Cosmic Censorship in Quantum Einstein Gravity
Bonanno, Alfio; Platania, Alessia
2016-01-01
We study the quantum gravity modification of the Kuroda-Papapetrou model induced by the running of the Newton's constant at high energy in Quantum Einstein Gravity. We argue that although the antiscreening character of the gravitational interaction favours the formation of a naked singularity, quantum gravity effects turn the classical singularity into a "whimper" singularity which remains naked for a finite amount of advanced time.
Quantum criticality in Einstein-Maxwell-dilaton gravity
Energy Technology Data Exchange (ETDEWEB)
Wen, Wen-Yu, E-mail: steve.wen@gmail.com [California Institute of Technology, Pasadena, CA 91125 (United States); Department of Physics and Center for Theoretical Sciences and Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 106, Taiwan (China); Department of Physics, Chung Yuan Christian University, Chung Li 32023, Taiwan (China)
2012-02-01
We investigate the quantum Lifshitz criticality in a general background of Einstein-Maxwell-dilaton gravity. In particular, we demonstrate the existence of critical point with dynamic critical exponent z by tuning a nonminimal coupling to its critical value. We also study the effect of nonminimal coupling and exponent z to the Efimov states and holographic RG flow in the overcritical region. We have found that the nonminimal coupling increases the instability for a probe scalar to condensate and its back reaction is discussed. At last, we give a quantum mechanics treatment to a solvable system with z=2, and comment for generic z>2.
Quantum gravity corrections to the standard model Higgs in Einstein and $R^2$ gravity
Abe, Yugo; Inami, Takeo
2016-01-01
We evaluate quantum gravity corrections to the standard model Higgs potential $V(\\phi)$ a la Coleman-Weinberg and examine the stability question of $V(\\phi)$ at scales of Planck mass $M_{\\rm Pl}$. We compute the gravity one-loop corrections by using the momentum cut-off in Einstein gravity. The gravity corrections affect the potential in a significant manner for the value of $\\Lambda= (1 - 3)M_{\\rm Pl}.$ In view of reducing the UV cut-off dependence we also make a similar study in the $R^2$ gravity.
Theory of Quantum Gravity Beyond Einstein and Space-time Dynamics with Quantum Inflation
Wu, Yue-Liang
2015-01-01
In this talk, I present a theory of quantum gravity beyond Einstein. The theory is established based on spinnic and scaling gauge symmetries by treating the gravitational force on the same footing as the electroweak and strong forces. A bi-frame space-time is initiated to describe the laws of nature. One frame space-time is a globally flat coordinate Minkowski space-time that acts as an inertial reference frame for the motions of fields, the other is a locally flat non-coordinate Gravifield space-time that functions as an interaction representation frame for the degrees of freedom of fields. The Gravifield is sided on both the globally flat coordinate space-time and locally flat non-coordinate space-time and characterizes the gravitational force. Instead of the principle of general coordinate invariance in Einstein theory of general relativity, some underlying principles with the postulates of coordinate independence and gauge invariance are motivated to establish the theory of quantum gravity. When transmuti...
Ward, B F L
2015-01-01
We argue that our recent success in using our resummed quantum gravity approach to Einstein's general theory of relativity, in the context of the Planck scale cosmology formulation of Bonanno and Reuter, to estimate the value of the cosmological constant \\Lambda supports the use of quantum mechanical consistency requirements to constrain the main uncertainty in that very promising result. This main uncertainty, which is due to the uncertainty in the value of the time t_{\\text{tr}} at which the transition from the Planck scale cosmology to the FRW model occurs, is shown to be reduced, by requiring consistency between the Heisenberg uncertainty principle and the known properties of the solutions of Einstein's equations, from four orders of magnitude to the level of a factor of {\\cal O}(10). This lends more credibility to the over-all resummed quantum gravity approach itself, in general, and to our estimate of $\\Lambda$ in particular.
The phase and critical point of quantum Einstein-Cartan gravity
Xue, She-Sheng
2012-05-01
By introducing diffeomorphism and local Lorentz gauge invariant holonomy fields, we study in the recent article [S.-S. Xue, Phys. Rev. D 82 (2010) 064039] the quantum Einstein-Cartan gravity in the framework of Regge calculus. On the basis of strong coupling expansion, mean-field approximation and dynamical equations satisfied by holonomy fields, we present in this Letter calculations and discussions to show the phase structure of the quantum Einstein-Cartan gravity, (i) the order phase: long-range condensations of holonomy fields in strong gauge couplings; (ii) the disorder phase: short-range fluctuations of holonomy fields in weak gauge couplings. According to the competition of the activation energy of holonomy fields and their entropy, we give a simple estimate of the possible ultra-violet critical point and correlation length for the second-order phase transition from the order phase to disorder one. At this critical point, we discuss whether the continuum field theory of quantum Einstein-Cartan gravity can be possibly approached when the macroscopic correlation length of holonomy field condensations is much larger than the Planck length.
Kiefer, Claus
2012-01-01
The search for a quantum theory of the gravitational field is one of the great open problems in theoretical physics. This book presents a self-contained discussion of the concepts, methods and applications that can be expected in such a theory. The two main approaches to its construction - the direct quantisation of Einstein's general theory of relativity and string theory - are covered. Whereas the first attempts to construct a viable theory for the gravitational field alone, string theory assumes that a quantum theory of gravity will be achieved only through a unification of all the interactions. However, both employ the general method of quantization of constrained systems, which is described together with illustrative examples relevant for quantum gravity. There is a detailed presentation of the main approaches employed in quantum general relativity: path-integral quantization, the background-field method and canonical quantum gravity in the metric, connection and loop formulations. The discussion of stri...
A new functional flow equation for Einstein-Cartan quantum gravity
Harst, U.; Reuter, M.
2015-03-01
We construct a special-purpose functional flow equation which facilitates non-perturbative renormalization group (RG) studies on theory spaces involving a large number of independent field components that are prohibitively complicated using standard methods. Its main motivation are quantum gravity theories in which the gravitational degrees of freedom are carried by a complex system of tensor fields, a prime example being Einstein-Cartan theory, possibly coupled to matter. We describe a sequence of approximation steps leading from the functional RG equation of the Effective Average Action to the new flow equation which, as a consequence, is no longer fully exact on the untruncated theory space. However, it is by far more "user friendly" when it comes to projecting the abstract equation on a concrete (truncated) theory space and computing explicit beta-functions. The necessary amount of (tensor) algebra reduces drastically, and the usually very hard problem of diagonalizing the pertinent Hessian operator is sidestepped completely. In this paper we demonstrate the reliability of the simplified equation by applying it to a truncation of the Einstein-Cartan theory space. It is parametrized by a scale dependent Holst action, depending on a O(4) spin-connection and the tetrad as the independent field variables. We compute the resulting RG flow, focusing in particular on the running of the Immirzi parameter, and compare it to the results of an earlier computation where the exact equation had been applied to the same truncation. We find consistency between the two approaches and provide further evidence for the conjectured non-perturbative renormalizability (asymptotic safety) of quantum Einstein-Cartan gravity. We also investigate a duality symmetry relating small and large values of the Immirzi parameter (γ → 1 / γ) which is displayed by the beta-functions in the absence of a cosmological constant.
A proper fixed functional for four-dimensional Quantum Einstein Gravity
Demmel, Maximilian; Zanusso, Omar
2015-01-01
Realizing a quantum theory for gravity based on Asymptotic Safety hinges on the existence of a non-Gaussian fixed point of the theory's renormalization group flow. In this work, we use the functional renormalization group equation for the effective average action to study the fixed point underlying Quantum Einstein Gravity at the functional level including an infinite number of scale-dependent coupling constants. We formulate a list of guiding principles underlying the construction of a partial differential equation encoding the scale-dependence of $f(R)$-gravity. We show that this equation admits a unique, globally well-defined fixed functional describing the non-Gaussian fixed point at the level of functions of the scalar curvature. This solution is constructed explicitly via a numerical double-shooting method. In the UV, this solution is in good agreement with results from polynomial expansions including a finite number of coupling constants, while it scales proportional to $R^2$, dressed up with non-analy...
Amaral, Marcelo M; Bubuianu, Laurenţiu; Irwin, Klee; Vacaru, Sergiu I; Woolridge, Daniel
2016-01-01
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...
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.
A new functional flow equation for Einstein-Cartan quantum gravity
Harst, Ulrich
2014-01-01
We construct a special-purpose functional flow equation which facilitates non-perturbative renormalization group (RG) studies on theory spaces involving a large number of independent field components that are prohibitively complicated using standard methods. Its main motivation are quantum gravity theories in which the gravitational degrees of freedom are carried by a complex system of tensor fields, a prime example being Einstein-Cartan theory, possibly coupled to matter. We describe a sequence of approximation steps leading from the functional RG equation of the Effective Average Action to the new flow equation which, as a consequence, is no longer fully exact on the untruncated theory space. However, it is by far more "user friendly" when it comes to projecting the abstract equation on a concrete (truncated) theory space and computing explicit beta-functions. The necessary amount of (tensor) algebra reduces drastically, and the usually very hard problem of diagonalizing the pertinent Hessian operator is si...
Continuum interpretation of the dynamical-triangulation formulation of quantum Einstein gravity
Smit, Jan
2013-01-01
In the time-space symmetric version of dynamical triangulation, a non-perturbative version of quantum Einstein gravity, numerical simulations without matter have shown two phases, with spacetimes that are either crumpled or elongated like branched polymers, with strong evidence of a first-order transition between them. These properties have generally been considered unphysical. Using previously unpublished numerical results, we give an interpretation in terms of continuum spacetimes that have constant positive an negative curvature, respectively in the 'elongated' and 'crumpled' phase. The magnitude of the positive curvature leads naturally to average spacetimes consisting solely of baby-universes in a branched-polymer structure, whereas the negative curvature accommodates easily a large mother universe, albeit with a crumpling singularity. Nevertheless, there is evidence for scaling in the crumpled phase, which we compare with the well-known scaling in the elongated phase. Using constraint effective-action m...
Quantum Einstein gravity. Advancements of heat kernel-based renormalization group studies
Energy Technology Data Exchange (ETDEWEB)
Groh, Kai
2012-10-15
The asymptotic safety scenario allows to define a consistent theory of quantized gravity within the framework of quantum field theory. The central conjecture of this scenario is the existence of a non-Gaussian fixed point of the theory's renormalization group flow, that allows to formulate renormalization conditions that render the theory fully predictive. Investigations of this possibility use an exact functional renormalization group equation as a primary non-perturbative tool. This equation implements Wilsonian renormalization group transformations, and is demonstrated to represent a reformulation of the functional integral approach to quantum field theory. As its main result, this thesis develops an algebraic algorithm which allows to systematically construct the renormalization group flow of gauge theories as well as gravity in arbitrary expansion schemes. In particular, it uses off-diagonal heat kernel techniques to efficiently handle the non-minimal differential operators which appear due to gauge symmetries. The central virtue of the algorithm is that no additional simplifications need to be employed, opening the possibility for more systematic investigations of the emergence of non-perturbative phenomena. As a by-product several novel results on the heat kernel expansion of the Laplace operator acting on general gauge bundles are obtained. The constructed algorithm is used to re-derive the renormalization group flow of gravity in the Einstein-Hilbert truncation, showing the manifest background independence of the results. The well-studied Einstein-Hilbert case is further advanced by taking the effect of a running ghost field renormalization on the gravitational coupling constants into account. A detailed numerical analysis reveals a further stabilization of the found non-Gaussian fixed point. Finally, the proposed algorithm is applied to the case of higher derivative gravity including all curvature squared interactions. This establishes an improvement
A noncompact Weyl-Einstein-Yang-Mills model: A semiclassical quantum gravity
Dengiz, Suat
2017-08-01
We construct and study perturbative unitarity (i.e., ghost and tachyon analysis) of a 3 + 1-dimensional noncompact Weyl-Einstein-Yang-Mills model. The model describes a local noncompact Weyl's scale plus SU(N) phase invariant Higgs-like field,conformally coupled to a generic Weyl-invariant dynamical background. Here, the Higgs-like sector generates the Weyl's conformal invariance of system. The action does not admit any dimensionful parameter and genuine presence of de Sitter vacuum spontaneously breaks the noncompact gauge symmetry in an analogous manner to the Standard Model Higgs mechanism. As to flat spacetime, the dimensionful parameter is generated within the dimensional transmutation in quantum field theories, and thus the symmetry is radiatively broken through the one-loop Effective Coleman-Weinberg potential. We show that the mere expectation of reducing to Einstein's gravity in the broken phases forbids anti-de Sitter space to be its stable vacua. The model is unitary in de Sitter and flat vacua around which a massless graviton, N2 - 1 massless scalar bosons, N massless Dirac fermions, N2 - 1 Proca-type massive Abelian and non-Abelian vector bosons are generically propagated.
Self Completeness of Einstein Gravity
Dvali, Gia
2010-01-01
We argue, that in Einsteinian gravity the Planck length is the shortest length of nature, and any attempt of resolving trans-Planckian physics bounces back to macroscopic distances due to black hole formation. In Einstein gravity trans-Planckian propagating quantum degrees of freedom cannot exist, instead they are equivalent to the classical black holes that are fully described by lighter infra-red degrees of freedom and give exponentially-soft contribution into the virtual processes. Based on this property we argue that pure-Einstein (super)gravity and its high-dimensional generalizations are self-complete in deep-UV, but not in standard Wilsonian sense. We suggest that certain strong-coupling limit of string theory is built-in in pure Einstein gravity, whereas the role of weakly-coupled string theory limit is to consistently couple gravity to other particle species, with their number being set by the inverse string coupling. We also discuss some speculative ideas generalizing the notion of non-Wilsonian sel...
From conformal to Einstein gravity
Anastasiou, Giorgos; Olea, Rodrigo
2016-10-01
We provide a simple derivation of the equivalence between Einstein and conformal gravity (CG) with Neumann boundary conditions given by Maldacena. As Einstein spacetimes are Bach flat, a generic solution to CG would contain both Einstein and non-Einstein parts. Using this decomposition of the spacetime curvature in the Weyl tensor makes manifest the equivalence between the two theories, both at the level of the action and the variation of it. As a consequence, we show that the on-shell action for critical gravity in four dimensions is given uniquely in terms of the Bach tensor.
From Conformal to Einstein Gravity
Anastasiou, Giorgos
2016-01-01
We provide a simple derivation of the equivalence between Einstein and Conformal Gravity (CG) with Neumann boundary conditions given by Maldacena. As Einstein spacetimes are Bach flat, a generic solution to CG would contain both Einstein and non-Einstein part. Using this decomposition of the spacetime curvature in the Weyl tensor, makes manifest the equivalence between the two theories, both at the level of the action and the variation of it. As a consequence, we show that the on-shell action for Critical Gravity in four dimensions is given uniquely in terms of the Bach tensor.
Modified gravity from the quantum part of the metric
Energy Technology Data Exchange (ETDEWEB)
Dzhunushaliev, Vladimir [KazNU, Department of Theoretical and Nuclear Physics, Almaty (Kazakhstan); IETP, Al-Farabi Kazakh National University, Almaty (Kazakhstan); NAS of the Kyrgyz Republic, Bishkek (Kyrgyzstan). Institute of Physicotechnical Problems and Material Science; Universitaet Oldenburg, Institut fuer Physik, Oldenburg (Germany); Folomeev, Vladimir [IETP, Al-Farabi Kazakh National University, Almaty (Kazakhstan); NAS of the Kyrgyz Republic, Bishkek (Kyrgyzstan). Institute of Physicotechnical Problems and Material Science; Kleihaus, Burkhard; Kunz, Jutta [Universitaet Oldenburg, Institut fuer Physik, Oldenburg (Germany)
2014-01-15
It is shown that if a metric in quantum gravity can be decomposed as a sum of classical and quantum parts, then Einstein quantum gravity looks approximately like modified gravity with a nonminimal interaction between gravity and matter. (orig.)
Twisted spacetime in Einstein gravity
Zhang, Hongsheng
2016-01-01
We find a vacuum stationary twisted solution in four-dimensional Einstein gravity. Its frame dragging angular velocities are antisymmetric with respect to the equatorial plane. It possesses a symmetry of joint inversion of time and parity with respect to the equatorial plane. Its Arnowitt-Deser-Misner (ADM) mass and angular momentum are zero. It is curved but regular all over the manifold. Its Komar mass and Komar angular momentum are also zero. Its infinite red-shift surface coincides with its event horizon, since the event horizon does not rotate. Furthermore we extend this solution to the massive case, and find some similar properties. This solution is a stationary axisymmetric solution, but not Kerr. It explicitly proves that pure Einstein gravity permits different rotational mode other than Kerr. Our results demonstrate that the Einstein theory may have much more rich structures than what we ever imagine.
Energy Technology Data Exchange (ETDEWEB)
Au, G.
1995-03-01
One of the greatest challenges facing theoretical physics lies in reconciling Einstein`s classical theory of gravity - general relativity -with quantum field theory. Although both theories have been experimentally supported in their respective regimes, they are as compatible as a square peg and a round hole. This article summarises the current status of the superstring approach to the problem, the status of the Ashtekar program, and problem of time in quantum gravity.
Einstein Gravity-Supergravity Correspondence
Chen, C M; Sharakin, S A; Chen, Chiang-Mei; Gal'tsov, Dmitri V.; Sharakin, Sergei A.
1999-01-01
A correspondence between the three-block truncated 11D supergravity and the 8D pure Einstein gravity with two commuting Killing symmetries is discussed. The Kaluza-Klein two-forms of the 6D theory obtained after dimensional reduction along the Killing orbits generate the four-form field of supergravity via an inverse dualization. Thus any solution to the vacuum Einstein equations in eight dimensions depending on six coordinates have 11D-supergravity counterparts with the non-trivial four-form field. Using this proposed duality we derive a new dyon solution of 11D supergravity describing the M2 and M5-branes intersecting at a point.
Gravity Before Einstein and Schwinger Before Gravity
Trimble, Virginia L.
2012-05-01
Julian Schwinger was a child prodigy, and Albert Einstein distinctly not; Schwinger had something like 73 graduate students, and Einstein very few. But both thought gravity was important. They were not, of course, the first, nor is the disagreement on how one should think about gravity that is being highlighted here the first such dispute. The talk will explore, first, several of the earlier dichotomies: was gravity capable of action at a distance (Newton), or was a transmitting ether required (many others). Did it act on everything or only on solids (an odd idea of the Herschels that fed into their ideas of solar structure and sunspots)? Did gravitational information require time for its transmission? Is the exponent of r precisely 2, or 2 plus a smidgeon (a suggestion by Simon Newcomb among others)? And so forth. Second, I will try to say something about Scwinger's lesser known early work and how it might have prefigured his "source theory," beginning with "On the Interaction of Several Electrons (the unpublished, 1934 "zeroth paper," whose title somewhat reminds one of "On the Dynamics of an Asteroid," through his days at Berkeley with Oppenheimer, Gerjuoy, and others, to his application of ideas from nuclear physics to radar and of radar engineering techniques to problems in nuclear physics. And folks who think good jobs are difficult to come by now might want to contemplate the couple of years Schwinger spent teaching elementary physics at Purdue before moving on to the MIT Rad Lab for war work.
Modifications of Einstein's theory of gravity at large distances
2015-01-01
In the last few years modified gravity theories have been proposed as extensions of Einstein's theory of gravity. Their main motivation is to explain the latest cosmological and astrophysical data on dark energy and dark matter. The study of general relativity at small scales has already produced important results (cf e.g. LNP 863 Quantum Gravity and Quantum Cosmology) while its study at large scales is challenging because recent and upcoming observational results will provide important information on the validity of these modified theories. In this volume, various aspects of modified gravity at large scales will be discussed: high-curvature gravity theories; general scalar-tensor theories; Galileon theories and their cosmological applications; F(R) gravity theories; massive, new massive and topologically massive gravity; Chern-Simons modifications of general relativity (including holographic variants) and higher-spin gravity theories, to name but a few of the most important recent developments. Edite...
Modesto, Leonardo
2013-01-01
We hereby present a class of multidimensional higher derivative theories of gravity that realizes an ultraviolet completion of Einstein general relativity. This class is marked by a "non-polynomal" entire function (form factor), which averts extra degrees of freedom (including ghosts) and improves the high energy behavior of the loop amplitudes. By power counting arguments, it is proved that the theory is super-renormalizable in any dimension, i.e. only one-loop divergences survive. Furthermore, in odd dimensions there are no counter terms for pure gravity and the theory turns out to be "finite." Finally, considering the infinite tower of massive states coming from dimensional reduction, quantum gravity is finite in even dimension as well.
Gravity before Einstein and Schwinger before gravity1
Trimble, V
2014-01-01
Julian Schwinger was a child prodigy, and Albert Einstein distinctly not; Schwinger had something like 73 graduate students, and Einstein very few. But both thought that gravity was important. They were not, of course, the first, nor is the disagreement on how one should think about gravity, which was highlighted at the June 2012 meeting of the American Astronomical Society, the first such dispute. Explored here are several views of what gravity is supposed to do: action at a distance versus ...
Lectures on Loop Quantum Gravity
Thiemann, T
2003-01-01
Quantum General Relativity (QGR), sometimes called Loop Quantum Gravity, has matured over the past fifteen years to a mathematically rigorous candidate quantum field theory of the gravitational field. The features that distinguish it from other quantum gravity theories are 1) background independence and 2) minimality of structures. Background independence means that this is a non-perturbative approach in which one does not perturb around a given, distinguished, classical background metric, rather arbitrary fluctuations are allowed, thus precisely encoding the quantum version of Einstein's radical perception that gravity is geometry. Minimality here means that one explores the logical consequences of bringing together the two fundamental principles of modern physics, namely general covariance and quantum theory, without adding any experimentally unverified additional structures. The approach is purposely conservative in order to systematically derive which basic principles of physics have to be given up and mu...
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.
Contravariant Gravity on Poisson Manifolds and Einstein Gravity
Kaneko, Yukio; Watamura, Satoshi
2016-01-01
A relation between a gravity on Poisson manifolds proposed in arXiv:1508.05706 and the 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 includes couplings between the metric and the Poisson tensor. The Weyl transformation is studied to reveal properties of those interactions. It is argued that the theory can have an equivalent description in terms of the Einstein gravity coupled to matter. As an example, it is shown that the contravariant gravity on a two-dimensional Poisson manifold has another description by a real scalar field coupling to the metric in a specific manner.
Finding Horndeski theories with Einstein gravity limits
McManus, Ryan; Peñarrubia, Jorge
2016-01-01
The Horndeski action is the most general scalar-tensor theory with at most second-order derivatives in the equations of motion, thus evading Ostrogradsky instabilities and making it of interest when modifying gravity at large scales. To pass local tests of gravity, these modifications predominantly rely on nonlinear screening mechanisms that recover Einstein's Theory of General Relativity in regions of high density. We derive a set of conditions on the four free functions of the Horndeski action that examine whether a specific model embedded in the action possesses an Einstein gravity limit or not. For this purpose, we develop a new and surprisingly simple scaling method that identifies dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified action. This enables us to find regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar fi...
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
Renormalizable Quantum Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning
2002-01-01
The quantum gravity is formulated based on the principle of local gauge invariance. The model discussedin this paper has local gravitational gauge symmetry, and gravitational field is represented by gauge field. In the leading-order approximation, it gives out classical Newton's theory of gravity. In the first-order approximation and for vacuum,it gives out Einstein's general theory of relativity. This quantum gauge theory of gravity is a renormalizable quantumtheory.
Velocity, acceleration and gravity in Einstein's relativity
Abramowicz, Marek A
2016-01-01
Einstein's relativity theory demands that all meaningful physical objects should be defined covariantly, i.e. in a coordinate independent way. Concepts of relative velocity, acceleration, gravity acceleration and gravity potential are fundamental in Newton's theory and they are imprinted in everyone's physical intuition. Unfortunately, relativistic definitions of them are not commonly known or appreciated. Every now and then some confused authors use wrong, non-covariant, definitions of velocity, acceleration and gravity, based on their vague Newtonian intuitions and hidden in a superficial, often purely semantic, relativistic disguise. A recent example of such a confusion (Gorkavyi & Vasilkov, 2016) is discussed at the end of this Note.
Gravity Resonance Spectroscopy and Einstein-Cartan Gravity
Abele, Hartmut; Jenke, Tobias; Pitschmann, Mario; Geltenbort, Peter
2015-01-01
The qBounce experiment offers a new way of looking at gravitation based on quantum interference. An ultracold neutron is reflected in well-defined quantum states in the gravity potential of the Earth by a mirror, which allows to apply the concept of gravity resonance spectroscopy (GRS). This experiment with neutrons gives access to all gravity parameters as the dependences on distance, mass, curvature, energy-momentum as well as on torsion. Here, we concentrate on torsion.
Criticality in Einstein-Gauss-Bonnet gravity: gravity without graviton
Energy Technology Data Exchange (ETDEWEB)
Fan, Zhong-Ying [Peking University, Center of High Energy Physics, Beijing (China); Chen, Bin [Peking University, Center of High Energy Physics, Beijing (China); Peking University, Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Lue, Hong [Beijing Normal University, Department of Physics, Center for Advanced Quantum Studies, Beijing (China)
2016-10-15
General Einstein-Gauss-Bonnet gravity with a cosmological constant allows two (A)dS spacetimes as its vacuum solutions. We find a critical point in the parameter space where the two (A)dS spacetimes coalesce into one and the linearized perturbations lack any bilinear kinetic terms. The vacuum perturbations hence lose their interpretation as linear graviton modes at the critical point. Nevertheless, the critical theory admits black hole solutions due to the nonlinear effect. We also consider Einstein gravity extended with general quadratic curvature invariants and obtain critical points where the theory has no bilinear kinetic terms for either the scalar trace mode or the transverse modes. Such critical phenomena are expected to occur frequently in general higher-derivative gravities. (orig.)
Finding Horndeski theories with Einstein gravity limits
McManus, Ryan; Lombriser, Lucas; Peñarrubia, Jorge
2016-11-01
The Horndeski action is the most general scalar-tensor theory with at most second-order derivatives in the equations of motion, thus evading Ostrogradsky instabilities and making it of interest when modifying gravity at large scales. To pass local tests of gravity, these modifications predominantly rely on nonlinear screening mechanisms that recover Einstein's Theory of General Relativity in regions of high density. We derive a set of conditions on the four free functions of the Horndeski action that examine whether a specific model embedded in the action possesses an Einstein gravity limit or not. For this purpose, we develop a new and surprisingly simple scaling method that identifies dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified action. This enables us to find regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar field profile, one can then further evaluate whether these limits can be attributed to a genuine screening effect. For illustration, we apply the analysis to both a cubic galileon and a chameleon model as well as to Brans-Dicke theory. Finally, we emphasise that the scaling method also provides a natural approach for performing post-Newtonian expansions in screened regimes.
The Quantum-Gravity Regime under Microgravity
Laemmerzahl, Claus; Könemann, Thorben
Gravity is the weakest of the four known interactions. Accordingly, one needs either huge masses to explore this interaction or a long time to accumulate its small influence. The latter is possible only under microgravity conditions. In this contribution we would like to focus on three issues related to basic problems in the quantum-gravity regime: (i) Search for fundamental decoherence: Decoherence describes the transition from the quantum world to the classical regime. There are many technical sources of decoherence but the question is whether there is a fundamental mechanism for such a decoherence which would be a solution for the measurement problem in quantum mechanics. Here we describe the estimates on such a fundamental decoherence from experiments with Bose-Einstein condensates in microgravity. (ii) Search for possible self-gravity effects: Self gravity has been proposed e.g. by Penrose to resolve the measurement problem. Self gravitating systems are also give Bose stars which are a model for the pyhsics around black holes or for dark matter. Here we would like to describe effects of self gravity in Bose-Einstein condensates. We calculate stationary spherically symmetric states and discuss the possibility to measure such effects related to self gravity. (iii) Test of the semiclassical Einstein equations. Since General Relativity and quantum theory appear to be incompatible, it has been discussed whether the semiclassical Einstein equations might be valid. Here we would like to discuss a proposal made by Peres and Lindner to use Bose-Einstein condensates for a true quantum test of these semiclassical Einstein equations from which one can decide whether such an ansatz is valid or not.
Gravity loop corrections to the standard model Higgs in Einstein gravity
Abe, Yugo; Inami, Takeo
2016-01-01
We study quantum gravity corrections to the standard model Higgs potential $V_{\\rm eff}(\\phi)$ $\\grave{\\rm a}$ la Coleman-Weinberg and examine the stability question of $V_{\\rm eff}(\\phi)$ around Planck mass scale, $\\mu\\simeq M_{\\rm Pl}$ ($M_{\\rm Pl}=1.22\\times10^{19}{\\rm GeV}$). We calculate the gravity one-loop corrections by using the momentum cut-off $\\Lambda$ in Einstein gravity. We show a significant difference between the effective potential $V_{\\rm eff}(\\phi)$ with and without gravity loop corrections in the energy region of $M_{\\rm Pl}$ for $\\Lambda= (1\\sim3)M_{\\rm Pl}$. We find that $V_{\\rm eff}(\\phi)$ possesses a minimum somewhere at $\\mu\\simeq M_{\\rm Pl}$; it implies that the stability condition for $V_{\\rm eff}(\\phi)$ holds after gravity corrections included.
Trugenberger, Carlo A
2016-01-01
In a recently developed approach, geometry is modelled as an emergent property of random networks. Here I show that one of these models I proposed is exactly quantum gravity defined in terms of the combinatorial Ricci curvature recently derived by Ollivier. Geometry in the weak (classical) gravity regime arises in a phase transition driven by the condensation of short graph cycles. The strong (quantum) gravity regime corresponds to "small world" random graphs with logarithmic distance scaling.
Einstein's gravity from an affine model
Castillo-Felisola, Oscar
2015-01-01
We show that the effective field equations for a recently formulated affine model of gravity, in the sector of a metric (torsion-free) connection, accept general Einstein manifolds --- with or without cosmological constant --- as solutions. Moreover, these effective field equations coincide with the ones obtained from a gravitational Yang--Mills theory known as Stephenson--Kilmister--Yang theory. Additionally, we find an equivalence between a minimally coupled massless scalar field in General Relativity with a "minimally" coupled scalar field in this affine model.
Newtonian gravity in loop quantum gravity
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.
Newtonian gravity in loop quantum gravity
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.
Finsler geometric extension of Einstein gravity
Pfeifer, Christian
2011-01-01
We construct gravitational dynamics for Finsler spacetimes in terms of an action integral on the unit tangent bundle. These spacetimes are generalizations of Lorentzian metric manifolds which satisfy necessary causality properties. A coupling procedure for matter fields to Finsler gravity completes our new theory that consistently becomes equivalent to Einstein gravity in the limit of metric geometry. We provide a precise geometric definition of observers and their measurements, and show that the transformations by means of which different observers communicate form a groupoid that generalizes the usual Lorentz group. Moreover, we discuss the implementation of Finsler spacetime symmetries. We use our results to analyze a particular spacetime model that leads to Finsler geometric refinements of the linearized Schwarzschild solution.
Finsler geometric extension of Einstein gravity
Pfeifer, Christian; Wohlfarth, Mattias N. R.
2012-03-01
We construct gravitational dynamics for Finsler spacetimes in terms of an action integral on the unit tangent bundle. These spacetimes are generalizations of Lorentzian metric manifolds which satisfy necessary causality properties. A coupling procedure for matter fields to Finsler gravity completes our new theory that consistently becomes equivalent to Einstein gravity in the limit of metric geometry. We provide a precise geometric definition of observers and their measurements and show that the transformations, by means of which different observers communicate, form a groupoid that generalizes the usual Lorentz group. Moreover, we discuss the implementation of Finsler spacetime symmetries. We use our results to analyze a particular spacetime model that leads to Finsler geometric refinements of the linearized Schwarzschild solution.
Quantum gravity as Escher's Dragon
Smilga, A. V.
2003-11-01
The main obstacle in attempts to construct a consistent quantum gravity is the absence of independent flat time. This can in principle be cured by going out to higher dimensions. The modern paradigm assumes that the fundamental theory of everything is some form of string theory living in space of more than four dimensions. We advocate another possibility that the fundamental theory is a form of D=4 higher-derivative gravity. This class of theories has a nice feature of renormalizability so that perturbative calculations are feasible. There are also finite N=4 supersymmetric conformal supergravity theories. This possibility is particularly attractive. Einstein's gravity is obtained in a natural way as an effective low-energy theory. The N=1 supersymmetric version of the theory has a natural higher-dimensional interpretation due to Ogievetsky and Sokatchev, which involves embedding of our curved Minkowsky space-time manifold into flat 8-dimensional space. Assuming that a variant of the finite N=4 theory also admit a similar interpretation, this may eventually allow one to construct consistent quantum theory of gravity. We argue, however, that even though future gravity theory will probably use higher dimensions as construction scaffolds, its physical content and meaning should refer to 4 dimensions where observer lives.
Phenomenological Quantum Gravity
Hossenfelder, Sabine
2009-01-01
If the history of science has taught us anything, it's that persistence and creativity makes the once impossible possible. It has long been thought experimental tests of quantum gravity are impossible. But during the last decade, several different approaches have been proposed that allow us to test, if not the fundamental theory of quantum gravity itself, so at least characteristic features this theory can have. For the first time we can probe experimentally domains in which quantum physics and gravity cohabit, in spite of our failure so far to make a convincing marriage of them on a theoretical level.
Quantum Computation Toward Quantum Gravity
Zizzi, P. A.
2001-08-01
The aim of this paper is to enlighten the emerging relevance of Quantum Information Theory in the field of Quantum Gravity. As it was suggested by J. A. Wheeler, information theory must play a relevant role in understanding the foundations of Quantum Mechanics (the "It from bit" proposal). Here we suggest that quantum information must play a relevant role in Quantum Gravity (the "It from qubit" proposal). The conjecture is that Quantum Gravity, the theory which will reconcile Quantum Mechanics with General Relativity, can be formulated in terms of quantum bits of information (qubits) stored in space at the Planck scale. This conjecture is based on the following arguments: a) The holographic principle, b) The loop quantum gravity approach and spin networks, c) Quantum geometry and black hole entropy. From the above arguments, as they stand in the literature, it follows that the edges of spin networks pierce the black hole horizon and excite curvature degrees of freedom on the surface. These excitations are micro-states of Chern-Simons theory and account of the black hole entropy which turns out to be a quarter of the area of the horizon, (in units of Planck area), in accordance with the holographic principle. Moreover, the states which dominate the counting correspond to punctures of spin j = 1/2 and one can in fact visualize each micro-state as a bit of information. The obvious generalization of this result is to consider open spin networks with edges labeled by the spin -1/ 2 representation of SU(2) in a superposed state of spin "on" and spin "down." The micro-state corresponding to such a puncture will be a pixel of area which is "on" and "off" at the same time, and it will encode a qubit of information. This picture, when applied to quantum cosmology, describes an early inflationary universe which is a discrete version of the de Sitter universe.
Phenomenological Quantum Gravity
Kimberly, D; Kimberly, Dagny; Magueijo, Joao
2005-01-01
These notes summarize a set of lectures on phenomenological quantum gravity which one of us delivered and the other attended with great diligence. They cover an assortment of topics on the border between theoretical quantum gravity and observational anomalies. Specifically, we review non-linear relativity in its relation to loop quantum gravity and high energy cosmic rays. Although we follow a pedagogic approach we include an open section on unsolved problems, presented as exercises for the student. We also review varying constant models: the Brans-Dicke theory, the Bekenstein varying $\\alpha$ model, and several more radical ideas. We show how they make contact with strange high-redshift data, and perhaps other cosmological puzzles. We conclude with a few remaining observational puzzles which have failed to make contact with quantum gravity, but who knows... We would like to thank Mario Novello for organizing an excellent school in Mangaratiba, in direct competition with a very fine beach indeed.
