components of gravitational equations. Conversely, if f(R) gravitational equation hold, the total entropy of the fluid should be extremum. Our work suggests a general and solid connection between f(R) gravity and thermodynamics.

Airborne Gravity: NGS' Gravity Data for EN08 (2013)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Vermont, New Hampshire, Massachusettes, Maine, and Canada collected in 2013 over 1 survey. This data set is part of the Gravity...

The earth's shape and gravity

CERN Document Server

Garland, G D; Wilson, J T

2013-01-01

The Earth's Shape and Gravity focuses on the progress of the use of geophysical methods in investigating the interior of the earth and its shape. The publication first offers information on gravity, geophysics, geodesy, and geology and gravity measurements. Discussions focus on gravity measurements and reductions, potential and equipotential surfaces, absolute and relative measurements, and gravity networks. The text then elaborates on the shape of the sea-level surface and reduction of gravity observations. The text takes a look at gravity anomalies and structures in the earth's crust; interp

Late-time cosmological approach in mimetic f(R, T) gravity

Energy Technology Data Exchange (ETDEWEB)

Baffou, E.H. [Institut de Mathematiques et de Sciences Physiques (IMSP), Porto-Novo (Benin); Houndjo, M.J.S. [Institut de Mathematiques et de Sciences Physiques (IMSP), Porto-Novo (Benin); Faculte des Sciences et Techniques de Natitingou, Natitingou (Benin); Hamani-Daouda, M. [Universite de Niamey, Departement de Physique, Niamey (Niger); Alvarenga, F.G. [Universidade Federal do Espirito Santo, Departamento de Engenharia e Ciencias Naturais, CEUNES, Sao Mateus, ES (Brazil)

2017-10-15

In this paper, we investigate the late-time cosmic acceleration in mimetic f(R, T) gravity with the Lagrange multiplier and potential in a Universe containing, besides radiation and dark energy, a self-interacting (collisional) matter. We obtain through the modified Friedmann equations the main equation that can describe the cosmological evolution. Then, with several models from Q(z) and the well-known particular model f(R, T), we perform an analysis of the late-time evolution. We examine the behavior of the Hubble parameter, the dark energy equation of state and the total effective equation of state and in each case we compare the resulting picture with the non-collisional matter (assumed as dust) and also with the collisional matter in mimetic f(R, T) gravity. The results obtained are in good agreement with the observational data and show that in the presence of the collisional matter the dark energy oscillations in mimetic f(R, T) gravity can be damped. (orig.)

Airborne Gravity: NGS' Gravity Data for AN08 (2016)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2016 over one survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...

Artificial gravity - The evolution of variable gravity research

Science.gov (United States)

Fuller, Charles A.; Sulzman, Frank M.; Keefe, J. Richard

1987-01-01

The development of a space life science research program based on the use of rotational facilities is described. In-flight and ground centrifuges can be used as artificial gravity environments to study the following: nongravitational biological factors; the effects of 0, 1, and hyper G on man; counter measures for deconditioning astronauts in weightlessness; and the development of suitable artificial gravity for long-term residence in space. The use of inertial fields as a substitute for gravity, and the relations between the radius of the centrifuge and rotation rate and specimen height and rotation radius are examined. An example of a centrifuge study involving squirrel monkeys is presented.

Airborne Gravity: NGS' Gravity Data for AS01 (2008)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2008 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for CS04 (2009)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for AN05 (2011)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for TS01 (2014)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Puerto Rico and the Virgin Islands collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the...

Airborne Gravity: NGS' Gravity Data for AN06 (2011)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for AS02 (2010)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for EN01 (2011)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Canada, and Lake Ontario collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the...

Airborne Gravity: NGS' Gravity Data for AN03 (2010)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 and 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...

Airborne Gravity: NGS' Gravity Data for AN04 (2010)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for CS05 (2014)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2014 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for EN06 (2016)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Maine, Canada, and the Atlantic Ocean collected in 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the...

Airborne Gravity: NGS' Gravity Data for AN02 (2010)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for ES01 (2013)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida, the Bahamas, and the Atlantic Ocean collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition of...

Analogue Gravity

Directory of Open Access Journals (Sweden)

Barceló Carlos

2005-12-01

Full Text Available Analogue models of (and for gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity.

NGS Absolute Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The...

Modified teleparallel gravity: Inflation without an inflaton

International Nuclear Information System (INIS)

Ferraro, Rafael; Fiorini, Franco

2007-01-01

The Born-Infeld strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of general relativity. Differing from other theories of modified gravity, modified teleparallelism leads to second order equations, since the teleparallel Lagrangian only contains first derivatives of the vierbein. We show that the Born-Infeld-modified teleparallelism solves the particle horizon problem in a spatially flat Friedmann-Robertson-Walker (FRW) universe by providing an initial exponential expansion without resorting to an inflaton field

Airborne Gravity: NGS' Gravity Data for CS08 (2015)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for CS08 collected in 2006 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...

Airborne Gravity: NGS' Gravity Data for ES02 (2013)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida and the Gulf of Mexico collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition of the American...

Classical Weyl transverse gravity

Energy Technology Data Exchange (ETDEWEB)

Oda, Ichiro [University of the Ryukyus, Department of Physics, Faculty of Science, Nishihara, Okinawa (Japan)

2017-05-15

We study various classical aspects of the Weyl transverse (WTDiff) gravity in a general space-time dimension. First of all, we clarify a classical equivalence among three kinds of gravitational theories, those are, the conformally invariant scalar tensor gravity, Einstein's general relativity and the WTDiff gravity via the gauge-fixing procedure. Secondly, we show that in the WTDiff gravity the cosmological constant is a mere integration constant as in unimodular gravity, but it does not receive any radiative corrections unlike the unimodular gravity. A key point in this proof is to construct a covariantly conserved energy-momentum tensor, which is achieved on the basis of this equivalence relation. Thirdly, we demonstrate that the Noether current for the Weyl transformation is identically vanishing, thereby implying that the Weyl symmetry existing in both the conformally invariant scalar tensor gravity and the WTDiff gravity is a ''fake'' symmetry. We find it possible to extend this proof to all matter fields, i.e. the Weyl-invariant scalar, vector and spinor fields. Fourthly, it is explicitly shown that in the WTDiff gravity the Schwarzschild black hole metric and a charged black hole one are classical solutions to the equations of motion only when they are expressed in the Cartesian coordinate system. Finally, we consider the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology and provide some exact solutions. (orig.)

Isotropic background for interacting two fluid scenario coupled with zero mass scalar field in modified gravity

International Nuclear Information System (INIS)

Chirde, V.R.; Shekh, S.H.

2016-01-01

The modified theories of gravity have engrossed much attention in the last decade, especially f(R) gravity. In this contextual exploration, we investigate interaction between barotropic fluid and dark energy with zero-mass scalar field for the spatially homogeneous and isotropic flat FRW universe. In this universe, the field equations correspond to the particular choice of f(R) = R+bR m . The exact solutions of the field equations are obtained by applying volumetric power law and exponential law of expansion. In power and exponential law of expansion, the universe shows both matter dominated and DE era for b ≤ 0 and b ≥ 0 and remain present in dark era respectively, but power law model is fully occupying with real matter for b > 0 and for b < 0 exponential model expands with negative pressure and remain present in matter dominated phase respectively. The physical behavior of the universe has been discussed by using some physical quantities

Southern Africa Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This data base (14,559 records) was received in January 1986. Principal gravity parameters include elevation and observed gravity. The observed gravity values are...

Non - minimal interaction of gravity with other physical fields: an overview

International Nuclear Information System (INIS)

Novello, M.; Oliveira, L.A.R. de.

1986-01-01

A review on some modern developments concerning the interaction of gravity with other physical fields. It is argued that a suitable context for an account of their dynamical interplay is that of the non-minimal (e.g., conformal) coupling of these fields to gravity. Some interesting features of non-minimal coupling, such as the connection with Weyl-integrable spacetime (WIST) structure, the generation of eternal Universes, the appearance of a cosmological constant and the possible induction of repulsive gravity via spontaneous symmetry breaking (SSB) mechanisms, are discussed. In particular, examines a simple case of strong interacting scalar particles (such as the well-Known elastic reaction ΠK → ΠK), in a curved background, thereby obtaining the curious result that the actual, observed value of the strong coupling constant and the minimum value allowable, in order to preclude antigravity, are related by Eddington's number 10 39 . (Author) [pt

Non-nominal interaction of gravity with other physical fields: An overiview

International Nuclear Information System (INIS)

Novello, M.; Oliveira, L.A.R. de

1987-01-01

A review is presented of some modern developments concerning the interaction of gravity with other physical fields. It is argued that a suitable context for an account of their dynamical interplay is that of the non-minimal (e.g. conformal) coupling of these fields to gravity. Some interesting features of non-minimal coupling, such as the connection with Weyl-integrable spacetime (WIST) structure, the generation of eternal Universes, the appearance of a cosmological constant and the possible induction of repulsive gravity via spontaneous breaking (SSB) mechanisms, are discussed. In particular, a simple case of strong-interacting scalar particles is examined (such as the well-Known elastic reaction ΠK -> ΠK), in a curved background, thereby obtaining the curious resul that the actual, observed value of the strong coupling constant and the minimum allowable value, in order to preclude antigravity, are related by Eddington's number 10 39 . (author) [pt

Einstein gravity emerging from quantum weyl gravity

International Nuclear Information System (INIS)

Zee, A.

1983-01-01

We advocate a conformal invariant world described by the sum of the Weyl, Dirac, and Yang-Mills action. Quantum fluctuations bring back Einstein gravity so that the long-distance phenomenology is as observed. Formulas for the induced Newton's constant and Eddington's constant are derived in quantized Weyl gravity. We show that the analogue of the trace anomaly for the Weyl action is structurally similar to that for the Yang-Mills action

Spherically symmetric analysis on open FLRW solution in non-linear massive gravity

Energy Technology Data Exchange (ETDEWEB)

Chiang, Chien-I; Izumi, Keisuke; Chen, Pisin, E-mail: chienichiang@berkeley.edu, E-mail: izumi@phys.ntu.edu.tw, E-mail: chen@slac.stanford.edu [Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 10617, Taiwan (China)

2012-12-01

We study non-linear massive gravity in the spherically symmetric context. Our main motivation is to investigate the effect of helicity-0 mode which remains elusive after analysis of cosmological perturbation around an open Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. The non-linear form of the effective energy-momentum tensor stemming from the mass term is derived for the spherically symmetric case. Only in the special case where the area of the two sphere is not deviated away from the FLRW universe, the effective energy momentum tensor becomes completely the same as that of cosmological constant. This opens a window for discriminating the non-linear massive gravity from general relativity (GR). Indeed, by further solving these spherically symmetric gravitational equations of motion in vacuum to the linear order, we obtain a solution which has an arbitrary time-dependent parameter. In GR, this parameter is a constant and corresponds to the mass of a star. Our result means that Birkhoff's theorem no longer holds in the non-linear massive gravity and suggests that energy can probably be emitted superluminously (with infinite speed) on the self-accelerating background by the helicity-0 mode, which could be a potential plague of this theory.

influence of gravity

Directory of Open Access Journals (Sweden)

Animesh Mukherjee

1991-01-01

Full Text Available Based upon Biot's [1965] theory of initial stresses of hydrostatic nature produced by the effect of gravity, a study is made of surface waves in higher order visco-elastic media under the influence of gravity. The equation for the wave velocity of Stonely waves in the presence of viscous and gravitational effects is obtained. This is followed by particular cases of surface waves including Rayleigh waves and Love waves in the presence of viscous and gravity effects. In all cases the wave-velocity equations are found to be in perfect agreement with the corresponding classical results when the effects of gravity and viscosity are neglected.

Getting Rid of Gravity--Alternative Ways of Looking at Trajectories

Science.gov (United States)

Dion, Peter W.; Ho, Anthony M. H.

2010-01-01

Problems in projectile motion are a time-honored staple of high school and even first-year university physics. They can become confusing for some students, yet boring for the stronger students. Herein we present two alternative approaches to such questions, one we call "breaking down gravity," which makes these questions easier to solve, and the…

Baby universes

International Nuclear Information System (INIS)

Strominger, A.

1988-01-01

This paper discusses how the subject of baby universes and their effects on spacetime coupling constants is in its infancy and rapidly developing. The subject is based on the non-existent (even by physicists' standards) Euclidean formulation of quantum gravity, and it is therefore necessary to make a number of assumptions in order to proceed. Nevertheless, the picture which has emerged is quite appealing: all spacetime coupling constants become dynamical variables when the effects of baby universes are taken into account. This fact might even solve the puzzle of the cosmological constant. The subject therefore seems worth further investigation

Comparing scalar-tensor gravity and f(R)-gravity in the Newtonian limit

International Nuclear Information System (INIS)

Capozziello, S.; Stabile, A.; Troisi, A.

2010-01-01

Recently, a strong debate has been pursued about the Newtonian limit (i.e. small velocity and weak field) of fourth order gravity models. According to some authors, the Newtonian limit of f(R)-gravity is equivalent to the one of Brans-Dicke gravity with ω BD =0, so that the PPN parameters of these models turn out to be ill-defined. In this Letter, we carefully discuss this point considering that fourth order gravity models are dynamically equivalent to the O'Hanlon Lagrangian. This is a special case of scalar-tensor gravity characterized only by self-interaction potential and that, in the Newtonian limit, this implies a non-standard behavior that cannot be compared with the usual PPN limit of General Relativity. The result turns out to be completely different from the one of Brans-Dicke theory and in particular suggests that it is misleading to consider the PPN parameters of this theory with ω BD =0 in order to characterize the homologous quantities of f(R)-gravity. Finally the solutions at Newtonian level, obtained in the Jordan frame for an f(R)-gravity, reinterpreted as a scalar-tensor theory, are linked to those in the Einstein frame.

Evolution of Bianchi I magnetized cosmic strings in Brans–Dicke gravity

International Nuclear Information System (INIS)

Sharif, M; Waheed, Saira

2013-01-01

In this paper, we consider a locally rotationally symmetric Bianchi I universe filled with magnetized viscous string fluid in Brans–Dicke gravity. For the exact solutions, we use the law of variation of the Hubble parameter that leads to volumetric expansion laws and assume power law ansatz for the scalar field. We discuss the nature of the resulting models through different parameters and their graphs. It is concluded that the constructed universe models yield an accelerated expanding behavior with an isotropic nature for the final stages of the universe evolution, which is consistent with recent observations. (paper)

Unimodular f(G) gravity

Energy Technology Data Exchange (ETDEWEB)

Houndjo, M.J.S. [Faculte des Sciences et Techniques de Natitingou, Natitingou (Benin); Institut de Mathematiques et de Sciences Physiques, Porto-Novo (Benin)

2017-09-15

In this paper we study a modified version of unimodular general relativity in the context of f(G), G denoting the Gauss-Bonnet invariant. We focus on Bianchi-type I and Friendmann-Robertson-Walker universes and search for unimodular f(G) models according to the de Sitter and power-law solutions. Assuming unimodular f(G) gravity as a perfect fluid and making use of the slow-roll parameters, the inflationary model has been reconstructed in concordance with the Planck observational data. Moreover, we investigate the realization of the bounce and loop quantum cosmological ekpyrotic paradigms. Assuming suitable and appropriate scale factors, unimodular f(G) models able to reproduce superbounce and ekpyrotic scenarios have been reconstructed. (orig.)

PREFACE: First Mediterranean Conference on Classical and Quantum Gravity (MCCQG 2009)

Science.gov (United States)

Basilakos, Spyros; Cadoni, Mariano; Cavaglia, Marco; Christodoulakis, Theodosios; Vagenas, Elias C.