`Iconoclastic', Categorical Quantum Gravity
Raptis, I
2005-01-01
This is a two-part, `2-in-1' paper. In Part I, the introductory talk at `Glafka--2004: Iconoclastic Approaches to Quantum Gravity' international theoretical physics conference is presented in paper form (without references). In Part II, the more technical talk, originally titled ``Abstract Differential Geometric Excursion to Classical and Quantum Gravity'', is presented in paper form (with citations). The two parts are closely entwined, as Part I makes general motivating remarks for Part II.
Quantum Gravity, CPT symmetry and Entangled States
Mavromatos, Nick E
2008-01-01
There may unique ("smoking-gun") signatures of the breakdown of CPT symmetry, induced in some models of Quantum Gravity entailing decoherence for quantum matter. Such effects can be observed in entangled states of neutral mesons via modifications of the respective Einstein-Podolsky-Rosen (EPR) correlators ("omega"-effect). In the talk I discuss experimental signatures and bounds of the omega-effect in Phi- and B-factories, and argue that the effect might be falsifiable at the next generation facilities.
Directory of Open Access Journals (Sweden)
Rovelli Carlo
1998-01-01
Full Text Available The problem of finding the quantum theory of the gravitational field, and thus understanding what is quantum spacetime, is still open. One of the most active of the current approaches is loop quantum gravity. Loop quantum gravity is a mathematically well-defined, non-perturbative and background independent quantization of general relativity, with its conventional matter couplings. Research in loop quantum gravity today forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained are: (i The computation of the physical spectra of geometrical quantities such as area and volume, which yields quantitative predictions on Planck-scale physics. (ii A derivation of the Bekenstein-Hawking black hole entropy formula. (iii An intriguing physical picture of the microstructure of quantum physical space, characterized by a polymer-like Planck scale discreteness. This discreteness emerges naturally from the quantum theory and provides a mathematically well-defined realization of Wheeler's intuition of a spacetime ``foam''. Long standing open problems within the approach (lack of a scalar product, over-completeness of the loop basis, implementation of reality conditions have been fully solved. The weak part of the approach is the treatment of the dynamics: at present there exist several proposals, which are intensely debated. Here, I provide a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
Albert Einstein and the Quantum Riddle
Lande, Alfred
1974-01-01
Derives a systematic structure contributing to the solution of the quantum riddle in Einstein's sense by deducing quantum mechanics from the postulates of symmetry, correspondence, and covariance. Indicates that the systematic presentation is in agreement with quantum mechanics established by Schroedinger, Born, and Heisenberg. (CC)
Chiou, Dah-Wei
2014-01-01
This article presents an "in-a-nutshell" yet self-contained introductory review on loop quantum gravity (LQG) -- a background-independent, nonperturbative approach to a consistent quantum theory of gravity. Instead of rigorous and systematic derivations, it aims to provide a general picture of LQG, placing emphasis on the fundamental ideas and their significance. The canonical formulation of LQG, as the central topic of the article, is presented in a logically orderly fashion with moderate details, while the spin foam theory, black hole thermodynamics, and loop quantum cosmology are covered briefly. Current directions and open issues are also summarized.
Directory of Open Access Journals (Sweden)
Cahill R. T.
2015-10-01
Full Text Available A new quantum gravity experiment is reported with the data confirming the generali- sation of the Schrödinger equation to include the interaction of the wave function with dynamical space. Dynamical space turbulence, via this interaction process, raises and lowers the energy of the electron wave function, which is detected by observing conse- quent variations in the electron quantum barrier tunnelling rate in reverse-biased Zener diodes. This process has previously been reported and enabled the measurement of the speed of the dynamical space flow, which is consistent with numerous other detection experiments. The interaction process is dependent on the angle between the dynamical space flow velocity and the direction of the electron flow in the diode, and this depen- dence is experimentally demonstrated. This interaction process explains gravity as an emergent quantum process, so unifying quantum phenomena and gravity. Gravitational waves are easily detected.
Intrinsic Time Quantum Gravity
Yu, Hoi Lai
2016-01-01
Correct identification of the true gauge symmetry of General Relativity being 3d spatial diffeomorphism invariant(3dDI) (not the conventional infinite tensor product group with principle fibre bundle structure), together with intrinsic time extracted from clean decomposition of the canonical structure yields a self-consistent theory of quantum gravity. A new set of fundamental commutation relations is also presented. The basic variables are the eight components of the unimodular part of the spatial dreibein and eight SU(3) generators which correspond to Klauder's momentric variables that characterize a free theory of quantum gravity. The commutation relations are not canonical, but have well defined group theoretical meanings. All fundamental entities are dimensionless; and the quantum wave functionals are preferentially in the dreibein representation. The successful quantum theory of gravity involves only broad spectrum of knowledge and deep insights but no exotic idea.
Fundamentals of quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Klauder, J R [Department of Physics and Department of Mathematics, University of Florida, Gainesville FL 32611-8440 (United States)
2007-11-15
The outline of a recent approach to quantum gravity is presented. Novel ingredients include: (1) Affine kinematical variables; (2) Affine coherent states; (3) Projection operator approach toward quantum constraints; (4) Continuous-time regularized functional integral representation without/with constraints; and (5) Hard core picture of nonrenormalizability. The 'diagonal representation' for operator representations, introduced by Sudarshan into quantum optics, arises naturally within this program.
A QCD analogy for quantum gravity
Holdom, Bob
2015-01-01
Quadratic gravity presents us with a renormalizable, asymptotically free theory of quantum gravity. When its couplings grow strong at some scale, as in QCD, then this strong scale sets the Planck mass. QCD has a gluon that does not appear in the physical spectrum. Quadratic gravity has a spin-2 ghost that we conjecture does not appear in the physical spectrum. We discuss how the QCD analogy leads to this conjecture and to the emergence of general relativity. Certain aspects of the QCD path integral and its measure could also be similar for quadratic gravity. With the addition of the Einstein-Hilbert term, quadratic gravity has a dimensionful parameter that seems to control a quantum phase transition and the size of a mass gap in the strong phase.
PBR theorem and Einstein's quantum hole argument
Weinstein, Galina
2013-01-01
This note discusses the latest hot topic: Quantum states: ontic or epistemic? and the PBR theorem. Upon reading Einstein's views on quantum incompleteness in publications or in his correspondence after 1935 (the EPR paradox), one gets a very intense feeling of deja-vu. Einstein presents a quantum hole argument, which somewhat reminds of the hole argument in his 1914 "Entwurf" general theory of relativity. In their paper, PBR write the following: "an important step towards the derivation of our result is the idea that the quantum state is physical if distinct quantum states correspond to non-overlapping distributions for [the set of possible physical states that a system can be in]", and they then refer to Einstein's argument and views.
Einstein Gravity Explorer–a medium-class fundamental physics mission
Schiller, S.; Tino, G.M.; Gill, E.; et al.
2008-01-01
The Einstein Gravity Explorer mission (EGE) is devoted to a precise measurement of the properties of space-time using atomic clocks. It tests one of the most fundamental predictions of Einstein’s Theory of General Relativity, the gravitational redshift, and thereby searches for hints of quantum effe
Einstein Gravity Explorer–a medium-class fundamental physics mission
Schiller, S.; Tino, G.M.; Gill, E.; et al.
2008-01-01
The Einstein Gravity Explorer mission (EGE) is devoted to a precise measurement of the properties of space-time using atomic clocks. It tests one of the most fundamental predictions of Einstein’s Theory of General Relativity, the gravitational redshift, and thereby searches for hints of quantum
Quantum massive conformal gravity
Energy Technology Data Exchange (ETDEWEB)
Faria, F.F. [Universidade Estadual do Piaui, Centro de Ciencias da Natureza, Teresina, PI (Brazil)
2016-04-15
We first find the linear approximation of the second plus fourth order derivative massive conformal gravity action. Then we reduce the linearized action to separated second order derivative terms, which allows us to quantize the theory by using the standard first order canonical quantization method. It is shown that quantum massive conformal gravity is renormalizable but has ghost states. A possible decoupling of these ghost states at high energies is discussed. (orig.)
A Demonstration of Einstein's Equivalence of Gravity and Acceleration
Newburgh, Ronald
2008-01-01
In 1907, Einstein described a "Gedankenexperiment" in which he showed that free fall in a gravitational field is indistinguishable from a body at rest in an elevator accelerated upwards in zero gravity. This paper describes an apparatus, which is simple to make and simple to operate, that acts as an observable footnote to Einstein's example. It…
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.
Loop quantum gravity and observations
Barrau, A
2014-01-01
Quantum gravity has long been thought to be completely decoupled from experiments or observations. Although it is true that smoking guns are still missing, there are now serious hopes that quantum gravity phenomena might be tested. We review here some possible ways to observe loop quantum gravity effects either in the framework of cosmology or in astroparticle physics.
A parametrix for quantum gravity?
Esposito, Giampiero
2015-01-01
In the sixties, DeWitt discovered that the advanced and retarded Green functions of the wave operator on metric perturbations in the de Donder gauge make it possible to define classical Poisson brackets on the space of functionals that are invariant under the action of the full diffeomorphism group of spacetime. He therefore tried to exploit this property to define invariant commutators for the quantized gravitational field, but the operator counterpart of such classical Poisson brackets turned out to be a hard task. On the other hand, the mathematical literature studies often an approximate inverse, the parametrix, which is, strictly, a distribution. We here suggest that such a construction might be exploited in canonical quantum gravity. We begin with the simplest case, i.e. fundamental solution and parametrix for the linear, scalar wave operator; the next step are tensor wave equations, again for linear theory, e.g. Maxwell theory in curved spacetime. Last, the nonlinear Einstein equations are studied, rel...
Quantum Gravity in D=5 Dimensions
Pinheiro, C; Pinheiro, Carlos
2000-01-01
We propose a topological Chern-Simons term in D=5 dimensions coupled to Einstein Hilbert theory. Hartree approximation for topological Lagrangian and the Chern-Simons term in D=3 is considered. An effective model of Quantum Gravity in D=5 dimensions is presented here. The analysis of residues is considered and the unitarity is guaranteed at tree level. The propagator is ghost and tachyon free.
Quantum gravity as Escher's dragon
Smilga, A V
2003-01-01
The main obstacle in attempts to construct a consistent quantum gravity is the absence of independent flat time. This can in principle be cured by going out to higher dimensions. The modern paradigm assumes that the fundamental theory of everything is some form of string theory living in space of more than four dimensions. We advocate another possibility that the fundamental theory is a form of D=4 higher-derivative gravity. This class of theories has a nice feature of renormalizability so that perturbative calculations are feasible. There are also finite N=4 supersymmetric conformal supergravity theories. This possibility is particularly attractive. Einstein's gravity is obtained in a natural way as an effective low-energy theory. The N=1 supersymmetric version of the theory has a natural higher-dimensional interpretation due to Ogievetsky and Sokatchev, which involves embedding of our curved Minkowsky space-time manifold into flat 8-dimensional space. Assuming that a variant of the finite N=4 theory also ad...
Einstein's Revolutionary Light-Quantum Hypothesis
Stuewer, Roger H.
2005-05-01
The paper in which Albert Einstein proposed his light-quantum hypothesis was the only one of his great papers of 1905 that he himself termed ``revolutionary.'' Contrary to widespread belief, Einstein did not propose his light-quantum hypothesis ``to explain the photoelectric effect.'' Instead, he based his argument for light quanta on the statistical interpretation of the second law of thermodynamics, with the photoelectric effect being only one of three phenomena that he offered as possible experimental support for it. I will discuss Einstein's light-quantum hypothesis of 1905 and his introduction of the wave-particle duality in 1909 and then turn to the reception of his work on light quanta by his contemporaries. We will examine the reasons that prominent physicists advanced to reject Einstein's light-quantum hypothesis in succeeding years. Those physicists included Robert A. Millikan, even though he provided convincing experimental proof of the validity of Einstein's equation of the photoelectric effect in 1915. The turning point came after Arthur Holly Compton discovered the Compton effect in late 1922, but even then Compton's discovery was contested both on experimental and on theoretical grounds. Niels Bohr, in particular, had never accepted the reality of light quanta and now, in 1924, proposed a theory, the Bohr-Kramers-Slater theory, which assumed that energy and momentum were conserved only statistically in microscopic interactions. Only after that theory was disproved experimentally in 1925 was Einstein's revolutionary light-quantum hypothesis generally accepted by physicists---a full two decades after Einstein had proposed it.
Introduction to Loop Quantum Gravity
Mercuri, Simone
2010-01-01
The questions I have been asked during the 5th International School on Field Theory and Gravitation, have compelled me to give an account of the premises that I consider important for a beginner's approach to Loop Quantum Gravity. After a description of some general arguments and an introduction to the canonical theory of gravity, I review the background independent approach to quantum gravity, giving only a brief survey of Loop Quantum Gravity.
Quantum cosmology of (loop) quantum gravity condensates: An example
Gielen, Steffen
2014-01-01
Spatially homogeneous universes can be described in (loop) quantum gravity as condensates of elementary excitations of space. Their treatment is easiest in the second-quantised group field theory formalism which allows the adaptation of techniques from the description of Bose-Einstein condensates in condensed matter physics. Dynamical equations for the states can be derived directly from the underlying quantum gravity dynamics. The analogue of the Gross-Pitaevskii equation defines an anisotropic quantum cosmology model, in which the condensate wavefunction becomes a quantum cosmology wavefunction on minisuperspace. To illustrate this general formalism, we give a mapping of the gauge-invariant geometric data for a tetrahedron to a minisuperspace of homogeneous anisotropic 3-metrics. We then study an example for which we give the resulting quantum cosmology model in the general anisotropic case and derive the general analytical solution for isotropic universes. We discuss the interpretation of these solutions a...
Einstein's strugges with quantum theory a reappraisal
Home, Dipankar
2007-01-01
Einstein’s Struggles with Quantum Theory: A Reappraisal by Dipankar Home and Andrew Whitaker provides a detailed account of Albert Einstein’s thinking in regard to quantum physics. Until recently, most of Einstein’s views on quantum physics were dismissed and even ridiculed; some critics even suggested that Einstein was not able to grasp the complexities of the formalism of quantum theory and subtleties of the standard interpretation of this theory known as the Copenhagen interpretation put forward by Niels Bohr and his colleagues. But was that true? Modern scholarship argues otherwise, insist Drs. Home and Whitaker, who painstakingly explain the questions Einstein raised as well as offer a detailed discussion of Einstein’s position and major contributions to quantum theory, connecting them with contemporary studies on fundamental aspects of this theory. This unique book presents a mathematical as well as a non-mathematical route through the theories, controversies, and investigations, making the disc...
Bahrami, M; McMillen, S; Paternostro, M; Ulbricht, H
2015-01-01
What gravitational field is generated by a massive quantum system in a spatial superposition? This is one of the most important questions in modern physics, and after decades of intensive theoretical and experimental research, we still do not know the answer. On the experimental side, the difficulty lies in the fact that gravity is weak and requires large masses to be detectable. But for large masses, it becomes increasingly difficult to generate spatial quantum superpositions, which live sufficiently long to be detected. A delicate balance between opposite quantum and gravitational demands is needed. Here we show that this can be achieved in an optomechanics scenario. We propose an experimental setup, which allows to decide whether the gravitational field generated by a quantum system in a spatial superposition is the superposition of the two alternatives, or not. We estimate the magnitude of the effect and show that it offers good perspectives for observability. Performing the experiment will mark a breakth...
Christiansen, Nicolai; Meibohm, Jan; Pawlowski, Jan M; Reichert, Manuel
2015-01-01
We investigate the ultraviolet behaviour of quantum gravity within a functional renormalisation group approach. The present setup includes the full ghost and graviton propagators and, for the first time, the dynamical graviton three-point function. The latter gives access to the coupling of dynamical gravitons and makes the system minimally self-consistent. The resulting phase diagram confirms the asymptotic safety scenario in quantum gravity with a non-trivial UV fixed point. A well-defined Wilsonian block spinning requires locality of the flow in momentum space. This property is discussed in the context of functional renormalisation group flows. We show that momentum locality of graviton correlation functions is non-trivially linked to diffeomorphism invariance, and is realised in the present setup.
Gomberoff, Andres
2006-01-01
The 2002 Pan-American Advanced Studies Institute School on Quantum Gravity was held at the Centro de Estudios Cientificos (CECS),Valdivia, Chile, January 4-14, 2002. The school featured lectures by ten speakers, and was attended by nearly 70 students from over 14 countries. A primary goal was to foster interaction and communication between participants from different cultures, both in the layman’s sense of the term and in terms of approaches to quantum gravity. We hope that the links formed by students and the school will persist throughout their professional lives, continuing to promote interaction and the essential exchange of ideas that drives research forward. This volume contains improved and updated versions of the lectures given at the School. It has been prepared both as a reminder for the participants, and so that these pedagogical introductions can be made available to others who were unable to attend. We expect them to serve students of all ages well.
Einstein's theory of gravity and the problem of missing mass.
Ferreira, Pedro G; Starkman, Glenn D
2009-11-01
The observed matter in the universe accounts for just 5% of the observed gravity. A possible explanation is that Newton's and Einstein's theories of gravity fail where gravity is either weak or enhanced. The modified theory of Newtonian dynamics (MOND) reproduces, without dark matter, spiral-galaxy orbital motions and the relation between luminosity and rotation in galaxies, although not in clusters. Recent extensions of Einstein's theory are theoretically more complete. They inevitably include dark fields that seed structure growth, and they may explain recent weak lensing data. However, the presence of dark fields reduces calculability and comes at the expense of the original MOND premise, that the matter we see is the sole source of gravity. Observational tests of the relic radiation, weak lensing, and the growth of structure may distinguish modified gravity from dark matter.
Bose-Einstein condensation in quantum glasses
2009-01-01
The role of geometrical frustration in strongly interacting bosonic systems is studied with a combined numerical and analytical approach. We demonstrate the existence of a novel quantum phase featuring both Bose-Einstein condensation and spin-glass behaviour. The differences between such a phase and the otherwise insulating "Bose glasses" are elucidated.
More on the dilatonic Einstein-Gauss-Bonnet gravity
Iihoshi, Masao
2010-01-01
Einstein-Gauss-Bonnet gravity coupled to a dynamical dilaton is examined from the viewpoint of Einstein's equivalence principle. We point out that the usual frame change that applies to the action without curvature correction does not cure the problem of nonminimal couplings by the dynamical nature of a dilaton field. Thus a modification of the Einstein frame is required. It is proposed that the kinetic term of a dilaton should be brought to a canonical form, which completely fixes the additional terms associated with the frame transformation.
Universe in a Black Hole in Einstein-Cartan Gravity
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.
Classical limit of quantum gravity in an accelerating universe
Schuller, F P; Schuller, Frederic P.; Wohlfarth, Mattias N.R.
2005-01-01
A one-parameter deformation of Einstein-Hilbert gravity with an inverse curvature term is derived as the classical limit of quantum gravity compatible with an accelerating universe. This result is based on the investigation of semi-classical theories with sectional curvature bounds which are shown not to admit static black holes if otherwise of phenomenological interest. Consequences for classical gravity and the canonical quantization program are briefly discussed.
Classical limit of quantum gravity in an accelerating universe
Energy Technology Data Exchange (ETDEWEB)
Schuller, Frederic P. [Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo N2L 2Y5 (Canada)]. E-mail: fschuller@perimeterinstitute.ca; Wohlfarth, Mattias N.R. [II. Institut fuer Theoretische Physik, Universitaet Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)]. E-mail: mattias.wohlfarth@desy.de
2005-04-21
A one-parameter deformation of Einstein-Hilbert gravity with an inverse Riemann curvature term is derived as the classical limit of quantum gravity compatible with an accelerating universe. This result is based on the investigation of semi-classical theories with sectional curvature bounds which are shown not to admit static spherically symmetric black holes if otherwise of phenomenological interest. We discuss the impact on the canonical quantization of gravity, and observe that worldsheet string theory is not affected.
Einstein-Riemann Gravity on Deformed Spaces
Directory of Open Access Journals (Sweden)
Julius Wess
2006-12-01
Full Text Available A differential calculus, differential geometry and the E-R Gravity theory are studied on noncommutative spaces. Noncommutativity is formulated in the star product formalism. The basis for the gravity theory is the infinitesimal algebra of diffeomorphisms. Considering the corresponding Hopf algebra we find that the deformed gravity is based on a deformation of the Hopf algebra.
Stability of the Einstein static universe in modified theories of gravity
Boehmer, Christian G.; Hollenstein, Lukas; Lobo, Francisco S. N.; Seahra, Sanjeev S.
2010-01-01
We present a brief overview of the stability analysis of the Einstein static universe in various modified theories of gravity, like f(R) gravity, Gauss-Bonnet or f(G) gravity, and Horava-Lifshitz gravity.
Stability of the Einstein static universe in modified theories of gravity
Boehmer, Christian G.; Hollenstein, Lukas; Lobo, Francisco S. N.; Seahra, Sanjeev S.
2010-01-01
We present a brief overview of the stability analysis of the Einstein static universe in various modified theories of gravity, like f(R) gravity, Gauss-Bonnet or f(G) gravity, and Horava-Lifshitz gravity.
Equivalence of Jordan and Einstein frames at the quantum level
Pandey, Sachin; Banerjee, Narayan
2017-03-01
It is shown that the Jordan frame and its conformally transformed version, the Einstein frame of nonminimally coupled theories of gravity, are actually equivalent at the quantum level. The example of the theory taken up is the Brans-Dicke theory, and the wave packet calculations are done for a homogeneous and isotropic cosmological model in the purest form of the theory, i.e., in the absence of any additional matter sector. The calculations are clean and exact, and the result obtained are unambiguous.
Equivalence of Jordan and Einstein frames at the quantum level
Pandey, Sachin
2016-01-01
It is shown that the Jordan frame and its conformally transformed version, the Einstein frame of nonminimally coupled theories of gravity, are actually equivalent at the quantum level. The example of the theory taken up is the Brans-Dicke theory, and the wave packet calculations are done for a homogeneous and isotropic cosmological model in the purest form of the theory, i.e., in the absence of any additional matter sector. The calculations are clean and exact, and the result obtained are unambiguous.
Lorentz breaking terms from Einstein gravity
Hirayama, Takayuki
2016-01-01
We construct an action which is invariant under the foliation preserving diffeomorphism from the Einstein Hilbert action. Starting from the Einstein Hilbert action, we introduce the gauge invariance under the anisotropic rescaling by using the St\\"uckelberg method. We then introduce the gauge field corresponds to the anisotropic rescaling, and the St\\"uckelberg field turns out to be the Nambu-Goldstone boson. The Nambu-Goldstone boson, however, is not completely eaten by the massive gauge field and the Nambu-Goldstone boson can be integrated out from the action. Then the resultant action is a Horava-Lifshitz type action which contains $R^3$ term.
An introduction to quantum gravity
Esposito, Giampiero
2011-01-01
Quantum gravity was born as that branch of modern theoretical physics that tries to unify its guiding principles, i.e., quantum mechanics and general relativity. Nowadays it is providing new insight into the unification of all fundamental interactions, while giving rise to new developments in mathematics. The various competing theories, e.g. string theory and loop quantum gravity, have still to be checked against observations. We review the classical and quantum foundations necessary to study field-theory approaches to quantum gravity, the passage from old to new unification in quantum field theory, canonical quantum gravity, the use of functional integrals, the properties of gravitational instantons, the use of spectral zeta-functions in the quantum theory of the universe, Hawking radiation, some theoretical achievements and some key experimental issues.
Testing quantum gravity through dumb holes
Pourhassan, Behnam; Faizal, Mir; Capozziello, Salvatore
2017-02-01
We propose a method to test the effects of quantum fluctuations on black holes by analyzing the effects of thermal fluctuations on dumb holes, the analogs for black holes. The proposal is based on the Jacobson formalism, where the Einstein field equations are viewed as thermodynamical relations, and so the quantum fluctuations are generated from the thermal fluctuations. It is well known that all approaches to quantum gravity generate logarithmic corrections to the entropy of a black hole and the coefficient of this term varies according to the different approaches to the quantum gravity. It is possible to demonstrate that such logarithmic terms are also generated from thermal fluctuations in dumb holes. In this paper, we claim that it is possible to experimentally test such corrections for dumb holes, and also obtain the correct coefficient for them. This fact can then be used to predict the effects of quantum fluctuations on realistic black holes, and so it can also be used, in principle, to experimentally test the different approaches to quantum gravity.
Testing quantum gravity through dumb holes
Energy Technology Data Exchange (ETDEWEB)
Pourhassan, Behnam, E-mail: b.pourhassan@du.ac.ir [School of Physics, Damghan University, Damghan (Iran, Islamic Republic of); Faizal, Mir, E-mail: f2mir@uwaterloo.ca [Department of Physics and Astronomy, University of Lethbridge, Lethbridge, AB T1K 3M4 (Canada); Irving K. Barber School of Arts and Sciences, University of British Columbia - Okanagan, Kelowna, BC V1V 1V7 (Canada); Capozziello, Salvatore, E-mail: capozzie@na.infn.it [Dipartimento di Fisica, Università di Napoli ”Frederico II” Complesso Universitario di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli (Italy); Gran Sasso Science Institute (INFN), Via F. Crispi 7, I-67100 L’ Aquila (Italy)
2017-02-15
We propose a method to test the effects of quantum fluctuations on black holes by analyzing the effects of thermal fluctuations on dumb holes, the analogs for black holes. The proposal is based on the Jacobson formalism, where the Einstein field equations are viewed as thermodynamical relations, and so the quantum fluctuations are generated from the thermal fluctuations. It is well known that all approaches to quantum gravity generate logarithmic corrections to the entropy of a black hole and the coefficient of this term varies according to the different approaches to the quantum gravity. It is possible to demonstrate that such logarithmic terms are also generated from thermal fluctuations in dumb holes. In this paper, we claim that it is possible to experimentally test such corrections for dumb holes, and also obtain the correct coefficient for them. This fact can then be used to predict the effects of quantum fluctuations on realistic black holes, and so it can also be used, in principle, to experimentally test the different approaches to quantum gravity.
Was Einstein Wrong on Quantum Physics?
Bhaumik, Mani
2015-01-01
Einstein is considered by many as the father of quantum physics in some sense. Yet there is an unshakable view that he was wrong on quantum physics. Although it may be a subject of considerable debate, the core of his allegedly wrong demurral was the insistence on finding an objective reality underlying the manifestly bizarre behavior of quantum objects. The uncanny wave-particle duality of a quantum particle is a prime example. In view of the latest developments, particularly in quantum field theory, objections of Einstein are substantially corroborated. Careful investigation suggests that a travelling quantum particle is a holistic wave packet consisting of an assemblage of irregular disturbances in quantum fields. It acts as a particle because only the totality of all the disturbances in the wave packet yields the energy momentum with the mass of a particle, along with its other conserved quantities such as charge and spin. Thus the wave function representing a particle is not just a fictitious mathematica...
Einstein Static Universe in Exponential $f(T)$ Gravity
Li, Jung-Tsung; Geng, Chao-Qiang
2013-01-01
We analyze the stability of the Einstein static closed and open universe in two types of exponential $f(T)$ gravity theories. We show that the stable solutions exist in these two models. In particular, we find that large regions of parameter space in equation of state $w=p/\\rho$ for the stable universe are allowed in the $f(T)$ theories.
Einstein static universe in exponential f(T) gravity
Energy Technology Data Exchange (ETDEWEB)
Li, Jung-Tsung; Lee, Chung-Chi; Geng, Chao-Qiang [National Tsing Hua University, Department of Physics, Hsinchu (China); National Center for Theoretical Sciences, Physics Division, Hsinchu (China)
2013-02-15
We analyze the stability of the Einstein static closed and open universe in two types of exponential f(T) gravity theory. We show that stable solutions exist in these two models. In particular, we find that large regions of parameter space in equation of state w=p/{rho} for the stable universe are allowed in the f(T) theories. (orig.)
Gauge dependence of the effective action in Einstein gravity
Energy Technology Data Exchange (ETDEWEB)
Lavrov, P.M.; Reshetnyak, A.A. [Tomsk State Pedagogical Institute (Russian Federation)
1995-10-01
Einstein gravity is considered in a special one-parameter background gauge. The one-loop effective action of the theory is calculated to the first order in the gauge parameter. It is shown that, on the mass shell, the effective action is independent of the gauge parameter. 57 refs.
Mannelli, L
2005-01-01
The main theme of this Thesis is the connection between Quantum Gravity and Cosmology. In the First Part (Chapters 1 to 5) I give an introduction to the Holographic Principle. The Second Part is a collection of my research work and it is articulated as follows. Chapter 7 is to an analysis of the renormalization properties of quantum field theories in de Sitter space. It is shown that only two of the maximally invariant vacuum states of free fields lead to consistent perturbation expansions. In Chapter 8 I first present a complete quantum mechanical description of a flat FRW universe with equation of state p = ρ. Then I show a detailed correspondence with an heuristic picture of such a universe as a dense black hole fluid. In the end it is explained how features of the geometry are derived from purely quantum input. Chapter 9 studies the problem of infrared renormalization of particle masses in de Sitter space. It is shown, in a toy model in which the graviton is replaced with a minimally coupled massl...
Observable Effects of Quantum Gravity
Chang, Lay Nam; Sun, Chen; Takeuchi, Tatsu
2016-01-01
We discuss the generic phenomenology of quantum gravity and, in particular, argue that the observable effects of quantum gravity, associated with new, extended, non-local, non-particle-like quanta, and accompanied by a dynamical energy-momentum space, are not necessarily Planckian and that they could be observed at much lower and experimentally accessible energy scales.
Quantum backreaction of quantum fluid in Bose-Einstein condensates
Institute of Scientific and Technical Information of China (English)
Xu Yan; Xiong Zu-Zhou; Chen Bing; Li Zhao-Xin; Tan Lei
2009-01-01
In this paper, with the full field operator φ expressed in terms of a particle-number-conserving mean-field ansatz, we investigate the dynamical behaviour of Bose-Einstein eondensates from microscopic physics. Including the firstorder term correction from single-particle excitation and the remaining higher-order term correction from collective excitations simultaneously, we obtain the formulation for a closed local expression of quantum backreaetion Q, and discuss the influence on static Bose-Einstein condensates. Even though the quantum backreaction is small, it still has some influence on its dynamics.
Exact solutions of three dimensional black holes: Einstein gravity vs F(R) gravity
Hendi, S H; Saffari, R
2014-01-01
In this paper, we consider Einstein gravity in the presence of a class of nonlinear electrodynamics, called power Maxwell invariant (PMI). We take into account $(2+1)$-dimensional spacetime in Einstein-PMI gravity and obtain its black hole solutions. Then, we regard pure $F(R)$ gravity as well as $F(R)$-conformally invariant Maxwell theory to obtain exact solutions of the field equations with black hole interpretation. Finally, we investigate the conserved and thermodynamic quantities and discuss about the first law of thermodynamics for the mentioned gravitational models.
Island of Stability for Consistent Deformations of Einstein's Gravity
Berkhahn, Felix; Hofmann, Stefan; Kühnel, Florian; Moyassari, Parvin
2011-01-01
We construct explicitly deformations of Einstein's theory of gravity that are consistent and phenomenologically viable since they respect, in particular, cosmological backgrounds. We show that these deformations have unique symmetries in accordance with unitarity requirements, and give rise to a curvature induced self-stabilizing mechanism. As a consequence, any nonlinear completed deformation must incorporate self-stabilization on generic spacetimes already at lowest order in perturbation theory. Furthermore, our findings include the possibility of consistent and phenomenologically viable deformations of general relativity that are solely operative on curved spacetime geometries, reducing to Einstein's theory on the Minkowski background.
Multidimensional Gravity with Einstein Internal Spaces
Ivashchuk, V D
1996-01-01
A multidimensional gravitational model on the manifold $M = M_0 \\times For $N_0 = dim M_0 > 2$ the $\\sigma$ model representation is considered and it is shown that the corresponding Euclidean Toda-like system does not satisfy the Adler-van-Moerbeke criterion. For $M_0 = R^{N_0}$, $N_0 = 3, 4, 6$ (and the total dimension $D = dim M = 11, 10, 11$, respectively) nonsingular spherically symmetric solutions to vacuum Einstein equations are obtained and their generalizations to arbitrary signatures are considered. It is proved that for a non-Euclidean signature the Riemann tensor squared of the solutions diverges on certain hypersurfaces in $R^{N_0}$.
Holographic bound in covariant loop quantum gravity
Tamaki, Takashi
2016-01-01
We investigate puncture statistics based on the covariant area spectrum in loop quantum gravity. First, we consider Maxwell-Boltzmann statistics with a Gibbs factor for punctures. We establish formulae which relate physical quantities such as horizon area to the parameter characterizing holographic degrees of freedom. We also perform numerical calculations and obtain consistency with these formulae. These results tell us that the holographic bound is satisfied in the large area limit and correction term of the entropy-area law can be proportional to the logarithm of the horizon area. Second, we also consider Bose-Einstein statistics and show that the above formulae are also useful in this case. By applying the formulae, we can understand intrinsic features of Bose-Einstein condensate which corresponds to the case when the horizon area almost consists of punctures in the ground state. When this phenomena occurs, the area is approximately constant against the parameter characterizing the temperature. When this ...
Discussion of the Entanglement Entropy in Quantum Gravity
Ma, Chen-Te
2016-01-01
Quantum gravity needs to be satisfied by the holographic principle, and the entanglement entropy already has holographic evidences via anti-de Sitter/ Conformal field theory correspondence. Thus, we explore principles of quantum gravity via the entanglement entropy. We compute the entanglement entropy in two dimensional Einstein-Hilbert action to understand quantum geometry and area law. Then we also discuss two dimensional conformal field theory because we expect strongly coupled conformal field theory can describe perturbative quantum gravity theory. We find universal terms of the entanglement entropy is independent of a choice of an entangling surface in two dimensional conformal field theory for one interval and some cases of multiple intervals. To extend our discussion to generic multiple intervals, we use a geometric method to determine the entanglement entropy. Finally, we argue translational invariance possibly be a necessary condition in quantum gravity theory from ruing out volume law of the entangl...
The curious history of relativity how Einstein's theory of gravity was lost and found again
Eisenstaedt, Jean
2006-01-01
Black holes may obliterate most things that come near them, but they saved the theory of general relativity. Einstein's theory was quickly accepted as the true theory of gravity after its publication in 1915, but soon took a back seat in physics to quantum mechanics and languished for decades on the blackboards of mathematicians. Not until the existence of black holes by Stephen Hawking and Roger Penrose in the 1960s, after Einstein's death, was the theory revived. Almost one hundred years after general relativity replaced Newton's theory of gravitation, The Curious History of Relativity tells the story of both events surrounding general relativity and the techniques employed by Einstein and the relativists to construct, develop, and understand his almost impenetrable theory. Jean Eisenstaedt, one of the world's leading experts on the subject, also discusses the theory's place in the evolution of twentieth-century physics. He describes the main stages in the development of general relativity: its beginnings,...
Kay, Bernard S
2015-01-01
We give an account of the matter-gravity entanglement hypothesis which, unlike the standard approach to entropy based on coarse-graining, offers a definition for the entropy of a closed system as a real and objective quantity. We explain how this new approach offers an explanation for the Second Law of Thermodynamics in general and a non-paradoxical understanding of information loss during black hole formation and evaporation in particular. We also very briefly review some recent related work on the nature of equilibrium states involving quantum black holes and point out how it promises to resolve some puzzling issues in the current version of the string theory approach to black hole entropy.
CPT and Decoherence in Quantum Gravity
Mavromatos, N E
2007-01-01
In this review, I first discuss briefly some theoretical motivations for potential Lorentz Violation and deviation from ordinary quantum mechanical behavior (decoherence) of field theoretic systems in the background of some quantum gravity (QG) models. Both types of effects lead to CPT violation, but they can be disentangled experimentally. I, then, proceed to a description of precision tests of CPT symmetry using neutral and charged Kaons, which are of direct relevance to the main theme of this conference. I emphasize the potentially unique r\\^ole of neutral meson factories in providing ``smoking-gun'' evidence of some QG-decoherence models in which the CPT quantum mechanical operator is not well defined. This is achieved by means of potential observations of QG-induced modifications of the pertinent Einstein-Podolsky-Rosen (EPR) particle correlations.
Choptuik's Critical Phenomenon in Einstein-Gauss-Bonnet Gravity
Golod, Sveta
2012-01-01
We investigate the effects of higher order curvature corrections to Einstein's Gravity on the critical phenomenon near the black hole threshold, namely the Choptuik phenomenon. We simulate numerically a five dimensional spherically symmetric gravitational collapse of massless scalar field in Einstein-Gauss-Bonnet gravity towards a black hole formation threshold. When the curvature is sufficiently large the additional higher order terms, affect the evolution of the whole system. Since high curvature characterizes the region when the critical behavior takes place this critical behavior is destroyed. Both the self similarity and the mass scaling relation disappear. Instead we find a different behavior near the black hole threshold, which depends on the coupling constant of the higher order terms. The new features include a change of the sign of the Ricci scalar on the origin which indicates changes in the local geometry of space-time, and never occurs in classical general relativity collapse, and oscillations wi...
On first attempts to reconcile quantum principles with gravity
Rocci, Alessio
2013-01-01
In his 1916's first paper on gravitational waves Einstein began to speculate on interactions between the principles of the old quantum theory and his theory of gravitation. With this contribution Einstein has stimulated a lot of similar speculations, during the dawn and the development of Quantum Mechanics. These speculations have culminated with the first attempt to quantize the gravitational field, that was provided by Rosenfeld in 1930. In this paper we briefly explain why this period (1916-1930) should be inserted into the history of Quantum Gravity and then we focus on Klein's approach to the problem of reconciling Wave Mechanics with gravity, during the two-years period 1926-1927. His attempt should be looked as the prehistory of Quantum Field Theory in a curved background.
Einstein Gravity, Lagrange-Finsler Geometry, and Nonsymmetric Metrics
Directory of Open Access Journals (Sweden)
Sergiu I. Vacaru
2008-10-01
Full Text Available We formulate an approach to the geometry of Riemann-Cartan spaces provided with nonholonomic distributions defined by generic off-diagonal and nonsymmetric metrics inducing effective nonlinear and affine connections. Such geometries can be modelled by moving nonholonomic frames on (pseudo Riemannian manifolds and describe various types of nonholonomic Einstein, Eisenhart-Moffat and Finsler-Lagrange spaces with connections compatible to a general nonsymmetric metric structure. Elaborating a metrization procedure for arbitrary distinguished connections, we define the class of distinguished linear connections which are compatible with the nonlinear connection and general nonsymmetric metric structures. The nonsymmetric gravity theory is formulated in terms of metric compatible connections. Finally, there are constructed such nonholonomic deformations of geometric structures when the Einstein and/or Lagrange-Finsler manifolds are transformed equivalently into spaces with generic local anisotropy induced by nonsymmetric metrics and generalized connections. We speculate on possible applications of such geometric methods in Einstein and generalized theories of gravity, analogous gravity and geometric mechanics.
Quantum Gravity in Two Dimensions
DEFF Research Database (Denmark)
Ipsen, Asger Cronberg
The topic of this thesis is quantum gravity in 1 + 1 dimensions. We will focus on two formalisms, namely Causal Dynamical Triangulations (CDT) and Dy- namical Triangulations (DT). Both theories regularize the gravity path integral as a sum over triangulations. The difference lies in the class...
Quantum Gravity in Two Dimensions
DEFF Research Database (Denmark)
Ipsen, Asger Cronberg
The topic of this thesis is quantum gravity in 1 + 1 dimensions. We will focus on two formalisms, namely Causal Dynamical Triangulations (CDT) and Dy- namical Triangulations (DT). Both theories regularize the gravity path integral as a sum over triangulations. The difference lies in the class...
Black hole merger estimates in Einstein-Maxwell and Einstein-Maxwell-dilaton gravity
Jai-akson, Puttarak; Chatrabhuti, Auttakit; Evnin, Oleg; Lehner, Luis
2017-01-01
The recent birth of gravitational wave astronomy invites a new generation of precision tests of general relativity. Signatures of black hole (BH) mergers must be systematically explored in a wide spectrum of modified gravity theories. Here, we turn to one such theory in which the initial value problem for BH mergers is well posed, the Einstein-Maxwell-dilaton system. We present conservative estimates for the merger parameters (final spins, quasinormal modes) based on techniques that have work...
Testing Brans-Dicke gravity using the Einstein telescope
Zhang, Xing; Yu, Jiming; Liu, Tan; Zhao, Wen; Wang, Anzhong
2017-06-01
Gravitational radiation is an excellent field for testing theories of gravity in strong gravitational fields. The current observations on the gravitational-wave (GW) bursts by LIGO have already placed various constraints on the alternative theories of gravity. In this paper, we investigate the possible bounds which could be placed on the Brans-Dicke gravity using GW detection from inspiraling compact binaries with the proposed Einstein Telescope, a third-generation GW detector. We first calculate in detail the waveforms of gravitational radiation in the lowest post-Newtonian approximation, including the tensor and scalar fields, which can be divided into the three polarization modes, i.e., "plus mode," "cross mode," and "breathing mode." Applying the stationary phase approximation, we obtain their Fourier transforms, and derive the correction terms in amplitude, phase, and polarization of GWs, relative to the corresponding results in general relativity. Imposing the noise level of the Einstein Telescope, we find that the GW detection from inspiraling compact binaries, composed of a neutron star and a black hole, can place stringent constraints on the Brans-Dicke gravity. The bound on the coupling constant ωBD depends on the mass, sky position, inclination angle, polarization angle, luminosity distance, redshift distribution, and total observed number NGW of the binary systems. Taking into account all the burst events up to redshift z =5 , we find that the bound could be ωBD≳1 06×(NGW/1 04)1/2. Even for the conservative estimation with 1 04 observed events, the bound is still more than one order tighter than the current limit from Solar System experiments. So, we conclude that the Einstein Telescope will provide a powerful platform to test alternative theories of gravity.
Semiclassical states in loop quantum gravity: an introduction
Institute of Scientific and Technical Information of China (English)
MA Yong-ge
2006-01-01
Unifying general relativity and quantum mechanics is a great challenge left to us by Einstein.To face this challenge,considerable progress has been made in non-perturbative canonical (loop) quantum gravity during the past 20 years.The kinematical Hilbert space of the quantum theory is constructed rigorously.However,the semiclassical analysis of the theory is still a crucial and open issue.In this review,we first introduce our work on constructing a semiclassical weave state,using the (Q)[ω]operator on the kinematical Hilbert space of loop quantum gravity.Then we give an introduction to the two different approaches currently investigated for constructing coherent states in the kinematical Hilbert space.The current status of semiclassical analysis in loop quantum gravity is then summarized.
Cosmological implications of modified gravity induced by quantum metric fluctuations
Liu, Xing; Liang, Shi-Dong
2016-01-01
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a nonminimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For...
Remarks on Cosmic Strings and Quantum Gravity
Anandan, Jeeva S
1999-01-01
A quantum equivalence principle is formulated by means of a gravitational phase operator which is an element of the Poincare group. This is applied to the spinning cosmic string which suggests that it may, but not necessarily, contain gravitational torsion. A new exact solution of the Einstein- Cartan-Sciama-Kibble equations for the gravitational field with torsion is obtained everywhere for a cosmic string with uniform energy density, spin density and flux. The quantization condition for fluxoid due to London and DeWitt is generalized to include the spin flux. A novel effect due to the quantized gravitational field of the cosmic string on the wave function of a particle outside the string is used to show that spacetime points are not meaningful in quantum gravity.
CPT Violation and Decoherence in Quantum Gravity
Mavromatos, Nick E
2009-01-01
In this brief review I discuss ways and tests of CPT-Violation in the context of quantum gravity theories with space-time foam vacua, which entail quantum decoherence of matter propagating in such backgrounds. I cover a wide variety of sensitive probes, ranging from cosmic neutrinos to meson factories. I pay particular emphasis on associating the latter with specific, probably unique ("smoking-gun"), effects of this type of CPT Violation, related to a modification of Einstein-Podolsky-Rosen (EPR) correlations in the entangled states of the relevant neutral mesons. I also present some semi-microscopic estimates of these latter effects, in the context of a specific string-inspired model of space-time foam ("D-particle foam").
Information Processing Structure of Quantum Gravity
Gyongyosi, Laszlo; Imre, Sandor
2014-05-01
The theory of quantum gravity is aimed to fuse general relativity with quantum theory into a more fundamental framework. Quantum gravity provides both the non-fixed causality of general relativity and the quantum uncertainty of quantum mechanics. In a quantum gravity scenario, the causal structure is indefinite and the processes are causally non-separable. We provide a model for the information processing structure of quantum gravity. We show that the quantum gravity environment is an information resource-pool from which valuable information can be extracted. We analyze the structure of the quantum gravity space and the entanglement of the space-time geometry. We study the information transfer capabilities of quantum gravity space and define the quantum gravity channel. We characterize the information transfer of the gravity space and the correlation measure functions of the gravity channel. We investigate the process of stimulated storage for quantum gravity memories, a phenomenon that exploits the information resource-pool property of quantum gravity. The results confirm that the benefits of the quantum gravity space can be exploited in quantum computations, particularly in the development of quantum computers. The results are supported by the grant COST Action MP1006.
QUANTUM GRAVITY AND REALITY SHOW
Directory of Open Access Journals (Sweden)
Trunev A. P.
2014-02-01
Full Text Available In this article, we consider quantum gravity in multidimensional space. The model of the metric satisfying the basic requirements of quantum theory is proposed. It is shown that gravitational waves are described by the Liouville equation, and matter waves associated with gravitational waves by a simple equation. The mechanism of generation of baryonic matter of dark energy is discussed
Two-Connection Renormalization and Nonholonomic Gauge Models of Einstein Gravity
Vacaru, Sergiu I
2009-01-01
A new framework to perturbative quantum gravity is proposed following the geometry of nonholonomic distributions on (pseudo) Riemannian manifolds. There are considered such distributions and adapted connections, also completely defined by a metric structure, when gravitational models with infinite many couplings reduce to two-loop renormalizable effective actions. We use a key result from our partner work arXiv: 0902.0911 that the classical Einstein gravity theory can be reformulated equivalently as a nonholonomic gauge model in the bundle of affine/ de Sitter frames on pseudo-Riemannian spacetime. It is proven that (for a class of nonholonomic constraints and splitting of the Levi-Civita connection into a "renormalizable" distinguished connection, on a base background manifold, and a gauge like distorsion tensor, in total space) a nonholonomic differential renormalization procedure for quantum gravitational fields can be elaborated. Calculation labor is reduced to one- and two-loop levels and renormalization...
Discrete Approaches to Quantum Gravity in Four Dimensions
Directory of Open Access Journals (Sweden)
Loll Renate
1998-01-01
Full Text Available The construction of a consistent theory of quantum gravity is a problem in theoretical physics that has so far defied all attempts at resolution. One ansatz to try to obtain a non-trivial quantum theory proceeds via a discretization of space-time and the Einstein action. I review here three major areas of research: gauge-theoretic approaches, both in a path-integral and a Hamiltonian formulation; quantum Regge calculus; and the method of dynamical triangulations, confining attention to work that is strictly four-dimensional, strictly discrete, and strictly quantum in nature.
Kinetic Quantum Theory of Gravity
DeAquino, F
2002-01-01
Starting from the action function we have derived a theoretical background that leads to quantization of gravity and the deduction of a correlation between the gravitational and inertial masses, which depends on the kinetic momentum of the particle. We show that there is a reaffirmation of the strong equivalence principle and consequently the Einstein's equations are preserved. In fact such equations are deduced here directly from this kinetic approach to Gravity. Moreover, we have obtained a generalized equation for inertial forces, which incorporates the Mach's principle into Gravitation. Also, we have deduced the equation of Entropy; the Hamiltonian for a particle in an electromagnetic field and the reciprocal fine structure constant. It is possible to deduce the expression of the Casimir force and also to explain the Inflation Period and the Missing Matter without assuming the existence of vacuum fluctuations. This new approach for Gravity will allow us to understand some crucial matters in Cosmology.
Kinetic Quantum Theory of Gravity
DeAquino, F
2002-01-01
Gravity is here quantized starting from the generalization of the action function. This leads to an equation of correlation between gravitational and inertial masses, which depends on the particle's kinetic energy. We show that there is a reaffirmation of the strong equivalence principle and consequently the Einstein's equations are preserved. In fact such equations are deduced here directly from this kinetic approach to Gravity. Moreover, we have obtained a generalized equation for inertial forces, which incorporates the Mach's principle into Gravitation. Also, we have deduced the equation of Entropy; the Hamiltonian for a particle in an electromagnetic field and the reciprocal fine structure constant. It is possible to deduce the expression of the Casimir force and also to explain the Inflation Period and the Missing Matter without assuming the existence of vacuum fluctuations. This new approach for Gravity will allow us to understand some crucial matters in Cosmology.
Black hole merger estimates in Einstein-Maxwell and Einstein-Maxwell-dilaton gravity
Jai-akson, Puttarak; Chatrabhuti, Auttakit; Evnin, Oleg; Lehner, Luis
2017-08-01
The recent birth of gravitational wave astronomy invites a new generation of precision tests of general relativity. Signatures of black hole (BH) mergers must be systematically explored in a wide spectrum of modified gravity theories. Here, we turn to one such theory in which the initial value problem for BH mergers is well posed, the Einstein-Maxwell-dilaton system. We present conservative estimates for the merger parameters (final spins, quasinormal modes) based on techniques that have worked well for ordinary gravity mergers and utilize information extracted from test particle motion in the final BH metric. The computation is developed in parallel for the modified gravity BHs (we specifically focus on the Kaluza-Klein value of the dilaton coupling, for which analytic BH solutions are known) and ordinary Kerr-Newman BHs. We comment on the possibility of obtaining final BHs with spins consistent with current observations.
Quantum Correlations Among Superradiant Bose–Einstein Condensate Atoms
Taşgın, Mehmet Emre; Öztop, B.; Oktel, M. Ö.; Müstecaplıoğlu, Özgür Esat
2009-01-01
Quantum correlations among atoms in superradiant Bose–Einstein condensates are discussed. It is shown that atoms in the superradiant atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein–Podolsky–Rosen (EPR)type quantum correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided.
Polyhedra in loop quantum gravity
Bianchi, Eugenio; Speziale, Simone
2010-01-01
Interwiners are the building blocks of spin-network states. The space of intertwiners is the quantization of a classical symplectic manifold introduced by Kapovich and Millson. Here we show that a theorem by Minkowski allows us to interpret generic configurations in this space as bounded convex polyhedra in Euclidean space: a polyhedron is uniquely described by the areas and normals to its faces. We provide a reconstruction of the geometry of the polyhedron: we give formulas for the edge lengths, the volume and the adjacency of its faces. At the quantum level, this correspondence allows us to identify an intertwiner with the state of a quantum polyhedron, thus generalizing the notion of quantum tetrahedron familiar in the loop quantum gravity literature. Moreover, coherent intertwiners result to be peaked on the classical geometry of a polyhedron. We discuss the relevance of this result for loop quantum gravity. In particular, coherent spin-network states with nodes of arbitrary valence represent a collection...
Quantum Gravity Effects in Scalar, Vector and Tensor Field Propagation
Dutta, Anindita
Quantum theory of gravity deals with the physics of the gravitational field at Planck length scale (10-35 m). Even though it is experimentally hard to reach the Planck length scale, on can look for evidence of quantum gravity that is detectable in astrophysics. In this thesis, we try to find effects of loop quantum gravity corrections on observable phenomena. We show that the quantum fluctuation strain for LIGO data would be 10 -125 on the Earth. Th correction is, however, substantial near the black hole horizon. We discuss the effect of this for scalar field propagation followed by vector and tensor fields. For the scalar field, the correction introduces a new asymmetry; for the vector field, we found a new perturbation solution and for the tensor field, we found the corrected Einstein equations which are yet to solve. These will affect phenomena like Hawking radiation, black hole entropy and gravitational waves.
Gravity induced from quantum spacetime
Beggs, Edwin J.; Majid, Shahn
2014-02-01
We show that tensoriality constraints in noncommutative Riemannian geometry in the two-dimensional bicrossproduct model quantum spacetime algebra [x, t] = λx drastically reduce the moduli of possible metrics g up to normalization to a single real parameter, which we interpret as a time in the past from which all timelike geodesics emerge and a corresponding time in the future at which they all converge. Our analysis also implies a reduction of moduli in n-dimensions and we study a suggested spherically symmetric classical geometry in n = 4 in detail, identifying two one-parameter subcases where the Einstein tensor matches that of a perfect fluid for (a) positive pressure, zero density and (b) negative pressure and positive density with ratio w_Q=-{1\\over 2}. The classical geometry is conformally flat and its geodesics motivate new coordinates which we extend to the quantum case as a new description of the quantum spacetime model as a quadratic algebra. The noncommutative Riemannian geometry is fully solved for n = 2 and includes the quantum Levi-Civita connection and a second, nonperturbative, Levi-Civita connection which blows up as λ → 0. We also propose a ‘quantum Einstein tensor’ which is identically zero for the main part of the moduli space of connections (as classically in 2D). However, when the quantum Ricci tensor and metric are viewed as deformations of their classical counterparts there would be an O(λ2) correction to the classical Einstein tensor and an O(λ) correction to the classical metric.
String Versus Einstein Frame in AdS/CFT Induced Quantum Dilatonic Brane-World Universe
Nojiri, S; Odintsov, S D; Tkach, V I; Nojiri, Shin'ichi; Obregon, Octavio; Odintsov, Sergei D.; Tkach, Vladimir I.
2001-01-01
AdS/CFT induced quantum dilatonic brane-world where 4d boundary is flat or de Sitter (inflationary) or Anti-de Sitter brane is considered. The classical brane tension is fixed but boundary QFT produces the effective brane tension via the account of corresponding conformal anomaly induced effective action. This results in inducing of brane-worlds in accordance with AdS/CFT set-up as warped compactification. The explicit, independent construction of quantum induced dilatonic brane-worlds in two frames: string and Einstein one is done. It is demonstrated their complete equivalency for all quantum cosmological brane-worlds under discussion, including several examples of classical brane-world black holes. This is different from quantum corrected 4d dilatonic gravity where de Sitter solution exists in Einstein but not in Jordan (string) frame. The role of quantum corrections on massive graviton perturbations around Anti-de Sitter brane is briefly discussed.
Quantum Gravity on the Lattice
Hamber, Herbert W
2009-01-01
I review the lattice approach to quantum gravity, and how it relates to the non-trivial ultraviolet fixed point scenario of the continuum theory. After a brief introduction covering the general problem of ultraviolet divergences in gravity and other non-renormalizable theories, I cover the general methods and goals of the lattice approach. An underlying theme is an attempt at establishing connections between the continuum renormalization group results, which are mainly based on diagrammatic perturbation theory, and the recent lattice results, which should apply to the strong gravity regime and are inherently non-perturbative. A second theme in this review is the ever-present natural correspondence between infrared methods of strongly coupled non-abelian gauge theories on the one hand, and the low energy approach to quantum gravity based on the renormalization group and universality of critical behavior on the other. Towards the end of the review I discuss possible observational consequences of path integral q...
Divergences in spinfoam quantum gravity
Smerlak, Matteo
2012-01-01
In this thesis we study the flat model, the main buidling block for the spinfoam approach to quantum gravity, with an emphasis on its divergences. Besides a personal introduction to the problem of quantum gravity, the manuscript consists in two part. In the first one, we establish an exact powercounting formula for the bubble divergences of the flat model, using tools from discrete gauge theory and twisted cohomology. In the second one, we address the issue of spinfoam continuum limit, both from the lattice field theory and the group field theory perspectives. In particular, we put forward a new proof of the Borel summability of the Boulatov-Freidel-Louapre model, with an improved control over the large-spin scaling behaviour. We conclude with an outlook of the renormalization program in spinfoam quantum gravity.
A Dynamics for Discrete Quantum Gravity
Gudder, Stan
2013-01-01
This paper is based on the causal set approach to discrete quantum gravity. We first describe a classical sequential growth process (CSGP) in which the universe grows one element at a time in discrete steps. At each step the process has the form of a causal set (causet) and the "completed" universe is given by a path through a discretely growing chain of causets. We then quantize the CSGP by forming a Hilbert space $H$ on the set of paths. The quantum dynamics is governed by a sequence of positive operators $\\rho_n$ on $H$ that satisfy normalization and consistency conditions. The pair $(H,\\brac{\\rho_n})$ is called a quantum sequential growth process (QSGP). We next discuss a concrete realization of a QSGP in terms of a natural quantum action. This gives an amplitude process related to the sum over histories" approach to quantum mechanics. Finally, we briefly discuss a discrete form of Einstein's field equation and speculate how this may be employed to compare the present framework with classical general rela...
Smooth quantum gravity: Exotic smoothness and Quantum gravity
Asselmeyer-Maluga, Torsten
2016-01-01
Over the last two decades, many unexpected relations between exotic smoothness, e.g. exotic $\\mathbb{R}^{4}$, and quantum field theory were found. Some of these relations are rooted in a relation to superstring theory and quantum gravity. Therefore one would expect that exotic smoothness is directly related to the quantization of general relativity. In this article we will support this conjecture and develop a new approach to quantum gravity called \\emph{smooth quantum gravity} by using smooth 4-manifolds with an exotic smoothness structure. In particular we discuss the appearance of a wildly embedded 3-manifold which we identify with a quantum state. Furthermore, we analyze this quantum state by using foliation theory and relate it to an element in an operator algebra. Then we describe a set of geometric, non-commutative operators, the skein algebra, which can be used to determine the geometry of a 3-manifold. This operator algebra can be understood as a deformation quantization of the classical Poisson alge...
Einstein gravity 3-point functions from conformal field theory
Afkhami-Jeddi, Nima; Kundu, Sandipan; Tajdini, Amirhossein
2016-01-01
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 $\\langle TTT\\rangle$, 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...
Impact of nonlinear effective interactions on GFT quantum gravity condensates
Pithis, Andreas G A; Tomov, Petar
2016-01-01
We present the numerical analysis of effectively interacting Group Field Theory (GFT) models in the context of the GFT quantum gravity condensate analogue of the Gross-Pitaevskii equation for real Bose-Einstein condensates including combinatorially local interaction terms. Thus we go beyond the usually considered construction for free models. More precisely, considering such interactions in a weak regime, we find solutions for which the expectation value of the number operator N is finite, as in the free case. When tuning the interaction to the strongly nonlinear regime, however, we obtain solutions for which N grows and eventually blows up, which is reminiscent of what one observes for real Bose-Einstein condensates, where a strong interaction regime can only be realized at high density. This behaviour suggests the breakdown of the Bogoliubov ansatz for quantum gravity condensates and the need for non-Fock representations to describe the system when the condensate constituents are strongly correlated. Furthe...
Nonlocal quantum gravity and the size of the universe
Energy Technology Data Exchange (ETDEWEB)
Reuter, M. [Institute of Physics, University of Mainz, Staudingerweg 7, 55099 Mainz (Germany); Saueressig, F. [Institute of Theoretical Physics, University of Jena, Max-Wien-Platz 1, 07743 Jena (Germany)
2004-06-01
Motivated by the conjecture that the cosmological constant problem is solved by strong quantum effects in the infrared we use the exact flow equation of Quantum Einstein Gravity to determine the renormalization group behavior of a class of nonlocal effective actions. They consist of the Einstein-Hilbert term and a general nonlinear function F{sub k}(V) of the Euclidean spacetime volume V. For the V+V ln V-invariant the renormalization group running enormously suppresses the value of the renormalized curvature which results from Planck-size parameters specified at the Planck scale. One obtains very large, i.e., almost flat universes without finetuning the cosmological constant. A critical infrared fixed point is found where gravity is scale invariant. (Abstract Copyright [2004], Wiley Periodicals, Inc.)
Rainbow metric from quantum gravity
Assaniousssi, Mehdi; Lewandowski, Jerzy
2014-01-01
In this letter, we describe a general mechanism for emergence of a rainbow metric from a quantum cosmological model. This idea is based on QFT on a quantum space-time. Under general assumptions, we discover that the quantum space-time on which the field propagates can be replaced by a classical space-time, whose metric depends explicitly on the energy of the field: as shown by an analysis of dispersion relations, quanta of different energy propagate on different metrics, similar to photons in a refractive material (hence the name "rainbow" used in the literature). In deriving this result, we do not consider any specific theory of quantum gravity: the qualitative behavior of high-energy particles on quantum space-time relies only on the assumption that the quantum space-time is described by a wave-function $\\Psi_o$ in a Hilbert space $\\mathcal{H}_G$.
Finite Conformal Quantum Gravity and Nonsingular Spacetimes
Modesto, Leonardo
2016-01-01
We explicitly prove that a class of finite quantum gravitational theories (in odd as well as in even dimension) is actually a range of anomaly-free conformally invariant theories in the spontaneously broken phase of the conformal Weyl symmetry. At classical level we show how the Weyl conformal invariance is likely able to tame the spacetime singularities that plague not only Einstein gravity, but also local and weakly non-local higher derivative theories. This latter statement is rigorously proved by a singularity theorem that applies to a large class of weakly non-local theories. Following the seminal paper by Narlikar and Kembhavi, we provide an explicit construction of singularity-free black hole exact solutions conformally equivalent to the Schwarzschild metric. Furthermore, we show that the FRW cosmological solutions and the Belinski, Khalatnikov, Lifshitz (BKL) spacetimes, which exactly solve the classical equations of motion, are conformally equivalent to regular spacetimes. Finally, we prove that the ...
Einstein's Photoemission from Quantum Confined Superlattices.
Debbarma, S; Ghatak, K P
2016-01-01
This paper is dedicated to the 83th Birthday of Late Professor B. R. Nag, D.Sc., formerly Head of the Departments of Radio Physics and Electronics and Electronic Science of the University of Calcutta, a firm believer of the concept of theoretical minimum of Landau and an internationally well known semiconductor physicist, to whom the second author remains ever grateful as a student and research worker from 1974-2004. In this paper, an attempt is made to study, the Einstein's photoemission (EP) from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum well heavily doped superlattices (QWHDSLs) with graded interfaces in the presence of quantizing magnetic field on the basis of newly formulated electron dispersion relations within the frame work of k · p formalism. The EP from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum wells of heavily doped effective mass superlattices respectively has been presented under magnetic quantization. Besides the said emissions, from the quantum dots of the aforementioned heavily doped SLs have further investigated for the purpose of comparison and complete investigation in the context of EP from quantum confined superlattices. Using appropriate SLs, it appears that the EP increases with increasing surface electron concentration and decreasing film thickness in spiky manners, which are the characteristic features of such quantized hetero structures. Under magnetic quantization, the EP oscillates with inverse quantizing magnetic field due to Shuvnikov-de Haas effect. The EP increases with increasing photo energy in a step-like manner and the numerical values of EP with all the physical variables are totally band structure dependent for all the cases. The most striking features are that the presence of poles in the dispersion relation of the materials in the absence of band tails create the complex energy spectra in the corresponding HD constituent materials of such quantum confined superlattices and effective electron
Comments on "Cahill's Quantum Foam Inflow Theory of Gravity"
Martin, T D
2004-01-01
We reveal an underlying flaw in Reginald T. Cahill's recently promoted quantum foam inflow theory of gravity. It appears to arise from a confusion of the idea of the Galilean invariance of the acceleration of an individual flow with what is obtained as an acceleration when a homogeneous flow is superposed with an inhomogeneous flow. We also point out that the General Relativistic covering theory he creates by substituting a generalized Painleve-Gullstrand metric into Einstein's field equations leads to absurd results.
Nonperturbative Studies of Quantum Gravity
Beirl, W; Riedler, J; Beirl, Wolfgang; Markum, Harald; Riedler, Juergen
1993-01-01
We investigate quantum gravity in the path integral formulation using the Regge calculus. Restricting the quadratic link lengths of the originally triangular lattice the path integral can be transformed to the partition function of a spin system with higher couplings on a Kagome lattice. Various measures acting as external field were considered. Extensions to matter fields and higher dimensions are discussed.
Rovelli, C
2003-01-01
The debate between loop quantum gravity and string theory is sometimes lively, and it is hard to present an impartial view on the issue. Leaving any attempt to impartiality aside, I report here, instead, a conversation on this issue, overheard in the cafeteria of a Major American University.
Quantum Corrections in Massive Gravity
de Rham, Claudia; Ribeiro, Raquel H
2013-01-01
We compute the one-loop quantum corrections to the potential of ghost-free massive gravity. We show how the mass of external matter fields contribute to the running of the cosmological constant, but do not change the ghost-free structure of the massive gravity potential at one-loop. When considering gravitons running in the loops, we show how the structure of the potential gets destabilized at the quantum level, but in a way which would never involve a ghost with a mass smaller than the Planck scale. This is done by explicitly computing the one-loop effective action and supplementing it with the Vainshtein mechanism. We conclude that to one-loop order the special mass structure of ghost-free massive gravity is technically natural.
Quantum corrections in massive gravity
de Rham, Claudia; Heisenberg, Lavinia; Ribeiro, Raquel H.
2013-10-01
We compute the one-loop quantum corrections to the potential of ghost-free massive gravity. We show how the mass of external matter fields contributes to the running of the cosmological constant, but does not change the ghost-free structure of the massive gravity potential at one-loop. When considering gravitons running in the loops, we show how the structure of the potential gets destabilized at the quantum level, but in a way which would never involve a ghost with a mass smaller than the Planck scale. This is done by explicitly computing the one-loop effective action and supplementing it with the Vainshtein mechanism. We conclude that to one-loop order the special mass structure of ghost-free massive gravity is technically natural.
BOOK REVIEW: Quantum Gravity: third edition Quantum Gravity: third edition
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
Quantum Gravity at Very High Energies
Gamboa-Rios, J
2001-01-01
The problem of time and the quantization of three dimensional gravity in the strong coupling regime is studied following path integral methods. The time is identified with the volume of spacetime. We show that the effective action describes an infinite set of massless relativistic particles moving in a curved three-dimensional target space, i.e. a tensionless 3-brane on a curved background. If the cosmological constant is zero the target space is flat and there is no ` ` graviton" propagation, i.e. $G[g_{ij} (2), g_{ij} (1)] = 0$). If the cosmological constant is different from zero, 3D gravity is both classical and quantum mechanically soluble. Indeed, we find the following results: i) The general exact solutions of the Einstein equations are singular at $t=0$ showing the existence of a big bang in this regime and ii) the propagation amplitude between two geometries $$ vanishes as $t \\to 0$, suggesting that big-bang is suppressed quantum mechanically. This result is also valid in $D>3$.
Foundations of quantum gravity
Lindesay, James
2013-01-01
Exploring how the subtleties of quantum coherence can be consistently incorporated into Einstein’s theory of gravitation, this book is ideal for researchers interested in the foundations of relativity and quantum physics. The book examines those properties of coherent gravitating systems that are most closely connected to experimental observations. Examples of consistent co-gravitating quantum systems whose overall effects upon the geometry are independent of the coherence state of each constituent are provided, and the properties of the trapping regions of non-singular black objects, black holes, and a dynamic de Sitter cosmology are discussed analytically, numerically, and diagrammatically. The extensive use of diagrams to summarise the results of the mathematics enables readers to bypass the need for a detailed understanding of the steps involved. Assuming some knowledge of quantum physics and relativity, the book provides textboxes featuring supplementary information for readers particularly interested ...
Universal Property of Quantum Gravity implied by Bekenstein-Hawking Entropy and Boltzmann formula
Saida, Hiromi
2013-01-01
We search for a universal property of quantum gravity. By "universal", we mean the independence from any existing model of quantum gravity (such as the super string theory, loop quantum gravity, causal dynamical triangulation, and so on). To do so, we try to put the basis of our discussion on theories established by some experiments. Thus, we focus our attention on thermodynamical and statistical-mechanical basis of the black hole thermodynamics: Let us assume that the Bekenstein-Hawking entropy is given by the Boltzmann formula applied to the underlying theory of quantum gravity. Under this assumption, the conditions justifying Boltzmann formula together with uniqueness of Bekenstein-Hawking entropy imply a reasonable universal property of quantum gravity. The universal property indicates a repulsive gravity at Planck length scale, otherwise stationary black holes can not be regarded as thermal equilibrium states of gravity. Further, in semi-classical level, we discuss a possible correction of Einstein equat...
Spacetime Singularities in Quantum Gravity
Minassian, Eric A.
2000-04-01
Recent advances in 2+1 dimensional quantum gravity have provided tools to study the effects of quantization of spacetime on black hole and big bang/big crunch type singularities. I investigate effects of quantization of spacetime on singularities of the 2+1 dimensional BTZ black hole and the 2+1 dimensional torus universe. Hosoya has considered the BTZ black hole, and using a "quantum generalized affine parameter" (QGAP), has shown that, for some specific paths, quantum effects "smear" the singularities. Using gaussian wave functions as generic wave functions, I found that, for both BTZ black hole and the torus universe, there are families of paths that still reach the singularities with a finite QGAP, suggesting that singularities persist in quantum gravity. More realistic calculations, using modular invariant wave functions of Carlip and Nelson for the torus universe, offer further support for this conclusion. Currently work is in progress to study more realistic quantum gravity effects for BTZ black holes and other spacetime models.
Information Processing Structure of Quantum Gravity
Gyongyosi, Laszlo
2014-01-01
The theory of quantum gravity is aimed to fuse general relativity with quantum theory into a more fundamental framework. The space of quantum gravity provides both the non-fixed causality of general relativity and the quantum uncertainty of quantum mechanics. In a quantum gravity scenario, the causal structure is indefinite and the processes are causally non-separable. In this work, we provide a model for the information processing structure of quantum gravity. We show that the quantum gravity environment is an information resource-pool from which valuable information can be extracted. We analyze the structure of the quantum gravity space and the entanglement of the space-time geometry. We study the information transfer capabilities of quantum gravity space and define the quantum gravity channel. We reveal that the quantum gravity space acts as a background noise on the local environment states. We characterize the properties of the noise of the quantum gravity space and show that it allows the separate local...
Remarks on osmosis, quantum mechanics, and gravity
Carroll, Robert
2011-01-01
Some relations of the quantum potential to Weyl geometry are indicated with applications to the Friedmann equations for a toy quantum cosmology. Osmotic velocity and pressure are briefly discussed in terms of quantum mechanics and superfluids with connections to gravity.
Ferroelectricity by Bose-Einstein condensation in a quantum magnet.
Kimura, S; Kakihata, K; Sawada, Y; Watanabe, K; Matsumoto, M; Hagiwara, M; Tanaka, H
2016-09-26
The Bose-Einstein condensation is a fascinating phenomenon, which results from quantum statistics for identical particles with an integer spin. Surprising properties, such as superfluidity, vortex quantization or Josephson effect, appear owing to the macroscopic quantum coherence, which spontaneously develops in Bose-Einstein condensates. Realization of Bose-Einstein condensation is not restricted in fluids like liquid helium, a superconducting phase of paired electrons in a metal and laser-cooled dilute alkali atoms. Bosonic quasi-particles like exciton-polariton and magnon in solids-state systems can also undergo Bose-Einstein condensation in certain conditions. Here, we report that the quantum coherence in Bose-Einstein condensate of the magnon quasi particles yields spontaneous electric polarization in the quantum magnet TlCuCl3, leading to remarkable magnetoelectric effect. Very soft ferroelectricity is realized as a consequence of the O(2) symmetry breaking by magnon Bose-Einstein condensation. The finding of this ferroelectricity will open a new window to explore multi-functionality of quantum magnets.
Ferroelectricity by Bose-Einstein condensation in a quantum magnet
Kimura, S.; Kakihata, K.; Sawada, Y.; Watanabe, K.; Matsumoto, M.; Hagiwara, M.; Tanaka, H.