2010-04-01

Fisica, Universidade de Sao Paulo, Brasil) Antoniadis, Ignatios (CERN, Geneva, Switzerland) Arminjon, Mayeul (CNRS, Section of Theoretical Physics, France) Banados, Max (University of Oxford, UK) Basilakos, Spyros (RCAAM, Academy of Athens, Greece) Bastos, Catarina (IST, Departamento de Física, Portugal) Bertolami, Orfeu (IST, Departamento de Física, Portugal) Bevilaqua, Leandro Ibiapina (Instituto de Fisica, Universidade de Sao Paulo, Brazil) Bezerra De Mello, Eugenio (Dept. de Física, CCEN Universidade Federal da Paraíba, Brazil) Blake, Russ (Readify Pty Ltd, Australia) Bogdanos, Charalampos (LPT-Orsay, France) Burinskii, Alexander (Gravity Research Group NSI, Russian Academy of Sciences, Russia) Cadonati, Laura (University of Massachusetts, Amherst, USA) Cadoni, Mariano (Università di Cagliari, Italy) Capone, Monica (University of Turin, Italy) Cavaglià, Marco (University of Mississippi, USA) Chirco, Goffredo (SISSA-International School for Advanced Studies, Italy) Christodoulakis, Theodosios (University of Athens, Greece) Domingues Zarro, Carlos Augusto ((IST, Departamento de Física, Portugal) Durrer, Ruth (Université de Genève, Département de Physique Théorique, Switzerland) Fagnocchi, Serena (SISSA-International School for Advanced Studies, Italy) Finazzi, Stefano (SISSA-International School for Advanced Studies, Italy) Francia, Dario (University Paris 7 - APC, France) Ghosh, Subir (Indian Statistical Institute, India) Gomberoff, Andres (Universidad Catolica de Chile, Chile) Grumiller, Daniel (Institute for Theoretical Physics Vienna University of Technology, Austria) Herrera-Aguilar, Alfredo (IFM, Universidad Michoacana de San Nicolas de Hidalgo, Mexico) Hsu, Steve (University of Oregon, USA) Ichinose, Shoichi (University of Shizuoka, SFNS, Japan) Kiefer, Claus (Institute for Theoretical Physics, University of Cologne, Germany) Kokkotas, Kostas (Theoretical Astrophysics, Eberhard Karls University of Tuebingen, Germany) Kothawala, Dawood (IUCAA, Pune

Scalar-Tensor Black Holes Embedded in an Expanding Universe

Science.gov (United States)

Tretyakova, Daria; Latosh, Boris

2018-02-01

In this review we focus our attention on scalar-tensor gravity models and their empirical verification in terms of black hole and wormhole physics. We focus on a black hole, embedded in an expanding universe, describing both cosmological and astrophysical scales. We show that in scalar-tensor gravity it is quite common that the local geometry is isolated from the cosmological expansion, so that it does not backreact on the black hole metric. We try to extract common features of scalar-tensor black holes in an expanding universe and point out the gaps that must be filled.

Scalar-Tensor Black Holes Embedded in an Expanding Universe

Directory of Open Access Journals (Sweden)

Daria Tretyakova

2018-02-01

Full Text Available In this review, we focus our attention on scalar-tensor gravity models and their empirical verification in terms of black hole and wormhole physics. We focus on black holes, embedded in an expanding universe, describing both cosmological and astrophysical scales. We show that in scalar-tensor gravity it is quite common that the local geometry is isolated from the cosmological expansion, so that it does not backreact on the black hole metric. We try to extract common features of scalar-tensor black holes in an expanding universe and point out the issues that are not fully investigated.

Cosmological D-instantons and cyclic universes

International Nuclear Information System (INIS)

Bergshoeff, E A; Collinucci, A; Roest, D; Russo, J G; Townsend, P K

2005-01-01

For models of gravity coupled to hyperbolic sigma models, such as the metric-scalar sector of IIB supergravity, we show how smooth trajectories in the 'augmented target space' connect FLRW cosmologies to non-extremal D-instantons through a cosmological singularity. In particular, we find closed cyclic universes that undergo an endless sequence of big-bang to big-crunch cycles separated by instanton 'phases'. We also find 'big-bounce' universes in which a collapsing closed universe bounces off its cosmological singularity to become an open expanding universe

Asymptotic safety of gravity with matter

Science.gov (United States)

Christiansen, Nicolai; Litim, Daniel F.; Pawlowski, Jan M.; Reichert, Manuel

2018-05-01

We study the asymptotic safety conjecture for quantum gravity in the presence of matter fields. A general line of reasoning is put forward explaining why gravitons dominate the high-energy behavior, largely independently of the matter fields as long as these remain sufficiently weakly coupled. Our considerations are put to work for gravity coupled to Yang-Mills theories with the help of the functional renormalization group. In an expansion about flat backgrounds, explicit results for beta functions, fixed points, universal exponents, and scaling solutions are given in systematic approximations exploiting running propagators, vertices, and background couplings. Invariably, we find that the gauge coupling becomes asymptotically free while the gravitational sector becomes asymptotically safe. The dependence on matter field multiplicities is weak. We also explain how the scheme dependence, which is more pronounced, can be handled without changing the physics. Our findings offer a new interpretation of many earlier results, which is explained in detail. The results generalize to theories with minimally coupled scalar and fermionic matter. Some implications for the ultraviolet closure of the Standard Model or its extensions are given.

Simulating Gravity: Dark Matter and Gravitational Lensing in the Classroom

Science.gov (United States)

Ford, Jes; Stang, Jared; Anderson, Catherine

2015-01-01

Dark matter makes up most of the matter in the universe but very little of a standard introductory physics curriculum. Here we present our construction and use of a spandex sheet-style gravity simulator to qualitatively demonstrate two aspects of modern physics related to dark matter. First, we describe an activity in which students explore the…

Is Gravity an Entropic Force?

Directory of Open Access Journals (Sweden)

Shan Gao

2011-04-01

Full Text Available The remarkable connections between gravity and thermodynamics seem to imply that gravity is not fundamental but emergent, and in particular, as Verlinde suggested, gravity is probably an entropic force. In this paper, we will argue that the idea of gravity as an entropic force is debatable. It is shown that there is no convincing analogy between gravity and entropic force in Verlinde’s example. Neither holographic screen nor test particle satisfies all requirements for the existence of entropic force in a thermodynamics system. Furthermore, we show that the entropy increase of the screen is not caused by its statistical tendency to increase entropy as required by the existence of entropic force, but in fact caused by gravity. Therefore, Verlinde’s argument for the entropic origin of gravity is problematic. In addition, we argue that the existence of a minimum size of spacetime, together with the Heisenberg uncertainty principle in quantum theory, may imply the fundamental existence of gravity as a geometric property of spacetime. This may provide a further support for the conclusion that gravity is not an entropic force.

The Multi-Universe Cosmos. The Origin and Fate of our Universe

Science.gov (United States)

Velan, Karel

18 billion yers ago our Universe, one of many in the Cosmos, emerged from a hot, dense fireball of matter and energy created in the 4-dimensional cosmic space-time from virtual particles receiving their rest mass from a powerful primordial radiation field, the missing link to any viable theory of creation. The cloud of elementary particles and radiation collapsed by gravity into a fireball until its trappped thermal radiation caused a titanic explosion that initiated the expansion and evolution of ours universe. As the universe expanded and cooled it spawned galaxies, stars, planets and life. Proven laws of physics, observationsl data and mathematical computations support the new cosmological model which proposes a large number of universes in the cosmos in varying stages of evolution

On universality in ergoregion mergers

International Nuclear Information System (INIS)

Elvang, Henriette; Figueras, Pau; Hubeny, Veronika E; Rangamani, Mukund; Horowitz, Gary T

2009-01-01

We study non-dynamical mergers of ergoregions in d + 1-dimensional vacuum gravity. At the merger point, where the ergosurfaces bounding each ergoregion just touch, solutions exhibit universal behavior when there is rotation only in one plane: the angle between the merging ergosurfaces depends only on the symmetries of the solution, not on any other details of the configuration. We show that universality follows from the fact that the relevant component of Einstein's equation reduces to Laplace's equation at the point of merger. Thus ergoregion mergers mimic mergers of Newtonian equipotentials and have similar universal behavior. For solutions with rotation in more than one plane, universality is lost. We demonstrate universality and non-universality in several explicit examples.

Strings and quantum gravity

International Nuclear Information System (INIS)

Vega, H.J. de

1990-01-01

One of the main challenges in theoretical physics today is the unification of all interactions including gravity. At present, string theories appear as the most promising candidates to achieve such a unification. However, gravity has not completely been incorporated in string theory, many technical and conceptual problems remain and a full quantum theory of gravity is still non-existent. Our aim is to properly understand strings in the context of quantum gravity. Attempts towards this are reviewed. (author)

Gravity interpretation via EULDPH

International Nuclear Information System (INIS)

Ebrahimzadeh Ardestani, V.

2003-01-01

Euler's homogeneity equation for determining the coordinates of the source body especially to estimate the depth (EULDPH) is discussed at this paper. This method is applied to synthetic and high-resolution real data such as gradiometric or microgravity data. Low-quality gravity data especially in the areas with a complex geology structure has rarely been used. The Bouguer gravity anomalies are computed from absolute gravity data after the required corrections. Bouguer anomaly is transferred to residual gravity anomaly. The gravity gradients are estimated from residual anomaly values. Bouguer anomaly is the gravity gradients, using EULDPH. The coordinates of the perturbing body will be determined. Two field examples one in the east of Tehran (Mard Abad) where we would like to determine the location of the anomaly (hydrocarbon) and another in the south-east of Iran close to the border with Afghanistan (Nosrat Abad) where we are exploring chromite are presented

Einstein Universe Revisited and End of Dark ERA

Science.gov (United States)

Nurgaliev, Ildus S.

2015-01-01

Historically the earliest general relativistic cosmological solution was received by Einstein himself as homogenous, isotropic one. In accordance with European cosmology it was expected static. The Eternal Universe as scientific model is conflicting with the existed theological model of the Universe created by God, therefore, of the limited age. Christianity, younger Islam, older Judaism are based on creationism. Much older oriental traditions such us Hinduism and Buddhism are based on conceptions of eternal and cyclic Universe which are closer to scientific worldview. To have static universe Einstein needed a factor to counteract gravity and postulated cosmological term and considered it as a disadvantage of the theory. This aesthetic dissatisfaction was amplified by interpretation distance-redshift relationship as a cosmological expansion effect. Emerged scientific cosmological community (excluding Hubble himself - almost always) endorsed the concept of expanding Universe. At the same time, as it is shown in this report, a natural well known factors do exist to counteract gravity. They are inertial centrifugal and Coriolis forces finding their geometrical presentation in the relativity theory.

Anomalies and gravity

International Nuclear Information System (INIS)

Mielke, Eckehard W.

2006-01-01

Anomalies in Yang-Mills type gauge theories of gravity are reviewed. Particular attention is paid to the relation between the Dirac spin, the axial current j5 and the non-covariant gauge spin C. Using diagrammatic techniques, we show that only generalizations of the U(1)- Pontrjagin four-form F and F = dC arise in the chiral anomaly, even when coupled to gravity. Implications for Ashtekar's canonical approach to quantum gravity are discussed

Macroscopic Spacetime Shortcuts in the Manyfold Universe

CERN Document Server

Loup, F

2004-01-01

Recently the idea of a Manyfold Universe was proposed by some authors to explain Dark Matter . In this study we assume that the Standard Model(SM) of particles and fields with gravity propagating in the Higher Dimensional Spacetime(Bulk) while other interactions are confined to 3+1 Einsteinian spacetime(Brane) is not due to open strings and closed loops but instead is due to the capability of gravity as the weakest and "smallest" interaction to penetrate these small Bulk size ($10^{-31}$m to $10^{-35}$m) while protons,neutrons and other interactions stronger and "larger" than gravity do not "fits" in the size of the Bulk and remains trapped on the Brane and we present a equation to justify this point of view. Our picture relies over the geometrical beauty of the Manyfold Universe proposal that Dark Matter is chemically identical to ordinary matter but lies on other Folds. Also the geometrical point of view for the small size of the Bulk eliminates the need of trapping mechanisms to confine matter in the Brane...

Airborne Gravity: NGS' Gravity Data for CN02 (2013 & 2014)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Nebraska collected in 2013 & 2014 over 3 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...

Gravity loop corrections to the standard model Higgs in Einstein gravity

International Nuclear Information System (INIS)

Yugo Abe; Masaatsu Horikoshi; Takeo Inami

2016-01-01

We study one-loop quantum gravity corrections to the standard model Higgs potential V(φ) à la Coleman-Weinberg and examine the stability question of V(φ) in the energy region of Planck mass scale, μ ≃ M_P_l (M_P_l = 1.22x10"1"9 GeV). We calculate the gravity one-loop corrections to V(φ) in Einstein gravity by using the momentum cut-off Λ. We have found that even small gravity corrections compete with the standard model term of V(φ) and affect the stability argument of the latter part alone. This is because the latter part is nearly zero in the energy region of M_P_l. (author)

Data reduction and tying in regional gravity surveys—results from a new gravity base station network and the Bouguer gravity anomaly map for northeastern Mexico

Science.gov (United States)

Hurtado-Cardador, Manuel; Urrutia-Fucugauchi, Jaime

2006-12-01

Since 1947 Petroleos Mexicanos (Pemex) has conducted oil exploration projects using potential field methods. Geophysical exploration companies under contracts with Pemex carried out gravity anomaly surveys that were referred to different floating data. Each survey comprises observations of gravity stations along highways, roads and trails at intervals of about 500 m. At present, 265 separate gravimeter surveys that cover 60% of the Mexican territory (mainly in the oil producing regions of Mexico) are available. This gravity database represents the largest, highest spatial resolution information, and consequently has been used in the geophysical data compilations for the Mexico and North America gravity anomaly maps. Regional integration of gravimeter surveys generates gradients and spurious anomalies in the Bouguer anomaly maps at the boundaries of the connected surveys due to the different gravity base stations utilized. The main objective of this study is to refer all gravimeter surveys from Pemex to a single new first-order gravity base station network, in order to eliminate problems of gradients and spurious anomalies. A second objective is to establish a network of permanent gravity base stations (BGP), referred to a single base from the World Gravity System. Four regional loops of BGP covering eight States of Mexico were established to support the tie of local gravity base stations from each of the gravimeter surveys located in the vicinity of these loops. The third objective is to add the gravity constants, measured and calculated, for each of the 265 gravimeter surveys to their corresponding files in the Pemex and Instituto Mexicano del Petroleo database. The gravity base used as the common datum is the station SILAG 9135-49 (Latin American System of Gravity) located in the National Observatory of Tacubaya in Mexico City. We present the results of the installation of a new gravity base network in northeastern Mexico, reference of the 43 gravimeter surveys

Airborne Gravity: NGS' Gravity Data for CS02 (2008-2009)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Louisana and Mississippi collected in 2008-2009 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American...

Quantum gravity from noncommutative spacetime

Energy Technology Data Exchange (ETDEWEB)

Lee, Jungjai [Daejin University, Pocheon (Korea, Republic of); Yang, Hyunseok [Korea Institute for Advanced Study, Seoul (Korea, Republic of)

2014-12-15

We review a novel and authentic way to quantize gravity. This novel approach is based on the fact that Einstein gravity can be formulated in terms of a symplectic geometry rather than a Riemannian geometry in the context of emergent gravity. An essential step for emergent gravity is to realize the equivalence principle, the most important property in the theory of gravity (general relativity), from U(1) gauge theory on a symplectic or Poisson manifold. Through the realization of the equivalence principle, which is an intrinsic property in symplectic geometry known as the Darboux theorem or the Moser lemma, one can understand how diffeomorphism symmetry arises from noncommutative U(1) gauge theory; thus, gravity can emerge from the noncommutative electromagnetism, which is also an interacting theory. As a consequence, a background-independent quantum gravity in which the prior existence of any spacetime structure is not a priori assumed but is defined by using the fundamental ingredients in quantum gravity theory can be formulated. This scheme for quantum gravity can be used to resolve many notorious problems in theoretical physics, such as the cosmological constant problem, to understand the nature of dark energy, and to explain why gravity is so weak compared to other forces. In particular, it leads to a remarkable picture of what matter is. A matter field, such as leptons and quarks, simply arises as a stable localized geometry, which is a topological object in the defining algebra (noncommutative *-algebra) of quantum gravity.