2016-09-01
The Bose-Einstein condensation is a fascinating phenomenon, which results from quantum statistics for identical particles with an integer spin. Surprising properties, such as superfluidity, vortex quantization or Josephson effect, appear owing to the macroscopic quantum coherence, which spontaneously develops in Bose-Einstein condensates. Realization of Bose-Einstein condensation is not restricted in fluids like liquid helium, a superconducting phase of paired electrons in a metal and laser-cooled dilute alkali atoms. Bosonic quasi-particles like exciton-polariton and magnon in solids-state systems can also undergo Bose-Einstein condensation in certain conditions. Here, we report that the quantum coherence in Bose-Einstein condensate of the magnon quasi particles yields spontaneous electric polarization in the quantum magnet TlCuCl3, leading to remarkable magnetoelectric effect. Very soft ferroelectricity is realized as a consequence of the O(2) symmetry breaking by magnon Bose-Einstein condensation. The finding of this ferroelectricity will open a new window to explore multi-functionality of quantum magnets.
Rovelli, Carlo
The debate between loop quantum gravity and string theory is sometime lively, and it is hard to present an impartial view on the issue. Leaving any attempt to impartiality aside, I report here, instead, a conversation on this issue, overheard in the cafeteria of a Major American University. The personae of the dialog are Professor Simp, a high energy physicist, and a graduate student, Sal. The Professor has heard that Sal has decided to work in loop gravity, and gently tries to talk her out. Here is what was heard.
Noncommutative Wormhole Solutions in Einstein Gauss-Bonnet Gravity
Directory of Open Access Journals (Sweden)
Shamaila Rani
2016-01-01
Full Text Available We explore static spherically symmetric wormhole solutions in the framework of n-dimensional Einstein Gauss-Bonnet gravity. Our objective is to find out wormhole solutions that satisfy energy conditions. For this purpose, we consider two frameworks such as Gaussian distributed and Lorentzian distributed noncommutative geometry. Taking into account constant redshift function, we obtain solutions in the form of shape function. The fifth and sixth dimensional solutions with positive as well as negative Gauss-Bonnet coefficient are discussed. Also, we check the equilibrium condition for the wormhole solutions with the help of generalized Tolman-Oppenheimer-Volkoff equation. It is interesting to mention here that we obtain fifth dimensional stable wormhole solutions in both distributions that satisfy the energy conditions.
Generalized BRST Symmetry and Gaugeon Formalism for Perturbative Quantum Gravity: Novel Observation
Upadhyay, Sudhaker
2014-01-01
In this paper the novel features of Yokoyama gaugeon formalism are stressed out for the theory of perturbative quantum gravity in Einstein curved spacetime. The quantum gauge transformations for the theory of perturbative gravity are demonstrated in the framework of gaugeon formalism. These quantum gauge transformations lead to renormalized gauge parameter. Further, we analyse the BRST symmetric gaugeon formalism which embeds more acceptable Kugo-Ojima subsidiary condition. Further, the BRST symmetry is made finite and field-dependent. Remarkably, the Jacobian of path integral under finite and field-dependent BRST symmetry amounts to the exact gaugeon action in the effective theory of perturbative quantum gravity.
Dadhich, Naresh; Pons, Josep M
We study static black hole solutions in Einstein and Einstein-Gauss-Bonnet gravity with the topology of the product of two spheres, [Formula: see text], in higher dimensions. There is an unusual new feature of the Gauss-Bonnet black hole: the avoidance of a non-central naked singularity prescribes a mass range for the black hole in terms of [Formula: see text]. For an Einstein-Gauss-Bonnet black hole a limited window of negative values for [Formula: see text] is also permitted. This topology encompasses black strings, branes, and generalized Nariai metrics. We also give new solutions with the product of two spheres of constant curvature.
Effects of quantum gravity on black holes
Chen, Deyou; Yang, Haitang; Yang, Shuzheng
2014-01-01
In this review, we discuss effects of quantum gravity on black hole physics. After a brief review of the origin of the minimal observable length from various quantum gravity theories, we present the tunneling method. To incorporate quantum gravity effects, we modify the Klein-Gordon equation and Dirac equation by the modified fundamental commutation relations. Then we use the modified equations to discuss the tunneling radiation of scalar particles and fermions. The corrected Hawking temperatures are related to the quantum numbers of the emitted particles. Quantum gravity corrections slow down the increase of the temperatures. The remnants are observed as $M_{\\hbox{Res}}\\gtrsim \\frac{M_p}{\\sqrt{\\beta_0}}$. The mass is quantized by the modified Wheeler-DeWitt equation and is proportional to $n$ in quantum gravity regime. The thermodynamical property of the black hole is studied by the influence of quantum gravity effects.
Quantum corrections to unimodular gravity
Energy Technology Data Exchange (ETDEWEB)
Álvarez, Enrique; González-Martín, Sergio; Herrero-Valea, Mario [Instituto de Física Teórica UAM/CSIC,C/Nicolas Cabrera, 13-15, C.University Cantoblanco, 28049 Madrid (Spain); Departamento de Física Teórica,Universidad Autónoma de Madrid, 20849 Madrid (Spain); Martín, Carmelo P. [Universidad Complutense de Madrid (UCM), Departamento de Física Téorica I,Facultad de Ciencias Físicas, Av. Complutense S/N (Ciudad University), 28040 Madrid (Spain)
2015-08-17
The problem of the comological constant appears in a new light in Unimodular Gravity. In particular, the zero momentum piece of the potential (that is, the constant piece independent of the matter fields) does not automatically produce a cosmological constant proportional to it. The aim of this paper is to give some details on a calculation showing that quantum corrections do not renormalize the classical value of this observable.
Directory of Open Access Journals (Sweden)
Bernard S. Kay
2015-12-01
Full Text Available We give a review, in the style of an essay, of the author’s 1998 matter-gravity entanglement hypothesis which, unlike the standard approach to entropy based on coarse-graining, offers a definition for the entropy of a closed system as a real and objective quantity. We explain how this approach offers an explanation for the Second Law of Thermodynamics in general and a non-paradoxical understanding of information loss during black hole formation and evaporation in particular. It also involves a radically different from usual description of black hole equilibrium states in which the total state of a black hole in a box together with its atmosphere is a pure state—entangled in just such a way that the reduced state of the black hole and of its atmosphere are each separately approximately thermal. We also briefly recall some recent work of the author which involves a reworking of the string-theory understanding of black hole entropy consistent with this alternative description of black hole equilibrium states and point out that this is free from some unsatisfactory features of the usual string theory understanding. We also recall the author’s recent arguments based on this alternative description which suggest that the Anti de Sitter space (AdS/conformal field theory (CFT correspondence is a bijection between the boundary CFT and just the matter degrees of freedom of the bulk theory.
Quantum Gravity Without Ghosts
DeWitt, Bryce Seligman; Witt, Bryce De; Molina-Paris, Carmen
1998-01-01
An outline is given of a recently discovered technique for building a quantum effective action that is completely independent of gauge-fixing choices and ghost determinants. One makes maximum use of the geometry and fibre-bundle structure of the space of field histories and introduces a set of nonlocal composite fields: the geodesic normal fields based on Vilkovisky's connection on the space of histories. The closed-time-path formalism of Schwinger, Bakshi, Mahantappa {\\it et al} can be adapted for these fields, and a set of gauge-fixing-independent dynamical equations for their expectation values (starting from given initial conditions) can be computed. An obvious application for such equations is to the study of the formation and radiative decay of black holes, and to other back-reaction problems.
`Third' Quantization of Vacuum Einstein Gravity and Free Yang-Mills Theories
Raptis, Ioannis
2007-05-01
Certain pivotal results from various applications of Abstract Differential Geometry (ADG) to gravity and gauge theories are presently collected and used to argue that we already possess a geometrically (pre)quantized, second quantized and manifestly background spacetime manifold independent vacuum Einstein gravitational field dynamics. The arguments carry also mutatis mutandis to the case of free Yang-Mills theories, since from the ADG-theoretic perspective gravity is regarded as another gauge field theory. The powerful algebraico-categorical, sheaf cohomological conceptual and technical machinery of ADG is then employed, based on the fundamental ADG-theoretic conception of a field as a pair ({mathcal{E}},{mathcal{D}}) consisting of a vector sheaf {mathcal{E}} and an algebraic connection {mathcal{D}} acting categorically as a sheaf morphism on {mathcal{E}}'s local sections, to introduce a ‘universal’, because expressly functorial, field quantization scenario coined third quantization. Although third quantization is fully covariant, on intuitive and heuristic grounds alone it formally appears to follow a canonical route; albeit, in a purely algebraic and, in contradistinction to geometric (pre)quantization and (canonical) second quantization, manifestly background geometrical spacetime manifold independent fashion, as befits ADG. All in all, from the ADG-theoretic vantage, vacuum Einstein gravity and free Yang-Mills theories are regarded as external spacetime manifold unconstrained, third quantized, pure gauge field theories. The paper abounds with philosophical smatterings and speculative remarks about the potential import and significance of our results to current and future Quantum Gravity research. A postscript gives a brief account of this author's personal encounters with Rafael Sorkin and his work.
Implications of Einstein-Weyl Causality on Quantum Mechanics
BenDaniel, D. J.
2008-01-01
A fundamental physical principle that has consequences for the topology of space-time is the principle of Einstein-Weyl causality. We show here that this may have implications on quantum mechanics, as well. Borchers and Sen have rigorously investigated the mathematical implications of Einstein-Weyl causality and shown the denumerable space-time Q^2 would be implied. They then imbedded this space in a non-denumerable space but were left with important philosophical paradoxes regarding the natu...
Noncommutative gravity and quantum field theory on noncummutative curved spacetimes
Energy Technology Data Exchange (ETDEWEB)
Schenkel, Alexander
2011-10-24
The purpose of the first part of this thesis is to understand symmetry reduction in noncommutative gravity, which then allows us to find exact solutions of the noncommutative Einstein equations. We propose an extension of the usual symmetry reduction procedure, which is frequently applied to the construction of exact solutions of Einstein's field equations, to noncommutative gravity and show that this leads to preferred choices of noncommutative deformations of a given symmetric system. We classify in the case of abelian Drinfel'd twists all consistent deformations of spatially flat Friedmann-Robertson-Walker cosmologies and of the Schwarzschild black hole. The deformed symmetry structure allows us to obtain exact solutions of the noncommutative Einstein equations in many of our models, for which the noncommutative metric field coincides with the classical one. In the second part we focus on quantum field theory on noncommutative curved spacetimes. We develop a new formalism by combining methods from the algebraic approach to quantum field theory with noncommutative differential geometry. The result is an algebra of observables for scalar quantum field theories on a large class of noncommutative curved spacetimes. A precise relation to the algebra of observables of the corresponding undeformed quantum field theory is established. We focus on explicit examples of deformed wave operators and find that there can be noncommutative corrections even on the level of free field theories, which is not the case in the simplest example of the Moyal-Weyl deformed Minkowski spacetime. The convergent deformation of simple toy-models is investigated and it is shown that these quantum field theories have many new features compared to formal deformation quantization. In addition to the expected nonlocality, we obtain that the relation between the deformed and the undeformed quantum field theory is affected in a nontrivial way, leading to an improved behavior of the
Newtonian gravity on quantum spacetime
Directory of Open Access Journals (Sweden)
Majid Shahn
2014-04-01
Full Text Available The bicrossproduct model λ-Minkowski (or ‘κ-Minkowski’ quantum space-time has an anomaly for the action of the Poincaré quantum group which was resolved by an extra cotangent direction θ’ not visible classically. We show that gauging a coefficient of θ′ introduces gravity into the model. We solve and analyse the model nonrelativisticaly in a 1/r potential, finding an induced constant term in the effective potential energy and a weakening and separation of the effective gravitational and inertial masses as the test particle Klein-Gordon mass increases. The present work is intended as a proof of concept but the approach could be relevant to an understanding of dark energy and possibly to macroscopic quantum systems.
Quantum Gravity Mathematical Models and Experimental Bounds
Fauser, Bertfried; Zeidler, Eberhard
2007-01-01
The construction of a quantum theory of gravity is the most fundamental challenge confronting contemporary theoretical physics. The different physical ideas which evolved while developing a theory of quantum gravity require highly advanced mathematical methods. This book presents different mathematical approaches to formulate a theory of quantum gravity. It represents a carefully selected cross-section of lively discussions about the issue of quantum gravity which took place at the second workshop "Mathematical and Physical Aspects of Quantum Gravity" in Blaubeuren, Germany. This collection covers in a unique way aspects of various competing approaches. A unique feature of the book is the presentation of different approaches to quantum gravity making comparison feasible. This feature is supported by an extensive index. The book is mainly addressed to mathematicians and physicists who are interested in questions related to mathematical physics. It allows the reader to obtain a broad and up-to-date overview on ...
Super-renormalizable Multidimensional Quantum Gravity
Modesto, Leonardo
2012-01-01
In this paper we introduce a perturbatively super-renormalizable and unitary theory of quantum gravity in any dimension D. The theory presents two entire functions, a.k.a. "form factors", and a finite number of local operators required by the quantum consistency of the theory itself. The main reason to introduce the entire functions is to avoid ghosts (states of negative norm) like the one in the four-dimensional Stelle's theory. The new theory is indeed ghost-free since the two entire functions have the property to generalize the Einstein-Hilbert action without introducing new poles in the propagator. The theory is renormalizable at one loop and finite from two loops upward. In this paper we essentially study three classes of form factors, systematically showing the tree-level unitarity. We prove that the gravitation potential is regular in r = 0 for all the choices of form factors compatible with renormalizability and unitarity. We also include Black hole spherical symmetric solutions omitting higher curvat...
Institute of Scientific and Technical Information of China (English)
陈光
2001-01-01
The static spherically symmetric solution of Einstein gravity coupled to electromagnetic and scalar fields is obtained under the consideration of the self-gravitational interaction of the electromagnetic and scalar fields, which is singularityfree and stable.
Einstein Gravity and Beyond: Aspects of Higher-Curvature Gravity and Black Holes
Chatterjee, Saugata
This thesis explores the different aspects of higher curvature gravity. The "membrane paradigm" of black holes in Einstein gravity is extended to black holes in f(R) gravity and it is shown that the higher curvature effects of f( R) gravity causes the membrane fluid to become non-Newtonian. Next a modification of the null energy condition in gravity is provided. The purpose of the null energy condition is to filter out ill-behaved theories containing ghosts. Conformal transformations, which are simple redefinitions of the spacetime, introduces serious violations of the null energy condition. This violation is shown to be spurious and a prescription for obtaining a modified null energy condition, based on the universality of the second law of thermodynamics, is provided. The thermodynamic properties of the black holes are further explored using merger of extremal black holes whose horizon entropy has topological contributions coming from the higher curvature Gauss-Bonnet term. The analysis refutes the prevalent belief in the literature that the second law of black hole thermodynamics is violated in the presence of the Gauss-Bonnet term in four dimensions. Subsequently a specific class of higher derivative scalar field theories called the galileons are obtained from a Kaluza-Klein reduction of Gauss-Bonnet gravity. Galileons are null energy condition violating theories which lead to violations of the second law of thermodynamics of black holes. These higher derivative scalar field theories which are non-minimally coupled to gravity required the development of a generalized method for obtaining the equations of motion. Utilizing this generalized method, it is shown that the inclusion of the Gauss-Bonnet term made the theory of gravity to become higher derivative, which makes it difficult to make any statements about the connection between the violation of the second law of thermodynamics and the galileon fields.
线性Einstein引力量子化%The Quantization of the linear Einstein gravity
Institute of Scientific and Technical Information of China (English)
周挽平
2012-01-01
将线性Einstein引力作用量用谐和坐标条件与无迹条件简化,用Gupta-Bleuler理论将线性Einstein引力成功量子化,得到引力子的能量动量表达式.%Using the harmonic coordinate condition and traceless condition,the action of linear Einstein gravity was simplified,the linear Einstein gravity was quantized.
Measurement Analysis and Quantum Gravity
Albers, Mark; Reginatto, Marcel
2008-01-01
We consider the question of whether consistency arguments based on measurement theory show that the gravitational field must be quantized. Motivated by the argument of Eppley and Hannah, we apply a DeWitt-type measurement analysis to a coupled system that consists of a gravitational wave interacting with a mass cube. We also review the arguments of Eppley and Hannah and of DeWitt, and investigate a second model in which a gravitational wave interacts with a quantized scalar field. We argue that one cannot conclude from the existing gedanken experiments that gravity has to be quantized. Despite the many physical arguments which speak in favor of a quantum theory of gravity, it appears that the justification for such a theory must be based on empirical tests and does not follow from logical arguments alone.
Introductory lectures to loop quantum gravity
Doná, Pietro
2010-01-01
We give a standard introduction to loop quantum gravity, from the ADM variables to spin network states. We include a discussion on quantum geometry on a fixed graph and its relation to a discrete approximation of general relativity.
Emergent Spacetime for Quantum Gravity
Yang, Hyun Seok
2016-01-01
We emphasize that noncommutative (NC) spacetime necessarily implies emergent spacetime if spacetime at microscopic scales should be viewed as NC. In order to understand NC spacetime correctly, we need to deactivate the thought patterns that we have installed in our brains and taken for granted for so many years. Emergent spacetime allows a background-independent formulation of quantum gravity that will open a new perspective to resolve the notorious problems in theoretical physics such as the cosmological constant problem, hierarchy problem, dark energy, dark matter, and cosmic inflation.
Quantum Gravity Constraints on Inflation
Conlon, Joseph P
2012-01-01
We study quantum gravity constraints on inflationary model building. Our approach is based on requiring the entropy associated to a given inflationary model to be less than that of the de Sitter entropy. We give two prescriptions for determining the inflationary entropy, based on either `bits per unit area' or entanglement entropy. The existence of transPlanckian flat directions, necessary for large tensor modes in the CMB, correlates with an inflationary entropy greater than that allowed by de Sitter space. Independently these techniques also constrain or exclude de Sitter models with large-rank gauge groups and high UV cutoffs, such as racetrack inflation or the KKLT construction.
Compact stars in alternative theories of gravity. Einstein-Dilaton-Gauss-Bonnet gravity
Pani, Paolo; Cardoso, Vitor; Read, Jocelyn
2011-01-01
We develop a theoretical framework to study slowly rotating compact stars in a rather general class of alternative theories of gravity, with the ultimate goal of investigating constraints on alternative theories from electromagnetic and gravitational-wave observations of compact stars. Our Lagrangian includes as special cases scalar-tensor theories (and indirectly f(R) theories) as well as models with a scalar field coupled to quadratic curvature invariants. As a first application of the formalism, we discuss (for the first time in the literature) compact stars in Einstein-Dilaton-Gauss-Bonnet gravity. We show that compact objects with central densities typical of neutron stars cannot exist for certain values of the coupling constants of the theory. In fact, the existence and stability of compact stars sets more stringent constraints on the theory than the existence of black hole solutions. This work is a first step in a program to systematically rule out (possibly using Bayesian model selection) theories tha...
Quantum Gravity, May Not Be The Right Question.
Farmer, Hontas
2017-01-01
To get sensible answers one must ask the right questions. ``How can we quantize gravity'' may not be the right question to ask if our goal is to unify quantum field theory (QFT) with general relativity (GR). The right question may be how can we relativize quantum field theory. The best and brighest physicist of the last 80 years have tried to answer the quantization question and gotten answers that while interesting, like loop quantum gravity and string/M theory, have not be accepted by all as being the answer. In this talk it will be proposed that the better question to ask is how can we realtivize quantum field theory. Relativization means to make a theory comply with Einsteins relativity. QFT is a result of the relativization of quantum theory. Quantum gravity would be the result of a sort of reverse relativization of General Relativity so we can quantize it. It may be that nature does not work that way. It may be that the unified theory of GR+QFT will be realtivized. In this talk I will briefly state the five axioms of realtivization, and show how to write the relativized standard model and use it to make predictions for particle physics and astrophysical observations.
Quantum Gravity and Phenomenological Philosophy
Rosen, Steven M.
2008-06-01
The central thesis of this paper is that contemporary theoretical physics is grounded in philosophical presuppositions that make it difficult to effectively address the problems of subject-object interaction and discontinuity inherent to quantum gravity. The core objectivist assumption implicit in relativity theory and quantum mechanics is uncovered and we see that, in string theory, this assumption leads into contradiction. To address this challenge, a new philosophical foundation is proposed based on the phenomenology of Maurice Merleau-Ponty and Martin Heidegger. Then, through the application of qualitative topology and hypernumbers, phenomenological ideas about space, time, and dimension are brought into focus so as to provide specific solutions to the problems of force-field generation and unification. The phenomenological string theory that results speaks to the inconclusiveness of conventional string theory and resolves its core contradiction.
Generation of magnetic fields in Einstein-Aether gravity
Saga, Shohei; Ichiki, Kiyotomo; Sugiyama, Naoshi
2013-01-01
Recently the lower bounds of the intergalactic magnetic fields $10^{-16} \\sim 10^{-20}$ Gauss are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in General Relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-Aether gravity model, in which the aether field can act as a new source of vector metric perturbations and thus of magnetic fields. We estimate the angular power spectra of temperature and B-mode polarization of the Cosmic Microwave Background (CMB) Anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the pow...
Inverse dualisation and non-local dualities between Einstein gravity and supergravities
Chen, C M; Sharakin, S A; Chen, Chiang-Mei; Gal'tsov, Dmitri V.; Sharakin, Sergei A.
2002-01-01
We investigate non-local dualities between suitably compactified higher-dimensional Einstein gravity and supergravities which can be revealed if one reinterprets the dualised Kaluza-Klein two-forms in $D>4$ as antisymmetric forms belonging to supergravities. We find several examples of such a correspondence including one between the six-dimensional Einstein gravity and the four-dimensional Einstein-Maxwell-dilaton-axion theory (truncated N=4 supergravity), and others between the compactified eleven and ten-dimensional supergravities and the eight or ten-dimensional pure gravity. The Killing spinor equation of the D=11 supergravity is shown to be equivalent to the geometric Killing spinor equation in the dual gravity. We give several examples of using new dualities for solution generation and demonstrate how $p$-branes can be interpreted as non-local duals of pure gravity solutions. New supersymmetric solutions are presented including $M2\\subset 5$-brane with two rotation parameters.
Inverse dualization and non-local dualities between Einstein gravity and supergravities
Chen Chiang Mei; Sharakin, S A
2002-01-01
We investigate non-local dualities between suitably compactified higher dimensional Einstein gravity and supergravities which can be revealed if one reinterprets the dualized Kaluza-Klein 2-forms in D>4 as antisymmetric forms belonging to supergravities. We find several examples of such a correspondence including one between the six-dimensional Einstein gravity and the four-dimensional Einstein-Maxwell-dilaton-axion theory (truncated N=4 supergravity), and others between the compactified eleven- and ten-dimensional supergravities and the eight- or ten-dimensional pure gravity. The Killing spinor equation of the D=11 supergravity is shown to be equivalent to the geometric Killing spinor equation in the dual gravity. We give several examples of using new dualities for solution generation and demonstrate how p-branes can be interpreted as non-local duals of pure gravity solutions. New supersymmetric solutions are presented including M2 subset of 5-brane with two rotation parameters.
Extreme Regimes in Quantum Gravity
Battista, Emmanuele
2016-01-01
The thesis is divided into two parts. In the first part the low-energy limit of quantum gravity is analysed, whereas in the second we deal with the high-energy domain. In the first part, by applying the effective field theory point of view to the quantization of general relativity, detectable, though tiny, quantum effects in the position of Newtonian Lagrangian points of the Earth-Moon system are found. In order to make more realistic the quantum corrected model proposed, the full three-body problem where the Earth and the Moon interact with a generic massive body and the restricted four-body problem involving the perturbative effects produced by the gravitational presence of the Sun in the Earth-Moon system are also studied. After that, a new quantum theory having general relativity as its classical counterpart is analysed. By exploiting this framework, an innovative interesting prediction involving the position of Lagrangian points within the context of general relativity is described. Furthermore, the new ...
Exotic smoothness and quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Asselmeyer-Maluga, T, E-mail: torsten.asselmeyer-maluga@dlr.d [German Aerospace Center, Berlin, Germany and Loyola University, New Orleans, LA (United States)
2010-08-21
Since the first work on exotic smoothness in physics, it was folklore to assume a direct influence of exotic smoothness to quantum gravity. Thus, the negative result of Duston (2009 arXiv:0911.4068) was a surprise. A closer look into the semi-classical approach uncovered the implicit assumption of a close connection between geometry and smoothness structure. But both structures, geometry and smoothness, are independent of each other. In this paper we calculate the 'smoothness structure' part of the path integral in quantum gravity assuming that the 'sum over geometries' is already given. For that purpose we use the knot surgery of Fintushel and Stern applied to the class E(n) of elliptic surfaces. We mainly focus our attention to the K3 surfaces E(2). Then we assume that every exotic smoothness structure of the K3 surface can be generated by knot or link surgery in the manner of Fintushel and Stern. The results are applied to the calculation of expectation values. Here we discuss the two observables, volume and Wilson loop, for the construction of an exotic 4-manifold using the knot 5{sub 2} and the Whitehead link Wh. By using Mostow rigidity, we obtain a topological contribution to the expectation value of the volume. Furthermore, we obtain a justification of area quantization.
Exotic Smoothness and Quantum Gravity
Asselmeyer-Maluga, Torsten
2010-01-01
Since the first work on exotic smoothness in physics, it was folklore to assume a direct influence of exotic smoothness to quantum gravity. Thus, the negative result of Duston (arXiv:0911.4068) was a surprise. A closer look into the semi-classical approach uncovered the implicit assumption of a close connection between geometry and smoothness structure. But both structures, geometry and smoothness, are independent of each other. In this paper we calculate the "smoothness structure" part of the path integral in quantum gravity assuming that the "sum over geometries" is already given. For that purpose we use the knot surgery of Fintushel and Stern applied to the class E(n) of elliptic surfaces. We mainly focus our attention to the K3 surfaces E(2). Then we assume that every exotic smoothness structure of the K3 surface can be generated by knot or link surgery a la Fintushel and Stern. The results are applied to the calculation of expectation values. Here we discuss the two observables, volume and Wilson loop, f...
Noncommutative Gravity and Quantum Field Theory on Noncommutative Curved Spacetimes
Schenkel, Alexander
2012-01-01
The focus of this PhD thesis is on applications, new developments and extensions of the noncommutative gravity theory proposed by Julius Wess and his group. In part one we propose an extension of the usual symmetry reduction procedure to noncommutative gravity. We classify in the case of abelian Drinfel'd twists all consistent deformations of spatially flat Friedmann-Robertson-Walker cosmologies and of the Schwarzschild black hole. The deformed symmetry structure allows us to obtain exact solutions of the noncommutative Einstein equations in many of our models. In part two we develop a new formalism for quantum field theory on noncommutative curved spacetimes by combining methods from the algebraic approach to quantum field theory with noncommutative differential geometry. We also study explicit examples of deformed wave operators and find that there can be noncommutative corrections even on the level of free field theories. The convergent deformation of simple toy models is investigated and it is found that ...
Quantum coherent oscillations between two coupled bose-einstein condensates
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The theoretical investigation of quantum coherent atomic oscillations between two coupled Bose-Einstein condensates(BECs) is studied. We apply the inseparable wave function of time-space to describe two trapped BECs in a double-well magnetic trap. According to Thomas-Fermi approximation, dynamical equations of the interwell phase difference and population imbalance are obtained. Using numerical method, coherent atomic tunneling and macroscopic quantum self-trapping(MQST) effect are investigated.
New Insights into Quantum Gravity from Gauge/gravity Duality
Engelhardt, Netta
2016-01-01
Using gauge/gravity duality, we deduce several nontrivial consequences of quantum gravity from simple properties of the dual field theory. These include: (1) a version of cosmic censorship, (2) restrictions on evolution through black hole singularities, and (3) the exclusion of certain cosmological bounces. In the classical limit, the latter implies a new singularity theorem.
New insights into quantum gravity from gauge/gravity duality
Engelhardt, Netta; Horowitz, Gary T.
2016-06-01
Using gauge/gravity duality, we deduce several nontrivial consequences of quantum gravity from simple properties of the dual field theory. These include: (1) a version of cosmic censorship, (2) restrictions on evolution through black hole singularities, and (3) the exclusion of certain cosmological bounces. In the classical limit, the latter implies a new singularity theorem.
Torsion, a multivalued gauge degree of freedom in Einstein's gravity
Energy Technology Data Exchange (ETDEWEB)
Kleinert, H, E-mail: h.k@fu-berlin.de [Institut fuer Theoretische Physik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin (Germany); ICRANet, Piazzale della Republica 10, 1-65122, Pescara (Italy)
2011-07-08
We show that there is an entire gauge symmetry of a novel kind which interpolates between an infinity of formulations of the laws of gravity, ranging from Einsteins pure curvature formulation to a pure torsion formulation in a teleparallel geometry. As a consequence, torsion and curvature are not independent and that torsion is an alternative description of curvature in gravity.
Quantum Effects of Bose-Einstein Condensates
Institute of Scientific and Technical Information of China (English)
YU Zhao-Xian; JIAO Zhi-Yong; SUN Jin-Zuo
2004-01-01
In this paper,we study quadrature squeezings of two Bose-Einstein condensates with collision and nonclassical properties of pair entanglement in four wave mixing in Bose-Einstein condensates.With the aid of a numerical method,we find that the two modes(pair entanglement modes)a1 and a2 may exhibit quadrature squeezing,in which they are affected by the initial phase.It is shown that the two pump modes exhibit the same super-Poissonian distribution.The analysis for the mode-mode correlation shows that there always exists a violation of the Cauchy-Schwartz inequality,which means that correlation between the two pump modes is nonclassical.
Lessons from Classical Gravity about the Quantum Structure of Spacetime
Padmanabhan, T
2010-01-01
I present the theoretical evidence which suggests that gravity is an emergent phenomenon like gas dynamics or elasticity with the gravitational field equations having the same status as, say, the equations of fluid dynamics/elasticity. This paradigm views a wide class of gravitational theories - including Einstein's theory - as describing the thermodynamic limit of the statistical mechanics of "atoms of spacetime". The evidence for this paradigm is hidden in several classical features of the gravitational theories and depends on just one quantum mechanical input, viz. the existence of Davies-Unruh temperature of horizons. I discuss several conceptual ingredients of this approach.
Generation of magnetic fields in Einstein-aether gravity
Saga, Shohei; Shiraishi, Maresuke; Ichiki, Kiyotomo; Sugiyama, Naoshi
2013-05-01
Recently the lower bounds of the intergalactic magnetic fields 10-16˜10-20G are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector-mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in general relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-aether gravity model, in which the aether field can act as a new source of vector metric perturbations. The vector metric perturbations induce the velocity difference between baryons and photons which then generate magnetic fields. This velocity difference arises from effects at the second order in the tight-coupling approximation. We estimate the angular power spectra of temperature and B-mode polarization of the cosmic microwave background anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the power spectrum of associated magnetic fields around the recombination epoch within this limit. It is found that the spectrum has a characteristic peak at k=0.1hMpc-1, and at that scale the amplitude can be as large as B˜10-22G where the upper bound comes from cosmic microwave background temperature anisotropies. The magnetic fields with this amplitude can be seeds of large scale magnetic fields observed today if the sufficient dynamo mechanism takes place. Analytic interpretation for the power spectra is also given.
Lattice Models of Quantum Gravity
Bittner, E R; Holm, C; Janke, W; Markum, H; Riedler, J
1998-01-01
Standard Regge Calculus provides an interesting method to explore quantum gravity in a non-perturbative fashion but turns out to be a CPU-time demanding enterprise. One therefore seeks for suitable approximations which retain most of its universal features. The $Z_2$-Regge model could be such a desired simplification. Here the quadratic edge lengths $q$ of the simplicial complexes are restricted to only two possible values $q=1+\\epsilon\\sigma$, with Ising model. To test whether this simpler model still contains the essential qualities of the standard Regge Calculus, we study both models in two dimensions and determine several observables on the same lattice size. In order to compare expectation values, e.g. of the average curvature or the Liouville field susceptibility, we employ in both models the same functional integration measure. The phase structure is under current investigation using mean field theory and numerical simulation.
Excursion into Quantum Gravity via Inflation
Calmet, Xavier
2014-01-01
The discovery of B-modes, and their effect on the fit to inflationary parameters, opens a window to explore quantum gravity. In this paper we adopt an effective theory approach to study quantum gravity effects in inflation. We apply this approach to chaotic and $\\phi^4$ inflation, and find that BICEP2 constrains these new operators to values which are consistent with the effective theory approach. This result opens the possibility to study quantum gravity in a systematic fashion, including its effect on Higgs inflation and other Starobisnky-like models.
PREFACE: Loops 11: Non-Perturbative / Background Independent Quantum Gravity
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
Cosmological implications of modified gravity induced by quantum metric fluctuations
Energy Technology Data Exchange (ETDEWEB)
Liu, Xing [Sun Yat-Sen University, School of Physics, Guangzhou (China); Sun Yat-Sen University, Yat Sen School, Guangzhou (China); Harko, Tiberiu [Babes-Bolyai University, Department of Physics, Cluj-Napoca (Romania); University College London, Department of Mathematics, London (United Kingdom); Liang, Shi-Dong [Sun Yat-Sen University, School of Physics, Guangzhou (China); Sun Yat-Sen University, State Key Laboratory of Optoelectronic Material and Technology, Guangdong Province Key Laboratory of Display Material and Technology, School of Physics, Guangzhou (China)
2016-08-15
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a non-minimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For each considered model we obtain the gravitational field equations, and the generalized Friedmann equations for the case of a flat homogeneous and isotropic geometry. In some of these models the divergence of the matter energy-momentum tensor is non-zero, indicating a process of matter creation, which corresponds to an irreversible energy flow from the gravitational field to the matter fluid, and which is direct consequence of the non-minimal curvature-matter coupling. The cosmological evolution equations of these modified gravity models induced by the quantum fluctuations of the metric are investigated in detail by using both analytical and numerical methods, and it is shown that a large variety of cosmological models can be constructed, which, depending on the numerical values of the model parameters, can exhibit both accelerating and decelerating behaviors. (orig.)
Cosmological implications of modified gravity induced by quantum metric fluctuations
Liu, Xing; Harko, Tiberiu; Liang, Shi-Dong
2016-08-01
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a non-minimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For each considered model we obtain the gravitational field equations, and the generalized Friedmann equations for the case of a flat homogeneous and isotropic geometry. In some of these models the divergence of the matter energy-momentum tensor is non-zero, indicating a process of matter creation, which corresponds to an irreversible energy flow from the gravitational field to the matter fluid, and which is direct consequence of the non-minimal curvature-matter coupling. The cosmological evolution equations of these modified gravity models induced by the quantum fluctuations of the metric are investigated in detail by using both analytical and numerical methods, and it is shown that a large variety of cosmological models can be constructed, which, depending on the numerical values of the model parameters, can exhibit both accelerating and decelerating behaviors.
On the quasi-linearity of the Einstein- "Gauss-Bonnet" gravity field equations
Deruelle, N; Deruelle, Nathalie; Madore, John
2003-01-01
We review some properties of the Einstein-"Gauss-Bonnet" equations for gravity--also called the Einstein-Lanczos equations in five and six dimensions, and the Lovelock equations in higher dimensions. We illustrate, by means of simple Kaluza-Klein and brane cosmological models, some consequences of the quasi-linearity of these equations on the Cauchy problem and structure of characteristics (a point first studied by Yvonne Choquet-Bruhat), as well as on "junction conditions".
Transition probability spaces in loop quantum gravity
Guo, Xiao-Kan
2016-01-01
We study the (generalized) transition probability spaces, in the sense of Mielnik and Cantoni, for spacetime quantum states in loop quantum gravity. First, we show that loop quantum gravity admits the structures of transition probability spaces. This is achieved by first checking such structures in covariant quantum mechanics, and then passing to spin foam models via the general boundary formulation. The transition probability space thus defined gives a simple way to reconstruct the Hilbert space of the canonical theory and the relevant quantum logical structure. Second, we show that the transition probability space and in particular the spin foam model are 2-categories. Then we discuss how to realize property transitions and causality in this categorical context in connection with presheaves on quantaloids and respectively causal categories. We conclude that transition probability spaces provide us with an alternative framework to understand various foundational questions of loop quantum gravity.
On Spectral Triples in Quantum Gravity I
DEFF Research Database (Denmark)
Aastrup, Johannes; M. Grimstrup, Jesper; Nest, Ryszard
2009-01-01
This paper establishes a link between Noncommutative Geometry and canonical quantum gravity. A semi-finite spectral triple over a space of connections is presented. The triple involves an algebra of holonomy loops and a Dirac type operator which resembles a global functional derivation operator....... The interaction between the Dirac operator and the algebra reproduces the Poisson structure of General Relativity. Moreover, the associated Hilbert space corresponds, up to a discrete symmetry group, to the Hilbert space of diffeomorphism invariant states known from Loop Quantum Gravity. Correspondingly......, the square of the Dirac operator has, in terms of canonical quantum gravity, the form of a global area-squared operator. Furthermore, the spectral action resembles a partition function of Quantum Gravity. The construction is background independent and is based on an inductive system of triangulations...
Minimal Length Scale Scenarios for Quantum Gravity
National Research Council Canada - National Science Library
Hossenfelder, Sabine
2013-01-01
.... First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity...
Quantum Gravity: The View From Particle Physics
Nicolai, Hermann
This lecture reviews aspects of and prospects for progress towards a theory of quantum gravity from a particle physics perspective, also paying attention to recent findings of the LHC experiments at CERN.
Quantum dilatonic gravity in d = 2,4 and 5 dimensions
Nojiri, S; Nojiri, Shin'ichi; Odintsov, Sergei D.
2001-01-01
We review (mainly) quantum effects in the theories where gravity sector is described by metric and dilaton. The one-loop effective action for dilatonic gravity in two and four dimensions is evaluated. Renormalization group equations are constructed. The conformal anomaly and induced effective action for 2d and 4d dilaton coupled theories are found. It is applied to study of quantum aspects of black hole thermodynamics, like calculation of Hawking radiation and quantum corrections to black hole parameters and investigation of quantum instability for such objects with multiple horizons. The use of above effective action in the construction of non-singular cosmological models in Einstein or Brans-Dicke (super)gravity and investigation of induced wormholes in supersymmetric Yang-Mills theory are given. 5d dilatonic gravity (bosonic sector of compactified IIB supergravity) is discussed in connection with bulk/boundary (or AdS/CFT) correspondence. Running gauge coupling and quark-antiquark potential for boundary ga...
Higher spin de Sitter quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Basu, Rudranil [Physique Théorique et Mathématique,Université Libre de Bruxelles and International Solvay Institutes,Campus Plaine C.P. 231, B-1050 Bruxelles (Belgium); Indian Institute of Science Education and Research,Dr. Homi Bhabha Road, Pashan, Pune 411008 (India)
2015-10-23
We consider Einstein gravity with positive cosmological constant coupled with higher spin interactions and calculate Euclidean path integral perturbatively. We confine ourselves to the static patch of the 3 dimensional de Sitter space. This geometry, when Euclideanlized is equivalent to 3-sphere. However, infinite number of topological quotients of this space by discrete subgroups of the isometry group are valid Euclidean saddles as well. The case of pure Einstein gravity is known to give a diverging answer, when all saddles are included as contribution to the thermal partition functions (also interpreted as the Hartle Hawking state in the cosmological scenario). We show how higher spins, described by metric-Fronsdal fields help making the partition function finite. We find a curious fact that this convergence is not achieved by mere inclusion of spin-3, but requires spin-4 interactions.
Higher Spin de Sitter Quantum Gravity
Basu, Rudranil
2015-01-01
We consider Einstein gravity with positive cosmological constant coupled with higher spin interactions and calculate Euclidean path integral perturbatively. We confine ourselves to the static patch of the 3 dimensional de Sitter space. This geometry, when Euclideanlized is equivalent to 3-sphere. However, infinite number of topological quotients of this space by discrete subgroups of the isometry group are valid Euclidean saddles as well. Pure Einstein gravity is known to diverge, when all saddles are included as contribution to the thermal partition functions (also interpreted as the Hartle Hawking state of in the cosmological scenario). We show how higher spins, described by metric-Fronsdal fields help making the partition function finite. Counter-intuitively, this convergence is not achieved by mere inclusion of spin-3, but requires spin-4 interactions.
Quantum gravity phenomenology. Achievements and challenges
Energy Technology Data Exchange (ETDEWEB)
Liberati, S. [International School for Advanced Study (SISSA), Trieste (Italy); INFN, Sezione di Trieste (Italy); Maccione, L. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2011-05-15
Motivated by scenarios of quantum gravity, Planck-suppressed deviations from Lorentz invariance are expected at observable energies. Ultra-High-Energy Cosmic Rays, the most energetic particles ever observed in nature, yielded in the last two years strong constraints on deviations suppressed by O(E{sup 2}/M{sup 2}{sub Pl}) and also, for the first time, on space-time foam, stringy inspired models of quantum gravity. We review the most important achievements and discuss future outlooks. (orig.)
Wilson loops in CDT quantum gravity
Ambjorn, J; Jurkiewicz, J; Loll, R
2015-01-01
By explicit construction, we show that one can in a simple way introduce and measure gravitational holonomies and Wilson loops in lattice formulations of nonperturbative quantum gravity based on (Causal) Dynamical Triangulations. We use this set-up to investigate a class of Wilson line observables associated with the world line of a point particle coupled to quantum gravity, and deduce from their expectation values that the underlying holonomies cover the group manifold of SO(4) uniformly
Quantum gravity phenomenology. Achievements and challenges
Energy Technology Data Exchange (ETDEWEB)
Liberati, S. [International School for Advanced Study (SISSA), Trieste (Italy); INFN, Sezione di Trieste (Italy); Maccione, L. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2011-05-15
Motivated by scenarios of quantum gravity, Planck-suppressed deviations from Lorentz invariance are expected at observable energies. Ultra-High-Energy Cosmic Rays, the most energetic particles ever observed in nature, yielded in the last two years strong constraints on deviations suppressed by O(E{sup 2}/M{sup 2}{sub Pl}) and also, for the first time, on space-time foam, stringy inspired models of quantum gravity. We review the most important achievements and discuss future outlooks. (orig.)
Cosmological constraints on a classical limit of quantum gravity
Easson, D A; Trodden, M; Wohlfarth, M N R; Easson, Damien A.; Schuller, Frederic P.; Trodden, Mark; Wohlfarth, Mattias N.R.
2005-01-01
We investigate the cosmology of a recently proposed deformation of Einstein gravity, emerging from quantum gravity heuristics. The theory is constructed to have de Sitter space as a vacuum solution, and thus to be relevant to the accelerating universe. However, this solution turns out to be unstable, and the true phase space of cosmological solutions is significantly more complex, displaying two late-time power-law attractors -- one accelerating and the other dramatically decelerating. It is also shown that non-accelerating cosmologies sit on a separatrix between the two basins of attraction of these attractors. Hence it is impossible to pass from a decelerating cosmology to an accelerating one, as required in standard cosmology for consistency with nucleosynthesis and structure formation and compatibility with the data inferred from supernovae Ia. We point out that alternative models of the early universe, such as the one investigated here might provide possible ways to circumvent these requirements.
Einstein against quantum mechanics: randomness, ignorance and our ignorance about randomness
Paz, Juan Pablo
2007-01-01
Albert Einstein made fundamental contributions to the development of quantum mechanics. However, he was never satisfied with the quantum worldview. In fact, during most of his life he attempted to find inconsistencies and paradoxes within quantum mechanics. His famous quote "God does not play dice" shows how disturbing was to Einstein one of the most important aspects of quantum mechanics: non-determinism. In this paper we will present the basic concepts of quantum mechanics, we will describe Einstein's attempts to destroy it and we will discuss why we can nowadays state that, in this regard, Albert Einstein was not right.
Quantum gravity via supersymmetry and holography
Elvang, Henriette; Horowitz, Gary T.
2013-01-01
We review the approach to quantum gravity based on supersymmetry, strings, and holography. This includes a survey of black holes in higher-dimensions, supersymmetry and supergravity, as well as string theory, black hole microstates, and the gauge/gravity duality. This presentation will appear as a chapter in "General Relativity and Gravitation: A Centennial Perspective", to be published by Cambridge University Press.
Quantum Einstein-Dirac Bianchi Universes
Damour, Thibault
2011-01-01
We study the mini--superspace quantization of spatially homogeneous (Bianchi) cosmological universes sourced by a Dirac spinor field. The quantization of the homogeneous spinor leads to a finite-dimensional fermionic Hilbert space and thereby to a multi-component Wheeler-DeWitt equation whose main features are: (i) the presence of spin-dependent Morse-type potentials, and (ii) the appearance of a q-number squared-mass term, which is of order ${\\cal O}(\\hbar^2)$, and which is affected by ordering ambiguities. We give the exact quantum solution of the Bianchi type-II system (which contains both scattering states and bound states), and discuss the main qualitative features of the quantum dynamics of the (classically chaotic) Bianchi type-IX system. We compare the exact quantum dynamics of fermionic cosmological billiards to previous works that described the spinor field as being either classical or Grassmann-valued.
Feynman propagator for spin foam quantum gravity.
Oriti, Daniele
2005-03-25
We link the notion causality with the orientation of the spin foam 2-complex. We show that all current spin foam models are orientation independent. Using the technology of evolution kernels for quantum fields on Lie groups, we construct a generalized version of spin foam models, introducing an extra proper time variable. We prove that different ranges of integration for this variable lead to different classes of spin foam models: the usual ones, interpreted as the quantum gravity analogue of the Hadamard function of quantum field theory (QFT) or as inner products between quantum gravity states; and a new class of causal models, the quantum gravity analogue of the Feynman propagator in QFT, nontrivial function of the orientation data, and implying a notion of "timeless ordering".
Gaugeon Formalism for Perturbative Quantum Gravity
Upadhyay, Sudhaker
2014-01-01
In this paper we investigate the Yokoyama gaugeon formalism for perturbative quantum gravity in general curved spacetime. Within the gaugeon formalism, we extend the configuration space by introducing vector gaugeon fields describing quantum gauge freedom. Such extended theory of perturbative gravity admits quantum gauge transformations leading to an natural shift in the gauge parameter. Further we impose the Gupta-Bleuler type subsidiary condition to remove the unphysical gaugeon modes. To replace the Gupta-Bleuler type condition by more acceptable Kugo-Ojima type subsidiary condition we analyse the BRST symmetric gaugeon formalism. Further, the physical Hilbert space is constructed for the perturbative quantum gravity which remains invariant under both the BRST symmetry and quantum gauge transformations.
Quantum gravity from theory to experimental search
Kiefer, Claus; Lämmerzahl, Claus
2003-01-01
The relation between quantum theory and the theory of gravitation remains one of the most outstanding unresolved issues of modern physics. According to general expectation, general relativity as well as quantum (field) theory in a fixed background spacetime cannot be fundamentally correct. Hence there should exist a broader theory comprising both in appropriate limits, i.e., quantum gravity. This book gives readers a comprehensive introduction accessible to interested non-experts to the main issues surrounding the search for quantum gravity. These issues relate to fundamental questions concerning the various formalisms of quantization; specific questions concerning concrete processes, like gravitational collapse or black-hole evaporation; and the all important question concerning the possibility of experimental tests of quantum-gravity effects.
Hendi, Seyed Hossein; Panah, Behzad Eslam
2015-01-01
In this paper, we are considering two first order corrections to both gravity and gauge sides of the Einstein-Maxwell gravity: Gauss-Bonnet gravity and quadratic Maxwell invariant as corrections. We obtain horizonless magnetic solutions by implying a metric which representing a topological defect. We analyze the geometric properties of the solutions and investigate the effects of both corrections, and find that these solutions may be interpreted as the magnetic branes. We study the singularity condition and find a nonsingular spacetime with a conical geometry. We also investigate the effects of different parameters on deficit angle of spacetime near the origin.
Energy Technology Data Exchange (ETDEWEB)
Hendi, Seyed Hossein [Shiraz University, Physics Department and Biruni Observatory, College of Sciences, Shiraz (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of); Panahiyan, Shahram; Panah, Behzad Eslam [Shiraz University, Physics Department and Biruni Observatory, College of Sciences, Shiraz (Iran, Islamic Republic of)
2015-06-15
In this paper, we consider two first order corrections to both the gravity and the gauge sides of the Einstein-Maxwell gravity: Gauss-Bonnet gravity and quadratic Maxwell invariant as corrections. We obtain horizonless magnetic solutions by implying a metric representing a topological defect. We analyze the geometric properties of the solutions and investigate the effects of both corrections, and find that these solutions may be interpreted as magnetic branes. We study the singularity condition and find a nonsingular spacetime with a conical geometry. We also investigate the effects of different parameters on the deficit angle of spacetime near the origin. (orig.)
Renormalisation in perturbative quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Rodigast, Andreas
2012-07-02
In this thesis, we derive the gravitational one-loop corrections to the propagators and interactions of the Standard Model field. We consider a higher dimensional brane world scenario: Here, gravitons can propagate in the whole D dimensional space-time whereas the matter fields are confined to a d dimensional sub-manifold (brane). In order to determine the divergent part of the one-loop diagrams, we develop a new regularisation scheme which is both sensitive for polynomial divergences and respects the Ward identities of the Yang-Mills theory. We calculate the gravitational contributions to the {beta} functions of non-Abelian gauge theories, the quartic scalar self-interaction and the Yukawa coupling between scalars and fermions. In the physically interesting case of a four dimensional matter brane, the gravitational contributions to the running of the Yang-Mills coupling constant vanish. The leading contributions to the other two couplings are positive. These results do not depend on the number of extra dimensions. We further compute the gravitationally induced one-loop counterterms with higher covariant derivatives for scalars, Dirac fermions and gauge bosons. In is shown that these counterterms do not coincide with the higher derivative terms in the Lee-Wick standard model. A possible connection between quantum gravity and the latter cannot be inferred.
Quantum gravity and inventory accumulation
Sheffield, Scott
2011-01-01
We begin by studying inventory accumulation at a LIFO (last-in-first-out) retailer with two products. In the simplest version, the following occur with equal probability at each time step: first product ordered, first product produced, second product ordered, second product produced. The inventory thus evolves as a simple random walk on Z^2. In more interesting versions, a p fraction of customers orders the "freshest available" product regardless of type. We show that the corresponding random walks scale to Brownian motions with diffusion matrices depending on p. We then turn our attention to the critical Fortuin-Kastelyn random planar map model, which gives, for each q>0, a probability measure on random (discretized) two-dimensional surfaces decorated by loops, related to the q-state Potts model. A longstanding open problem is to show that as the discretization gets finer, the surfaces converge in law to a limiting (loop-decorated) random surface. The limit is expected to be a Liouville quantum gravity surfa...
Perturbative Quantum Gravity and its Relation to Gauge Theory
Directory of Open Access Journals (Sweden)
Bern Zvi
2002-01-01
Full Text Available In this review we describe a non-trivial relationship between perturbative gauge theory and gravity scattering amplitudes. At the semi-classical or tree-level, the scattering amplitudes of gravity theories in flat space can be expressed as a sum of products of well defined pieces of gauge theory amplitudes. These relationships were first discovered by Kawai, Lewellen, and Tye in the context of string theory, but hold more generally. In particular, they hold for standard Einstein gravity. A method based on $D$-dimensional unitarity can then be used to systematically construct all quantum loop corrections order-by-order in perturbation theory using as input thegravity tree amplitudes expressed in terms of gauge theory ones. More generally, the unitarity method provides a means for perturbatively quantizing massless gravity theories without the usual formal apparatus associated with the quantization of constrained systems. As one application, this method was used to demonstrate that maximally supersymmetric gravity is less divergent in the ultraviolet than previously thought.
Analogue Cosmological Particle Creation: Quantum Correlations in Expanding Bose Einstein Condensates
Prain, Angus; Liberati, Stefano
2010-01-01
We investigate the structure of quantum correlations in an expanding Bose Einstein Condensate (BEC) through the analogue gravity framework. We consider both a 3+1 isotropically expanding BEC as well as the experimentally relevant case of an elongated, effectively 1+1 dimensional, expanding condensate. In this case we include the effects of inhomogeneities in the condensate, a feature rarely included in the analogue gravity literature. In both cases we link the BEC expansion to a simple model for an expanding spacetime and then study the correlation structure numerically and analytically (in suitable approximations). We also discuss the expected strength of such correlation patterns and experimentally feasible BEC systems in which these effects might be detected in the near future.
Black Hole Interior in Quantum Gravity.
Nomura, Yasunori; Sanches, Fabio; Weinberg, Sean J
2015-05-22
We discuss the interior of a black hole in quantum gravity, in which black holes form and evaporate unitarily. The interior spacetime appears in the sense of complementarity because of special features revealed by the microscopic degrees of freedom when viewed from a semiclassical standpoint. The relation between quantum mechanics and the equivalence principle is subtle, but they are still consistent.
Loop quantum gravity; Gravedad cuantica de lazos
Energy Technology Data Exchange (ETDEWEB)
Pullin, J.
2015-07-01
Loop quantum gravity is one of the approaches that are being studied to apply the rules of quantum mechanics to the gravitational field described by the theory of General Relativity . We present an introductory summary of the main ideas and recent results. (Author)
Quantum and gravity. Blend or melange?
Energy Technology Data Exchange (ETDEWEB)
Wuethrich, Christian [University of Geneva (Switzerland)
2016-07-01
Do we need to quantize gravity, as it is tacitly assumed in much of fundamental physics? The standard lore falls short of justifying an affirmative answer. Black hole thermodynamics is widely considered, faint though it may be, our firmest hint at a quantum theory of gravity - despite the failure to date to observe Hawking radiation or any other effect that would require going beyond a classical description of black holes. Hawking radiation hitherto merely enjoys a theoretical derivation in a semi-classical theory combining quantum matter with classical gravity. But how can a semi-classical melange of physical principles possibly justify that the quantum and gravity are blended into a unified fundamental theory when the latter is generally expected to reject at least some of the principles in the former?.
The Spin Foam Approach to Quantum Gravity
Perez, Alejandro
2012-01-01
This article reviews the present status of the spin foam approach to the quantization of gravity. Special attention is payed to the pedagogical presentation of the recently introduced new models for four dimensional quantum gravity. The models are motivated by a suitable implementation of the path integral quantization of the Plebanski formulation of gravity on a simplicial regularization. The article also includes a self-contained treatment of the 2+1 gravity. The simple nature of the latter provides the basis and a perspective for the analysis of both conceptual and technical issues that remain open in four dimensions.
Implications of Einstein-Weyl Causality on Quantum Mechanics
Bendaniel, David
A fundamental physical principle that has consequences for the topology of space-time is the principle of Einstein-Weyl causality. This also has quantum mechanical manifestations. Borchers and Sen have rigorously investigated the mathematical implications of Einstein-Weyl causality and shown the denumerable space-time Q2 would be implied. They were left with important philosophical paradoxes regarding the nature of the physical real line E, e.g., whether E = R, the real line of mathematics. In order to remove these paradoxes an investigation into a constructible foundation is suggested. We have pursued such a program and find it indeed provides a dense, denumerable space-time and, moreover, an interesting connection with quantum mechanics. We first show that this constructible theory contains polynomial functions which are locally homeomorphic with a dense, denumerable metric space R* and are inherently quantized. Eigenfunctions governing fields can then be effectively obtained by computational iteration. Postulating a Lagrangian for fields in a compactified space-time, we get a general description of which the Schrodinger equation is a special case. From these results we can then also show that this denumerable space-time is relational (in the sense that space is not infinitesimally small if and only if it contains a quantized field) and, since Q2 is imbedded in R*2, it directly fulfills the strict topological requirements for Einstein-Weyl causality. Therefore, the theory predicts that E = R*.
Einstein versus the Simple Pendulum Formula: Does Gravity Slow All Clocks?
Puri, Avinash
2015-01-01
According to the Newtonian formula for a simple pendulum, the period of a pendulum is inversely proportional to the square root of "g", the gravitational field strength. Einstein's theory of general relativity leads to the result that time slows down where gravity is intense. The two claims look contradictory and can muddle student and…
One-loop effective action for Einstein gravity in special background gauge
Lavrov, P M; Lavrov, P M; Reshetnyak, A A
1995-01-01
The one-loop effective action for Einstein gravity in a special one-parameter background gauge is calculated up to first order in a gauge parameter. It is shown that the effective action does not depend upon the gauge parameter on shell.
Quantum Gravity: A Brief History of Ideas and Some Prospects
Carlip, Steven; Ni, Wei-Tou; Woodard, Richard
2015-01-01
We present a bird's-eye survey on the development of fundamental ideas of quantum gravity, placing emphasis on perturbative approaches, string theory, loop quantum gravity, and black hole thermodynamics. The early ideas at the dawn of quantum gravity as well as the possible observations of quantum gravitational effects in the foreseeable future are also briefly discussed.
Quantum Gravito-Optics: A Light Route from Semiclassical Gravity to Quantum Gravity
Unnikrishnan, C S
2015-01-01
Quantum gravity remains an elusive theory, in spite of our thorough understanding of the quantum theory and the general theory of relativity separately, presumably due to the lack of any observational clues. We argue that the theory of quantum gravity has a strong constraining anchor in the sector of gravitational radiation ensuring reliable physical clues, albeit in a limited observable form. In particular, all types of gravitational waves expected to be observable in LIGO-like advanced detectors are fully quantum mechanical states of radiation. Exact equivalence of the full quantum gravity theory with the familiar semiclassical theory is ensured in the radiation sector, in most real situations where the relevant quantum operator functions are normal ordered, by the analogue of the optical equivalence theorem in quantum optics. We show that this is indeed the case for detection of the waves from a massive binary system, a single gravitational atom, that emits coherent radiation. The idea of quantum-gravitati...
Einstein against quantum mechanics: randomness, ignorance and our ignorance about randomness
Paz, Juan Pablo
2007-01-01
Albert Einstein made fundamental contributions to the development of quantum mechanics. However, he was never satisfied with the quantum worldview. In fact, during most of his life he attempted to find inconsistencies and paradoxes within quantum mechanics. His famous quote "God does not play dice" shows how disturbing was to Einstein one of the most important aspects of quantum mechanics: non-determinism. In this paper we will present the basic concepts of quantum mechanics, we will describe...
Dispelling the Quantum Spooks -- a Clue that Einstein Missed?
Price, Huw
2013-01-01
It is well-known that Bell's Theorem and other No Hidden Variable theorems have a "retrocausal loophole", because they assume that the values of pre-existing hidden variables are independent of future measurement settings. (This is often referred to, misleadingly, as the assumption of "free will".) However, it seems to have gone unnoticed until recently that a violation of this assumption is a straightforward consequence of time-symmetry, given an understanding of the quantization of light that would have seemed natural to Einstein after 1905. The new argument shows precisely why quantization makes a difference, and why time-symmetry alone does not imply retrocausality, in the classical context. It is true that later developments in quantum theory provide a way to avoid retrocausality, without violating time-symmetry; but this escape route relies on the "ontic" conception of the wave function that Einstein rejected. Had this new argument been noticed much sooner, then, it seems likely that retrocausality woul...
Hsu, Jong-Ping
2013-01-01
Yang-Mills gravity is a new theory, consistent with experiments, that brings gravity back to the arena of gauge field theory and quantum mechanics in flat space-time. It provides solutions to long-standing difficulties in physics, such as the incompatibility between Einstein's principle of general coordinate invariance and modern schemes for a quantum mechanical description of nature, and Noether's 'Theorem II' which showed that the principle of general coordinate invariance in general relativity leads to the failure of the law of conservation of energy. Yang-Mills gravity in flat space-time a
Conformal invariance and renormalization group in quantum gravity near two dimensions
Aida, Toshiaki; Kitazawa, Yoshihisa; Kawai, Hikaru; Ninomiya, Masao
1994-09-01
We study quantum gravity in 2 + ɛ dimensions in such a way as to preserve the volume-preserving diffeomorphism invariance. In such a formulation, we prove the following trinity: the general covariance, the conformal invariance and the renormalization group flow to the Einstein theory at long distance. We emphasize that the consistent and macroscopic universes like our own can only exist for a matter central charge 0 effect and universes are found to bounce back from the big crunch. Our formulation may be viewed as a Ginzburg-Landau theory which can describe both the broken and the unbroken phase of quantum gravity and the phase transition between them.
A Cosmological Sector in Loop Quantum Gravity
Koslowski, Tim A
2007-01-01
We use the method of embedding a subsystem (i.e. its observable algebra) into a larger quantum system to extract a cosmological sector from full Loop Quantum Gravity. The application of this method provides a setting for a systematic study of the interplay between diffeomorphism invariance and symmetry reduction. The non-triviality of this relation is shown by extracting a cosmological system that has configurations variables that are very similar to the ones of a super-selection sector of standard Loop Quantum Cosmology. The full operator algebra however turns out to be different from standard Loop Quantum Cosmology. The homogeneous isotropic sector of pure gravity turns out to be quantum mechanics on a circle. The dynamics of our system seems pathological at first sight, and we give both mathematical and physical reasons for this behavior and we explain a strategy to cure these pathologies.
Quantum gravity kinematics from extended TQFTs
Dittrich, Bianca
2016-01-01
We show how extended topological quantum field theories (TQFTs) can be used to obtain a kinematical setup for quantum gravity, i.e. a kinematical Hilbert space together with a representation of the observable algebra including operators of quantum geometry. In particular, we consider the holonomy-flux algebra of (2+1)-dimensional Euclidean loop quantum gravity, and construct a new representation of this algebra that incorporates a positive cosmological constant. The vacuum state underlying our representation is defined by the Turaev-Viro TQFT. We therefore construct here a generalization, or more precisely a quantum deformation at root of unity, of the previously-introduced SU(2) BF representation. The extended Turaev-Viro TQFT provides a description of the excitations on top of the vacuum, which are essential to allow for a representation of the holonomies and fluxes. These excitations agree with the ones induced by massive and spinning particles, and therefore the framework presented here allows automatical...
Einstein Revisited - Gravity in Curved Spacetime Without Event Horizons
Leiter, Darryl
2000-04-01
In terms of covariant derivatives with respect to flat background spacetimes upon which the physical curved spacetime is imposed (1), covariant conservation of energy momentum requires, via the Bianchi Identity, that the Einstein tensor be equated to the matter energy momentum tensor. However the Einstein tensor covariantly splits (2) into two tensor parts: (a) a term proportional to the gravitational stress energy momentum tensor, and (b) an anti-symmetric tensor which obeys a covariant 4-divergence identity called the Freud Identity. Hence covariant conservation of energy momentum requires, via the Freud Identity, that the Freud tensor be equal to a constant times the matter energy momentum tensor. The resultant field equations (3) agree with the Einstein equations to first order, but differ in higher orders (4) such that black holes are replaced by "red holes" i.e., dense objects collapsed inside of their photon orbits with no event horizons. (1) Rosen, N., (1963), Ann. Phys. v22, 1; (2) Rund, H., (1991), Alg. Grps. & Geom. v8, 267; (3) Yilmaz, Hl, (1992), Nuo. Cim. v107B, 946; (4) Roberstson, S., (1999),Ap.J. v515, 365.
Cosmological dynamics of $f(R)$ gravity scalar degree of freedom in Einstein frame
Goswami, Umananda Dev
2013-01-01
$f(R)$ gravity models belong to an important class of modified gravity models where the late time cosmic accelerated expansion is considered as the manifestation of the large scale modification of the force of gravity. $f(R)$ gravity models can be expressed in terms of a scalar degree of freedom by redefinition of models variable. The conformal transformation of the action from Jordan frame to Einstein frame makes the scalar degree of freedom more explicit and can be studied conveniently. We have investigated the features of the scalar degree of freedoms and the consequent cosmological implications of the power-law ($\\xi R^n$) and the Starobinsky (disappearing cosmological constant) $f(R)$ gravity models numerically in the Einstein frame. Both the models show interesting behaviour of their scalar degree of freedom and could produce the accelerated expansion of the Universe in the Einstein frame with the negative equation of state of the scalar field. However the scalar field potential for the power-law model ...
Dynamics of Anisotropic Collapsing Spheres in Einstein Gauss-Bonnet Gravity
Abbas, G
2015-01-01
This paper is devoted to investigate the dynamics of the self gravitating adiabatic and anisotropic source in $5D$ Einstein Gauss-Bonnet gravity. To this end, the source has been taken as Tolman-Bondi model which preserve inhomogeneity in nature. The field equations, Misner-Sharp mass and dynamical equations have formulated in Einstein Gauss-Bonnet gravity in $5D$. The junction conditions have been explored between the anisotropic source and vacuum solution in Gauss-Bonnet gravity in detail. The Misner and Sharp approach has been applied to define the proper time and radial derivatives. Further, these helps to formulate general dynamical equations. The equations show that the mass of the collapsing system increases with the same amount as the effective radial pressure increases. The dynamical system preserve retardation which implies that system under-consideration goes to gravitational collapse.
Satin, Seema
2015-01-01
We attempt to introduce an new approach towards study of certain interesting issues in classical gravity. This can be done for few confined, but interesting and meaningful physical situations, which can be modeled by a classical stochastic Einstein equation. The Einstein equation can be looked upon as an equation of motion, while introducing to it a classical stochastic source or classical fluctuations as driving source. This is analogous to the Langevin equation formalism, in Brownian motion studies. A justification for the validity of such an ansatz for classical gravity is given. The regime of validity of such an approach and the consequences and possible outcomes of this formulation are discussed. We also mention, further relevant directions and applications of the same,that act as motivation towards the new proposal. This field of study can be seen to emerge out of well established ideas and results in Brownian motion theory as well as the Stochastic Semiclassical Gravity (which is already an active area...
Superbounce and Loop Quantum Cosmology Ekpyrosis from Modified Gravity
Oikonomou, V K
2014-01-01
As is known, in modified cosmological theories of gravity many of the cosmologies which could not be generated by standard Einstein gravity, can be consistently described by $F(R)$ theories. Using known reconstruction techniques, we investigate which $F(R)$ theories can lead to a Hubble parameter describing two types of cosmological bounces, the superbounce model, related to supergravity and non-supersymmetric models of contracting ekpyrosis and also the Loop Quantum Cosmology modified ekpyrotic model. Since our method is an approximate method, we investigate the problem at large and small curvatures. As we evince, both models yield power law reconstructed $F(R)$ gravities, with the most interesting new feature being that both lead to an $R+aR^2$ gravity in the large curvature approximation. As we explicitly show, this result is not accidental and we study the general case which, within the approximations imposed by the employed reconstruction method, always leads to an $R^2$ in the large curvature limit. As ...
F(R) gravity's rainbow and their Einstein counterpart
Hendi, S H; Panahiyan, S; Momennia, M
2016-01-01
Motivated by UV completion of general relativity with a modification of a geometry at high energy scale, it is expected to have an energy dependent geometry. In this paper, we introduce charged black hole solutions with power Maxwell invariant source in the context of gravity's rainbow. In addition, we investigate two classes of F(R) gravity's rainbow solutions. At first, we study energy dependent F(R) gravity without energy momentum tensor, and then we obtain F(R) gravity's rainbow in the presence of conformally invariant Maxwell source. We study geometrical properties of the mentioned solutions and compare their results. We also give some related comments regarding to thermodynamical behavior of the obtained solutions and discuss thermal stability of the solutions.
Gravitational Waves in Effective Quantum Gravity
Energy Technology Data Exchange (ETDEWEB)
Calmet, Xavier; Kuntz, Ibere; Mohapatra, Sonali [University of Sussex, Physics and Astronomy, Brighton (United Kingdom)
2016-08-15
In this short paper we investigate quantum gravitational effects on Einstein's equations using Effective Field Theory techniques. We consider the leading order quantum gravitational correction to the wave equation. Besides the usual massless mode, we find a pair of modes with complex masses. These massive particles have a width and could thus lead to a damping of gravitational waves if excited in violent astrophysical processes producing gravitational waves such as e.g. black hole mergers. We discuss the consequences for gravitational wave events such as GW 150914 recently observed by the Advanced LIGO collaboration. (orig.)
Chiral fermions in asymptotically safe quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Meibohm, J. [Gothenburg University, Department of Physics, Goeteborg (Sweden); Universitaet Heidelberg, Institut fuer Theoretische Physik, Heidelberg (Germany); Pawlowski, J.M. [Universitaet Heidelberg, Institut fuer Theoretische Physik, Heidelberg (Germany); GSI Helmholtzzentrum fuer Schwerionenforschung mbH, ExtreMe Matter Institute EMMI, Darmstadt (Germany)
2016-05-15
We study the consistency of dynamical fermionic matter with the asymptotic safety scenario of quantum gravity using the functional renormalisation group. Since this scenario suggests strongly coupled quantum gravity in the UV, one expects gravity-induced fermion self-interactions at energies of the Planck scale. These could lead to chiral symmetry breaking at very high energies and thus to large fermion masses in the IR. The present analysis which is based on the previous works (Christiansen et al., Phys Rev D 92:121501, 2015; Meibohm et al., Phys Rev D 93:084035, 2016), concludes that gravity-induced chiral symmetry breaking at the Planck scale is avoided for a general class of NJL-type models. We find strong evidence that this feature is independent of the number of fermion fields. This finding suggests that the phase diagram for these models is topologically stable under the influence of gravitational interactions. (orig.)
Chiral fermions in asymptotically safe quantum gravity
Meibohm, Jan
2016-01-01
We study the consistency of dynamical fermionic matter with the asymptotic safety scenario of quantum gravity using the functional renormalisation group. Since this scenario suggests strongly coupled quantum gravity in the UV, one expects gravity-induced fermion self-interactions at energies of the Planck-scale. These could lead to chiral symmetry breaking at very high energies and thus to large fermion masses in the IR. The present analysis which is based on the previous works \\cite{Christiansen:2015rva, Meibohm:2015twa}, concludes that gravity-induced chiral symmetry breaking at the Planck scale is avoided for a general class of NJL-type models, regardless of the number of fermion flavours. This suggests that the phase diagram for these models is topologically stable under the influence of gravitational interactions.
Loop Quantum Gravity and the The Planck Regime of Cosmology
Ashtekar, Abhay
2013-01-01
The very early universe provides the best arena we currently have to test quantum gravity theories. The success of the inflationary paradigm in accounting for the observed inhomogeneities in the cosmic microwave background already illustrates this point to a certain extent because the paradigm is based on quantum field theory on the curved cosmological space-times. However, this analysis excludes the Planck era because the background space-time satisfies Einstein's equations all the way back to the big bang singularity. Using techniques from loop quantum gravity, the paradigm has now been extended to a self-consistent theory from the Planck regime to the onset of inflation, covering some 11 orders of magnitude in curvature. In addition, for a narrow window of initial conditions, there are departures from the standard paradigm, with novel effects, such as a modification of the consistency relation involving the scalar and tensor power spectra and a new source for non-Gaussianities. Thus, the genesis of the lar...
Quantum Gravity signatures in the Unruh effect
Alkofer, Natalia; Saueressig, Frank; Versteegen, Fleur
2016-01-01
We study quantum gravity signatures emerging from phenomenologically motivated multiscale models, spectral actions, and Causal Set Theory within the detector approach to the Unruh effect. We show that while the Unruh temperature is unaffected, Lorentz-invariant corrections to the two-point function leave a characteristic fingerprint in the induced emission rate of the accelerated detector. Generically, quantum gravity models exhibiting dynamical dimensional reduction exhibit a suppression of the Unruh rate at high energy while the rate is enhanced in Kaluza-Klein theories with compact extra dimensions. We quantify this behavior by introducing the "Unruh dimension" as the effective spacetime dimension seen by the Unruh effect and show that it is related, though not identical, to the spectral dimension used to characterize spacetime in quantum gravity. We comment on the physical origins of these effects and their relevance for black hole evaporation.