Quantum gravity from noncommutative spacetime

International Nuclear Information System (INIS)

Lee, Jungjai; Yang, Hyunseok

2014-01-01

We review a novel and authentic way to quantize gravity. This novel approach is based on the fact that Einstein gravity can be formulated in terms of a symplectic geometry rather than a Riemannian geometry in the context of emergent gravity. An essential step for emergent gravity is to realize the equivalence principle, the most important property in the theory of gravity (general relativity), from U(1) gauge theory on a symplectic or Poisson manifold. Through the realization of the equivalence principle, which is an intrinsic property in symplectic geometry known as the Darboux theorem or the Moser lemma, one can understand how diffeomorphism symmetry arises from noncommutative U(1) gauge theory; thus, gravity can emerge from the noncommutative electromagnetism, which is also an interacting theory. As a consequence, a background-independent quantum gravity in which the prior existence of any spacetime structure is not a priori assumed but is defined by using the fundamental ingredients in quantum gravity theory can be formulated. This scheme for quantum gravity can be used to resolve many notorious problems in theoretical physics, such as the cosmological constant problem, to understand the nature of dark energy, and to explain why gravity is so weak compared to other forces. In particular, it leads to a remarkable picture of what matter is. A matter field, such as leptons and quarks, simply arises as a stable localized geometry, which is a topological object in the defining algebra (noncommutative *-algebra) of quantum gravity.

Ricci dark energy in Chern-Simons modified gravity

Energy Technology Data Exchange (ETDEWEB)

Silva, J.G.; Santos, A.F. [Universidade Federal de Mato Grosso (UFMT), Campo Grande, MT (Brazil)

2013-07-01

Full text: Currently the accelerated expansion of the universe has been strongly confirmed by some independent experiments such as the Cosmic Microwave Background Radiation (CMBR) and Sloan Digital Sky Survey (SDSS). In an attempt to explain this phenomenon there are two possible paths; first option - propose corrections to general relativity, second option - assuming that there is a dominant component of the universe, a kind of antigravity called dark energy. Any way that we intend to follow, there are numerous models that attempt to explain this effect. One of the models of modified gravity that has stood out in recent years is the Chern-Simons modified gravity. This modification consists in the addition of the Pontryagin density, which displays violation of parity symmetry in Einstein-Hilbert action. From among the various models proposed for dark energy there are some that are based on the holographic principle, known as holographic dark energy. Such models are based on the idea that the energy density of a given system is proportional to the inverse square of some characteristic length of the system. From these studies, here we consider the model proposed by Gao et. al., a model of dark energy where the characteristic length is given by the average radius of the Ricci scalar. Thus, the dark energy density is proportional to the Ricci scalar, i.e., ρ{sub x} ∝ R. It is a phenomenologically viable model and displays results similar to that presented by the cosmological model ACDM. In this work, we have considered the Ricci dark energy model in the dynamic Chern-Simons modified gravity. We show that in this context the evolution of the scale factor is similar to that displayed by the modified Chaplygin gas. (author)

Ricci dark energy in Chern-Simons modified gravity

International Nuclear Information System (INIS)

Silva, J.G.; Santos, A.F.

2013-01-01

Full text: Currently the accelerated expansion of the universe has been strongly confirmed by some independent experiments such as the Cosmic Microwave Background Radiation (CMBR) and Sloan Digital Sky Survey (SDSS). In an attempt to explain this phenomenon there are two possible paths; first option - propose corrections to general relativity, second option - assuming that there is a dominant component of the universe, a kind of antigravity called dark energy. Any way that we intend to follow, there are numerous models that attempt to explain this effect. One of the models of modified gravity that has stood out in recent years is the Chern-Simons modified gravity. This modification consists in the addition of the Pontryagin density, which displays violation of parity symmetry in Einstein-Hilbert action. From among the various models proposed for dark energy there are some that are based on the holographic principle, known as holographic dark energy. Such models are based on the idea that the energy density of a given system is proportional to the inverse square of some characteristic length of the system. From these studies, here we consider the model proposed by Gao et. al., a model of dark energy where the characteristic length is given by the average radius of the Ricci scalar. Thus, the dark energy density is proportional to the Ricci scalar, i.e., ρ x ∝ R. It is a phenomenologically viable model and displays results similar to that presented by the cosmological model ACDM. In this work, we have considered the Ricci dark energy model in the dynamic Chern-Simons modified gravity. We show that in this context the evolution of the scale factor is similar to that displayed by the modified Chaplygin gas. (author)

The gravity field and GGOS

DEFF Research Database (Denmark)

Forsberg, René; Sideris, M.G.; Shum, C.K.

2005-01-01

The gravity field of the earth is a natural element of the Global Geodetic Observing System (GGOS). Gravity field quantities are like spatial geodetic observations of potential very high accuracy, with measurements, currently at part-per-billion (ppb) accuracy, but gravity field quantities are also...... unique as they can be globally represented by harmonic functions (long-wavelength geopotential model primarily from satellite gravity field missions), or based on point sampling (airborne and in situ absolute and superconducting gravimetry). From a GGOS global perspective, one of the main challenges...... is to ensure the consistency of the global and regional geopotential and geoid models, and the temporal changes of the gravity field at large spatial scales. The International Gravity Field Service, an umbrella "level-2" IAG service (incorporating the International Gravity Bureau, International Geoid Service...

Thermodynamics in f(G,T Gravity

Directory of Open Access Journals (Sweden)

M. Sharif

2018-01-01

Full Text Available This paper explores the nonequilibrium behavior of thermodynamics at the apparent horizon of isotropic and homogeneous universe model in f(G,T gravity (G and T represent the Gauss-Bonnet invariant and trace of the energy-momentum tensor, resp.. We construct the corresponding field equations and analyze the first as well as generalized second law of thermodynamics in this scenario. It is found that an auxiliary term corresponding to entropy production appears due to the nonequilibrium picture of thermodynamics in first law. The universal condition for the validity of generalized second law of thermodynamics is also obtained. Finally, we check the validity of generalized second law of thermodynamics for the reconstructed f(G,T models (de Sitter and power-law solutions. We conclude that this law holds for suitable choices of free parameters.

Superconducting gravity gradiometer for sensitive gravity measurements. II. Experiment

International Nuclear Information System (INIS)

Chan, H.A.; Moody, M.V.; Paik, H.J.

1987-01-01

A sensitive superconducting gravity gradiometer has been constructed and tested. Coupling to gravity signals is obtained by having two superconducting proof masses modulate magnetic fields produced by persistent currents. The induced electrical currents are differenced by a passive superconducting circuit coupled to a superconducting quantum interference device. The experimental behavior of this device has been shown to follow the theoretical model closely in both signal transfer and noise characteristics. While its intrinsic noise level is shown to be 0.07 E Hz/sup -1/2/ (1 Eequivalent10/sup -9/ sec/sup -2/), the actual performance of the gravity gradiometer on a passive platform has been limited to 0.3--0.7 E Hz/sup -1/2/ due to its coupling to the environmental noise. The detailed structure of this excess noise is understood in terms of an analytical error model of the instrument. The calibration of the gradiometer has been obtained by two independent methods: by applying a linear acceleration and a gravity signal in two different operational modes of the instrument. This device has been successfully operated as a detector in a new null experiment for the gravitational inverse-square law. In this paper we report the design, fabrication, and detailed test results of the superconducting gravity gradiometer. We also present additional theoretical analyses which predict the specific dynamic behavior of the gradiometer and of the test

Studying Antimatter Gravity with Muonium

Directory of Open Access Journals (Sweden)

Aldo Antognini

2018-04-01

Full Text Available The gravitational acceleration of antimatter, g ¯ , has yet to be directly measured; an unexpected outcome of its measurement could change our understanding of gravity, the universe, and the possibility of a fifth force. Three avenues are apparent for such a measurement: antihydrogen, positronium, and muonium, the last requiring a precision atom interferometer and novel muonium beam under development. The interferometer and its few-picometer alignment and calibration systems appear feasible. With 100 nm grating pitch, measurements of g ¯ to 10%, 1%, or better can be envisioned. These could constitute the first gravitational measurements of leptonic matter, of 2nd-generation matter, and possibly, of antimatter.

Airborne Gravity: NGS' Gravity Data for EN07 (2012-2013)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Maine and Canada collected in 2012 and 2013 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American...

Airborne Gravity: NGS' Gravity Data for AS03 (2010-2012)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 and 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...

Novel Probes of Gravity and Dark Energy

Energy Technology Data Exchange (ETDEWEB)

Jain, Bhuvnesh; et al.

2013-09-20

The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and spectroscopy and radio observations. In the coming decade, searches for these effects have the potential for discovering fundamental new physics. We discuss how the searches can be carried out using experiments that are already under way or with modest adaptations of existing telescopes or planned experiments. The accompanying paper on the Growth of Cosmic Structure describes complementary tests of gravity with observations of large-scale structure.

Gravity wave astronomy

International Nuclear Information System (INIS)

Pinheiro, R.

1979-01-01

The properties and production of gravitational radiation are described. The prospects for their detection are considered including the Weber apparatus and gravity-wave telescopes. Possibilities of gravity-wave astronomy are noted

Cineradiographic Analysis of Mouse Postural Response to Alteration of Gravity and Jerk (Gravity Deceleration Rate

Directory of Open Access Journals (Sweden)

Katsuya Hasegawa

2014-04-01

Full Text Available The ability to maintain the body relative to the external environment is important for adaptation to altered gravity. However, the physiological limits for adaptation or the disruption of body orientation are not known. In this study, we analyzed postural changes in mice upon exposure to various low gravities. Male C57BL6/J mice (n = 6 were exposed to various gravity-deceleration conditions by customized parabolic flight-maneuvers targeting the partial-gravity levels of 0.60, 0.30, 0.15 and μ g (<0.001 g. Video recordings of postural responses were analyzed frame-by-frame by high-definition cineradiography and with exact instantaneous values of gravity and jerk. As a result, the coordinated extension of the neck, spine and hindlimbs was observed during the initial phase of gravity deceleration. Joint angles widened to 120%–200% of the reference g level, and the magnitude of the thoracic-curvature stretching was correlated with gravity and jerk, i.e., the gravity deceleration rate. A certain range of jerk facilitated mouse skeletal stretching efficiently, and a jerk of −0.3~−0.4 j (g/s induced the maximum extension of the thoracic-curvature. The postural response of animals to low gravity may undergo differential regulation by gravity and jerk.

Mimetic Gravity: A Review of Recent Developments and Applications to Cosmology and Astrophysics

Directory of Open Access Journals (Sweden)

Lorenzo Sebastiani

2017-01-01

Full Text Available Mimetic gravity is a Weyl-symmetric extension of General Relativity, related to the latter by a singular disformal transformation, wherein the appearance of a dust-like perfect fluid can mimic cold dark matter at a cosmological level. Within this framework, it is possible to provide a unified geometrical explanation for dark matter, the late-time acceleration, and inflation, making it a very attractive theory. In this review, we summarize the main aspects of mimetic gravity, as well as extensions of the minimal formulation of the model. We devote particular focus to the reconstruction technique, which allows the realization of any desired expansionary history of the universe by an accurate choice of potential or other functions defined within the theory (as in the case of mimetic f(R gravity. We briefly discuss cosmological perturbation theory within mimetic gravity. As a case study within which we apply the concepts previously discussed, we study a mimetic Hořava-like theory, of which we explore solutions and cosmological perturbations in detail. Finally, we conclude the review by discussing static spherically symmetric solutions within mimetic gravity and apply our findings to the problem of galactic rotation curves. Our review provides an introduction to mimetic gravity, as well as a concise but self-contained summary of recent findings, progress, open questions, and outlooks on future research directions.

Observing coseismic gravity change from the Japan Tohoku-Oki 2011 earthquake with GOCE gravity gradiometry

NARCIS (Netherlands)

Fuchs, M.J.; Bouman, J.; Broerse, D.B.T.; Visser, P.N.A.M.; Vermeersen, L.L.A.

2013-01-01

The Japan Tohoku-Oki earthquake (9.0 Mw) of 11 March 2011 has left signatures in the Earth's gravity field that are detectable by data of the Gravity field Recovery and Climate Experiment (GRACE) mission. Because the European Space Agency's (ESA) satellite gravity mission Gravity field and

Gravity effects on wind-induced flutter of leaves

Science.gov (United States)

Clemmer, Nickalaus; Kopperstad, Karsten; Solano, Tomas; Shoele, Kourosh; Ordonez, Juan

2017-11-01

Wind-Induced flutter of leaves depends on both wind velocity and the gravity. To study the gravitational effects on the oscillatory behavior of leaves in the wind, a wind tunnel that can be tilted about the center of the test section is created. This unique rotation capability allows systematic investigation of gravitational effects on the fluttering response of leaves. The flow-induced vibration will be studied for three different leaves at several different tilting angles including the wind travels horizontally, vertically downward and vertically upward. In each situation, the long axis of a leaf is placed parallel to the wind direction and its response is studied at different flow speed. Oscillation of the leaf is recorded via high-speed camera at each of setup, and the effect of the gravity on stabilizing or destabilizing the fluttering response is investigated. Summer REU student at Florida State University.

Disformal theories of gravity: from the solar system to cosmology

Energy Technology Data Exchange (ETDEWEB)

Sakstein, Jeremy, E-mail: j.a.sakstein@damtp.cam.ac.uk [DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

2014-12-01

This paper is concerned with theories of gravity that contain a scalar coupled both conformally and disformally to matter through the metric. By systematically deriving the non-relativistic limit, it is shown that no new non-linear screening mechanisms are present beyond the Vainshtein mechanism and chameleon-like screening. If one includes the cosmological expansion of the universe, disformal effects that are usually taken to be absent can be present in the solar system. When the conformal factor is absent, fifth-forces can be screened on all scales when the cosmological field is slowly-rolling. We investigate the cosmology of these models and use local tests of gravity to place new constraints on the disformal coupling and find M ∼> O(eV), which is not competitive with laboratory tests. Finally, we discuss the future prospects for testing these theories and the implications for other theories of modified gravity. In particular, the Vainshtein radius of solar system objects can be altered from the static prediction when cosmological time-derivatives are non-negligible.

Can modified gravity from extra dimensions explain dark matter effects?

International Nuclear Information System (INIS)

Kar, S.; Bharadwaj, S.; Pal, S.

2006-01-01

Observations on galaxy rotation curves and X-ray profiles of galaxy clusters over several decades have shown us that there exists a need for non-luminous (dark) matter. Cosmological observations also point towards the existence of dark components of two kinds - dark matter and dark energy - which, together, seem to be most of what is there the universe. However, for several years, there has been a line of thought which proposes modified gravity as an alternative to dark matter. In this article, we show, how the effective Einstein equations which arise in the context of the currently fashionable warped braneworld models, can explain the effects of dark matter as a manifestation of the consequences of the existence of extra dimensions. Finally, in order to distinguish between the effects of material dark matter and modified gravity, we calculate gravitational lensing in our modified gravity theory and show distinct differences in the deflection angles. If confirmed with observations, our results may shed new light on the existence of extra dimensions and dark matter. (authors)

Disformal theories of gravity: from the solar system to cosmology

International Nuclear Information System (INIS)

Sakstein, Jeremy

2014-01-01

This paper is concerned with theories of gravity that contain a scalar coupled both conformally and disformally to matter through the metric. By systematically deriving the non-relativistic limit, it is shown that no new non-linear screening mechanisms are present beyond the Vainshtein mechanism and chameleon-like screening. If one includes the cosmological expansion of the universe, disformal effects that are usually taken to be absent can be present in the solar system. When the conformal factor is absent, fifth-forces can be screened on all scales when the cosmological field is slowly-rolling. We investigate the cosmology of these models and use local tests of gravity to place new constraints on the disformal coupling and find M ∼> O(eV), which is not competitive with laboratory tests. Finally, we discuss the future prospects for testing these theories and the implications for other theories of modified gravity. In particular, the Vainshtein radius of solar system objects can be altered from the static prediction when cosmological time-derivatives are non-negligible

Cosmic Tsunamis in Modified Gravity: Disruption of Screening Mechanisms from Scalar Waves.