Quantum gravity signatures in the Unruh effect
Alkofer, Natalia; D'Odorico, Giulio; Saueressig, Frank; Versteegen, Fleur
2016-11-01
We study quantum gravity signatures emerging from phenomenologically motivated multiscale models, spectral actions, and causal set theory within the detector approach to the Unruh effect. We show that while the Unruh temperature is unaffected, Lorentz-invariant corrections to the two-point function leave a characteristic fingerprint in the induced emission rate of the accelerated detector. Generically, quantum gravity models exhibiting dynamical dimensional reduction exhibit a suppression of the Unruh rate at high energy while the rate is enhanced in Kaluza-Klein theories with compact extra dimensions. We quantify this behavior by introducing the "Unruh dimension" as the effective spacetime dimension seen by the Unruh effect and show that it is related, though not identical, to the spectral dimension used to characterize spacetime in quantum gravity. We comment on the physical origins of these effects and their relevance for black hole evaporation.
Loop quantum gravity as an effective theory
Bojowald, Martin
2012-01-01
As a canonical and generally covariant gauge theory, loop quantum gravity requires special techniques to derive effective actions or equations. If the proper constructions are taken into account, the theory, in spite of considerable ambiguities at the dynamical level, allows for a meaningful phenomenology to be developed, by which it becomes falsifiable. The tradiational problems plaguing canonical quantum-gravity theories, such as the anomaly issue or the problem of time, can be overcome or are irrelevant at the effective level, resulting in consistent means of physical evaluations. This contribution presents aspects of canonical equations and related notions of (deformed) space-time structures and discusses implications in loop quantum gravity, such as signature change at high density from holonomy corrections, and falsifiability thanks to inverse-triad corrections.
Coordinate time dependence in Quantum Gravity
Bojowald, M; Skirzewski, A; Bojowald, Martin; Singh, Parampreet; Skirzewski, Aureliano
2004-01-01
The intuitive classical space-time picture breaks down in quantum gravity, which makes a comparison and the development of semiclassical techniques quite complicated. Using ingredients of the group averaging method to solve constraints one can nevertheless introduce a classical coordinate time into the quantum theory, and use it to investigate the way a semiclassical continuous description emerges from discrete quantum evolution. Applying this technique to test effective classical equations of loop cosmology and their implications for inflation and bounces, we show that the effective semiclassical theory is in good agreement with the quantum description even at short scales.
Prima Facie Questions in Quantum Gravity
Isham, C J
2009-01-01
The long history of the study of quantum gravity has thrown up a complex web of ideas and approaches. The aim of this article is to unravel this web a little by analysing some of the {\\em prima facie\\/} questions that can be asked of almost any approach to quantum gravity and whose answers assist in classifying the different schemes. Particular emphasis is placed on (i) the role of background conceptual and technical structure; (ii) the role of spacetime diffeomorphisms; and (iii) the problem of time.
Effective constraints of loop quantum gravity
Bojowald, M; Kagan, M; Skirzewski, A; Bojowald, Martin; Hernandez, Hector; Kagan, Mikhail; Skirzewski, Aureliano
2006-01-01
Within a perturbative cosmological regime of loop quantum gravity corrections to effective constraints are computed. This takes into account all inhomogeneous degrees of freedom relevant for scalar metric modes around flat space and results in explicit expressions for modified coefficients and of higher order terms. It also illustrates the role of different scales determining the relative magnitude of corrections. Our results demonstrate that loop quantum gravity has the correct classical limit, at least in its sector of cosmological perturbations around flat space, in the sense of perturbative effective theory.
Palatini Actions and Quantum Gravity Phenomenology
Olmo, Gonzalo J
2011-01-01
We show that a quadratic gravitational Lagrangian in the Palatini formulation is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, we show 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. Also, the resulting isotropic and anisotropic cosmologies are free from the big bang singularity. This singularity avoidance occurs non-perturbatively and shares some similitudes with the effective dynamics of loop quantum cosmology.
Conformastatic disk-haloes in Einstein-Maxwell gravity
Gutiérrez-Piñeres, Antonio C; Quevedo, Hernando
2012-01-01
We present a relativistic model describing a thin disk surrounded by a halo in presence of an electromagnetic field. The model is obtained by solving the Einstein-Maxwell equations on a particular conformastatic spacetime background and by using the distributional approach for the energy-momentum tensor. A class of solutions is obtained in which the gravitational and electromagnetic potentials are completely determined by a harmonic function only. A particular solution is given that is asymptotically flat and singularity-free, and satisfies all the energy conditions.
Black holes in loop quantum gravity.
Perez, Alejandro
2017-07-11
This is a review of the results on black hole physics in the framework of loop quantum gravity. The key feature underlying the results is the discreteness of geometric quantities at the Planck scale predicted by this approach to quantum gravity. Quantum discreteness follows directly from the canonical quantization prescription when applied to the action of general relativity that is suitable for the coupling of gravity with gauge fields and specially with fermions. Planckian discreteness and causal considerations provide the basic structure for the understanding of the thermal properties of black holes close to equilibrium. Discreteness also provides a fresh new look at more (at the moment) speculative issues such as those concerning the fate of information in black hole evaporation. The hypothesis of discreteness leads also to interesting phenomenology with possible observational consequences. The theory of loop quantum gravity is a developing program. This review reports its achievements and open questions in a pedagogical manner with an emphasis on quantum aspects of black hole physics. . © 2017 IOP Publishing Ltd.
Quantum optics. Gravity meets quantum physics
Energy Technology Data Exchange (ETDEWEB)
Adams, Bernhard W. [Argonne National Lab. (ANL), Argonne, IL (United States)
2015-02-27
Albert Einstein’s general theory of relativity is a classical formulation but a quantum mechanical description of gravitational forces is needed, not only to investigate the coupling of classical and quantum systems but simply to give a more complete description of our physical surroundings. In this issue of Nature Photonics, Wen-Te Liao and Sven Ahrens reveal a link between quantum and gravitational physics. They propose that in the quantum-optical effect of superradiance, the world line of electromagnetic radiation is changed by the presence of a gravitational field.
Fidelity of quantum state for interacting system of light field and atomic Bose-Einstein condensate
Institute of Scientific and Technical Information of China (English)
Chunjia Huang; Ming Zhou; Fanzhi Kong; Jiayuan Fang; Kewei Mo
2005-01-01
@@ The evolution characteristics of quantum state fidelity in an interacting system of single-mode light field and atomic Bose-Einstein condensate have been studied and the influence of the initial light field intensity and the interaction among atoms of Bose-Einstein condensate on the quantum state fidelity respectively have been discussed.
Testing an Ansatz for the Leading Secular Loop Corrections from Quantum Gravity during Inflation
Basu, S
2016-01-01
It is widely believed that the leading secular loop corrections from quantum gravity can be subsumed into a coordinate redefinition. Hence the apparent infrared logarithm corrections to any quantity would be just the result of taking the expectation value of the tree order quantity at the transformed coordinates in the graviton vacuum. We term this the Transformation Ansatz and we compare its predictions against explicit one loop computations in Maxwell + Einstein and Dirac + Einstein on de Sitter background. In each case the ansatz fails.
Testing an ansatz for the leading secular loop corrections from quantum gravity during inflation
Basu, S.; Woodard, R. P.
2016-10-01
It is widely believed that the leading secular loop corrections from quantum gravity can be subsumed into a coordinate redefinition. Hence the apparent infrared logarithm corrections to any quantity would be just the result of taking the expectation value of the tree order quantity at the transformed coordinates in the graviton vacuum. We term this the transformation ansatz and we compare its predictions against explicit one loop computations in Maxwell + Einstein and Dirac + Einstein on de Sitter background. In each case the ansatz fails.
Quantum Gravity and Higher Curvature Actions
Bojowald, M; Bojowald, Martin; Skirzewski, Aureliano
2006-01-01
Effective equations are often useful to extract physical information from quantum theories without having to face all technical and conceptual difficulties. One can then describe aspects of the quantum system by equations of classical type, which correct the classical equations by modified coefficients and higher derivative terms. In gravity, for instance, one expects terms with higher powers of curvature. Such higher derivative formulations are discussed here with an emphasis on the role of degrees of freedom and on differences between Lagrangian and Hamiltonian treatments. A general scheme is then provided which allows one to compute effective equations perturbatively in a Hamiltonian formalism. Here, one can expand effective equations around any quantum state and not just a perturbative vacuum. This is particularly useful in situations of quantum gravity or cosmology where perturbations only around vacuum states would be too restrictive. The discussion also demonstrates the number of free parameters expect...
New commutation relations for quantum gravity
Soo, Chopin
2016-01-01
A new set of fundamental commutation relations for quantum gravity is presented. The basic variables are the eight components of the unimodular part of the spatial dreibein and eight SU(3) generators which correspond to Klauder's momentric variables. The commutation relations are not canonical, but they have well defined group theoretical meanings. All fundamental entities are dimensionless; and quantum wave functionals are preferentially selected to be in the dreibein representation.
Quantum turbulence in trapped atomic Bose–Einstein condensates
Energy Technology Data Exchange (ETDEWEB)
Tsatsos, Marios C., E-mail: marios@ifsc.usp.br [São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP (Brazil); Tavares, Pedro E.S.; Cidrim, André; Fritsch, Amilson R.; Caracanhas, Mônica A. [São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP (Brazil); Santos, F. Ednilson A. dos [Department of Physics, Federal University of São Carlos, 13565-905, São Carlos, SP (Brazil); Barenghi, Carlo F. [Joint Quantum Centre Durham-Newcastle, and School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne NE1 7RU (United Kingdom); Bagnato, Vanderlei S., E-mail: vander@ifsc.usp.br [São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970, São Carlos, SP (Brazil)
2016-03-25
Turbulence, the complicated fluid behavior of nonlinear and statistical nature, arises in many physical systems across various disciplines, from tiny laboratory scales to geophysical and astrophysical ones. The notion of turbulence in the quantum world was conceived long ago by Onsager and Feynman, but the occurrence of turbulence in ultracold gases has been studied in the laboratory only very recently. Albeit new as a field, it already offers new paths and perspectives on the problem of turbulence. Herein we review the general properties of quantum gases at ultralow temperatures paying particular attention to vortices, their dynamics and turbulent behavior. We review the recent advances both from theory and experiment. We highlight, moreover, the difficulties of identifying and characterizing turbulence in gaseous Bose–Einstein condensates compared to ordinary turbulence and turbulence in superfluid liquid helium and spotlight future possible directions.
Quantum filaments in dipolar Bose-Einstein condensates
Wächtler, F.; Santos, L.
2016-06-01
Collapse in dipolar Bose-Einstein condensates may be arrested by quantum fluctuations. Due to the anisotropy of the dipole-dipole interactions, the dipole-driven collapse induced by soft excitations is compensated by the repulsive Lee-Huang-Yang contribution resulting from quantum fluctuations of hard excitations, in a similar mechanism as that recently proposed for Bose-Bose mixtures. The arrested collapse results in self-bound filamentlike droplets, providing an explanation for the intriguing results of recent dysprosium experiments. Arrested instability and droplet formation are general features directly linked to the nature of the dipole-dipole interactions, and should hence play an important role in all future experiments with strongly dipolar gases.
Quantum Gravity Constraints from Unitarity and Analyticity
Bellazzini, Brando; Remmen, Grant N
2015-01-01
We derive rigorous bounds on corrections to Einstein gravity using unitarity and analyticity of graviton scattering amplitudes. In $D\\geq 4$ spacetime dimensions, these consistency conditions mandate positive coefficients for certain quartic curvature operators. We systematically enumerate all such positivity bounds in $D=4$ and $D=5$ before extending to $D\\geq 6$. Afterwards, we derive positivity bounds for supersymmetric operators and verify that all of our constraints are satisfied by weakly-coupled string theories. Among quadratic curvature operators, we find that the Gauss-Bonnet term in $D\\geq5 $ is inconsistent unless new degrees of freedom enter at the natural cutoff scale defined by the effective theory. Our bounds apply to perturbative ultraviolet completions of gravity.
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''
Einstein's quantum theory of the monatomic ideal gas: non-statistical arguments for a new statistics
Pérez, Enric
2010-01-01
In this article, we analyze the third of three papers, in which Einstein presented his quantum theory of the ideal gas of 1924-1925. Although it failed to attract the attention of Einstein's contemporaries and although also today very few commentators refer to it, we argue for its significance in the context of Einstein's quantum researches. It contains an attempt to extend and exhaust the characterization of the monatomic ideal gas without appealing to combinatorics. Its ambiguities illustrate Einstein's confusion with his initial success in extending Bose's results and in realizing the consequences of what later became to be called Bose-Einstein statistics. We discuss Einstein's motivation for writing a non-combinatorial paper, partly in response to criticism by his friend Ehrenfest, and we paraphrase its content. Its arguments are based on Einstein's belief in the complete analogy between the thermodynamics of light quanta and of material particles and invoke considerations of adiabatic transformations as ...
Can chaos be observed in quantum gravity?
Directory of Open Access Journals (Sweden)
Bianca Dittrich
2017-06-01
Full Text Available Full general relativity is almost certainly ‘chaotic’. We argue that this entails a notion of non-integrability: a generic general relativistic model, at least when coupled to cosmologically interesting matter, likely possesses neither differentiable Dirac observables nor a reduced phase space. It follows that the standard notion of observable has to be extended to include non-differentiable or even discontinuous generalized observables. These cannot carry Poisson-algebraic structures and do not admit a standard quantization; one thus faces a quantum representation problem of gravitational observables. This has deep consequences for a quantum theory of gravity, which we investigate in a simple model for a system with Hamiltonian constraint that fails to be completely integrable. We show that basing the quantization on standard topology precludes a semiclassical limit and can even prohibit any solutions to the quantum constraints. Our proposed solution to this problem is to refine topology such that a complete set of Dirac observables becomes continuous. In the toy model, it turns out that a refinement to a polymer-type topology, as e.g. used in loop gravity, is sufficient. Basing quantization of the toy model on this finer topology, we find a complete set of quantum Dirac observables and a suitable semiclassical limit. This strategy is applicable to realistic candidate theories of quantum gravity and thereby suggests a solution to a long-standing problem which implies ramifications for the very concept of quantization. Our work reveals a qualitatively novel facet of chaos in physics and opens up a new avenue of research on chaos in gravity which hints at deep insights into the structure of quantum gravity.
Can chaos be observed in quantum gravity?
Dittrich, Bianca; Höhn, Philipp A.; Koslowski, Tim A.; Nelson, Mike I.
2017-06-01
Full general relativity is almost certainly 'chaotic'. We argue that this entails a notion of non-integrability: a generic general relativistic model, at least when coupled to cosmologically interesting matter, likely possesses neither differentiable Dirac observables nor a reduced phase space. It follows that the standard notion of observable has to be extended to include non-differentiable or even discontinuous generalized observables. These cannot carry Poisson-algebraic structures and do not admit a standard quantization; one thus faces a quantum representation problem of gravitational observables. This has deep consequences for a quantum theory of gravity, which we investigate in a simple model for a system with Hamiltonian constraint that fails to be completely integrable. We show that basing the quantization on standard topology precludes a semiclassical limit and can even prohibit any solutions to the quantum constraints. Our proposed solution to this problem is to refine topology such that a complete set of Dirac observables becomes continuous. In the toy model, it turns out that a refinement to a polymer-type topology, as e.g. used in loop gravity, is sufficient. Basing quantization of the toy model on this finer topology, we find a complete set of quantum Dirac observables and a suitable semiclassical limit. This strategy is applicable to realistic candidate theories of quantum gravity and thereby suggests a solution to a long-standing problem which implies ramifications for the very concept of quantization. Our work reveals a qualitatively novel facet of chaos in physics and opens up a new avenue of research on chaos in gravity which hints at deep insights into the structure of quantum gravity.
A non-equilibrium extension of quantum gravity
Mandrin, Pierre A
2016-01-01
A variety of quantum gravity models (including spin foams) can be described using a path integral formulation. A path integral has a well-known statistical mechanical interpretation in connection with a canonical ensemble. In this sense, a path integral describes the thermodynamic equilibrium of a local system in a thermal bath. This interpretation is in contrast to solutions of Einstein's Equations which depart from local thermodynamical equilibrium (one example is shown explicitly). For this reason, we examine an extension of the path integral model to a (locally) non-equilibrium description. As a non-equilibrium description, we propose to use a global microcanonical ensemble with constraints. The constraints reduce the set of admissible microscopic states to be consistent with the macroscopic geometry. We also analyse the relation between the microcanonical description and a statistical approach not based on dynamical assumptions which has been proposed recently. This analysis is of interest for the test o...
Gravity beyond Einstein? Part I: Physics and the Trouble with Experiments
Hauser, Jochem; Dröscher, Walter
2017-05-01
This article provides a review of the latest experimental results in quantum physics and astrophysics, discussing their repercussions on the advanced physical theories that go beyond both the SMs (standard models) of particle physics and cosmology. It will be shown that many of the essential concepts of the advanced theoretical models developed over the past 40 years are no longer tenable because they are contradicting the novel data. Most recent results (December 2016) from the Large Hadron Collider revealed no new matter particles up to particle masses of 1.6 TeV/c2, which is in accordance with recent ACME experimental data (2014) that saw no electric dipole moment for the electron as predicted by these theories. Moreover, the LUX experiment (since 2013) did not see any dark matter particles either, thus independently supporting LHC and ACME measurements. Furthermore, experimental particle physics seems to be telling us that dark matter particles (LHC results) do not exist, suggesting that dark matter particles either are more exotic or are more difficult to detect than had been predicted in the past decades (less likely with recent LHC results). Astrophysical observations since 1933, starting with Caltech astronomer Zwicky, however, have provided irrefutable evidence for the existence of dark matter, for instance, based on the phenomenon of gravitational lensing as well as observed rotational velocities of stars orbiting the galactic center that are deviating from Newton's law. Surprisingly, recent astronomical observations by Bidin, ESO (2010, 2012, 2014), seem to indicate the absence of dark matter within galaxies. In addition, cosmology at present has no explanation for about 68 % of the energy in the Universe that comes in the form of dark energy. Recently, measured data from three entirely different types of experiments both on earth and in space (2006-2011) are hinting at completely novel features of gravity that, if confirmed, must be outside Einstein
New formulation of Horava-Lifshitz quantum gravity as a master constraint theory
Soo, Chopin; Yu, Hoi-Lai
2010-01-01
Horava-Lifshitz theory of quantum gravity attempts to preserve unitarity by relinquishing space-time covariance, and improve renormalizability by including higher order (spatial) derivatives. For theories without full space-time covariance, departures of the constraint algebra from the Dirac algebra are to be expected. In the non-projectable version of Horava-Lifshitz gravity, the commutator of two local Hamiltonian constraints leads to severely restrictive secondary constraints and perplexing "troubles". On the other hand, the projectable version has an integrated Hamiltonian constraint and consistent constraint algebra. But an extra graviton mode which can be problematic is then allowed, whereas in Einstein's theory the spurious mode is eliminated precisely by the local Hamiltonian constraint. A new formulation of Horava-Lifshitz gravity, naturally realized as a representation of the master constraint algebra studied by loop quantum gravity researchers, is presented in this work. This reformulation yields a...
Semiclassical analysis of loop quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Conrady, F.
2005-10-17
In this Ph.D. thesis, we explore and develop new methods that should help in determining an effective semiclassical description of canonical loop quantum gravity and spin foam gravity. A brief introduction to loop quantum gravity is followed by three research papers that present the results of the Ph.D. project. In the first article, we deal with the problem of time and a new proposal for implementing proper time as boundary conditions in a sum over histories: we investigate a concrete realization of this formalism for free scalar field theory. In the second article, we translate semiclassical states of linearized gravity into states of loop quantum gravity. The properties of the latter indicate how semiclassicality manifests itself in the loop framework, and how this may be exploited for doing semiclassical expansions. In the third part, we propose a new formulation of spin foam models that is fully triangulation- and background-independent: by means of a symmetry condition, we identify spin foam models whose triangulation-dependence can be naturally removed. (orig.)
Why does a ball fall?: A new visualization for Einstein's model of gravity
Gould, Roy R.
2016-05-01
Many physics teachers seek a simple illustration of Einstein's model of gravity, suitable for the introductory physics classroom. In this article, we show that an ordinary wall map of the world can be used to contrast Newton's and Einstein's explanations for why a ball falls when released. Trajectories on the map are analogous to the trajectories of the ball through spacetime, because the geometry of the map is remarkably similar to the geometry of spacetime near Earth's surface. To aid in the pedagogy, we focus on the concept of scale rather than curvature. We show that, contrary to popular visualizations of Einstein's model, it is primarily the warping of time, not space, that causes a ball to fall, and we address the question of why we do not see the distortion of spacetime around us. Finally, we recover Newton's results for the falling ball from our geometrical treatment.
Black hole entropy in loop quantum gravity
Agulló, Iván; Barbero G, J. Fernando; Borja, E. F.; Díaz-Polo, Jacobo; Villaseñor, Eduardo J. S.
2012-05-01
We discuss the recent progress on black hole entropy in loop quantum gravity, focusing in particular on the recently discovered discretization effect for microscopic black holes. Powerful analytical techniques have been developed to perform the exact computation of entropy. A statistical analysis of the structures responsible for this effect shows its progressive damping and eventual disappearance as one increases the considered horizon area.
Holonomy loops, spectral triples and quantum gravity
DEFF Research Database (Denmark)
Johannes, Aastrup; Grimstrup, Jesper Møller; Nest, Ryszard
2009-01-01
We review the motivation, construction and physical interpretation of a semi-finite spectral triple obtained through a rearrangement of central elements of loop quantum gravity. The triple is based on a countable set of oriented graphs and the algebra consists of generalized holonomy loops...
Gravity Dual of Quantum Information Metric
Miyaji, Masamichi; Shiba, Noburo; Takayanagi, Tadashi; Watanabe, Kento
2015-01-01
We study a quantum information metric (or fidelity susceptibility) in conformal field theories with respect to a small perturbation by a primary operator. We argue that its gravity dual is approximately given by a volume of maximal time slice in an AdS spacetime when the perturbation is exactly marginal. We confirm our claim in several examples.
Dimension and dimensional reduction in quantum gravity
Carlip, S.
2017-10-01
A number of very different approaches to quantum gravity contain a common thread, a hint that spacetime at very short distances becomes effectively two dimensional. I review this evidence, starting with a discussion of the physical meaning of ‘dimension’ and concluding with some speculative ideas of what dimensional reduction might mean for physics.
CDT: an entropic theory of quantum gravity
Ambjorn, J.; Goerlich, A.; Jurkiewicz, J.; Loll, R.
2010-01-01
In these lectures we describe how a theory of quantum gravity may be constructed in terms of a lattice formulation based on so-called causal dynamical triangulations (CDT). We discuss how the continuum limit can be obtained and how to define and measure diffeomorphism-invariant correlators. In four
Generalized BF state in quantum gravity
Yamashita, Shinji; Fukuda, Makoto
2014-01-01
The BF state is known as a simple wave function which satisfies three constraints in canonical quantum gravity without a cosmological constant. It is constructed from a product of the group delta functions. Applying the chiral asymmetric extension, the BF state is generalized to the state for the real values of the Barbero-Immirzi parameter.
Quantum gravity and the holographic principle
Haro Ollé, S. de
2001-01-01
In this thesis we study two different approaches to holography, and comment on the possible relation between them. The first approach is an analysis of the high-energy regime of quantum gravity in the eikonal approximation, where the theory reduces to a topological field theory. This is the re
The strange equation of quantum gravity
2015-01-01
Appeared in the Classical and Quantum Gravity Focus issue: Milestones of general relativity. 7 pages; International audience; Disavowed by one its fathers, ill defined, never empirically tested, the Wheeler-DeWitt equation has nevertheless had a powerful influence on fundamental physics. A well deserved one.
Astrophysical limits on quantum gravity motivated birefringence
Gleiser, R J; Gleiser, Reinaldo J.; Kozameh, Carlos N.
2001-01-01
We obtain observational upper bounds on a class of quantum gravity related birefringence effects, by analyzing the presence of linear polarization in the optical and ultraviolet spectrum of some distant sources. In the notation of Gambini and Pullin we find $\\chi < 10^{-3}$.
Gauges and functional measures in quantum gravity II: Higher derivative gravity
Ohta, N; Pereira, A D
2016-01-01
We compute the one-loop divergences in a higher-derivative theory of gravity including Ricci tensor squared and Ricci scalar squared terms, in addition to the Hilbert and cosmological terms, on an (generally off-shell) Einstein background. We work with a two-parameter family of path integral measures, corresponding to different ways of parametrizing the graviton field, and a two-parameter family of gauges. Only the logarithmic divergences are independent of these choices, but there are some choices of gauge or parametrization that reduce the dependence on the remaining parameters. The results are invariant under a recently discovered "duality" that involves the replacement of the densitized metric by a densitized inverse metric as the fundamental quantum variable.
Generalized Parametrization Dependence in Quantum Gravity
Gies, Holger; Lippoldt, Stefan
2015-01-01
We critically examine the gauge, and field-parametrization dependence of renormalization group flows in the vicinity of non-Gau\\ss{}ian fixed points in quantum gravity. While physical observables are independent of such calculational specifications, the construction of quantum gravity field theories typically relies on off-shell quantities such as $\\beta$ functions and generating functionals and thus face potential stability issues with regard to such generalized parametrizations. We analyze a two-parameter class of covariant gauge conditions, the role of momentum-dependent field rescalings and a class of field parametrizations. Using the product of Newton and cosmological constant as an indicator, the principle of minimum sensitivity identifies stationary points in this parametrization space which show a remarkable insensitivity to the parametrization. In the most insensitive cases, the quantized gravity system exhibits a non-Gau\\ss{}ian UV stable fixed point, lending further support to asymptotically free q...
Stability of anti-de sitter space in Einstein-Gauss-Bonnet gravity.
Deppe, Nils; Kolly, Allison; Frey, Andrew; Kunstatter, Gabor
2015-02-20
Recently it has been argued that in Einstein gravity anti-de Sitter spacetime is unstable against the formation of black holes for a large class of arbitrarily small perturbations. We examine the effects of including a Gauss-Bonnet term. In five dimensions, spherically symmetric Einstein-Gauss-Bonnet gravity has two key features: Choptuik scaling exhibits a radius gap, and the mass function goes to a finite value as the horizon radius vanishes. These suggest that black holes will not form dynamically if the total mass-energy content of the spacetime is too small, thereby restoring the stability of anti-de Sitter spacetime in this context. We support this claim with numerical simulations and uncover a rich structure in horizon radii and formation times as a function of perturbation amplitude.
Quantum gravity, effective fields and string theory
Bjerrum-Bohr, N E J
2004-01-01
We look at the various aspects of treating general relativity as a quantum theory. It is briefly studied how to consistently quantize general relativity as an effective field theory. A key achievement here is the long-range low-energy leading quantum corrections to both the Schwarzschild and Kerr metrics. The leading quantum corrections to the pure gravitational potential between two sources are also calculated, both in the mixed theory of scalar QED and quantum gravity and in the pure gravitational theory. The (Kawai-Lewellen-Tye) string theory gauge/gravity relations is next dealt with. We investigate if the KLT-operator mapping extends to the case of higher derivative effective operators. The KLT-relations are generalized, taking the effective field theory viewpoint, and remarkable tree-level amplitude relations between the field theory operators are derived. Quantum gravity is finally looked at from the the perspective of taking the limit of infinitely many spatial dimensions. It is verified that only a c...
The present and late universe in the Einstein frame, metric-affine 1/R gravity
Poplawski, N J
2006-01-01
We derive the gravitational field equations and the equations of evolution for the present and late universe in 1/R-modified gravity. We use the metric-affine (Palatini) variational principle and the Einstein conformal frame. We solve these equations for the flat FLRW universe in the quadratic approximation of the corresponding small quantities. We show that the largest deviation of the energy density scaling from the nonrelativistic dust scaling occurs in the intermediate region between the present and late epoch.
Light-like Scattering in Quantum Gravity
Bjerrum-Bohr, N E J; Holstein, Barry R; Plante, 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 hbar dependent terms using the same eikonal method.
Quantum Geometry and Gravity Recent Advances
Ashtekar, Abhay
2001-01-01
Over the last three years, a number of fundamental physical issues were addressed in loop quantum gravity. These include: A statistical mechanical derivation of the horizon entropy, encompassing astrophysically interesting black holes as well as cosmological horizons; a natural resolution of the big-bang singularity; the development of spin-foam models which provide background independent path integral formulations of quantum gravity and `finiteness proofs' of some of these models; and, the introduction of semi-classical techniques to make contact between the background independent, non-perturbative theory and the perturbative, low energy physics in Minkowski space. These developments spring from a detailed quantum theory of geometry that was systematically developed in the mid-nineties and have added a great deal of optimism and intellectual excitement to the field. The goal of this article is to communicate these advances in general physical terms, accessible to researchers in all areas of gravitational phy...
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 models - brief conceptual summary
Lukierski, jerzy
2014-01-01
After short historical overview we describe the difficulties with application of standard QFT methods in quantum gravity (QG). The incompatibility of QG with the use of classical continuous space-time required conceptually new approach. We present briefly three proposals: loop quantum gravity (LQG), the field-theoretic framework on noncommutative space-time and QG models formulated on discretized (triangularized) space-time. We evaluate these models as realizing expected important properties of QG: background independence, consistent quantum diffeomorphisms, noncommutative or discrete structure of space-time at very short distances, finite/renormalizable QG corrections. We only briefly outline an important issue of embedding QG into larger geometric and dynamical frameworks (e.g. supergravity, (super)strings, p-branes, M-theory), with the aim to achieve full unification of all fundamental interactions.
Recent Results Regarding Affine Quantum Gravity
Klauder, John R
2012-01-01
Recent progress in the quantization of nonrenormalizable scalar fields has found that a suitable non-classical modification of the ground state wave function leads to a result that eliminates term-by-term divergences that arise in a conventional perturbation analysis. After a brief review of both the scalar field story and the affine quantum gravity program, examination of the procedures used in the latter surprisingly shows an analogous formulation which already implies that affine quantum gravity is not plagued by divergences that arise in a standard perturbation study. Additionally, guided by the projection operator method to deal with quantum constraints, trial reproducing kernels are introduced that satisfy the diffeomorphism constraints. Furthermore, it is argued that the trial reproducing kernels for the diffeomorphism constraints may also satisfy the Hamiltonian constraint as well.
Light-like scattering in quantum gravity
Bjerrum-Bohr, N. E. J.; Donoghue, John F.; Holstein, Barry R.; Planté, Ludovic; Vanhove, Pierre
2016-11-01
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.
What is Dynamics in Quantum Gravity?
Malkiewicz, Przemyslaw
2015-01-01
Dynamics of general relativistic systems is given with respect to internal clocks. We investigate the extent to which the choice of internal clock in quantum description of the gravitational field determines the quantum dynamics. We develop our method by making use of the Hamilton-Jacobi theory, which is extended to include time coordinate transformations. Next, we apply our method to a quantum model of the flat Friedmann universe and compute some clock-induced deviations to semiclassical phase space portrait. Within a fixed quantization we find the abundance of possible semiclassical extensions to general relativity by switching between clocks. It follows that quantities like minimal volume, maximal curvature and even a number of quantum bounces, often used to describe quantum effects in gravity, are ill-defined.
Minimal Length Scale Scenarios for Quantum Gravity
Directory of Open Access Journals (Sweden)
Sabine Hossenfelder
2013-01-01
Full Text Available We review the question of whether the fundamental laws of nature limit our ability to probe arbitrarily short distances. First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity. Then we discuss some models that have been developed to implement a minimal length scale in quantum mechanics and quantum field theory. These models have entered the literature as the generalized uncertainty principle or the modified dispersion relation, and have allowed the study of the effects of a minimal length scale in quantum mechanics, quantum electrodynamics, thermodynamics, black-hole physics and cosmology. Finally, we touch upon the question of ways to circumvent the manifestation of a minimal length scale in short-distance physics.
Minimal Length Scale Scenarios for Quantum Gravity.
Hossenfelder, Sabine
2013-01-01
We review the question of whether the fundamental laws of nature limit our ability to probe arbitrarily short distances. First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity. Then we discuss some models that have been developed to implement a minimal length scale in quantum mechanics and quantum field theory. These models have entered the literature as the generalized uncertainty principle or the modified dispersion relation, and have allowed the study of the effects of a minimal length scale in quantum mechanics, quantum electrodynamics, thermodynamics, black-hole physics and cosmology. Finally, we touch upon the question of ways to circumvent the manifestation of a minimal length scale in short-distance physics.
On the Weyl - Eddington - Einstein affine gravity in the context of modern cosmology
Filippov, A T
2010-01-01
We propose new models of affine theory of gravity in $D$-dimensional space-times with symmetric connections. They are based on ideas of Weyl, Eddington and Einstein and, in particular, on Einstein's proposal to specify the space - time geometry by use of the Hamilton principle, i.e. to derive the connection coefficients for any Lagrangian that depends on the generalized (non - symmetric) Ricci curvature tensor expressed in terms of the independent connections coefficients. In addition to the standard Einstein gravity it predicts dark energy (the cosmological constant, in the first approximation), a neutral massive (or, tachyonic) vector field, and scalar fields with the same masses. These fields couple only to gravity and may generate dark matter and/or inflation. The masses (real or imaginary) have geometric origin and one cannot avoid their appearance in any concrete model. Further details of the theory (e.g., the nature of the vector and scalar fields that can describe massive particles, tachyons, or even ...
Quantum gravity and scalar fields
Energy Technology Data Exchange (ETDEWEB)
Mackay, Paul T. [School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom); Toms, David J., E-mail: d.j.toms@newcastle.ac.u [School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, NE1 7RU (United Kingdom)
2010-02-15
In this Letter we consider the quantization of a scalar field coupled to gravity at one loop order. We investigate the divergences appearing in the mass (i.e. phi{sup 2}) term in the effective action. We use the Vilkovisky-DeWitt effective action technique which guarantees that the result is gauge invariant as well as gauge condition independent in contrast to traditional calculations. Our final result is to identify the complete pole part of the effective action.
Some cosmological solutions in Einstein-Chern-Simons gravity
Avilés, Luis; Quinzacara, Cristian; Salgado, Patricio
2016-01-01
In this paper we find new solutions for the so called Einstein-Chern-Simons Friedmann-Robertson-Walker field equations studied in refs. (Phys. Rev. D 84 (2011) 063506, Eur. Phys. J. C 74 (2014) 3087). We consider three cases:(i) in the first case we find some solutions of the five-dimensional ChS-FRW field equations when the $h^a$ field is a perfect fluid that obeys a barotropic equation of state; (ii) in the second case we study the solutions, for the cases $\\gamma =1/2,\\ 3/4$, when the $h^a$ field is a five dimensional politropic fluid that obeys the equation $P^{(h)}=\\omega ^{(h)}\\rho ^{(h)\\gamma }$; (iii) in the third case we find the scale factor and the state parameter $\\omega (t)$ when the $h^a$ field is a variable modified Chaplygin gas. We consider also a space-time metric which contains as a subspace to the usual four-dimensional FRW and then we study the same three cases considered in the five-dimensional, namely when (i) the $h^a$ field is a perfect fluid, (ii) the $h^a$ field is a five dimensiona...
Howl, Richard; Bruschi, David Edward; Fuentes, Ivette
2016-01-01
At the beginning of the previous century, Newtonian mechanics fell victim to two new revolutionary theories, Quantum Mechanics (QM) and General Relativity (GR). Both theories have transformed our view of physical phenomena, with QM accurately predicting the results of experiments taking place at small length scales, and GR correctly describing observations at larger length scales. However, despite the impressive predictive power of each theory in their respective regimes, their unification still remains unresolved. Theories and proposals for their unification exist but we are lacking experimental guidance towards the true unifying theory. Probing GR at small length scales where quantum effects become relevant is particularly problematic but recently there has been a growing interest in probing the opposite regime, QM at large scales where relativistic effects are important. This is principally due to the fact that experimental techniques in quantum physics have developed rapidly in recent years with the promi...