Science.gov (United States)

Hagala, R; Llinares, C; Mota, D F

2017-03-10

Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories. Specifically, we show that the waves produced in the symmetron model can increase the amplitude of the fifth force and the parametrized post Newtonian parameters by several orders of magnitude.

Evidence for the quantum birth of our Universe

Indian Academy of Sciences (India)

Abstract. We present evidence for a nonsingular origin of the Universe with intial conditions de- termined by quantum physics and relativistic gravity. In particular, we establish that the present temperature of the microwave background and the present density of the Universe agree well with our predictions from these intial ...

Airborne Gravity: NGS' Gravity Data for ES05 (2015-2016)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida and the Atlantic Ocean collected in two surveys, FL15-1 and FL15-2. This data set is part of the Gravity for the Re-definition of...

Airborne Gravity: NGS' Gravity Data for AS04 (2015-2016)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2015 and 2016 over 2 surveys, AK15 and AK16. This data set is part of the Gravity for the Re-definition of the American...

Space-time philosophy reconstructed via massive Nordström scalar gravities? Laws vs. geometry, conventionality, and underdetermination

Science.gov (United States)

Pitts, J. Brian

2016-02-01

What if gravity satisfied the Klein-Gordon equation? Both particle physics from the 1920-30s and the 1890s Neumann-Seeliger modification of Newtonian gravity with exponential decay suggest considering a "graviton mass term" for gravity, which is algebraic in the potential. Unlike Nordström's "massless" theory, massive scalar gravity is strictly special relativistic in the sense of being invariant under the Poincaré group but not the 15-parameter Bateman-Cunningham conformal group. It therefore exhibits the whole of Minkowski space-time structure, albeit only indirectly concerning volumes. Massive scalar gravity is plausible in terms of relativistic field theory, while violating most interesting versions of Einstein's principles of general covariance, general relativity, equivalence, and Mach. Geometry is a poor guide to understanding massive scalar gravity(s): matter sees a conformally flat metric due to universal coupling, but gravity also sees the rest of the flat metric (barely or on long distances) in the mass term. What is the 'true' geometry, one might wonder, in line with Poincaré's modal conventionality argument? Infinitely many theories exhibit this bimetric 'geometry,' all with the total stress-energy's trace as source; thus geometry does not explain the field equations. The irrelevance of the Ehlers-Pirani-Schild construction to a critique of conventionalism becomes evident when multi-geometry theories are contemplated. Much as Seeliger envisaged, the smooth massless limit indicates underdetermination of theories by data between massless and massive scalar gravities-indeed an unconceived alternative. At least one version easily could have been developed before General Relativity; it then would have motivated thinking of Einstein's equations along the lines of Einstein's newly re-appreciated "physical strategy" and particle physics and would have suggested a rivalry from massive spin 2 variants of General Relativity (massless spin 2, Pauli and Fierz

Development of a new generation gravity map of Antarctica: ADGRAV Antarctic Digital Gravity Synthesis

Directory of Open Access Journals (Sweden)

R. A. Arko

1999-06-01

Full Text Available The U.S. National Science Foundation (NSF has agreed to support the development of a new generation gravity map of Antarctica (ADGRAV - Antarctic Digital Gravity Synthesis, funding the development of a web based access tool. The goal of this project is the creation of an on-line Antarctic gravity database which will facilitate access to improved high resolution satellite gravity models, in conjunction with shipboard, airborne, and land based gravity measurements for the continental regions. This database will complement parallel projects underway to develop new continental bedrock (BEDMAP and magnetic (ADMAP maps of Antarctica.

Black Holes in Our Universe

Indian Academy of Sciences (India)

are humanity's high-technology windows onto the universe. For reasons that will ... instrument ever built; and it was the first direct ... gravity will drive it to collapse into a black hole. Indeed, in 2007, ... Given their large X-ray power, it has been ...

Gravity signatures of terrane accretion

Science.gov (United States)

Franco, Heather; Abbott, Dallas

1999-01-01

In modern collisional environments, accreted terranes are bracketed by forearc gravity lows, a gravitational feature which results from the abandonment of the original trench and the initiation of a new trench seaward of the accreted terrane. The size and shape of the gravity low depends on the type of accreted feature and the strength of the formerly subducting plate. Along the Central American trench, the accretion of Gorgona Island caused a seaward trench jump of 48 to 66 km. The relict trench axes show up as gravity lows behind the trench with minimum values of -78 mgal (N of Gorgona) and -49 mgal (S of Gorgona) respectively. These forearc gravity lows have little or no topographic expression. The active trench immediately seaward of these forearc gravity lows has minimum gravity values of -59 mgal (N of Gorgona) and -58 mgal (S of Gorgona), respectively. In the north, the active trench has a less pronounced gravity low than the sediment covered forearc. In the Mariana arc, two Cretaceous seamounts have been accreted to the Eocene arc. The northern seamount is most likely a large block, the southern seamount may be a thrust slice. These more recent accretion events have produced modest forearc topographic and gravity lows in comparison with the topographic and gravity lows within the active trench. However, the minimum values of the Mariana forearc gravity lows are modest only by comparison to the Mariana Trench (-216 mgal); their absolute values are more negative than at Gorgona Island (-145 to -146 mgal). We speculate that the forearc gravity lows and seaward trench jumps near Gorgona Island were produced by the accretion of a hotspot island from a strong plate. The Mariana gravity lows and seaward trench jumps (or thrust slices) were the result of breaking a relatively weak plate close to the seamount edifice. These gravity lows resulting from accretion events should be preserved in older accreted terranes.

Studies into the nature of cosmic acceleration: Dark energy or a modification to gravity on cosmological scales

Science.gov (United States)

Dossett, Jason Nicholas

Since its discovery more than a decade ago, the problem of cosmic acceleration has become one of the largest in cosmology and physics as a whole. An unknown dark energy component of the universe is often invoked to explain this observation. Mathematically, this works because inserting a cosmic fluid with a negative equation of state into Einstein's equations provides an accelerated expansion. There are, however, alternative explanations for the observed cosmic acceleration. Perhaps the most promising of the alternatives is that, on the very largest cosmological scales, general relativity needs to be extended or a new, modified gravity theory must be used. Indeed, many modified gravity models are not only able to replicate the observed accelerated expansion without dark energy, but are also more compatible with a unified theory of physics. Thus it is the goal of this dissertation to develop and study robust tests that will be able to distinguish between these alternative theories of gravity and the need for a dark energy component of the universe. We will study multiple approaches using the growth history of large-scale structure in the universe as a way to accomplish this task. These approaches include studying what is known as the growth index parameter, a parameter that describes the logarithmic growth rate of structure in the universe, which describes the rate of formation of clusters and superclusters of galaxies over the entire age of the universe. We will explore the effectiveness of this parameter to distinguish between general relativity and modifications to gravity physics given realistic expectations of results from future experiments. Next, we will explore the modified growth formalism wherein deviations from the growth expected in general relativity are parameterized via changes to the growth equations, i.e. the perturbed Einstein's equations. We will also explore the impact of spatial curvature on these tests. Finally, we will study how dark energy

Geneva University

CERN Multimedia

2008-01-01

Ecole de physique - Département de physique nucléaire et corpusculaire 24, Quai Ernest-Ansermet 1211 GENEVE 4 Tél: (022) 379 62 73 Fax: (022) 379 69 92 Monday 28 April 2008 PHYSICS COLLOQUIUM at 17.00 – Stückelberg Auditorium Gravity : an Emergent Perspective by Prof. Thanu Padmanabhan, Pune University Dean, Ganeshkhind, Pune, India I will motivate and describe a novel perspective in which gravity arises as an emergent phenomenon, somewhat like elasticity. This perspective throws light on several issues which are somewhat of a mystery in the conventional approach. Moreover it provides new insights on the dark energy problem. In fact, I will show that it is necessary to have such an alternative perspective in order to solve the cosmological constant problem.Information: http://theory.physics.unige.ch/~fiteo/seminars/COL/collist.html

2nd International Workshop on Antimatter and Gravity

CERN Document Server

Scampoli, P

2013-01-01

The purpose of this meeting is to review the experimental and theoretical aspects of the interaction of antimatter with gravity. Tests of the weak equivalence principle with e.g. positronium, muonium and antihydrogen with be discussed. Progress reports on the experiments at the CERN Antiproton Decelerator and on the available future facilities will be presented. A session on the relevance of antimatter with respect to Dark Energy and Dark Matter in the Universe (theory and experiments) is also foreseen.

NONSINGULAR UNIVERSES IN GAUSS–BONNET GRAVITY’S RAINBOW

International Nuclear Information System (INIS)

Hendi, Seyed Hossein; Momennia, Mehrab; Panah, Behzad Eslam; Faizal, Mir

2016-01-01

In this paper, we study the rainbow deformation of Friedmann-Robertson-Walker (FRW) cosmology in both Einstein gravity and Gauss–Bonnet (GB) gravity. We demonstrate that the singularity in FRW cosmology can be removed because of the rainbow deformation of the FRW metric. We obtain the general constraints required for FRW cosmology to be free of singularities. We observe that the inclusion of GB gravity can significantly change the constraints required to obtain nonsingular universes. We use rainbow functions motivated by the hard spectra of gamma-ray bursts to deform FRW cosmology and explicitly demonstrate that such a deformation removes the singularity in FRW cosmology.

NONSINGULAR UNIVERSES IN GAUSS–BONNET GRAVITY’S RAINBOW

Energy Technology Data Exchange (ETDEWEB)

Hendi, Seyed Hossein; Momennia, Mehrab; Panah, Behzad Eslam [Physics Department and Biruni Observatory, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Faizal, Mir [Department of Physics and Astronomy, University of Lethbridge, Lethbridge, AB T1K 3M4 (Canada)

2016-08-20

In this paper, we study the rainbow deformation of Friedmann-Robertson-Walker (FRW) cosmology in both Einstein gravity and Gauss–Bonnet (GB) gravity. We demonstrate that the singularity in FRW cosmology can be removed because of the rainbow deformation of the FRW metric. We obtain the general constraints required for FRW cosmology to be free of singularities. We observe that the inclusion of GB gravity can significantly change the constraints required to obtain nonsingular universes. We use rainbow functions motivated by the hard spectra of gamma-ray bursts to deform FRW cosmology and explicitly demonstrate that such a deformation removes the singularity in FRW cosmology.

Reconstructions of f(T) gravity from entropy-corrected holographic and new agegraphic dark energy models in power-law and logarithmic versions

Energy Technology Data Exchange (ETDEWEB)

Saha, Pameli; Debnath, Ujjal [Indian Institute of Engineering Science and Technology, Department of Mathematics, Howrah (India)

2016-09-15

Here, we peruse cosmological usage of the most promising candidates of dark energy in the framework of f(T) gravity theory where T represents the torsion scalar teleparallel gravity. We reconstruct the different f(T) modified gravity models in the spatially flat Friedmann-Robertson-Walker universe according to entropy-corrected versions of the holographic and new agegraphic dark energy models in power-law and logarithmic corrections, which describe an accelerated expansion history of the universe. We conclude that the equation of state parameter of the entropy-corrected models can transit from the quintessence state to the phantom regime as indicated by recent observations or can lie entirely in the phantom region. Also, using these models, we investigate the different areas of the stability with the help of the squared speed of sound. (orig.)

Airborne Gravity: NGS' Gravity Data for CS07 (2014 & 2016)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2014 & 2016 over 3 surveys,TX14-2, TX16-1 and TX16-2. This data set is part of the Gravity for the Re-definition of...

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation.

Science.gov (United States)

Tie, Junbo; Cao, Juliang; Chang, Lubing; Cai, Shaokun; Wu, Meiping; Lian, Junxiang

2018-03-16

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method.

A Model of Gravity Vector Measurement Noise for Estimating Accelerometer Bias in Gravity Disturbance Compensation

Science.gov (United States)

Cao, Juliang; Cai, Shaokun; Wu, Meiping; Lian, Junxiang

2018-01-01

Compensation of gravity disturbance can improve the precision of inertial navigation, but the effect of compensation will decrease due to the accelerometer bias, and estimation of the accelerometer bias is a crucial issue in gravity disturbance compensation. This paper first investigates the effect of accelerometer bias on gravity disturbance compensation, and the situation in which the accelerometer bias should be estimated is established. The accelerometer bias is estimated from the gravity vector measurement, and a model of measurement noise in gravity vector measurement is built. Based on this model, accelerometer bias is separated from the gravity vector measurement error by the method of least squares. Horizontal gravity disturbances are calculated through EGM2008 spherical harmonic model to build the simulation scene, and the simulation results indicate that precise estimations of the accelerometer bias can be obtained with the proposed method. PMID:29547552

BOOK REVIEW: Quantum Gravity: third edition Quantum Gravity: third edition

Science.gov (United States)

Rovelli, Carlo

2012-09-01

The request by Classical and Quantum Gravity to review the third edition of Claus Kiefer's 'Quantum Gravity' puts me in a slightly awkward position. This is a remarkably good book, which every person working in quantum gravity should have on the shelf. But in my opinion quantum gravity has undergone some dramatic advances in the last few years, of which the book makes no mention. Perhaps the omission only attests to the current vitality of the field, where progress is happening fast, but it is strange for me to review a thoughtful, knowledgeable and comprehensive book on my own field of research, which ignores what I myself consider the most interesting results to date. Kiefer's book is unique as a broad introduction and a reliable overview of quantum gravity. There are numerous books in the field which (often notwithstanding titles) focus on a single approach. There are also countless conference proceedings and article collections aiming to be encyclopaedic, but offering disorganized patchworks. Kiefer's book is a careful and thoughtful presentation of all aspects of the immense problem of quantum gravity. Kiefer is very learned, and brings together three rare qualities: he is pedagogical, he is capable of simplifying matter to the bones and capturing the essential, and he offers a serious and balanced evaluation of views and ideas. In a fractured field based on a major problem that does not yet have a solution, these qualities are precious. I recommend Kiefer's book to my students entering the field: to work in quantum gravity one needs a vast amount of technical knowledge as well as a grasp of different ideas, and Kiefer's book offers this with remarkable clarity. This novel third edition simplifies and improves the presentation of several topics, but also adds very valuable new material on quantum gravity phenomenology, loop quantum cosmology, asymptotic safety, Horava-Lifshitz gravity, analogue gravity, the holographic principle, and more. This is a testament

DNAG Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The Decade of North American Geology (DNAG) gravity grid values, spaced at 6 km, were used to produce the Gravity Anomaly Map of North America (1987; scale...

Space, time, and gravity. The theory of the big bang and black holes

Energy Technology Data Exchange (ETDEWEB)

Wald, R.M.

1977-01-01

In Einstein's theory of gravity, gravitation is described in terms of the curved geometry of space--time. The implications of these ideas for the universe: its origin, evolution, and large-scale structure are considered. Also discussed are gravitational collapse and black holes. (JFP)

Review of Electrical and Gravity Methods of Near-Surface Exploration for Groundwater

Directory of Open Access Journals (Sweden)

W. O. Raji

2014-12-01

Full Text Available The theory and practice of electrical and gravity methods of geophysics for groundwater exploration was reviewed with illustrations and data examples. With the goal of reducing cases of borehole/water-well failure attributed to the lack of the knowledge of the methods of geophysics for groundwater exploration and development, the paper reviews the basic concepts, field procedures for data acquisition, data processing, and interpretation as applied to the subject matter. Given a case study of groundwater exploration in University of Ilorin Campus, the three important techniques of electrical method of groundwater exploration are explained and illustrated using field data obtained in a previous study. Interpretation of resistivity data shows that an area measuring low resistivity (high conductivity, having thick pile of unconsolidated rock, and underlained by fracture crystalline is a ‘bright spot’ for citing borehole for groundwater abstraction in a basement complex area. Further to this, gravity method of groundwater exploration was discussed with field data from Wokbedilo community in Ethopia. Bouguer and reduced gravity anomaly results were presented as maps and contours to demonstrate how gravity data can be inverted to map groundwater aquifers and subsurface geological structures during groundwater exploration.

Measuring Gravity in International Trade Flows

Directory of Open Access Journals (Sweden)

E. Young Song

2004-12-01

Full Text Available The purpose of this paper is two-fold. One is to clarify the concept of gravity in international trade flows. The other is to measure the strength of gravity in international trade flows in a way that is consistent with a well-defined concept of gravity. This paper shows that the widely accepted belief that specialization is the source of gravity is not well grounded on theory. We propose to define gravity in international trade as the force that makes the market shares of an exporting country constant in all importing countries, regardless of their sizes. In a stochastic context, we should interpret it as implying that the strength of gravity increases i as the correlation between market shares and market sizes gets weaker and ii as the variance of market shares gets smaller. We estimate an empirical gravity equation thoroughly based on this definition of gravity. We find that a strong degree of gravity exists in most bilateral trade, regardless of income levels of countries, and in trade of most manThe purpose of this paper is two-fold. One is to clarify the concept of gravity in international trade flows. The other is to measure the strength of gravity in international trade flows in a way that is consistent with a well-defined concept of gravity. This paper shows that the widely accepted belief that specialization is the source of gravity is not well grounded on theory. We propose to define gravity in international trade as the force that makes the market shares of an exporting country constant in all importing countries, regardless of their sizes. In a stochastic context, we should interpret it as implying that the strength of gravity increases i as the correlation between market shares and market sizes gets weaker and ii as the variance of market shares gets smaller. We estimate an empirical gravity equation thoroughly based on this definition of gravity. We find that a strong degree of gravity exists in most bilateral trade, regardless of

TINJAUAN ULANG MATERI AJAR GERAK LURUS BERATURAN MELALUI PERCOBAAN GRAVITY CURRENT DALAM SKALA LABORATORIUM

Directory of Open Access Journals (Sweden)

A. K. Wardani

2013-07-01

Full Text Available ABSTRAKDalam konteks problem-based learning, salah satu masalah belajar fisika di sekolah dan di universitas adalah keterkaitan antara materi ajar dan fenomena alam dalam kehidupan sehari-hari masih minimum. Siswa, mahasiswa, guru, dan dosen masih mengalami kesulitan dalam memberikan contoh nyata GLB. Penelitian ini meninjau ulang materi ajar gerak lurus beraturan melalui percobaan gravity current sebagai sistem dua fluida dengan beda kerapatan di laboratorium dalam upaya mencari contoh nyata sistem fisis yang bergerak sepanjang garis lurus dengan kecepatan tetap. Penelitian ini dapat dipandang sebagai model proses intrusi air laut di estuari, tempat pertukaran massa air laut dan air sungai. Fokus penelitian adalah membuktikan bahwa gravity current bergerak dengan kecepatan tetap dan menentukan faktor-faktor dinamik kecepatan. Pengukuran akurat waktu tempuh dan tinggi permukaan air dalam tangki percobaan memberikan kecepatan tak-berdimensi gravity current sebesar 0,45 ± 0,03 dengan beda kerapatan massa dan tinggi awal permukaan air merupakan dua faktor dinamik penentu kecepatan. ABSTRACTIn the context of problem-based learning, one of learning difficulties in physics at schools and universities is theminimum relevance of learning materials to natural phenomena. School and university students still have difficulties in giving real examples of uniform motion. This research examines uniform motion by performing laboratory experiments on gravity current as a system of two fluids with different densities. The experiments were designed to provide a factual case of a moving system with constant speed and to model salt intrusion in an estuary, where sea water and river stream meets. The research focused on the dynamics of gravity currents and determines factors affecting the speed. Based on measurements of travel time and initial height of water surface in all experiments, the results showed that the non-dimensional speed was found to be 0.45 ± 0

Strings - Links between conformal field theory, gauge theory and gravity

International Nuclear Information System (INIS)

Troost, J.

2009-05-01

String theory is a candidate framework for unifying the gauge theories of interacting elementary particles with a quantum theory of gravity. The last years we have made considerable progress in understanding non-perturbative aspects of string theory, and in bringing string theory closer to experiment, via the search for the Standard Model within string theory, but also via phenomenological models inspired by the physics of strings. Despite these advances, many deep problems remain, amongst which a non-perturbative definition of string theory, a better understanding of holography, and the cosmological constant problem. My research has concentrated on various theoretical aspects of quantum theories of gravity, including holography, black holes physics and cosmology. In this Habilitation thesis I have laid bare many more links between conformal field theory, gauge theory and gravity. Most contributions were motivated by string theory, like the analysis of supersymmetry preserving states in compactified gauge theories and their relation to affine algebras, time-dependent aspects of the holographic map between quantum gravity in anti-de-Sitter space and conformal field theories in the bulk, the direct quantization of strings on black hole backgrounds, the embedding of the no-boundary proposal for a wave-function of the universe in string theory, a non-rational Verlinde formula and the construction of non-geometric solutions to supergravity

Nucleate Boiling Heat Transfer Studied Under Reduced-Gravity Conditions

Science.gov (United States)

Chao, David F.; Hasan, Mohammad M.

2000-01-01

Boiling is known to be a very efficient mode of heat transfer, and as such, it is employed in component cooling and in various energy-conversion systems. In space, boiling heat transfer may be used in thermal management, fluid handling and control, power systems, and on-orbit storage and supply systems for cryogenic propellants and life-support fluids. Recent interest in the exploration of Mars and other planets and in the concept of in situ resource utilization on the Martian and Lunar surfaces highlights the need to understand how gravity levels varying from the Earth's gravity to microgravity (1g = or > g/g(sub e) = or > 10(exp -6)g) affect boiling heat transfer. Because of the complex nature of the boiling process, no generalized prediction or procedure has been developed to describe the boiling heat transfer coefficient, particularly at reduced gravity levels. Recently, Professor Vijay K. Dhir of the University of California at Los Angeles proposed a novel building-block approach to investigate the boiling phenomena in low-gravity to microgravity environments. This approach experimentally investigates the complete process of bubble inception, growth, and departure for single bubbles formed at a well-defined and controllable nucleation site. Principal investigator Professor Vijay K. Dhir, with support from researchers from the NASA Glenn Research Center at Lewis Field, is performing a series of pool boiling experiments in the low-gravity environments of the KC 135 microgravity aircraft s parabolic flight to investigate the inception, growth, departure, and merger of bubbles from single- and multiple-nucleation sites as a function of the wall superheat and the liquid subcooling. Silicon wafers with single and multiple cavities of known characteristics are being used as test surfaces. Water and PF5060 (an inert liquid) were chosen as test liquids so that the role of surface wettability and the magnitude of the effect of interfacial tension on boiling in reduced

PREFACE: Fourth Meeting on Constrained Dynamics and Quantum Gravity

Science.gov (United States)

Cadoni, Mariano; Cavaglia, Marco; Nelson, Jeanette E.

2006-04-01

The formulation of a quantum theory of gravity seems to be the unavoidable endpoint of modern theoretical physics. Yet the quantum description of the gravitational field remains elusive. The year 2005 marks the tenth anniversary of the First Meeting on Constrained Dynamics and Quantum Gravity, held in Dubna (Russia) due to the efforts of Alexandre T. Filippov (JINR, Dubna) and Vittorio de Alfaro (University of Torino, Italy). At the heart of this initiative was the desire for an international forum where the status and perspectives of research in quantum gravity could be discussed from the broader viewpoint of modern gauge field theories. Since the Dubna meeting, an increasing number of scientists has joined this quest. Progress was reported in two other conferences in this series: in Santa Margherita Ligure (Italy) in 1996 and in Villasimius (Sardinia, Italy) in 1999. After a few years of ``working silence'' the time was now mature for a new gathering. The Fourth Meeting on Constrained Dynamics and Quantum Gravity (QG05) was held in Cala Gonone (Sardinia, Italy) from Monday 12th to Friday 16th September 2005. Surrounded by beautiful scenery, 100 scientists from 23 countries working in field theory, general relativity and related areas discussed the latest developments in the quantum treatment of gravitational systems. The QG05 edition covered many of the issues that had been addressed in the previous meetings and new interesting developments in the field, such as brane world models, large extra dimensions, analogue models of gravity, non-commutative techniques etc. The format of the meeting was similar to the previous ones. The programme consisted of invited plenary talks and parallel sessions on cosmology, quantum gravity, strings and phenomenology, gauge theories and quantisation and black holes. A major goal was to bring together senior scientists and younger people at the beginning of their scientific career. We were able to give financial support to both

Quantum Gravity

International Nuclear Information System (INIS)

Giribet, G E

2005-01-01

Claus Kiefer presents his book, Quantum Gravity, with his hope that '[the] book will convince readers of [the] outstanding problem [of unification and quantum gravity] and encourage them to work on its solution'. With this aim, the author presents a clear exposition of the fundamental concepts of gravity and the steps towards the understanding of its quantum aspects. The main part of the text is dedicated to the analysis of standard topics in the formulation of general relativity. An analysis of the Hamiltonian formulation of general relativity and the canonical quantization of gravity is performed in detail. Chapters four, five and eight provide a pedagogical introduction to the basic concepts of gravitational physics. In particular, aspects such as the quantization of constrained systems, the role played by the quadratic constraint, the ADM decomposition, the Wheeler-de Witt equation and the problem of time are treated in an expert and concise way. Moreover, other specific topics, such as the minisuperspace approach and the feasibility of defining extrinsic times for certain models, are discussed as well. The ninth chapter of the book is dedicated to the quantum gravitational aspects of string theory. Here, a minimalistic but clear introduction to string theory is presented, and this is actually done with emphasis on gravity. It is worth mentioning that no hard (nor explicit) computations are presented, even though the exposition covers the main features of the topic. For instance, black hole statistical physics (within the framework of string theory) is developed in a pedagogical and concise way by means of heuristical arguments. As the author asserts in the epilogue, the hope of the book is to give 'some impressions from progress' made in the study of quantum gravity since its beginning, i.e., since the end of 1920s. In my opinion, Kiefer's book does actually achieve this goal and gives an extensive review of the subject. (book review)

Butterfly effect in 3D gravity

Science.gov (United States)

Qaemmaqami, Mohammad M.

2017-11-01

We study the butterfly effect by considering shock wave solutions near the horizon of the anti-de Sitter black hole in some three-dimensional gravity models including 3D Einstein gravity, minimal massive 3D gravity, new massive gravity, generalized massive gravity, Born-Infeld 3D gravity, and new bigravity. We calculate the butterfly velocities of these models and also we consider the critical points and different limits in some of these models. By studying the butterfly effect in the generalized massive gravity, we observe a correspondence between the butterfly velocities and right-left moving degrees of freedom or the central charges of the dual 2D conformal field theories.

Type II universal spacetimes

Czech Academy of Sciences Publication Activity Database

Hervik, S.; Málek, Tomáš; Pravda, Vojtěch; Pravdová, Alena

2015-01-01

Roč. 32, č. 24 (2015), s. 245012 ISSN 0264-9381 R&D Projects: GA ČR GA13-10042S Institutional support: RVO:67985840 Keywords : einstein spacetimes * generalized gravities * universal spacetimes Subject RIV: BA - General Mathematics Impact factor: 2.837, year: 2015 http://iopscience.iop.org/article/10.1088/0264-9381/32/24/245012

Quantum gravity extension of the inflationary scenario.

Science.gov (United States)

Agullo, Ivan; Ashtekar, Abhay; Nelson, William

2012-12-21

Since the standard inflationary paradigm is based on quantum field theory on classical space-times, it excludes the Planck era. Using techniques from loop quantum gravity, the paradigm is extended to a self-consistent theory from the Planck scale to the onset of slow roll inflation, covering some 11 orders of magnitude in energy density and curvature. This preinflationary dynamics also opens a small window for novel effects, e.g., a source for non-Gaussianities, which could extend the reach of cosmological observations to the deep Planck regime of the early Universe.

Induced quantum conformal gravity

International Nuclear Information System (INIS)

Novozhilov, Y.V.; Vassilevich, D.V.

1988-11-01

Quantum gravity is considered as induced by matter degrees of freedom and related to the symmetry breakdown in the low energy region of a non-Abelian gauge theory of fundamental fields. An effective action for quantum conformal gravity is derived where both the gravitational constant and conformal kinetic term are positive. Relation with induced classical gravity is established. (author). 15 refs

Airborne Gravity: NGS' Airborne Gravity Data for AN01 (2009-2010)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2009-2010 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...

Emergent gravity and noncommutative branes from Yang-Mills matrix models

International Nuclear Information System (INIS)

Steinacker, Harold

2009-01-01

The framework of emergent gravity arising from Yang-Mills matrix models is developed further, for general noncommutative branes embedded in R D . The effective metric on the brane turns out to have a universal form reminiscent of the open string metric, depending on the dynamical Poisson structure and the embedding metric in R D . A covariant form of the tree-level equations of motion is derived, and the Newtonian limit is discussed. This points to the necessity of branes in higher dimensions. The quantization is discussed qualitatively, which singles out the IKKT model as a prime candidate for a quantum theory of gravity coupled to matter. The Planck scale is then identified with the scale of N=4 SUSY breaking. A mechanism for avoiding the cosmological constant problem is exhibited

Dynamical 3-Space Gravity Theory: Effects on Polytropic Solar Models

Directory of Open Access Journals (Sweden)

May R. D.

2011-01-01

Full Text Available Numerous experiments and observations have confirmed the existence of a dynamical 3-space, detectable directly by light-speed anisotropy experiments, and indirectly by means of novel gravitational effects, such as bore hole g anomalies, predictable black hole masses, flat spiral-galaxy rotation curves, and the expansion of the universe, all without dark matter and dark energy. The dynamics for this 3-space follows from a unique generalisation of Newtonian gravity, once that is cast into a velocity formalism. This new theory of gravity is applied to the solar model of the sun to compute new density, pressure and temperature profiles, using polytrope modelling of the equation of state for the matter. These results should be applied to a re-analysis of solar neutrino production, and to stellar evolution in general.

Interior Alaska Bouguer Gravity Anomaly

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — A 1 kilometer Complete Bouguer Anomaly gravity grid of interior Alaska. Only those grid cells within 10 kilometers of a gravity data point have gravity values....

The Rh = ct universe in alternative theories of gravity

Science.gov (United States)

Sultana, Joseph; Kazanas, Demosthenes

2017-12-01

The Λ cold dark matter (ΛCDM) model (one comprising of a cosmological constant Λ and cold dark matter) is generally considered the standard model in cosmology. One of the alternatives that has received attention in the last few years is the Rh = ct universe, which provides an age for the Universe similar to that of ΛCDM and whose (vanishing) deceleration parameter is apparently not inconsistent with observations. Like the ΛCDM, the Rh = ct universe is based on a Friedmann-Robertson-Walker cosmology with the total energy density ρ and pressure p of the cosmic fluid satisfying the simple equation of state ρ + 3p = 0, i.e. a vanishing total active gravitational mass. In an earlier paper, we examined the possible sources for the Rh = ct universe within general relativity, and we have shown that it still contains a dark energy component, albeit not in the form of a cosmological constant. The growing interest in gravitational theories, alternative to Einstein's general relativity, in cosmology, is mainly driven by the need for cosmological models that attain a late-time accelerated expansion without the presence of a cosmological constant as in the ΛCDM, and thereby avoiding the problems associated with it. In this paper, we discuss some of these common alternative theories and show that the Rh = ct is also a solution to some of them.