Testing Quantum Gravity Induced Nonlocality via Optomechanical Quantum Oscillators.
Belenchia, Alessio; Benincasa, Dionigi M T; Liberati, Stefano; Marin, Francesco; Marino, Francesco; Ortolan, Antonello
2016-04-22
Several quantum gravity scenarios lead to physics below the Planck scale characterized by nonlocal, Lorentz invariant equations of motion. We show that such nonlocal effective field theories lead to a modified Schrödinger evolution in the nonrelativistic limit. In particular, the nonlocal evolution of optomechanical quantum oscillators is characterized by a spontaneous periodic squeezing that cannot be generated by environmental effects. We discuss constraints on the nonlocality obtained by past experiments, and show how future experiments (already under construction) will either see such effects or otherwise cast severe bounds on the nonlocality scale (well beyond the current limits set by the Large Hadron Collider). This paves the way for table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology.
Testing Quantum Gravity Induced Nonlocality via Optomechanical Quantum Oscillators
Belenchia, Alessio; Benincasa, Dionigi M. T.; Liberati, Stefano; Marin, Francesco; Marino, Francesco; Ortolan, Antonello
2016-04-01
Several quantum gravity scenarios lead to physics below the Planck scale characterized by nonlocal, Lorentz invariant equations of motion. We show that such nonlocal effective field theories lead to a modified Schrödinger evolution in the nonrelativistic limit. In particular, the nonlocal evolution of optomechanical quantum oscillators is characterized by a spontaneous periodic squeezing that cannot be generated by environmental effects. We discuss constraints on the nonlocality obtained by past experiments, and show how future experiments (already under construction) will either see such effects or otherwise cast severe bounds on the nonlocality scale (well beyond the current limits set by the Large Hadron Collider). This paves the way for table top, high precision experiments on massive quantum objects as a promising new avenue for testing some quantum gravity phenomenology.
Unitarity bounds on low scale quantum gravity
Atkins, Michael
2010-01-01
We study the unitarity of models with low scale quantum gravity both in four dimensions and in models with a large extra-dimensional volume. We find that models with low scale quantum gravity have problems with unitarity below the scale at which gravity becomes strong. An important consequence of our work is that their first signal at the Large Hadron Collider would not be of a gravitational nature such as graviton emission or small black holes, but rather linked to the mechanism which fixes the unitarity problem. We also study models with scalar fields with non minimal couplings to the Ricci scalar. We consider the strength of gravity in these models and study the consequences for inflation models with non-minimally coupled scalar fields. We show that a single scalar field with a large non-minimal coupling can lower the Planck mass in the TeV region. In that model, it is possible to lower the scale at which gravity becomes strong down to 14 TeV without violating unitarity below that scale.
Quantum leaps of black holes: Magnifying glasses of quantum gravity
Chakraborty, Sumanta
2016-01-01
We show using simple arguments, that the conceptual triad of a {\\it classical} black hole, semi-classical Hawking emission and geometry quantization is inherently, mutually incompatible. Presence of any two explicitly violates the third. We argue that geometry quantization, if realized in nature, magnifies the quantum gravity features hugely to catapult them into the realm of observational possibilities. We also explore a quantum route towards extremality of the black holes.
Quantum leaps of black holes: Magnifying glasses of quantum gravity
Chakraborty, Sumanta; Lochan, Kinjalk
2016-10-01
We show using simple arguments, that the conceptual triad of a classical black hole, semi-classical Hawking emission and geometry quantization is inherently, mutually incompatible. Presence of any two explicitly violates the third. We argue that geometry quantization, if realized in nature, magnifies the quantum gravity features hugely to catapult them into the realm of observational possibilities. We also explore a quantum route towards extremality of the black holes.
Terminating black holes in quantum gravity
Bambi, Cosimo; Modesto, Leonardo
2014-01-01
We study the homogeneous gravitational collapse of a spherical cloud composed of radiation or dust in a super-renormalizable and asymptotically free theory of gravity. The central singularity appearing in classical general relativity is resolved in both cases. The singularity is replaced by a bounce, after which the cloud re-expands indefinitely. In this model, strictly speaking, a black hole never forms and the high density state governed by quantum-gravitational physics is visible to faraway observers. Our result is quite general, and it holds for gravity theories with form factors suggested by string field theory and non-commutative geometries.
Bose-Einstein condensation of dipolar excitons in quantum wells
Energy Technology Data Exchange (ETDEWEB)
Timofeev, V B; Gorbunov, A V, E-mail: timofeev@issp.ac.r [Institute of Solid State Physics, Russian Academy of Sciences, 142432, Chernogolovka, Moscow region (Russian Federation)
2009-02-01
The experiments on Bose-Einstein condensation (BEC) of dipolar (spatially-indirect) excitons in the lateral traps in GaAs/AlGaAs Schottky-diode heterostructures with double and single quantum wells are presented. The condensed part of dipolar excitons under detection in the far zone is placed in k-space in the range which is almost two orders of magnitude less than thermal exciton wave vector. BEC occurs spontaneously in a reservoir of thermalized excitons. Luminescence images of Bose-condensate of dipolar excitons exhibit along perimeter of circular trap axially symmetrical spatial structures of equidistant bright spots which strongly depend on excitation power and temperature. By means of two-beam interference experiments with the use of cw and pulsed photoexcitation it was found that the state of dipolar exciton Bose-condensate is spatially coherent and the whole patterned luminescence configuration in real space is described by a common wave function.
Finitary Topos for Locally Finite, Causal and Quantal Vacuum Einstein Gravity
Raptis, Ioannis
2007-03-01
natural transformations of the relevant sheaf categories, we observe that the functorial ADG-theoretic version of the principle of general covariance of GeneralRelativity is preserved under topological refinement. The paper closes with a thorough discussion of four future routes we could take in order to further develop our topos-theoretic perspective on ADG-gravity along certain categorical trends in current quantum gravity research.
Quantum Loops in Non-Local Gravity
Talaganis, Spyridon
2015-01-01
In this proceedings, I will consider quantum aspects of a non-local, infinite-derivative scalar field theory - a ${\\it toy \\, model}$ depiction of a covariant infinite-derivative, non-local extension of Einstein's general relativity which has previously been shown to be free from ghosts around the Minkowski background. The graviton propagator in this theory gets an exponential suppression making it ${\\it asymptotically \\, free}$, thus providing strong prospects of resolving various classical and quantum divergences. In particular, I will find that at $1$-loop, the $2$-point function is still divergent, but once this amplitude is renormalized by adding appropriate counter terms, the ultraviolet (UV) behavior of all other $1$-loop diagrams as well as the $2$-loop, $2$-point function remains well under control. I will go on to discuss how one may be able to generalize our computations and arguments to arbitrary loops.
Canonical Quantum Gravity on Noncommutative Spacetime
Kober, Martin
2014-01-01
In this paper canonical quantum gravity on noncommutative space-time is considered. The corresponding generalized classical theory is formulated by using the moyal star product, which enables the representation of the field quantities depending on noncommuting coordinates by generalized quantities depending on usual coordinates. But not only the classical theory has to be generalized in analogy to other field theories. Besides, the necessity arises to replace the commutator between the gravitational field operator and its canonical conjugated quantity by a corresponding generalized expression on noncommutative space-time. Accordingly the transition to the quantum theory has also to be performed in a generalized way and leads to extended representations of the quantum theoretical operators. If the generalized representations of the operators are inserted to the generalized constraints, one obtains the corresponding generalized quantum constraints including the Hamiltonian constraint as dynamical constraint. Af...
Quantum Cosmology of f( R, T) gravity
Xu, Min-Xing; Harko, Tiberiu; Liang, Shi-Dong
2016-08-01
Modified gravity theories have the potential of explaining the recent acceleration of the Universe without resorting to the mysterious concept of dark energy. In particular, it has been pointed out that matter-geometry coupling may be responsible for the recent cosmological dynamics of the Universe, and matter itself may play a more fundamental role in the description of the gravitational processes that usually assumed. In the present paper we study the quantum cosmology of the f( R, T) theory of gravity, in which the effective Lagrangian of the gravitational field is given by an arbitrary function of the Ricci scalar, and the trace of the matter energy-momentum tensor, respectively. For the background geometry we adopt the Friedmann-Robertson-Walker metric, and we assume that matter content of the Universe consists of a perfect fluid. In this framework we obtain the general form of the gravitational Hamiltonian, of the quantum potential, and of the canonical momenta, respectively. This allows us to formulate the full Wheeler-de Witt equation describing the quantum properties of this modified gravity model. As a specific application we consider in detail the quantum cosmology of the f(R,T)=F^0(R)+θ RT model, in which F^0(R) is an arbitrary function of the Ricci scalar, and θ is a function of the scale factor only. The Hamiltonian form of the equations of motion, and the Wheeler-de Witt equations are obtained, and a time parameter for the corresponding dynamical system is identified, which allows one to formulate the Schrödinger-Wheeler-de Witt equation for the quantum-mechanical description of the model under consideration. A perturbative approach for the study of this equation is developed, and the energy levels of the Universe are obtained by using a twofold degenerate perturbation approach. A second quantization approach for the description of quantum time is also proposed and briefly discussed.
Quantum gravity kinematics from extended TQFTs
Dittrich, Bianca; Geiller, Marc
2017-01-01
In this paper, we show how extended topological quantum field theories (TQFTs) can be used to obtain a kinematical setup for quantum gravity, i.e. a kinematical Hilbert space together with a representation of the observable algebra including operators of quantum geometry. In particular, we consider the holonomy-flux algebra of (2 + 1)-dimensional Euclidean loop quantum gravity, and construct a new representation of this algebra that incorporates a positive cosmological constant. The vacuum state underlying our representation is defined by the Turaev-Viro TQFT. This vacuum state can be thought of as being peaked on connections with homogeneous curvature. We therefore construct here a generalization, or more precisely a quantum deformation at root of unity, of the previously introduced SU(2) BF representation. The extended Turaev-Viro TQFT provides a description of the excitations on top of the vacuum. These curvature and torsion excitations are classified by the Drinfeld center category of the quantum deformation of SU(2), and are essential in order to allow for a representation of the holonomies and fluxes. The holonomies and fluxes are generalized to ribbon operators which create and interact with the excitations. These excitations agree with the ones induced by massive and spinning particles, and therefore the framework presented here allows automatically for a description of the coupling of such matter to (2+1)-dimensional gravity with a cosmological constant. The new representation constructed here presents a number of advantages over the representations which exist so far. In particular, it possesses a very useful finiteness property which guarantees the discreteness of spectra for a wide class of quantum (intrinsic and extrinsic) geometrical operators. Also, the notion of basic excitations leads to a so-called fusion basis which offers exciting possibilities for the construction of states with interesting global properties, as well as states with certain
From General Relativity to Quantum Gravity
Ashtekar, Abhay; Rovelli, Carlo
2014-01-01
In general relativity (GR), spacetime geometry is no longer just a background arena but a physical and dynamical entity with its own degrees of freedom. We present an overview of approaches to quantum gravity in which this central feature of GR is at the forefront. However, the short distance dynamics in the quantum theory are quite different from those of GR and classical spacetimes and gravitons emerge only in a suitable limit. Our emphasis is on communicating the key strategies, the main results and open issues. In the spirit of this volume, we focus on a few avenues that have led to the most significant advances over the past 2-3 decades.
Quantum gravity extension of the inflationary scenario.
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.
BOOK REVIEW: Quantum Gravity (2nd edn)
Husain, Viqar
2008-06-01
There has been a flurry of books on quantum gravity in the past few years. The first edition of Kiefer's book appeared in 2004, about the same time as Carlo Rovelli's book with the same title. This was soon followed by Thomas Thiemann's 'Modern Canonical Quantum General Relativity'. Although the main focus of each of these books is non-perturbative and non-string approaches to the quantization of general relativity, they are quite orthogonal in temperament, style, subject matter and mathematical detail. Rovelli and Thiemann focus primarily on loop quantum gravity (LQG), whereas Kiefer attempts a broader introduction and review of the subject that includes chapters on string theory and decoherence. Kiefer's second edition attempts an even wider and somewhat ambitious sweep with 'new sections on asymptotic safety, dynamical triangulation, primordial black holes, the information-loss problem, loop quantum cosmology, and other topics'. The presentation of these current topics is necessarily brief given the size of the book, but effective in encapsulating the main ideas in some cases. For instance the few pages devoted to loop quantum cosmology describe how the mini-superspace reduction of the quantum Hamiltonian constraint of LQG becomes a difference equation, whereas the discussion of 'dynamical triangulations', an approach to defining a discretized Lorentzian path integral for quantum gravity, is less detailed. The first few chapters of the book provide, in a roughly historical sequence, the covariant and canonical metric variable approach to the subject developed in the 1960s and 70s. The problem(s) of time in quantum gravity are nicely summarized in the chapter on quantum geometrodynamics, followed by a detailed and effective introduction of the WKB approach and the semi-classical approximation. These topics form the traditional core of the subject. The next three chapters cover LQG, quantization of black holes, and quantum cosmology. Of these the chapter on LQG is
The extended loop representation of quantum gravity
Di Bartolo, C; Griego, J R
1995-01-01
A new representation of Quantum Gravity is developed. This formulation is based on an extension of the group of loops. The enlarged group, that we call the Extended Loop Group, behaves locally as an infinite dimensional Lie group. Quantum Gravity can be realized on the state space of extended loop dependent wavefunctions. The extended representation generalizes the loop representation and contains this representation as a particular case. The resulting diffeomorphism and hamiltonian constraints take a very simple form and allow to apply functional methods and simplify the loop calculus. In particular we show that the constraints are linear in the momenta. The nondegenerate solutions known in the loop representation are also solutions of the constraints in the new representation. The practical calculation advantages allows to find a new solution to the Wheeler-DeWitt equation. Moreover, the extended representation puts in a precise framework some of the regularization problems of the loop representation. We sh...
String Theory, Unification and Quantum Gravity
Stelle, K S
2012-01-01
An overview is given of the way in which the unification program of particle physics has evolved into the proposal of superstring theory as a prime candidate for unifying quantum gravity with the other forces and particles of nature. A key concern with quantum gravity has been the problem of ultraviolet divergences, which is naturally solved in string theory by replacing particles with spatially extended states as the fundamental excitations. String theory turns out, however, to contain many more extended-object states than just strings. Combining all this into an integrated picture, called M-theory, requires recognition of the r\\^ole played by a web of nonperturbative duality symmetries suggested by the nonlinear structures of the field-theoretic supergravity limits of string theory.
Cosmography in testing loop quantum gravity
Szydlowski, Marek; Stachowiak, Tomasz
2007-01-01
It was recently suggested by Martin Bojowald that quantum gravity effects give rise to new, potentially observable effects. We check whether this is the case for astronomical tests by trying to constrain the density parameters of the Friedmann equation with a $(-)(1+z)^6$ type of contribution. We describe different interpretations of such an additional term: geometric effects of Loop Quantum Cosmology, effects of braneworld cosmological models, non-standard cosmological models in metric-affine gravity, and models with spinning fluid. Kinematical (or geometrical) tests based on null geodesics are insufficient to separate individual matter components when they behave like perfect fluid and scale in the same way. Still, it is possible to measure their overall effect. We use recent measurements of the coordinate distances from Fanaroff-Riley type IIb (FRIIb) radio galaxy (RG) data, supernovae type Ia (SNIa) data, baryon oscillation peak and cosmic microwave background radiation (CMBR) observations to obtain stron...
Algebraic Quantum Gravity (AQG) II. Semiclassical Analysis
Giesel, K
2006-01-01
In the previous article a new combinatorial and thus purely algebraical approach to quantum gravity, called Algebraic Quantum Gravity (AQG), was introduced. In the framework of AQG existing semiclassical tools can be applied to operators that encode the dynamics of AQG such as the Master constraint operator. In this article we will analyse the semiclassical limit of the (extended) algebraic Master constraint operator and show that it reproduces the correct infinitesimal generators of General Relativity. Therefore the question whether General Relativity is included in the semiclassical sector of the theory, which is still an open problem in LQG, can be significantly improved in the framework of AQG. For the calculations we will substitute SU(2) by U(1)^3. That this substitution is justified will be demonstrated in the third article of this series
Energy Technology Data Exchange (ETDEWEB)
Petrov, A N, E-mail: anpetrov@rol.ru [Relativistic Astrophysics Group, Sternberg Astronomical Institute, Universitetskii Pr., 13, Moscow 119992 (Russian Federation)
2011-11-07
In the framework of an arbitrary D-dimensional metric theory, perturbations are considered on arbitrary backgrounds that are however solutions of the theory. Conserved currents for perturbations are presented following two known prescriptions: the canonical Noether theorem and the Belinfante symmetrization rule. Using generalized formulae, currents in the Einstein-Gauss-Bonnet (EGB) gravity for arbitrary types of perturbations on arbitrary curved backgrounds (not only vacuum) are constructed in an explicit covariant form. Special attention is paid to the energy-momentum tensors for perturbations which are an important part in the structure of the currents. We use the derived expressions for two applied calculations: (a) to present the energy density for weak flat gravitational waves in D-dimensional EGB gravity; (b) to construct the mass flux for the Maeda-Dadhich-Molina 3D radiating black holes of a Kaluza-Klein type in 6D EGB gravity. (paper)
Petrov, A N
2011-01-01
In the framework of an arbitrary D-dimensional metric theory, perturbations are considered on arbitrary backgrounds, which, however, are solutions of the theory. Conserved currents for perturbations are presented following two known prescriptions: of the canonical Noether theorem and of the Belinfante symmetrization rule. On the basis of the generalized formulae, currents in the Einstein-Gauss-Bonnet (EGB) gravity for arbitrary types of perturbations on arbitrary curved backgrounds (not only vacuum) are constructed in the explicit covariant form. A more attention is paid to the energy-momentum tensors for perturbations as more important parts in the structure of the currents. To be tested the new expressions are used a) to present energy density for weak flat gravitational waves in D-dimensional EGB gravity; b) to present mass flux for the Maeda-Dadhich-Molina 3D radiating black holes of the Kaluza-Klein type in 6D EGB gravity.
Quantum Gravity signals in neutrino oscillations
Sprenger, Martin; Bleicher, Marcus
2011-01-01
We investigate the effect of a Quantum Gravity-induced minimal length on neutrino oscillations. The minimal length is implemented in a phenomenological framework, allowing us to make predictions independently of any fundamental approach. We obtain clear minimal length signatures and discuss their observability in current and future experiments. We present an overview over other scenarios in which the minimal length leaves its signature and show new results concerning minimal length thermodynamics.
Bouncing cosmologies from quantum gravity condensates
Oriti, Daniele; Sindoni, Lorenzo; Wilson-Ewing, Edward
2017-02-01
We show how the large-scale cosmological dynamics can be obtained from the hydrodynamics of isotropic group field theory condensate states in the Gross–Pitaevskii approximation. The correct Friedmann equations are recovered in the classical limit for some choices of the parameters in the action for the group field theory, and quantum gravity corrections arise in the high-curvature regime causing a bounce which generically resolves the big-bang and big-crunch singularities.
Superrenormalizable quantum gravity with complex ghosts
Modesto, Leonardo
2015-01-01
We suggest and briefly review a new sort of superrenormalizable models of higher derivative quantum gravity. The higher derivative terms in the action can be introduced in such a way that all the unphysical massive states have complex poles. According to the literature on Lee-Wick quantization, in this case the theory can be formulated as unitary, since all massive ghosts-like degrees of freedom are unstable.
Recent results in CDT quantum gravity
Ambjorn, Jan; Gizbert-Studnicki, Jakub; Jurkiewicz, Jerzy
2015-01-01
We review some recent results from the causal dynamical triangulation (CDT) approach to quantum gravity. We review recent observations of dimensional reduction at a number of previously undetermined points in the parameter space of CDT, and discuss their possible relevance to the asymptotic safety scenario. We also present an updated phase diagram of CDT, discussing properties of a newly discovered phase and its possible relation to a signature change of the metric.
Superrenormalizable quantum gravity with complex ghosts
Directory of Open Access Journals (Sweden)
Leonardo Modesto
2016-04-01
Full Text Available We suggest and briefly review a new sort of superrenormalizable models of higher derivative quantum gravity. The higher derivative terms in the action can be introduced in such a way that all the unphysical massive states have complex poles. According to the literature on Lee–Wick quantization, in this case the theory can be formulated as unitary, since all massive ghosts-like degrees of freedom are unstable.
Cosmological perturbation theory and quantum gravity
Brunetti, Romeo; Hack, Thomas-Paul; Pinamonti, Nicola; Rejzner, Katarzyna
2016-01-01
It is shown how cosmological perturbation theory arises from a fully quantized perturbative theory of quantum gravity. Central for the derivation is a non-perturbative concept of gauge-invariant local observables by means of which perturbative invariant expressions of arbitrary order are generated. In particular, in the linearised theory, first order gauge-invariant observables familiar from cosmological perturbation theory are recovered. Explicit expressions of second order quantities are presented as well.
Bouncing cosmologies from quantum gravity condensates
Oriti, Daniele; Wilson-Ewing, Edward
2016-01-01
We show how the large-scale cosmological dynamics can be obtained from the hydrodynamics of isotropic group field theory condensate states in the Gross-Pitaevskii approximation. The correct Friedmann equations are recovered in the semi-classical limit for some choices of the parameters in the action for the group field theory, and quantum gravity corrections arise in the high-curvature regime causing a bounce which generically resolves the big-bang and big-crunch singularities.
Cosmological perturbation theory and quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Brunetti, Romeo [Dipartimento di Matematica, Università di Trento,Via Sommarive 14, 38123 Povo TN (Italy); Fredenhagen, Klaus [II Institute für Theoretische Physik, Universität Hamburg,Luruper Chaussee 149, 22761 Hamburg (Germany); Hack, Thomas-Paul [Institute für Theoretische Physik, Universität Leipzig,Brüderstr. 16, 04103 Leipzig (Germany); Pinamonti, Nicola [Dipartimento di Matematica, Università di Genova,Via Dodecaneso 35, 16146 Genova (Italy); INFN, Sezione di Genova,Via Dodecaneso 33, 16146 Genova (Italy); Rejzner, Katarzyna [Department of Mathematics, University of York,Heslington, York YO10 5DD (United Kingdom)
2016-08-04
It is shown how cosmological perturbation theory arises from a fully quantized perturbative theory of quantum gravity. Central for the derivation is a non-perturbative concept of gauge-invariant local observables by means of which perturbative invariant expressions of arbitrary order are generated. In particular, in the linearised theory, first order gauge-invariant observables familiar from cosmological perturbation theory are recovered. Explicit expressions of second order quantities are presented as well.
Quantum gravity corrections in Chandrasekhar limits
Moussa, Mohamed
2017-01-01
It is agreed that Chandrasekhar mass and central density of white dwarfs are independent, which means that there is a whole series of stars having radius and central density as parameters that all have the same Chandrasekhar mass. In this article the influence of a quantum gravity is shown so the Chandrasekhar limits (mass and radius) depend explicitly on the central density and gravity parameters. A new polytropic relation between degenerate pressure of the star and its density is investigated. This leads to a modification in Lane-Emden equation and mass and radius formulas of the star. A modified Lane-Emden equation is solved numerically with consideration to the mass density of the star depends on its radius. The solution was used in calculating the mass and radius limit of the white dwarf. It was found that mass and radius limits decrease due to increase in central density and gravity parameters in a comparison with the original values. We can say that central density and quantum gravity constitute a new tool that can help to make the theoretical values corresponding to experimental observations apply in a better manner.
Hu, Ya-Peng; Wu, Xiao-Ning
2014-01-01
Basing the previous paper arXiv:1207.5309, we investigate the probability to find out the bulk viscosity of dual fluid at the finite cutoff surface via gravity/fluid correspondence in Einstein-Maxwell Gravity. We find that if we adopt new conditions to fix the undetermined parameters contained in the stress tensor and charged current of the dual fluid, two new terms could appear in the stress tensor of the dual fluid. One new term is related to the bulk viscosity term, while the other could be related to the perturbation of energy density. In addition, since the parameters contained in the charged current are the same, the charged current is not changed.
BOOK REVIEW: A First Course in Loop Quantum Gravity A First Course in Loop Quantum Gravity
Dittrich, Bianca
2012-12-01
Students who are interested in quantum gravity usually face the difficulty of working through a large amount of prerequisite material before being able to deal with actual quantum gravity. A First Course in Loop Quantum Gravity by Rodolfo Gambini and Jorge Pullin, aimed at undergraduate students, marvellously succeeds in starting from the basics of special relativity and covering basic topics in Hamiltonian dynamics, Yang Mills theory, general relativity and quantum field theory, ending with a tour on current (loop) quantum gravity research. This is all done in a short 173 pages! As such the authors cannot cover any of the subjects in depth and indeed this book should be seen more as a motivation and orientation guide so that students can go on to follow the hints for further reading. Also, as there are many subjects to cover beforehand, slightly more than half of the book is concerned with more general subjects (special and general relativity, Hamiltonian dynamics, constrained systems, quantization) before the starting point for loop quantum gravity, the Ashtekar variables, are introduced. The approach taken by the authors is heuristic and uses simplifying examples in many places. However they take care in motivating all the main steps and succeed in presenting the material pedagogically. Problem sets are provided throughout and references for further reading are given. Despite the shortness of space, alternative viewpoints are mentioned and the reader is also referred to experimental results and bounds. In the second half of the book the reader gets a ride through loop quantum gravity; the material covers geometric operators and their spectra, the Hamiltonian constraints, loop quantum cosmology and, more broadly, black hole thermodynamics. A glimpse of recent developments and open problems is given, for instance a discussion on experimental predictions, where the authors carefully point out the very preliminary nature of the results. The authors close with an
Algebras of Quantum Variables for Loop Quantum Gravity, I. Overview
Kaminski, Diana
2011-01-01
The operator algebraic framework plays an important role in mathematical physics. Many different operator algebras exist for example for a theory of quantum mechanics. In Loop Quantum Gravity only two algebras have been introduced until now. In the project about 'Algebras of Quantum Variables (AQV) for LQG' the known holonomy-flux *-algebra and the Weyl C*-algebra will be modified and a set of new algebras will be proposed and studied. The idea of the construction of these algebras is to establish a finite set of operators, which generates (in the sense of Woronowicz, Schm\\"udgen and Inoue) the different O*- or C*-algebras of quantum gravity and to use inductive limits of these algebras. In the Loop Quantum Gravity approach usually the basic classical variables are connections and fluxes. Studying the three constraints appearing in the canonical quantisation of classical general relativity in the ADM-formalism some other variables like curvature appear. Consequently the main difficulty of a quantisation of gr...
Cosmology of the Planck Era from a Renormalization Group for Quantum Gravity
Bonanno, A
2002-01-01
Homogeneous and isotropic cosmologies of the Planck era before the classical Einstein equations become valid are studied taking quantum gravitational effects into account. The cosmological evolution equations are renormalization group improved by including the scale dependence of Newton's constant and of the cosmological constant as it is given by the flow equation of the effective average action for gravity. It is argued that the Planck regime can be treated reliably in this framework because gravity is found to become asymptotically free at short distances. The epoch immediately after the initial singularity of the Universe is described by an attractor solution of the improved equations which is a direct manifestation of an ultraviolet attractive renormalization group fixed point. It is shown that quantum gravity effects in the very early Universe might provide a resolution to the horizon and flatness problem of standard cosmology, and could generate a scale-free spectrum of primordial density fluctuations.
Mukhopadhyay, Banibrata
2016-01-01
Observations of several peculiar, under- and over-luminous type Ia supernovae (SNeIa) argue for exploding masses widely different from the Chandrasekhar-limit. We explore the modification to Einstein's gravity in white dwarfs for the first time in the literature, which shows that depending on the (density dependent) modified gravity parameter $\\alpha$, chosen for the present purpose of representation, limiting mass of white dwarfs could be significantly sub- as well as super-Chandrasekhar. Hence, this unifies the apparently disjoint classes of SNeIa, establishing the importance of modified Einstein's gravity in white dwarfs. Our discovery questions both the global validity of Einstein's gravity and the uniqueness of Chandrasekhar's limit.
Smith, Peter D
2003-01-01
Albert Einstein re-wrote the textbooks of science in 1905: physics since has been little more than a series of footnotes to the theories of a 26-year-old patent-office clerk. Einstein's science and emotional life come together in this vivid portrait of a rebellious and contradictory figure, a pacifist whose legendary equation E=mc2 opened scientists' eyes to the terrible power within every atom. 'To punish me for my contempt for authority,' he lamented, 'Fate has made me an authority myself.'
Quantum billiards with branes on product of Einstein spaces
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Ivashchuk, V.D. [VNIIMS, Center for Gravitation and Fundamental Metrology, Moscow (Russian Federation); Peoples' Friendship University of Russia, Institute of Gravitation and Cosmology, Moscow (Russian Federation)
2016-05-15
We consider a gravitational model in dimension D with several forms, l scalar fields and a Λ-term. We study cosmological-type block-diagonal metrics defined on a product of an 1-dimensional interval and n oriented Einstein spaces. As an electromagnetic composite brane ansatz is adopted and certain restrictions on the branes are imposed the conformally covariant Wheeler-DeWitt (WDW) equation for the model is studied. Under certain restrictions, asymptotic solutions to the WDW equation are found in the limit of the formation of the billiard walls. These solutions reduce the problem to the so-called quantum billiard in (n + l -1)-dimensional hyperbolic space. Several examples of quantum billiards in the model with electric and magnetic branes, e.g. corresponding to hyperbolic Kac-Moody algebras, are considered. In the case n = 2 we find a set of basis asymptotic solutions to the WDW equation and derive asymptotic solutions for the metric in the classical case. (orig.)
Quantum billiards with branes on product of Einstein spaces
Ivashchuk, V. D.
2016-05-01
We consider a gravitational model in dimension D with several forms, l scalar fields and a Λ -term. We study cosmological-type block-diagonal metrics defined on a product of an 1-dimensional interval and n oriented Einstein spaces. As an electromagnetic composite brane ansatz is adopted and certain restrictions on the branes are imposed the conformally covariant Wheeler-DeWitt (WDW) equation for the model is studied. Under certain restrictions, asymptotic solutions to the WDW equation are found in the limit of the formation of the billiard walls. These solutions reduce the problem to the so-called quantum billiard in (n + l -1)-dimensional hyperbolic space. Several examples of quantum billiards in the model with electric and magnetic branes, e.g. corresponding to hyperbolic Kac-Moody algebras, are considered. In the case n=2 we find a set of basis asymptotic solutions to the WDW equation and derive asymptotic solutions for the metric in the classical case.
Euclidean and Lorentzian Quantum Gravity – Lessons from Two Dimensions
Ambjørn, J.; Loll, R.; Nielsen, J. L.; Rolf, J.
1998-01-01
No theory of four-dimensional quantum gravity exists as yet. In this situation the two-dimensional theory, which can be analyzed by conventional field-theoretical methods, can serve as a toy model for studying some aspects of quantum gravity. It represents one of the rare settings in a quantum-gravi
Quantum Gravity: physics from supergeometries
Cirilo-Lombardo, Diego Julio
2013-01-01
We show that the metric (line element) is the first geometrical object to be associated to a discrete (quantum) structure of the spacetime without necessity of black hole-entropy-area arguments, in sharp contrast with other attempts in the literature. To this end, an emergent metric solution obtained previously in [Physics Letters B 661, 186-191 (2008)] from a particular non-degenerate Riemmanian superspace is introduced. This emergent metric is described by a physical coherent state belonging to the metaplectic group Mp (n) with a Poissonian distribution at lower n (number basis) restoring the classical thermal continuum behaviour at large n (n ! 1), or leading to non-classical radiation states, as is conjectured in a quite general basis by mean the Bekenstein- Mukhanov effect. Group-dependent conditions that control the behavior of the macroscopic regime spectrum (thermal or not), as the relationship with the problem of area / entropy of the black hole are presented and discussed.
On a new approach for constructing wormholes in Einstein-Born-Infeld gravity
Kim, Jin Young; Park, Mu-In
2016-11-01
We study a new approach for the wormhole construction in Einstein-Born-Infeld gravity, which does not require exotic matters in the Einstein equation. The Born-Infeld field equation is not modified by coordinate independent conditions of continuous metric tensor and its derivatives, even though the Born-Infeld fields have discontinuities in their derivatives at the throat in general. We study the relation of the newly introduced conditions with the usual continuity equation for the energy-momentum tensor and the gravitational Bianchi identity. We find that there is no violation of energy conditions for the Born-Infeld fields contrary to the usual approaches. The exoticity of the energy-momentum tensor is not essential for sustaining wormholes. Some open problems are discussed.
On a New Approach for Constructing Wormholes in Einstein-Born-Infeld Gravity
Kim, Jin Young
2016-01-01
We study a new approach for the wormhole construction in Einstein-Born-Infeld gravity, which does not require exotic matters in the Einstein equation. The Born-Infeld field equation is not modified from "coordinate independent" conditions of continuous metric tensor and its derivatives, even though the Born-Infeld fields have discontinuities in their derivatives at the throat in general. We study the relation of the newly introduced conditions with the usual continuity equation for the energy-momentum tensor and the gravitational Bianchi identity. We find that there is no violation of energy conditions for the Born-Infeld fields contrary to the usual approaches. The exoticity of energy-momentum tensor is not essential for sustaining wormholes. Some open problems are discussed.
On a new approach for constructing wormholes in Einstein-Born-Infeld gravity
Energy Technology Data Exchange (ETDEWEB)
Kim, Jin Young [Kunsan National University, Department of Physics, Kunsan (Korea, Republic of); Park, Mu-In [Sogang University, Research Institute for Basic Science, Seoul (Korea, Republic of)
2016-11-15
We study a new approach for the wormhole construction in Einstein-Born-Infeld gravity, which does not require exotic matters in the Einstein equation. The Born-Infeld field equation is not modified by coordinate independent conditions of continuous metric tensor and its derivatives, even though the Born-Infeld fields have discontinuities in their derivatives at the throat in general. We study the relation of the newly introduced conditions with the usual continuity equation for the energy-momentum tensor and the gravitational Bianchi identity. We find that there is no violation of energy conditions for the Born-Infeld fields contrary to the usual approaches. The exoticity of the energy-momentum tensor is not essential for sustaining wormholes. Some open problems are discussed. (orig.)
Entropic Phase Maps in Discrete Quantum Gravity
Directory of Open Access Journals (Sweden)
Benjamin F. Dribus
2017-06-01
Full Text Available Path summation offers a flexible general approach to quantum theory, including quantum gravity. In the latter setting, summation is performed over a space of evolutionary pathways in a history configuration space. Discrete causal histories called acyclic directed sets offer certain advantages over similar models appearing in the literature, such as causal sets. Path summation defined in terms of these histories enables derivation of discrete Schrödinger-type equations describing quantum spacetime dynamics for any suitable choice of algebraic quantities associated with each evolutionary pathway. These quantities, called phases, collectively define a phase map from the space of evolutionary pathways to a target object, such as the unit circle S 1 ⊂ C , or an analogue such as S 3 or S 7 . This paper explores the problem of identifying suitable phase maps for discrete quantum gravity, focusing on a class of S 1 -valued maps defined in terms of “structural increments” of histories, called terminal states. Invariants such as state automorphism groups determine multiplicities of states, and induce families of natural entropy functions. A phase map defined in terms of such a function is called an entropic phase map. The associated dynamical law may be viewed as an abstract combination of Schrödinger’s equation and the second law of thermodynamics.