R 2 inflation to probe non-perturbative quantum gravity

Science.gov (United States)

Koshelev, Alexey S.; Sravan Kumar, K.; Starobinsky, Alexei A.

2018-03-01

It is natural to expect a consistent inflationary model of the very early Universe to be an effective theory of quantum gravity, at least at energies much less than the Planck one. For the moment, R + R 2, or shortly R 2, inflation is the most successful in accounting for the latest CMB data from the PLANCK satellite and other experiments. Moreover, recently it was shown to be ultra-violet (UV) complete via an embedding into an analytic infinite derivative (AID) non-local gravity. In this paper, we derive a most general theory of gravity that contributes to perturbed linear equations of motion around maximally symmetric space-times. We show that such a theory is quadratic in the Ricci scalar and the Weyl tensor with AID operators along with the Einstein-Hilbert term and possibly a cosmological constant. We explicitly demonstrate that introduction of the Ricci tensor squared term is redundant. Working in this quadratic AID gravity framework without a cosmological term we prove that for a specified class of space homogeneous space-times, a space of solutions to the equations of motion is identical to the space of backgrounds in a local R 2 model. We further compute the full second order perturbed action around any background belonging to that class. We proceed by extracting the key inflationary parameters of our model such as a spectral index ( n s ), a tensor-to-scalar ratio ( r) and a tensor tilt ( n t ). It appears that n s remains the same as in the local R 2 inflation in the leading slow-roll approximation, while r and n t get modified due to modification of the tensor power spectrum. This class of models allows for any value of r complete R 2 gravity a natural target for future CMB probes.

MarsSedEx III: linking Computational Fluid Dynamics (CFD) and reduced gravity experiments

Science.gov (United States)

Kuhn, N. J.; Kuhn, B.; Gartmann, A.

2015-12-01

Nikolaus J. Kuhn (1), Brigitte Kuhn (1), and Andres Gartmann (2) (1) University of Basel, Physical Geography, Environmental Sciences, Basel, Switzerland (nikolaus.kuhn@unibas.ch), (2) Meteorology, Climatology, Remote Sensing, Environmental Sciences, University of Basel, Switzerland Experiments conducted during the MarsSedEx I and II reduced gravity experiments showed that using empirical models for sediment transport on Mars developed for Earth violates fluid dynamics. The error is caused by the interaction between runing water and sediment particles, which affect each other in a positive feedback loop. As a consequence, the actual flow conditions around a particle cannot be represented by drag coefficients derived on Earth. This study exmines the implications of such gravity effects on sediment movement on Mars, with special emphasis on the limits of sandstones and conglomerates formed on Earth as analogues for sedimentation on Mars. Furthermore, options for correctiong the errors using a combination of CFD and recent experiments conducted during the MarsSedEx III campaign are presented.

(2+1)-dimensional quantum gravity

International Nuclear Information System (INIS)

Hosoya, Akio; Nakao, Ken-ichi.

1989-05-01

The (2+1)-dimensional pure Einstein gravity is studied in the canonical ADM formalism, assuming that the spatial surface is closed and compact. Owing to the constraints, the dynamical variables are reduced to the moduli parameters of the 2-surface. Upon quantization, the system becomes a quantum mechanics of moduli parameters in a curved space endowed with the Weil-Petersson metric. In the case of torus in particular, the superspace, on which the wave function of universe is defined, turns out to be the fundamental region is the moduli space. The solution of the Wheeler-DeWitt equation is explicitly given as the Maass form which is perfectly regular in the superspace. (author)

Cosmological attractors in massive gravity

CERN Document Server

Dubovsky, S; Tkachev, I I

2005-01-01

We study Lorentz-violating models of massive gravity which preserve rotations and are invariant under time-dependent shifts of the spatial coordinates. In the linear approximation the Newtonian potential in these models has an extra ``confining'' term proportional to the distance from the source. We argue that during cosmological expansion the Universe may be driven to an attractor point with larger symmetry which includes particular simultaneous dilatations of time and space coordinates. The confining term in the potential vanishes as one approaches the attractor. In the vicinity of the attractor the extra contribution is present in the Friedmann equation which, in a certain range of parameters, gives rise to the cosmic acceleration.

Elliptic solutions of generalized Brans-Dicke gravity with a non-universal coupling

Energy Technology Data Exchange (ETDEWEB)

Alimi, J.M.; Reverdy, V. [Observatoire de Paris, Laboratoire Univers et Theories (LUTh), Meudon (France); Golubtsova, A.A. [Observatoire de Paris, Laboratoire Univers et Theories (LUTh), Meudon (France); Peoples' Friendship University of Russia, Institute of Gravitation and Cosmology, Moscow (Russian Federation)

2014-10-15

We study a model of the generalized Brans-Dicke gravity presented in both the Jordan and in the Einstein frames, which are conformally related. We show that the scalar field equations in the Einstein frame are reduced to the geodesics equations on the target space of the nonlinear sigma model. The analytical solutions in elliptical functions are obtained when the conformal couplings are given by reciprocal exponential functions. The behavior of the scale factor in the Jordan frame is studied using numerical computations. For certain parameters the solutions can describe an accelerated expansion. We also derive an analytical approximation in exponential functions. (orig.)

Gravothermal aspects in evolution of the stars and the universe

International Nuclear Information System (INIS)

Sugimoto, Daiichiro; Eriguchi, Yoshiharu; Hachisu, Izumi.

1982-01-01

In celestial bodies and the universe self-gravity plays an essential role in determining their nature and evolution. Global thermodynamics of such self-gravitating systems is discussed. They exhibit thermodynamically peculiar nature such as negative specific heat, and, depending on parameters involved, they have no state of stable thermal equilibrium within the framework of Newtonian gravity. The expansion of the universe produces a change in the thermodynamic boundary conditions for subsystems embedded in the universe. Such situations are related with the origin of their evolution (or, in other words, emergence of diversities, orders or spatial structures) and generation of information. Such phenomena are known in relation to stellar evolution, gravothermal catastrophe of self-gravitating systems (star itself or gravitational many body system), formation of black holes and evolution of the universe. Their inter-relations are clarified from the standpoint of thermodynamics of self-gravitating systems, black holes, dissipative open systems and irreversible processes, and of cosmology. It is shown that the expansion of the universe and the effect of self-gravity are essential in generation of information and as a ponderamotive force of evolution. The laws of physics including the second law of thermodynamics hold even in such processes. Thus, the generation of information is formulated rigorously, while the concept of evolution can be defined not in a simple and unique fashion but in relation with ''apparent'' concept of common sense in which some interaction is overlooked. (author)

The organization of the Universe

International Nuclear Information System (INIS)

Wilkinson, D.

1981-01-01

In this introductory lecture of a series on the nature of matter the author establishes the range and scale of the particles and forces involved and considers the Universe in which they are found. Gravity, electromagnetism, the strong and the weak forces and their possible unification in Grand Unified Theories are discussed. The origin of the Universe, the Big Bang model and the present observable Universe, its dimensions and the forces that shape it are considered. Present thinking is examined concerning the structure of the atom, sub-nuclear forces and the possible constituents of protons and the forces holding them together. (U.K.)

Inflationary universe from higher derivative quantum gravity coupled with scalar electrodynamics

Energy Technology Data Exchange (ETDEWEB)

Myrzakulov, R. [Department of General & Theoretical Physics and Eurasian Center for Theoretical Physics, Eurasian National University, Astana 010008 (Kazakhstan); Odintsov, S.D. [Consejo Superior de Investigaciones Científicas, ICE/CSIC-IEEC, Campus UAB, Facultat de Ciències, Torre C5-Parell-2a pl, E-08193 Bellaterra, Barcelona (Spain); Institut de Ciencies de l' Espai (IEEC-CSIC), Campus UAB, Carrer de Can Magrans, s/n 08193 Cerdanyola del Valles, Barcelona (Spain); Tomsk State Pedagogical University, 634050 Tomsk (Russian Federation); Tomsk State University of Control Systems and Radioelectronics (TUSUR) 634050 Tomsk (Russian Federation); Sebastiani, L., E-mail: lorenzo.sebastiani@unitn.it [Department of General & Theoretical Physics and Eurasian Center for Theoretical Physics, Eurasian National University, Astana 010008 (Kazakhstan)

2016-06-15

We study inflation for a quantum scalar electrodynamics model in curved space–time and for higher-derivative quantum gravity (QG) coupled with scalar electrodynamics. The corresponding renormalization-group (RG) improved potential is evaluated for both theories in Jordan frame where non-minimal scalar-gravitational coupling sector is explicitly kept. The role of one-loop quantum corrections is investigated by showing how these corrections enter in the expressions for the slow-roll parameters, the spectral index and the tensor-to-scalar ratio and how they influence the bound of the Hubble parameter at the beginning of the primordial acceleration. We demonstrate that the viable inflation maybe successfully realized, so that it turns out to be consistent with last Planck and BICEP2/Keck Array data.

Is our universe an open system?

International Nuclear Information System (INIS)

Page, D.N.

1983-01-01

The author gives a brief summary of the arguments which might indicate the universe to be an open system. The arguments concern the formation and evaporation of black holes and the asymptotic completeness or incompleteness of the Hilbert space of quantum gravity. (Auth.)

Determination of angle of light deflection in higher-derivative gravity theories

Science.gov (United States)

Xu, Chenmei; Yang, Yisong

2018-03-01

Gravitational light deflection is known as one of three classical tests of general relativity and the angle of deflection may be computed explicitly using approximate or exact solutions describing the gravitational force generated from a point mass. In various generalized gravity theories, however, such explicit determination is often impossible due to the difficulty in obtaining an exact expression for the deflection angle. In this work, we present some highly effective globally convergent iterative methods to determine the angle of semiclassical gravitational deflection in higher- and infinite-derivative formalisms of quantum gravity theories. We also establish the universal properties that the deflection angle always stays below the classical Einstein angle and is a strictly decreasing function of the incident photon energy, in these formalisms.

Metastable gravity on classical defects

International Nuclear Information System (INIS)

Ringeval, Christophe; Rombouts, Jan-Willem

2005-01-01

We discuss the realization of metastable gravity on classical defects in infinite-volume extra dimensions. In dilatonic Einstein gravity, it is found that the existence of metastable gravity on the defect core requires violation of the dominant energy condition for codimension N c =2 defects. This is illustrated with a detailed analysis of a six-dimensional hyperstring minimally coupled to dilaton gravity. We present the general conditions under which a codimension N c >2 defect admits metastable modes, and find that they differ from lower codimensional models in that, under certain conditions, they do not require violation of energy conditions to support quasilocalized gravity

Gravity gradient preprocessing at the GOCE HPF

Science.gov (United States)

Bouman, J.; Rispens, S.; Gruber, T.; Schrama, E.; Visser, P.; Tscherning, C. C.; Veicherts, M.

2009-04-01

One of the products derived from the GOCE observations are the gravity gradients. These gravity gradients are provided in the Gradiometer Reference Frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. In order to use these gravity gradients for application in Earth sciences and gravity field analysis, additional pre-processing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and non-tidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10-3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10-2 level with this method.

Formalism for testing theories of gravity using lensing by compact objects. II. Probing post-post-Newtonian metrics

International Nuclear Information System (INIS)

Keeton, Charles R.; Petters, A.O.

2006-01-01

We study gravitational lensing by compact objects in gravity theories that can be written in a post-post-Newtonian (PPN) framework: i.e., the metric is static and spherically symmetric, and can be written as a Taylor series in m /r, where m is the gravitational radius of the compact object. Working invariantly, we compute corrections to standard weak-deflection lensing observables at first and second order in the perturbation parameter ε=θ/θ E , where θ is the angular gravitational radius and θ E is the angular Einstein ring radius of the lens. We show that the first-order corrections to the total magnification and centroid position vanish universally for gravity theories that can be written in the PPN framework. This arises from some surprising, fundamental relations among the lensing observables in PPN gravity models. We derive these relations for the image positions, magnifications, and time delays. A deep consequence is that any violation of the universal relations would signal the need for a gravity model outside the PPN framework (provided that some basic assumptions hold). In practical terms, the relations will guide observational programs to test general relativity, modified gravity theories, and possibly the cosmic censorship conjecture. We use the new relations to identify lensing observables that are accessible to current or near-future technology, and to find combinations of observables that are most useful for probing the spacetime metric. We give explicit applications to the galactic black hole, microlensing, and the binary pulsar J0737-3039

New standards for reducing gravity data: The North American gravity database

Science.gov (United States)

Hinze, W. J.; Aiken, C.; Brozena, J.; Coakley, B.; Dater, D.; Flanagan, G.; Forsberg, R.; Hildenbrand, T.; Keller, Gordon R.; Kellogg, J.; Kucks, R.; Li, X.; Mainville, A.; Morin, R.; Pilkington, M.; Plouff, D.; Ravat, D.; Roman, D.; Urrutia-Fucugauchi, J.; Veronneau, M.; Webring, M.; Winester, D.

2005-01-01

The North American gravity database as well as databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revising procedures for calculating gravity anomalies, taking into account our enhanced computational power, improved terrain databases and datums, and increased interest in more accurately defining long-wavelength anomaly components. Users of the databases may note minor differences between previous and revised database values as a result of these procedures. Generally, the differences do not impact the interpretation of local anomalies but do improve regional anomaly studies. The most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conventionally used geoid or sea level. Principal facts of gravity observations and anomalies based on both revised and previous procedures together with germane metadata will be available on an interactive Web-based data system as well as from national agencies and data centers. The use of the revised procedures is encouraged for gravity data reduction because of the widespread use of the global positioning system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with North American and national databases. Anomalies based on the revised standards should be preceded by the adjective "ellipsoidal" to differentiate anomalies calculated using heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid. ?? 2005 Society of Exploration Geophysicists. All rights reserved.

LINKING TESTS OF GRAVITY ON ALL SCALES: FROM THE STRONG-FIELD REGIME TO COSMOLOGY

Energy Technology Data Exchange (ETDEWEB)

Baker, Tessa [Astrophysics, Denys Wilkinson Building, Keble Road, University of Oxford, Oxford, OX1 3RH (United Kingdom); Psaltis, Dimitrios [Astronomy Department, University of Arizona, 933 North Cherry Avenue., Tucson, AZ 85721 (United States); Skordis, Constantinos, E-mail: tessa.baker@astro.ox.ac.uk, E-mail: dpsaltis@email.arizona.edu, E-mail: skordis@ucy.ac.cy [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2015-03-20

The current effort to test general relativity (GR) employs multiple disparate formalisms for different observables, obscuring the relations between laboratory, astrophysical, and cosmological constraints. To remedy this situation, we develop a parameter space for comparing tests of gravity on all scales in the universe. In particular, we present new methods for linking cosmological large-scale structure, the cosmic microwave background, and gravitational waves with classic PPN tests of gravity. Diagrams of this gravitational parameter space reveal a noticeable untested regime. The untested window, which separates small-scale systems from the troubled cosmological regime, could potentially hide the onset of corrections to GR.

Scale-invariant gravity: geometrodynamics

International Nuclear Information System (INIS)

Anderson, Edward; Barbour, Julian; Foster, Brendan; Murchadha, Niall O

2003-01-01

We present a scale-invariant theory, conformal gravity, which closely resembles the geometrodynamical formulation of general relativity (GR). While previous attempts to create scale-invariant theories of gravity have been based on Weyl's idea of a compensating field, our direct approach dispenses with this and is built by extension of the method of best matching w.r.t. scaling developed in the parallel particle dynamics paper by one of the authors. In spatially compact GR, there is an infinity of degrees of freedom that describe the shape of 3-space which interact with a single volume degree of freedom. In conformal gravity, the shape degrees of freedom remain, but the volume is no longer a dynamical variable. Further theories and formulations related to GR and conformal gravity are presented. Conformal gravity is successfully coupled to scalars and the gauge fields of nature. It should describe the solar system observations as well as GR does, but its cosmology and quantization will be completely different

Early Universe Higgs dynamics in the presence of the Higgs-inflaton and non-minimal Higgs-gravity couplings

Energy Technology Data Exchange (ETDEWEB)

Ema, Yohei [Department of Physics, Faculty of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Karčiauskas, Mindaugas [University of Jyväskylä, Department of Physics, P.O. Box 35 (YFL), FI-40014, Jyväskylä (Finland); Lebedev, Oleg; Zatta, Marco, E-mail: ema@hep-th.phys.s.u-tokyo.ac.jp, E-mail: mindaugas.m.karciauskas@jyu.fi, E-mail: oleg.lebedev@helsinki.fi, E-mail: marco.zatta@helsinki.fi [University of Helsinki and Helsinki Institute of Physics, P.O. Box 64, FI-00014, Helsinki (Finland)

2017-06-01

Apparent metastability of the electroweak vacuum poses a number of cosmological questions. These concern evolution of the Higgs field to the current vacuum, and its stability during and after inflation. Higgs-inflaton and non-minimal Higgs-gravity interactions can make a crucial impact on these considerations potentially solving the problems. In this work, we allow for these couplings to be present simultaneously and study their interplay. We find that different combinations of the Higgs-inflaton and non-minimal Higgs-gravity couplings induce effective Higgs mass during and after inflation. This crucially affects the Higgs stability considerations during preheating. In particular, a wide range of the couplings leading to stable solutions becomes allowed.

Research Regarding High Gravity Brewing in the Pilot Station USAMV Cluj-Napoca

Directory of Open Access Journals (Sweden)

Andrei Borsa

2013-11-01

Full Text Available This paper aims to present preliminary research results obtained while developing and implementing a high gravity beer fermentation process. Production trials were performed in brewery pilot plant from University of Agricultural Sciences and Veterinary Medicine, Faculty of Food Science and Technology. The tehnological parameters were adapted and monitored during the making.

Dual geometric-gauge field aspects of gravity

International Nuclear Information System (INIS)

Huei Peng; Wang, K.

1992-01-01

We propose that the geometric and standard gauge field aspects of gravity are equally essential for a complete description of gravity and can be reconciled. We show that this dualism of gravity resolves the dimensional Newtonian constant problem in both quantum gravity and unification schemes involving gravity (i.e., the Newtonian constant is no longer the coupling constant in the gauge aspect of gravity) and reveals the profound similarity between gravity and other fields. 23 refs., 3 tabs

A comparison of Horava-Lifshitz gravity and Einstein gravity through thin-shell wormhole construction

Energy Technology Data Exchange (ETDEWEB)

Rahaman, F [Department of Mathematics, Jadavpur University, Kolkata 700032 (India); Kuhfittig, P K F [Department of Mathematics, Milwaukee School of Engineering, Milwaukee, WI 53202-3109 (United States); Kalam, M [Department of Physics, Aliah University, Sector V, Salt Lake, Kolkata 700091 (India); Usmani, A A [Department of Physics, Aligarh Muslim University, Aligarh 202002, Uttar Pradesh (India); Ray, S, E-mail: farook-rahaman@yahoo.com, E-mail: kuhfitti@msoe.edu, E-mail: mehedikalam@yahoo.co.in, E-mail: anisul@iucaa.ernet.in, E-mail: saibal@iucaa.ernet.in [Department of Physics, Govt College of Engineering and Ceramic Technology, Kolkata 700010 (India)

2011-08-07

In this paper, we have constructed a new class of thin-shell wormholes from black holes in Horava-Lifshitz gravity. Particular emphasis is placed on those aspects that allow a comparison of Horava-Lifshitz gravity to Einstein gravity. The former enjoys a number of advantages for small values of the throat radius.

Holography as a highly efficient renormalization group flow. I. Rephrasing gravity

Science.gov (United States)

Behr, Nicolas; Kuperstein, Stanislav; Mukhopadhyay, Ayan

2016-07-01

We investigate how the holographic correspondence can be reformulated as a generalization of Wilsonian renormalization group (RG) flow in a strongly interacting large-N quantum field theory. We first define a highly efficient RG flow as one in which the Ward identities related to local conservation of energy, momentum and charges preserve the same form at each scale. To achieve this, it is necessary to redefine the background metric and external sources at each scale as functionals of the effective single-trace operators. These redefinitions also absorb the contributions of the multitrace operators to these effective Ward identities. Thus, the background metric and external sources become effectively dynamical, reproducing the dual classical gravity equations in one higher dimension. Here, we focus on reconstructing the pure gravity sector as a highly efficient RG flow of the energy-momentum tensor operator, leaving the explicit constructive field theory approach for generating such RG flows to the second part of the work. We show that special symmetries of the highly efficient RG flows carry information through which we can decode the gauge fixing of bulk diffeomorphisms in the corresponding gravity equations. We also show that the highly efficient RG flow which reproduces a given classical gravity theory in a given gauge is unique provided the endpoint can be transformed to a nonrelativistic fixed point with a finite number of parameters under a universal rescaling. The results obtained here are used in the second part of this work, where we do an explicit field-theoretic construction of the RG flow and obtain the dual classical gravity theory.

Gamma-ray bursts as cosmological probes: ΛCDM vs. conformal gravity

International Nuclear Information System (INIS)

Diaferio, Antonaldo; Ostorero, Luisa; Cardone, Vincenzo

2011-01-01

ΛCDM, for the currently preferred cosmological density Ω 0 and cosmological constant Ω Λ , predicts that the Universe expansion decelerates from early times to redshift z ≈ 0.9 and accelerates at later times. On the contrary, the cosmological model based on conformal gravity predicts that the cosmic expansion has always been accelerating. To distinguish between these two very different cosmologies, we resort to gamma-ray bursts (GRBs), which have been suggested to probe the Universe expansion history at z > 1, where identified type Ia supernovae (SNe) are rare. We use the full Bayesian approach to infer the cosmological parameters and the additional parameters required to describe the GRB data available in the literature. For the first time, we use GRBs as cosmological probes without any prior information from other data. In addition, when we combine the GRB samples with SNe, our approach neatly avoids all the inconsistencies of most numerous previous methods that are plagued by the so-called circularity problem. In fact, when analyzed properly, current data are consistent with distance moduli of GRBs and SNe that can respectively be, in a variant of conformal gravity, ∼ 15 and ∼ 3 magnitudes fainter than in ΛCDM. Our results indicate that the currently available SN and GRB samples are accommodated equally well by both ΛCDM and conformal gravity and do not exclude a continuous accelerated expansion. We conclude that GRBs are currently far from being effective cosmological probes, as they are unable to distinguish between these two very different expansion histories

Dark matter universe

Science.gov (United States)

Bahcall, Neta A.

2015-01-01

Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations—from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is “cold” (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology—a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)—fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle. PMID:26417091

Dark matter universe.

Science.gov (United States)

Bahcall, Neta A

2015-10-06

Most of the mass in the universe is in the form of dark matter--a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations--from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is "cold" (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology--a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)--fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle.

Testing Einstein's Gravity on Large Scales

Science.gov (United States)

Prescod-Weinstein, Chandra

2011-01-01

A little over a decade has passed since two teams studying high redshift Type Ia supernovae announced the discovery that the expansion of the universe was accelerating. After all this time, we?re still not sure how cosmic acceleration fits into the theory that tells us about the large-scale universe: General Relativity (GR). As part of our search for answers, we have been forced to question GR itself. But how will we test our ideas? We are fortunate enough to be entering the era of precision cosmology, where the standard model of gravity can be subjected to more rigorous testing. Various techniques will be employed over the next decade or two in the effort to better understand cosmic acceleration and the theory behind it. In this talk, I will describe cosmic acceleration, current proposals to explain it, and weak gravitational lensing, an observational effect that allows us to do the necessary precision cosmology.

Newton's Gravity An Introductory Guide to the Mechanics of the Universe

CERN Document Server

MacDougal, Douglas W

2012-01-01

“Newton’s Gravity” conveys the power of simple mathematics to tell the fundamental truth about nature. Many people know the tides are caused by the pull of the Moon and to a lesser extent the Sun. But very few can explain exactly how and why that happens. Fewer still can calculate the  actual pulls of the Moon and Sun on the oceans. This book shows in clear detail how to do this with simple tools. It uniquely crosses disciplines – history, astronomy, physics and mathematics – and takes pains to explain things frequently passed over or taken for granted in other books. Using a problem-based approach, “Newton’s Gravity” explores the surprisingly basic mathematics behind gravity, the most fundamental force that governs the movements of satellites, planets, and the stars.

Quantum Gravity

OpenAIRE

Alvarez, Enrique

2004-01-01

Gravitons should have momentum just as photons do; and since graviton momentum would cause compression rather than elongation of spacetime outside of matter; it does not appear that gravitons are compatible with Swartzchild's spacetime curvature. Also, since energy is proportional to mass, and mass is proportional to gravity; the energy of matter is proportional to gravity. The energy of matter could thus contract space within matter; and because of the inter-connectedness of space, cause the...

Cosmology based on f(R) gravity admits 1 eV sterile neutrinos.

Science.gov (United States)

Motohashi, Hayato; Starobinsky, Alexei A; Yokoyama, Jun'ichi

2013-03-22

It is shown that the tension between recent neutrino oscillation experiments, favoring sterile neutrinos with masses of the order of 1 eV, and cosmological data which impose stringent constraints on neutrino masses from the free streaming suppression of density fluctuations, can be resolved in models of the present accelerated expansion of the Universe based on f(R) gravity.

Modular Extended-Stay HyperGravity Facility Design Concept: An Artificial-Gravity Space-Settlement Ground Analogue

Science.gov (United States)

Dorais, Gregory A.

2015-01-01

This document defines the design concept for a ground-based, extended-stay hypergravity facility as a precursor for space-based artificial-gravity facilities that extend the permanent presence of both human and non-human life beyond Earth in artificial-gravity settlements. Since the Earth's current human population is stressing the environment and the resources off-Earth are relatively unlimited, by as soon as 2040 more than one thousand people could be living in Earthorbiting artificial-gravity habitats. Eventually, the majority of humanity may live in artificialgravity habitats throughout this solar system as well as others, but little is known about the longterm (multi-generational) effects of artificial-gravity habitats on people, animals, and plants. In order to extend life permanently beyond Earth, it would be useful to create an orbiting space facility that generates 1g as well as other gravity levels to rigorously address the numerous challenges of such an endeavor. Before doing so, developing a ground-based artificial-gravity facility is a reasonable next step. Just as the International Space Station is a microgravity research facility, at a small fraction of the cost and risk a ground-based artificial-gravity facility can begin to address a wide-variety of the artificial-gravity life-science questions and engineering challenges requiring long-term research to enable people, animals, and plants to live off-Earth indefinitely.

Black holes in pure Lovelock gravities

International Nuclear Information System (INIS)

Cai Ronggen; Ohta, Nobuyoshi

2006-01-01

Lovelock gravity is a fascinating extension of general relativity, whose action consists of dimensionally extended Euler densities. Compared to other higher order derivative gravity theories, Lovelock gravity is attractive since it has a lot of remarkable features such as the fact that there are no more than second order derivatives with respect to the metric in its equations of motion, and that the theory is free of ghosts. Recently, in the study of black strings and black branes in Lovelock gravity, a special class of Lovelock gravity is considered, which is named pure Lovelock gravity, where only one Euler density term exists. In this paper we study black hole solutions in the special class of Lovelock gravity and associated thermodynamic properties. Some interesting features are found, which are quite different from the corresponding ones in general relativity

Active Response Gravity Offload System

Science.gov (United States)

Valle, Paul; Dungan, Larry; Cunningham, Thomas; Lieberman, Asher; Poncia, Dina

2011-01-01

The Active Response Gravity Offload System (ARGOS) provides the ability to simulate with one system the gravity effect of planets, moons, comets, asteroids, and microgravity, where the gravity is less than Earth fs gravity. The system works by providing a constant force offload through an overhead hoist system and horizontal motion through a rail and trolley system. The facility covers a 20 by 40-ft (approximately equals 6.1 by 12.2m) horizontal area with 15 ft (approximately equals4.6 m) of lifting vertical range.

Gravity model improvement investigation. [improved gravity model for determination of ocean geoid

Science.gov (United States)

Siry, J. W.; Kahn, W. D.; Bryan, J. W.; Vonbun, F. F.

1973-01-01

This investigation was undertaken to improve the gravity model and hence the ocean geoid. A specific objective is the determination of the gravity field and geoid with a space resolution of approximately 5 deg and a height resolution of the order of five meters. The concept of the investigation is to utilize both GEOS-C altimeter and satellite-to-satellite tracking data to achieve the gravity model improvement. It is also planned to determine the geoid in selected regions with a space resolution of about a degree and a height resolution of the order of a meter or two. The short term objectives include the study of the gravity field in the GEOS-C calibration area outlined by Goddard, Bermuda, Antigua, and Cape Kennedy, and also in the eastern Pacific area which is viewed by ATS-F.

Quantum cosmology and the early universe

International Nuclear Information System (INIS)

Hartle, J.B.

1983-01-01

Despite the absence of a complete and manageable quantum theory of gravity, it is shown that considerable progress has been made in constructing cosmological models displaying the possible implications such a theory might have for the structure and dynamics of the very early universe. (U.K.)

Baby universe theory

International Nuclear Information System (INIS)

Nielsen, H.B.; Ninomiya, Masao

1989-12-01

We give an elementary review of the so called 'the theory of baby universes' which is a series of ideas or speculations about some effects in quantum gravity, viz. the effect of a certain type of wormholes, representing the exchange of small 3-space universes called baby universes. We consider this 'theory' as being physically and scientifically a very promising candidate for a theory of everything. It is, however, mathematically lacking any strong foundation at all. It solves several fine-tuning problems: First of all the cosmological constant problem, and also the strong CP-problem and the hierarchy problem. We also speculate that it might predict the possibility of influencing the probability distributions of the outcome of quantum mechanical measurements at one time by acts at a later time. (orig.)

UV caps, IR modification of gravity, and recovery of 4D gravity in regularized braneworlds

International Nuclear Information System (INIS)

Kobayashi, Tsutomu

2008-01-01

In the context of six-dimensional conical braneworlds we consider a simple and explicit model that incorporates long-distance modification of gravity and regularization of codimension-2 singularities. To resolve the conical singularities we replace the codimension-2 branes with ringlike codimension-1 branes, filling in the interiors with regular caps. The six-dimensional Planck scale in the cap is assumed to be much greater than the bulk Planck scale, which gives rise to the effect analogous to brane-induced gravity. Weak gravity on the regularized brane is studied in the case of a sharp conical bulk. We show by a linear analysis that gravity at short distances is effectively described by the four-dimensional Brans-Dicke theory, while the higher dimensional nature of gravity emerges at long distances. The linear analysis breaks down at some intermediate scale, below which four-dimensional Einstein gravity is shown to be recovered thanks to the second-order effects of the brane bending.

Quantum Gravity Effects in Cosmology

Directory of Open Access Journals (Sweden)

Gu Je-An

2018-01-01

Full Text Available Within the geometrodynamic approach to quantum cosmology, we studied the quantum gravity effects in cosmology. The Gibbons-Hawking temperature is corrected by quantum gravity due to spacetime fluctuations and the power spectrum as well as any probe field will experience the effective temperature, a quantum gravity effect.

Gravity Probe B Encapsulated

Science.gov (United States)

2004-01-01

In this photo, the Gravity Probe B (GP-B) space vehicle is being encapsulated atop the Delta II launch vehicle. The GP-B is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at a 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies that are already enlivening other branches of science and engineering. Launched April 20, 2004 , the GP-B program was managed for NASA by the Marshall Space Flight Center. Development of the GP-B is the responsibility of Stanford University along with major subcontractor Lockheed Martin Corporation. (Image credit to Russ Underwood, Lockheed Martin Corporation).

Airborne Gravity: NGS' Gravity Data for the US and Territories (2008-2022) - National Geospatial Data Asset (NGDA) Airborne Gravity (GRAV-D)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Gravity for the Re-definition of the American Vertical Datum (GRAV-D) is a project initiated by NOAA's National Geodetic Survey to collect and monitor gravity data...

Dynamics of an Anisotropic Universe in f(R,T) Theory

International Nuclear Information System (INIS)

Mishra, B.; Tarai, Sankarsan; Tripathy, S. K.

2016-01-01

Dynamics of an anisotropic universe is studied in f(R,T) gravity using a rescaled functional f(R,T), where R is the Ricci Scalar and T is the trace of energy-momentum tensor. Three models have been constructed assuming a power law expansion of the universe. Physical features of the models are discussed. The model parameters are constrained from a dimensional analysis. It is found from the work that the anisotropic Bianchi type VI_h (BVI_h) model in the modified gravity generally favours a quintessence phase when the parameter h is either -1 or 0. We may not get viable models in conformity with the present day observation for h=1.

Urine specific gravity test

Science.gov (United States)

... medlineplus.gov/ency/article/003587.htm Urine specific gravity test To use the sharing features on this page, please enable JavaScript. Urine specific gravity is a laboratory test that shows the concentration ...

Northern Oklahoma Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (710 records) were compiled by Professor Ahern. This data base was received in June 1992. Principal gravity parameters include latitude,...

Vaidya spacetime in massive gravity's rainbow

Directory of Open Access Journals (Sweden)

Yaghoub Heydarzade

2017-11-01

Full Text Available In this paper, we will analyze the energy dependent deformation of massive gravity using the formalism of massive gravity's rainbow. So, we will use the Vainshtein mechanism and the dRGT mechanism for the energy dependent massive gravity, and thus analyze a ghost free theory of massive gravity's rainbow. We study the energy dependence of a time-dependent geometry, by analyzing the radiating Vaidya solution in this theory of massive gravity's rainbow. The energy dependent deformation of this Vaidya metric will be performed using suitable rainbow functions.

Physics of Trans-Planckian Gravity

CERN Document Server

Dvali, Gia; Germani, Cristiano

2011-01-01

We study aspects of the phenomenon of gravitational UV-self-completeness and its implications for deformations of Einstein gravity. In a ghost-free theory flowing to Einstein gravity in the IR trans-Planckian propagating quantum degrees of freedom cannot exist. The only physical meaning of a trans-Planckian pole is the one of a classical state (Black Hole) which is fully described by the light IR quantum degrees of freedom and gives exponentially-suppressed contributions to virtual processes. In this sense Einstein gravity is UV self-complete, although not Wilsonian. We show that this UV/IR correspondence puts a severe constraint on any attempt of conventional Wilsonian UV-completion of trans-Planckian gravity. In particular, there is no well-defined energy domain in which gravity could become asymptotically weak or safe.

Stochastic Gravity: Theory and Applications

Directory of Open Access Journals (Sweden)

Hu Bei Lok

2008-05-01

Full Text Available Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein–Langevin equation, which has, in addition, sources due to the noise kernel. The noise kernel is the vacuum expectation value of the (operator-valued stress-energy bitensor, which describes the fluctuations of quantum-matter fields in curved spacetimes. A new improved criterion for the validity of semiclassical gravity may also be formulated from the viewpoint of this theory. In the first part of this review we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. The axiomatic approach is useful to see the structure of the theory from the framework of semiclassical gravity, showing the link from the mean value of the stress-energy tensor to the correlation functions. The functional approach uses the Feynman–Vernon influence functional and the Schwinger–Keldysh closed-time-path effective action methods. In the second part, we describe three applications of stochastic gravity. First, we consider metric perturbations in a Minkowski spacetime, compute the two-point correlation functions of these perturbations and prove that Minkowski spacetime is a stable solution of semiclassical gravity. Second, we discuss structure formation from the stochastic-gravity viewpoint, which can go beyond the standard treatment by incorporating the full quantum effect of the inflaton fluctuations. Third, using the Einstein–Langevin equation, we discuss the backreaction of Hawking radiation and the behavior of metric fluctuations for both the quasi-equilibrium condition of a black-hole in a box and the fully nonequilibrium condition of an evaporating black hole spacetime. Finally, we briefly discuss the theoretical structure of stochastic gravity in relation to quantum gravity and point out

A strong coupling simulation of Euclidean quantum gravity

International Nuclear Information System (INIS)

Berg, B.; Hamburg Univ.

1984-12-01

Relying on Regge calculus a systematic numerical investigation of models of 4d Euclidean gravity is proposed. The scale a = 1 0 is set by fixing the expectation value of a length. Possible universality of such models is discussed. The strong coupling limit is defined by taking Planck mass msub(p) -> 0 (in units of 1 0 -1 ). The zero order approximation msub(p) = 0 is called 'fluctuating space' and investigated numerically in two 4d models. Canonical dimensions are realized and both models give a negative expectation value for the scalar curvature density. (orig.)

Active Response Gravity Offload and Method

Science.gov (United States)

Dungan, Larry K. (Inventor); Valle, Paul S. (Inventor); Bankieris, Derek R. (Inventor); Lieberman, Asher P. (Inventor); Redden, Lee (Inventor); Shy, Cecil (Inventor)

2015-01-01

A variable gravity field simulator can be utilized to provide three dimensional simulations for simulated gravity fields selectively ranging from Moon, Mars, and micro-gravity environments and/or other selectable gravity fields. The gravity field simulator utilizes a horizontally moveable carriage with a cable extending from a hoist. The cable can be attached to a load which experiences the effects of the simulated gravity environment. The load can be a human being or robot that makes movements that induce swinging of the cable whereby a horizontal control system reduces swinging energy. A vertical control system uses a non-linear feedback filter to remove noise from a load sensor that is in the same frequency range as signals from the load sensor.

Idaho State Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (24,284 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...

Physics of trans-Planckian gravity

International Nuclear Information System (INIS)

Dvali, Gia; Folkerts, Sarah; Germani, Cristiano

2011-01-01

We study the field theoretical description of a generic theory of gravity flowing to Einstein general relativity in IR. We prove that, if ghost-free, in the weakly-coupled regime such a theory can never become weaker than general relativity. Using this fact, as a by-product, we suggest that in a ghost-free theory of gravity trans-Planckian propagating quantum degrees of freedom cannot exist. The only physical meaning of a trans-Planckian pole is the one of a classical state (black hole) which is described by the light IR quantum degrees of freedom and gives exponentially-suppressed contributions to virtual processes. In this picture Einstein gravity is UV self-complete, although not Wilsonian, and sub-Planckian distances are unobservable in any healthy theory of gravity. We then finally show that this UV/IR correspondence puts a severe constraint on any attempt of conventional Wilsonian UV-completion of trans-Planckian gravity. Specifically, there is no well-defined energy domain in which gravity could become asymptotically weak or safe.

Dilaton gravity, Poisson sigma models and loop quantum gravity

International Nuclear Information System (INIS)

Bojowald, Martin; Reyes, Juan D

2009-01-01

Spherically symmetric gravity in Ashtekar variables coupled to Yang-Mills theory in two dimensions and its relation to dilaton gravity and Poisson sigma models are discussed. After introducing its loop quantization, quantum corrections for inverse triad components are shown to provide a consistent deformation without anomalies. The relation to Poisson sigma models provides a covariant action principle of the quantum-corrected theory with effective couplings. Results are also used to provide loop quantizations of spherically symmetric models in arbitrary D spacetime dimensions.

Modification of the gravity model and application to the metropolitan Seoul subway system.

Science.gov (United States)

Goh, Segun; Lee, Keumsook; Park, Jong Soo; Choi, M Y

2012-08-01

The Metropolitan Seoul Subway system is examined through the use of the gravity model. Exponents describing the power-law dependence on the time distance between stations are obtained, which reveals a universality for subway lines of the same topology. In the short (time) distance regime the number of passengers between stations does not grow with the decrease in the distance, thus deviating from the power-law behavior. It is found that such reduction in passengers is well described by the Hill function. Further, temporal fluctuations in the passenger flow data, fitted to the gravity model modified by the Hill function, are analyzed to reveal the Yule-type nature inherent in the structure of Seoul.

Andes 1997 Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The Central Andes gravity data (6,151 records) were compiled by Professor Gotze and the MIGRA Group. This data base was received in April, 1997. Principal gravity...

Progress in the global standardization of gravity: an analysis of the Woollard and Rose international gravity values

International Nuclear Information System (INIS)

Woollard, G.P.; Godley, V.M.

1980-12-01

The history of improvements in the global standarization of gravity values since the advent of high range gravimeters in 1948 is reviewed. In particular the gravity base values given in SEG special publication International Gravity Measurements (Woolard and Rose, 1963) are evaluated against the most recent set of standarized gravity base values, The International Gravity Standardization Net, 1971 (Morelli et al, 1974). Adjunct IGSN 71 values prepared by the US Defense Mapping Agency Aerospace Center (unpublished) are also used to give a more comprehensive worldwide comparison of values

The Superheavy Elements and Anti-Gravity

International Nuclear Information System (INIS)

Anastasovski, Petar K.

2004-01-01

The essence of any propulsion concept is to overcome gravity. Anti-gravity is a natural means to achieve this. Thus, the technology to pursue anti-gravity, by using superheavy elements, may provide a new propulsion paradigm. The theory of superluminal relativity provides a hypothesis for existence of elements with atomic number up to Z = 145, some of which may possess anti-gravity properties. Analysis results show that curved space-time exists demonstrating both gravitic and anti-gravitic properties not only around nuclei but inside the nuclei as well. Two groups of elements (Z < 64 and 63 < Z <145) exist that demonstrate these capabilities. The nuclei of the first group of elements have the masses with only the property of gravity. The nuclei of the elements of the second group have the masses with both properties: gravity and anti-gravity in two different ranges of curved space-time around the nuclei.. The hypothetical element with Z = 145 is the unique among all elements whose nucleus has only anti-gravity property. It is proposed that this element be named Hawking, in honour of Stephen W. Hawking

Frozen-wave instability in near-critical hydrogen subjected to horizontal vibration under various gravity fields.

Science.gov (United States)

Gandikota, G; Chatain, D; Amiroudine, S; Lyubimova, T; Beysens, D

2014-01-01

The frozen-wave instability which appears at a liquid-vapor interface when a harmonic vibration is applied in a direction tangential to it has been less studied until now. The present paper reports experiments on hydrogen (H2) in order to study this instability when the temperature is varied near its critical point for various gravity levels. Close to the critical point, a liquid-vapor density difference and surface tension can be continuously varied with temperature in a scaled, universal way. The effect of gravity on the height of the frozen waves at the interface is studied by performing the experiments in a magnetic facility where effective gravity that results from the coupling of the Earth's gravity and magnetic forces can be varied. The stability diagram of the instability is obtained. The experiments show a good agreement with an inviscid model [Fluid Dyn. 21 849 (1987)], irrespective of the gravity level. It is observed in the experiments that the height of the frozen waves varies weakly with temperature and increases with a decrease in the gravity level, according to a power law with an exponent of 0.7. It is concluded that the wave height becomes of the order of the cell size as the gravity level is asymptotically decreased to zero. The interface pattern thus appears as a bandlike pattern of alternate liquid and vapor phases, a puzzling phenomenon that was observed with CO2 and H2 near their critical point in weightlessness [Acta Astron. 61 1002 (2007); Europhys. Lett. 86 16003 (2009)].

Cadiz, California Gravity Data

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (32 records) were gathered by Mr. Seth I. Gutman for AridTech Inc., Denver, Colorado using a Worden Prospector gravity meter. This data base...

Leading gravitational corrections and a unified universe

DEFF Research Database (Denmark)

Codello, Alessandro; Jain, Rajeev Kumar

2016-01-01

Leading order gravitational corrections to the Einstein-Hilbert action can lead to a consistent picture of the universe by unifying the epochs of inflation and dark energy in a single framework. While the leading local correction induces an inflationary phase in the early universe, the leading...... nonlocal term leads to an accelerated expansion of the universe at the present epoch. We argue that both the leading UV and IR terms can be obtained within the framework of a covariant effective field theory of gravity. The perturbative gravitational corrections therefore provide a fundamental basis...

Extended Theories of Gravity

International Nuclear Information System (INIS)

Capozziello, Salvatore; De Laurentis, Mariafelicia

2011-01-01

Extended Theories of Gravity can be considered as a new paradigm to cure shortcomings of General Relativity at infrared and ultraviolet scales. They are an approach that, by preserving the undoubtedly positive results of Einstein’s theory, is aimed to address conceptual and experimental problems recently emerged in astrophysics, cosmology and High Energy Physics. In particular, the goal is to encompass, in a self-consistent scheme, problems like inflation, dark energy, dark matter, large scale structure and, first of all, to give at least an effective description of Quantum Gravity. We review the basic principles that any gravitational theory has to follow. The geometrical interpretation is discussed in a broad perspective in order to highlight the basic assumptions of General Relativity and its possible extensions in the general framework of gauge theories. Principles of such modifications are presented, focusing on specific classes of theories like f(R)-gravity and scalar–tensor gravity in the metric and Palatini approaches. The special role of torsion is also discussed. The conceptual features of these theories are fully explored and attention is paid to the issues of dynamical and conformal equivalence between them considering also the initial value problem. A number of viability criteria are presented considering the post-Newtonian and the post-Minkowskian limits. In particular, we discuss the problems of neutrino oscillations and gravitational waves in extended gravity. Finally, future perspectives of extended gravity are considered with possibility to go beyond a trial and error approach.

No slip gravity

Science.gov (United States)

Linder, Eric V.

2018-03-01

A subclass of the Horndeski modified gravity theory we call No Slip Gravity has particularly interesting properties: 1) a speed of gravitational wave propagation equal to the speed of light, 2) equality between the effective gravitational coupling strengths to matter and light, Gmatter and Glight, hence no slip between the metric potentials, yet difference from Newton's constant, and 3) suppressed growth to give better agreement with galaxy clustering observations. We explore the characteristics and implications of this theory, and project observational constraints. We also give a simple expression for the ratio of the gravitational wave standard siren distance to the photon standard candle distance, in this theory and others, and enable a direct comparison of modified gravity in structure growth and in gravitational waves, an important crosscheck.

Zero-gravity movement studies

Science.gov (United States)

Badler, N. I.; Fishwick, P.; Taft, N.; Agrawala, M.

1985-01-01

The use of computer graphics to simulate the movement of articulated animals and mechanisms has a number of uses ranging over many fields. Human motion simulation systems can be useful in education, medicine, anatomy, physiology, and dance. In biomechanics, computer displays help to understand and analyze performance. Simulations can be used to help understand the effect of external or internal forces. Similarly, zero-gravity simulation systems should provide a means of designing and exploring the capabilities of hypothetical zero-gravity situations before actually carrying out such actions. The advantage of using a simulation of the motion is that one can experiment with variations of a maneuver before attempting to teach it to an individual. The zero-gravity motion simulation problem can be divided into two broad areas: human movement and behavior in zero-gravity, and simulation of articulated mechanisms.