On the "Spin-Connection Foam" Picture of Quantum Gravity from Precanonical Quantization
Kanatchikov, I V
2015-01-01
Precanonical quantization uses a different generalization of Hamiltonian formalism to field theory, the so-called De Donder--Weyl (DW) theory, which does not require a space-time decomposition and treats the space-time variables on the equal footing. Quantum dynamics is encoded in precanonical wave function on the space of field coordinates and space-time coordinates, which satisfies a partial derivative precanonical Schr\\"odinger equation on this space. Based on analysis of constraints within the De Donder--Weyl Hamiltonian formulation of Einstein-Palatini vielbein formulation of GR and quantization of generalized Dirac brackets defined on differential forms, we derived the covariant analogue of the Schr\\"odinger equation for precanonical wave function of quantum gravity. The resulting dynamics of quantum gravity is encoded in the wave function on the bundle of spin-connections over the space-time or, equivalently, the transition amplitudes on this space. Thus the precanonical quantization leads to the "spin...
Particle creation phenomenology, Dirac sea and the induced Weyl and Einstein-dilaton gravity
Berezin, V. A.; Dokuchaev, V. I.; Eroshenko, Yu. N.
2017-01-01
We constructed the conformally invariant model for scalar particle creation induced by strong gravitational fields. Starting from the "usual" hydrodynamical description of the particle motion written in the Eulerian coordinates we substituted the particle number conservation law (which enters the formalism) by "the particle creation law", proportional to the square of the Weyl tensor (following the famous result by Ya.B. Zel'dovich and A.A. Starobinsky). Then, demanding the conformal invariance of the whole dynamical system, we have got both the (Weyl)-conformal gravity and the Einstein-Hilbert gravity action integral with dilaton field. Thus, we obtained something like the induced gravity suggested first by A.D. Sakharov. It is shown that the resulting system is self-consistent. We considered also the vacuum equations. It is shown that, beside the "empty vacuum", there may exist the "dynamical vacuum", which is nothing more but the Dirac sea. The latter is described by the unexpectedly elegant equation which includes both the Bach and Einstein tensors and the cosmological terms.
Quantum gravity as a Fermi liquid
Alexander, Stephon H S
2008-01-01
We present a reformulation of loop quantum gravity with a cosmological constant and no matter as a Fermi-liquid theory. When the topological sector is deformed and large gauge symmetry is broken, we show that the Chern-Simons state reduces to Jacobson's degenerate sector describing 1+1 dimensional propagating fermions with nonlocal interactions. The Hamiltonian admits a dual description which we realize in the simple BCS model of superconductivity. On one hand, Cooper pairs are interpreted as wormhole correlations at the de Sitter horizon; their number yields the de Sitter entropy. On the other hand, BCS is mapped into a deformed conformal field theory reproducing the structure of quantum spin networks. When area measurements are performed, Cooper-pair insertions are activated on those edges of the spin network intersecting the given area, thus providing a description of quantum measurements in terms of excitations of a Fermi sea to superconducting levels. The cosmological constant problem is naturally addres...
The Problem of Time in Quantum Gravity
Anderson, Edward
2010-01-01
The problem of time in quantum gravity occurs because `time' is taken to have a different meaning in each of general relativity and ordinary quantum theory. This incompatibility creates serious problems with trying to replace these two branches of physics with a single framework in regimes in which neither quantum theory nor general relativity can be neglected, such as in black holes or in the very early universe. Strategies for resolving the Problem of Time have evolved somewhat since Kuchar and Isham's well-known reviews from the early 90's. These come in the following divisions I) time before quantization, such as hidden time or matter time. II) Time after quantization, such as emergent semiclassical time. III) Timeless strategies of Type 1: naive Schrodinger interpretation, conditional probabilities interpretation and various forms of records theories, and Type 2 `Rovelli': in terms of evolving constants of the motion, complete observables and partial observables. IV) I argue for histories theories to be ...
Can chaos be observed in quantum gravity?
Dittrich, Bianca; Koslowski, Tim A; Nelson, Mike I
2016-01-01
Full general relativity is almost certainly non-integrable and likely chaotic and therefore almost certainly possesses neither differentiable Dirac observables nor a reduced phase space. It follows that the standard notion of observable has to be extended to include non-differentiable or even discontinuous generalized observables. These cannot carry Poisson-algebraic structures and do not admit a standard quantization. This has deep consequences for a quantum theory of gravity, which we investigate in a simple model for a system with Hamiltonian constraint that fails to be completely integrable. We show that basing the quantization on standard topology precludes a semiclassical limit and can even prohibit any solutions to the quantum constraints. Our proposed solution to this problem is to refine topology such that a complete set of Dirac observables becomes continuous. In the toy model it turns out that a refinement to a polymer-type topology, as e.g. used in loop quantum cosmology, is sufficient. Basing qua...
Quantum reduced loop gravity: extension to gauge vector field
Bilski, Jakub; Cianfrani, Francesco; Donà, Pietro; Marciano, Antonino
2016-01-01
Within the framework of Quantum Reduced Loop Gravity we quantize the Hamiltonian for a gauge vector field. The regularization can be performed using tools analogous to the ones adopted in full Loop Quantum Gravity, while the matrix elements of the resulting operator between basis states are analytic coefficients. This analysis is the first step towards deriving the full quantum gravity corrections to the vector field semiclassical dynamics.
Quantum-gravity effects on a Higgs-Yukawa model
Eichhorn, Astrid; Held, Aaron; Pawlowski, Jan M.
2016-11-01
A phenomenologically viable theory of quantum gravity must accommodate all observed matter degrees of freedom and their properties. Here, we explore whether a toy model of the Higgs-Yukawa sector of the Standard Model is compatible with asymptotically safe quantum gravity. We discuss the phenomenological implications of our result in the context of the Standard Model. We analyze the quantum scaling dimension of the system and find an irrelevant Yukawa coupling at a joint gravity-matter fixed point. Further, we explore the impact of gravity-induced couplings between scalars and fermions, which are nonvanishing in asymptotically safe gravity.
Approaches to quantum gravity. Loop quantum gravity, spinfoams and topos approach
Energy Technology Data Exchange (ETDEWEB)
Flori, Cecilia
2010-07-23
One of the main challenges in theoretical physics over the last five decades has been to reconcile quantum mechanics with general relativity into a theory of quantum gravity. However, such a theory has been proved to be hard to attain due to i) conceptual difficulties present in both the component theories (General Relativity (GR) and Quantum Theory); ii) lack of experimental evidence, since the regimes at which quantum gravity is expected to be applicable are far beyond the range of conceivable experiments. Despite these difficulties, various approaches for a theory of Quantum Gravity have been developed. In this thesis we focus on two such approaches: Loop Quantum Gravity and the Topos theoretic approach. The choice fell on these approaches because, although they both reject the Copenhagen interpretation of quantum theory, their underpinning philosophical approach to formulating a quantum theory of gravity are radically different. In particular LQG is a rather conservative scheme, inheriting all the formalism of both GR and Quantum Theory, as it tries to bring to its logical extreme consequences the possibility of combining the two. On the other hand, the Topos approach involves the idea that a radical change of perspective is needed in order to solve the problem of quantum gravity, especially in regard to the fundamental concepts of 'space' and 'time'. Given the partial successes of both approaches, the hope is that it might be possible to find a common ground in which each approach can enrich the other. This thesis is divided in two parts: in the first part we analyse LQG, paying particular attention to the semiclassical properties of the volume operator. Such an operator plays a pivotal role in defining the dynamics of the theory, thus testing its semiclassical limit is of uttermost importance. We then proceed to analyse spin foam models (SFM), which are an attempt at a covariant or path integral formulation of canonical Loop Quantum
Black Holes with Scalar Hairs in Einstein-Gauss-Bonnet Gravity
Brihaye, Y
2015-01-01
The Einstein-Gauss-Bonnet gravity in five dimensions is extended by scalar fields and the corresponding equations are reduced to a system of non-linear differential equations. A large family of regular solutions of these equations is shown to exist. Generically, these solutions are spinning black holes with scalar hairs. They can be characterized (but not uniquely) by an horizon and an angular velocity on this horizon. Taking particular limits the black holes approach boson star or become extremal, in any case the limiting configurations remain hairy.
The Gravity of Photons and the Necessary Rectification of Einstein Equation
Directory of Open Access Journals (Sweden)
Lo C. Y.
2006-01-01
Full Text Available It is pointed out that Special Relativity together with the principle of causality implies that the gravity of an electromagnetic wave is an accompanying gravitational wave propagating with the same speed. Since a gravitational wave carries energy-momentum, this accompanying wave would make the energy-stress tensor of the light to be different from the electromagnetic energy-stress tensor, and thus can produce a geodesic equation for the photons. Moreover, it is found that the appropriate Einstein equation must additionally have the photonic energy-stress tensor with the antigravity coupling in the source term. This would correct that, in disagreement with the calculations for the bending of light, existing solutions of gravity for an electromagnetic wave, is unbounded. This rectification is confirmed by calculating the gravity of electromagnetic plane-waves. The gravity of an electromagnetic wave is indeed an accompanying gravitational wave. Moreover, these calculations show the first time that Special Relativity and General Relativity are compatible because the physical meaning of coordinates has been clarified. The success of this rectification makes General Relativity standing out further among theories of gravity.
Gravitational Decoherence, Alternative Quantum Theories and Semiclassical Gravity
Hu, B L
2014-01-01
In this report we discuss three aspects: 1) Semiclassical gravity theory (SCG): 4 levels of theories describing the interaction of quantum matter with classical gravity; 2) Alternative Quantum Theories: Discerning those which are derivable from general relativity (GR) plus quantum field theory (QFT) from those which are not; 3) Gravitational Decoherence: Derivation of a master equation and examination of the assumptions which led to the claims of observational possibilities. We list three sets of corresponding problems worthy of pursuit: a) Newton-Schr\\"odinger Equations in relation to SCG; b) Master equation of gravity-induced effects serving as discriminator of 2); and c) Role of gravity in macroscopic quantum phenomena.
Quantum Gravity and a Time Operator in Relativistic Quantum Mechanics
Bauer, M
2016-01-01
The problem of time in the quantization of gravity arises from the fact that time in Schroedinger's equation is a parameter. This sets time apart from the spatial coordinates, represented by operators in quantum mechanics (QM). Thus "time" in QM and "time" in General Relativity (GR) are seen as mutually incompatible notions. The introduction of a dy- namical time operator in relativistic quantum mechanics (RQM), that in the Heisenberg representation is also a function of the parameter t (iden- tifed as the laboratory time), prompts to examine whether it can help to solve the disfunction referred to above. In particular, its application to the conditional interpretation of the canonical quantization approach toquantum gravity is developed. 1
Quantum Gravity as a Deformed Topological Quantum Field Theory
Energy Technology Data Exchange (ETDEWEB)
Mikovic, Aleksandar [Departamento de Matematica, Universidade Lusofona de Humanidades e Tecnologias, Av. do Campo Grande, 376, 1749-024 Lisbon (Portugal)
2006-03-01
It is known that the Einstein-Hilbert action with a positive cosmological constant can be represented as a perturbation of the SO(4, 1) BF theory by a symmetry-breaking term quadratic in the B field. Introducing fermionic matter generates additional terms in the action which are polynomial in the tetrads and the spin connection. We describe how to construct the generating functional in the spin foam formalism for a generic BF theory when the sources for the B and the gaugefield are present. This functional can be used to obtain a path integral for General Relativity with matter as a perturbative series whose the lowest order term is a path integral for a topological gravity coupled to matter.
Loop quantum gravity: an outside view
Nicolai, Hermann C; Zamaklar, M; Nicolai, Hermann; Peeters, Kasper; Zamaklar, Marija
2005-01-01
We present a pedagogical review of loop quantum gravity, with the aim of enabling a precise but critical assessment of its achievements so far. Special attention is paid to the appearance of a large number of ambiguities in the theory, in particular in the formulation of the Hamiltonian constraint. We emphasise that the off-shell (`strong') closure of the constraint algebra is a crucial test of the consistency of the theory, and should be used as the main tool to select one (if any) of the proposed Hamiltonians. Developing suitable approximation methods to establish a connection with classical gravity on the one hand, and with the physics of elementary particles on the other, remains a major challenge.
An alternative path integral for quantum gravity
Krishnan, Chethan; Kumar, K. V. Pavan; Raju, Avinash
2016-10-01
We define a (semi-classical) path integral for gravity with Neumann boundary conditions in D dimensions, and show how to relate this new partition function to the usual picture of Euclidean quantum gravity. We also write down the action in ADM Hamiltonian formulation and use it to reproduce the entropy of black holes and cosmological horizons. A comparison between the (background-subtracted) covariant and Hamiltonian ways of semi-classically evaluating this path integral in flat space reproduces the generalized Smarr formula and the first law. This "Neumann ensemble" perspective on gravitational thermodynamics is parallel to the canonical (Dirichlet) ensemble of Gibbons-Hawking and the microcanonical approach of Brown-York.
An Alternate Path Integral for Quantum Gravity
Krishnan, Chethan; Raju, Avinash
2016-01-01
We define a (semi-classical) path integral for gravity with Neumann boundary conditions in $D$ dimensions, and show how to relate this new partition function to the usual picture of Euclidean quantum gravity. We also write down the action in ADM Hamiltonian formulation and use it to reproduce the entropy of black holes and cosmological horizons. A comparison between the (background-subtracted) covariant and Hamiltonian ways of semi-classically evaluating this path integral in flat space reproduces the generalized Smarr formula and the first law. This "Neumann ensemble" perspective on gravitational thermodynamics is parallel to the canonical (Dirichlet) ensemble of Gibbons-Hawking and the microcanonical approach of Brown-York.
An alternative path integral for quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Krishnan, Chethan; Kumar, K.V. Pavan; Raju, Avinash [Center for High Energy Physics, Indian Institute of Science,Bangalore 560012 (India)
2016-10-10
We define a (semi-classical) path integral for gravity with Neumann boundary conditions in D dimensions, and show how to relate this new partition function to the usual picture of Euclidean quantum gravity. We also write down the action in ADM Hamiltonian formulation and use it to reproduce the entropy of black holes and cosmological horizons. A comparison between the (background-subtracted) covariant and Hamiltonian ways of semi-classically evaluating this path integral in flat space reproduces the generalized Smarr formula and the first law. This “Neumann ensemble” perspective on gravitational thermodynamics is parallel to the canonical (Dirichlet) ensemble of Gibbons-Hawking and the microcanonical approach of Brown-York.
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.
Gheorghiu, Tamara; Vacaru, Olivia; Vacaru, Sergiu I
2016-01-01
We study geometric relativistic flow and Ricci soliton equations which (for respective nonholonomic constraints and self-similarity conditions) are equivalent to the gravitational field equations of $R^2$ gravity and/or to the Einstein equations with scalar field in general relativity, GR. Perelman's functionals are generalized for modified gravity theories, MGTs, which allows to formulate an analogous statistical thermodynamics for geometric flows and Ricci solitons. There are constructed and analyzed generic off-diagonal black ellipsoid, black hole and solitonic exact solutions in MGTs and GR encoding geometric flow evolution scenarios and nonlinear parametric interactions. Such new classes of solutions in MGTs can be with polarized and/or running constants, nonholonomically deformed horizons and/or imbedded self-consistently into solitonic backgrounds. They exist also in GR as generic off-diagonal vacuum configurations with effective cosmological constant and/or mimicking effective scalar field interaction...
Most general flat space boundary conditions in three-dimensional Einstein gravity
Grumiller, Daniel; Merbis, Wout; Riegler, Max
2017-09-01
We consider the most general asymptotically flat boundary conditions in three-dimensional Einstein gravity in the sense that we allow for the maximal number of independent free functions in the metric, leading to six towers of boundary charges and six associated chemical potentials. We find as associated asymptotic symmetry algebra an isl(2)k current algebra. Restricting the charges and chemical potentials in various ways recovers previous cases, such as bms3 , Heisenberg or Detournay–Riegler, all of which can be obtained as contractions of corresponding AdS3 constructions. Finally, we show that a flat space contraction can induce an additional Carrollian contraction. As examples we provide two novel sets of boundary conditions for Carroll gravity.
Three types of superpotentials for perturbations in the Einstein-Gauss-Bonnet gravity
Petrov, A N
2009-01-01
Superpotentials (antisymmetric tensor densities) in Einstein-Gauss-Bonnet (EGB) gravity for arbitrary types of perturbations on arbitrary curved backgrounds are constructed. As a basis, the generalized conservation laws in the framework of an arbitrary D-dimensional metric theory, where conserved currents are expressed through divergences of superpotentials, are used. Such a derivation is exact (perturbations are not infinitesimal) and is approached, when a one solution (dynamical) is considered as a perturbed system with respect to another solution (background). Three known prescriptions are elaborated: these are the canonical N{\\oe}ther theorem, the Belinfante symmetrization rule and the field-theoretical derivation. All the three approaches are presented in an unique way convenient for comparisons and a development. Exact expressions for the 01-component of the three types of the superpotentials are derived in the case, when an arbitrary static Schwarzschild-like solution in the EGB gravity is considered a...
Mobile quantum gravity sensor with unprecedented stability
Leykauf, Bastian; Freier, Christian; Schkolnik, Vladimir; Krutzik, Markus; Peters, Achim
2017-04-01
The gravimetric atom interferometer GAIN is based on interfering ensembles of laser-cooled 87Rb atoms in a fountain setup, using stimulated Raman transitions. GAIN's rugged design allows for transports to sites of geodetic and geophysical interest while maintaining a high accuracy compatible with the best classical instruments. We compared our instrument's performance with falling corner-cube and superconducting gravimeters in two measurement campaigns at geodetic observatories in Wettzell, Germany and Onsala, Sweden. Our instrument's long-term stability of 0.5 nm/s2 is the best value for absolute gravimeters reported to date [1]. Our measured gravity value agrees with other state-of-the-art gravimeters on the 10-9 level in g, demonstrating effective control over systematics including wavefront distortions of the Raman beams [2]. By using the juggling technique [3], we are able to perform gravity measurements on two atomic clouds simultaneously. Advantages include the suppression of common mode phase noise, enabling differential phase shift extraction without the need for vibration isolation. We will present the results of our first gravity gradient measurements. [1] Freier, Hauth, Schkolnik, Leykauf, Schilling, Wziontek, Scherneck, Müller and Peters (2016). Mobile quantum gravity sensor with unprecedented stability. Journal of Physics: Conference Series, 8th Symposium on Frequency Standards and Metrology 2015, 723, 12050. [2] Schkolnik, Leykauf, Hauth, Freier and Peters (2015). The effect of wavefront aberrations in atom interferometry. Applied Physics B, 120(2), 311 - 316. [3] Legere and Gibble (1998). Quantum Scattering in a Juggling Atomic Fountain. Physical Review Letters, 81(1), 5780 - 5783.
Puzzles in quantum gravity : what can black hole microstates teach us about quantum gravity?
El-Showk, S.
2009-01-01
In this thesis we review two independent lines of research directed towards helping us construct a theory of Quantum Gravity. While, in string/M-theory, we already enjoy a potential theory of this type there remain many unanswered foundational questions and missing precepts. By probing the
Eikonal quantum gravity and Planckian scattering
Kabat, D; Kabat, Dan; Ortiz, Miguel
1992-01-01
Various approaches to high energy forward scattering in quantum gravity are compared using the eikonal approximation. The massless limit of the eikonal is shown to be equivalent to other approximations for the same process, specifically the semiclassical calculation due to G. 't Hooft and the topological field theory due to H. and E. Verlinde. This comparison clarifies these previous results, as it is seen that the amplitude arises purely from a linearised gravitational interaction. The interpretation of poles in the scattering amplitude is also clarified.
Noether symmetries in extended gravity quantum cosmology
Capozziello, Salvatore
2013-01-01
We summarize the use of Noether symmetries in Minisuperspace Quantum Cosmology. In particular, we consider minisuperspace models, showing that the existence of conserved quantities gives selection rules that allow to recover classical behaviors in cosmic evolution according to the so called Hartle criterion. Such a criterion selects correlated regions in the configuration space of dynamical variables whose meaning is related to the emergence of classical observable universes. Some minisuperspace models are worked out starting from Extended Gravity, in particular coming from scalar tensor, f(R) and f(T) theories. Exact cosmological solutions are derived.
New length operator for loop quantum gravity
Ma, Yongge; Yang, Jinsong
2010-01-01
An alternative expression for the length operator in loop quantum gravity is presented. The operator is background-independent, symmetric, positive semi-definite, and well-defined on the kinematical Hilbert space. The expression for the regularized length operator can moreover be understood both from a simple geometrical perspective as the average of a formula relating the length to area, volume and flux operators, and also consistently as the result of direct substitution of the densitized triad operator with the functional derivative operator into the regularized expression of the length. Both these derivations are discussed, and the origin of an undetermined overall factor in each case is also elucidated.
Quantum Gravity and Cosmology: an intimate interplay
Sakellariadou, Mairi
2017-08-01
I will briefly discuss three cosmological models built upon three distinct quantum gravity proposals. I will first highlight the cosmological rôle of a vector field in the framework of a string/brane cosmological model. I will then present the resolution of the big bang singularity and the occurrence of an early era of accelerated expansion of a geometric origin, in the framework of group field theory condensate cosmology. I will then summarise results from an extended gravitational model based on non-commutative spectral geometry, a model that offers a purely geometric explanation for the standard model of particle physics.
Phase Transition in Loop Quantum Gravity
Mäkelä, Jarmo
2016-01-01
We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature $T_C$. In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature $T_C$ may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect to the hole the characteristic temperature $T_C$ corresponds to the Hawking temperature of the hole.
On gauge-independence in quantum gravity
Vasilevich, D V
1995-01-01
We prove gauge-independence of one-loop path integral for on-shell quantum gravity obtained in a framework of modified geometric approach. We use projector on pure gauge directions constructed via quadratic form of the action. This enables us to formulate the proof entirely in terms of determinants of non-degenerate elliptic operators without reference to any renormalization procedure. The role of the conformal factor rotation in achieving gauge-independence is discussed. Direct computations on CP^2 in a general three-parameter background gauge are presented. We comment on gauge dependence of previous results by Ichinose.
Hypercuboidal renormalization in spin foam quantum gravity
Bahr, Benjamin; Steinhaus, Sebastian
2017-06-01
In this article, we apply background-independent renormalization group methods to spin foam quantum gravity. It is aimed at extending and elucidating the analysis of a companion paper, in which the existence of a fixed point in the truncated renormalization group flow for the model was reported. Here, we repeat the analysis with various modifications and find that both qualitative and quantitative features of the fixed point are robust in this setting. We also go into details about the various approximation schemes employed in the analysis.
Towards lattice-regularized Quantum Gravity
Diakonov, Dmitri
2011-01-01
Using the Cartan formulation of General Relativity, we construct a well defined lattice-regularized theory capable to describe large non-perturbative quantum fluctuations of the frame field (or the metric) and of the spin connection. To that end we need to present the tetrad by a composite field built as a bilinear combination of fermion fields. The theory is explicitly invariant under local Lorentz transformations and, in the continuum limit, under general covariant transformations, or diffeomorphisms. Being well defined for large and fast varying fields at the ultraviolet cutoff, the theory simultaneously has chances of reproducing standard General Relativity in the infrared continuum limit. The present regularization of quantum gravity opens new possibilities of its unification with the Standard Model.
Liouville quantum gravity on complex tori
David, François; Rhodes, Rémi; Vargas, Vincent
2016-02-01
In this paper, we construct Liouville Quantum Field Theory (LQFT) on the toroidal topology in the spirit of the 1981 seminal work by Polyakov [Phys. Lett. B 103, 207 (1981)]. Our approach follows the construction carried out by the authors together with Kupiainen in the case of the Riemann sphere ["Liouville quantum gravity on the Riemann sphere," e-print arXiv:1410.7318]. The difference is here that the moduli space for complex tori is non-trivial. Modular properties of LQFT are thus investigated. This allows us to integrate the LQFT on complex tori over the moduli space, to compute the law of the random Liouville modulus, therefore recovering (and extending) formulae obtained by physicists, and make conjectures about the relationship with random planar maps of genus one, eventually weighted by a conformal field theory and conformally embedded onto the torus.
The asymptotic safety scenario in quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Saueressig, Frank [Institute of Physics, University of Mainz, D-55099 Mainz (Germany)
2011-07-01
Asymptotic safety offers the possibility that gravity constitutes a consistent and predictive quantum field theory within Wilsons generalized framework of renormalization. The key ingredient of this scenario is a non-trivial fixed point of the gravitational renormalization group flow which governs the UV behavior of the theory. The fixed point itself thereby guarantees the absence of unphysical UV divergences while its associated finite-dimensional UV-critical surface ensures the predictivity of the resulting quantum theory. This talk summarizes the evidence for the existence of such a fixed point, which emerged from the flow equation for the effective average action, the gravitational beta-functions in 2+{epsilon} dimensions, the 2-Killing vector reduction of the gravitational path-integral and lattice simulations. Possible phenomenological consequences are discussed in detail.
Liouville quantum gravity on complex tori
Energy Technology Data Exchange (ETDEWEB)
David, François [Institut de Physique Théorique, CNRS, URA 2306, CEA, IPhT, Gif-sur-Yvette (France); Rhodes, Rémi [Université Paris-Est Marne la Vallée, LAMA, Champs sur Marne (France); Vargas, Vincent [ENS Paris, DMA, 45 rue d’Ulm, 75005 Paris (France)
2016-02-15
In this paper, we construct Liouville Quantum Field Theory (LQFT) on the toroidal topology in the spirit of the 1981 seminal work by Polyakov [Phys. Lett. B 103, 207 (1981)]. Our approach follows the construction carried out by the authors together with Kupiainen in the case of the Riemann sphere [“Liouville quantum gravity on the Riemann sphere,” e-print arXiv:1410.7318]. The difference is here that the moduli space for complex tori is non-trivial. Modular properties of LQFT are thus investigated. This allows us to integrate the LQFT on complex tori over the moduli space, to compute the law of the random Liouville modulus, therefore recovering (and extending) formulae obtained by physicists, and make conjectures about the relationship with random planar maps of genus one, eventually weighted by a conformal field theory and conformally embedded onto the torus.
Quantum gravity momentum representation and maximum energy
Moffat, J. W.
2016-11-01
We use the idea of the symmetry between the spacetime coordinates xμ and the energy-momentum pμ in quantum theory to construct a momentum space quantum gravity geometry with a metric sμν and a curvature tensor Pλ μνρ. For a closed maximally symmetric momentum space with a constant 3-curvature, the volume of the p-space admits a cutoff with an invariant maximum momentum a. A Wheeler-DeWitt-type wave equation is obtained in the momentum space representation. The vacuum energy density and the self-energy of a charged particle are shown to be finite, and modifications of the electromagnetic radiation density and the entropy density of a system of particles occur for high frequencies.
Topological black holes for Einstein-Gauss-Bonnet gravity with a nonminimal scalar field
Gaete, Moises Bravo
2013-01-01
We consider the Einstein-Gauss-Bonnet gravity with a negative cosmological constant together with a source given by a scalar field nonminimally coupled in arbitrary dimension D. For a certain election of the cosmological and Gauss-Bonnet coupling constants, we derive two classes of AdS black hole solutions whose horizon is planar. The first family of black holes obtained for a particular value of the nonminimal coupling parameter only depends on a constant M, and the scalar field vanishes as M=0. The second class of solutions corresponds to a two-parametric (with constants M and A) black hole stealth configuration, that is a nontrivial scalar field with a black hole metric such that both side (gravity and matter parts) of the Einstein equations vanishes. In this case, in the vanishing M, the solution reduces to a stealth scalar field on the pure AdS metric. We note that the existence of these two classes of solutions is inherent of the particular choice of the coupling constants and, they can not be promoted ...
Holographic Gravity and the Surface term in the Einstein-Hilbert Action
Padmanabhan, T
2004-01-01
Certain peculiar features of Einstein-Hilbert (EH) action provide clues towards a holographic approach to gravity which is independent of the detailed microstructure of spacetime. These features of the EH action include: (a) the existence of second derivatives of dynamical variables; (b) a non trivial relation between the surface term and the bulk term; (c) the fact that surface term is non analytic in the coupling constant, when gravity is treated as a spin-2 perturbation around flat spacetime and (d) the form of the variation of the surface term under infinitesimal coordinate transformations. The surface term can be derived directly from very general considerations and using (d) one can obtain Einstein's equations {\\it just from the surface term of the action}. Further one can relate the bulk term to the surface term and derive the full EH action based on purely thermodynamic considerations. The features (a), (b) and (c) above emerge in a natural fashion in this approach. It is shown that action $A_{grav}$ ...
Quantum Reduced Loop Gravity and the foundation of Loop Quantum Cosmology
Alesci, Emanuele
2016-01-01
Quantum Reduced Loop Gravity is a promising framework for linking Loop Quantum Gravity and the effective semiclassical dynamics of Loop Quantum Cosmology. We review its basic achievements and its main perspectives, outlining how it provides a quantum description of the Universe in terms of a cuboidal graph which constitutes the proper framework for applying loop techniques in a cosmological setting.
Energy Technology Data Exchange (ETDEWEB)
Dadhich, Naresh [Jamia Millia Islamia, Centre for Theoretical Physics, New Delhi (India); Inter-University Centre for Astronomy and Astrophysics, Pune (India); Pons, Josep M. [Universitat de Barcelona, Departament d' Estructura i Constituents de la Materia y Institut de Ciencies del Cosmos (ICCUB), Facultat de Fsica, Barcelona, Catalonia (Spain)
2015-06-15
We study static black hole solutions in Einstein and Einstein-Gauss-Bonnet gravity with the topology of the product of two spheres, S{sup n} x S{sup n}, in higher dimensions. There is an unusual new feature of the Gauss-Bonnet black hole: the avoidance of a non-central naked singularity prescribes a mass range for the black hole in terms of Λ > 0. For an Einstein-Gauss-Bonnet black hole a limited window of negative values for Λ is also permitted. This topology encompasses black strings, branes, and generalized Nariai metrics. We also give new solutions with the product of two spheres of constant curvature. (orig.)
Three types of superpotentials for perturbations in the Einstein-Gauss-Bonnet gravity
Energy Technology Data Exchange (ETDEWEB)
Petrov, A N, E-mail: anpetrov@rol.r [Relativistic Astrophysics Group, Sternberg Astronomical Institute, Universitetskii pr., 13, Moscow 119992 (Russian Federation)
2009-07-07
Superpotentials (antisymmetric tensor densities) in the Einstein-Gauss-Bonnet (EGB) gravity for arbitrary types of perturbations on arbitrary curved backgrounds are constructed. As a basis, the generalized conservation laws in the framework of an arbitrary D-dimensional metric theory, where conserved currents are expressed through divergences of superpotentials, are used. Such a derivation is exact (perturbations are not infinitesimal) and is approached when a solution (dynamical) is considered as a perturbed system with respect to another solution (background). Three known prescriptions are elaborated: they are the canonical Noether theorem, the Belinfante symmetrization rule and the field-theoretical derivation. All three approaches are presented in a unique way convenient for comparisons and development. Exact expressions for the 01-component of the three types of the superpotentials are derived in the case when an arbitrary static Schwarzschild-like solution in the EGB gravity is considered as a perturbed system with respect to a background of the same type. These formulae are used for calculating the mass of the Schwarzschild-anti-de Sitter black hole in the EGB gravity. As a background, both the anti-de Sitter spacetime in arbitrary dimensions and a 'mass gap' vacuum, which has no maximal set of symmetries, in five dimensions are considered. Problems and perspectives for future development, including the Lovelock gravity, are discussed.
Einstein-Born-Infeld-massive gravity: adS-black hole solutions and their thermodynamical properties
Energy Technology Data Exchange (ETDEWEB)
Hendi, S.H. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM),P.O. Box 55134-441, Maragha (Iran, Islamic Republic of); Panah, B. Eslam; Panahiyan, S. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University,Shiraz 71454 (Iran, Islamic Republic of)
2015-11-23
In this paper, we study massive gravity in the presence of Born-Infeld nonlinear electrodynamics. First, we obtain metric function related to this gravity and investigate the geometry of the solutions and find that there is an essential singularity at the origin (r=0). It will be shown that due to contribution of the massive part, the number, type and place of horizons may be changed. Next, we calculate the conserved and thermodynamic quantities and check the validation of the first law of thermodynamics. We also investigate thermal stability of these black holes in context of canonical ensemble. It will be shown that number, type and place of phase transition points are functions of different parameters which lead to dependency of stability conditions to these parameters. Also, it will be shown how the behavior of temperature is modified due to extension of massive gravity and strong nonlinearity parameter. Next, critical behavior of the system in extended phase space by considering cosmological constant as pressure is investigated. A study regarding neutral Einstein-massive gravity in context of extended phase space is done. Geometrical approach is employed to study the thermodynamical behavior of the system in context of heat capacity and extended phase space. It will be shown that GTs, heat capacity and extended phase space have consistent results. Finally, critical behavior of the system is investigated through use of another method. It will be pointed out that the results of this method is in agreement with other methods and follow the concepts of ordinary thermodynamics.
String Field Theory from Quantum Gravity
Crane, Louis
2012-01-01
Recent work on neutrino oscillations suggests that the three generations of fermions in the standard model are related by representations of the finite group A(4), the group of symmetries of the tetrahedron. Motivated by this, we explore models which extend the EPRL model for quantum gravity by coupling it to a bosonic quantum field of representations of A(4). This coupling is possible because the representation category of A(4) is a module category over the representation categories used to construct the EPRL model. The vertex operators which interchange vacua in the resulting quantum field theory reproduce the bosons and fermions of the standard model, up to issues of symmetry breaking which we do not resolve. We are led to the hypothesis that physical particles in nature represent vacuum changing operators on a sea of invisible excitations which are only observable in the A(4) representation labels which govern the horizontal symmetry revealed in neutrino oscillations. The quantum field theory of the A(4) ...
Quantum Gravity and the Holographic Principle
De Haro, S
2001-01-01
In this thesis we study two different approaches to holography, and comment on the possible relation between them. The first approach is an analysis of the high-energy regime of quantum gravity in the eikonal approximation, where the theory reduces to a topological field theory. This is the regime where particles interact at high energies but with small momentum transfer. We do this for the cases of asymptotically dS and AdS geometries and find that in both cases the theory is topological. We discuss the relation of our solutions in AdS to those of Horowitz and Itzhaki. We also consider quantum gravity away from the extreme eikonal limit and explain the sense in which the covariance of the theory is equivalent to taking into account transfer of momentum. The second approach we pursue is the AdS/CFT correspondence. We provide a holographic reconstruction of the bulk space-time metric and of bulk fields on this space-time, out of conformal field theory data. Knowing which sources are turned on is sufficient in ...
A Simple Theory of Quantum Gravity
Horndeski, Gregory W
2015-01-01
A novel theory of Quantum Gravity is presented in which the real gravitons manifest themselves as holes in space. In general, these holes propagate at the speed of light through an expanding universe with boundary denoted by U, which is comprised of pulsating cells. These holes can form bound and semi-bound states. The geometry of U is non-Euclidean on a small scale, but there are indications that it can become Euclidean on a large scale. The motions of elementary particles through U are governed by probability 4 and 7-vectors, which are related to the momentum vectors in Minkowski space. The connection of this theory to Newtonian gravity is discussed, and an expression for the gravitational redshift of photons is derived which relates the redshift to the probability that a photon absorbs a virtual graviton. The theory also provides a possible explanation of dark matter and dark energy as gravitational phenomena, which do not require the introduction of any new particles. A quantum cosmology is presented in w...
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.
Quantum gravity and the KPZ formula
Garban, Christophe
2012-01-01
This text is a survey (Bourbaki seminar) on the paper "Liouville quantum gravity and KPZ" By B.Duplantier and S.Sheffield. The study of statistical physics models in two dimensions (d=2) at their critical point is in general a significantly hard problem (not to mention the d=3 case). In the eighties, three physicists, Knizhnik, Polyakov et Zamolodchikov (KPZ) came up in \\cite{\\KPZ} with a novel and far-reaching approach in order to understand the critical behavior of these models. Among these, one finds for example random walks, percolation as well as the Ising model. The main underlying idea of their approach is to study these models along a two-step procedure as follows: a/ First of all, instead of considering the model on some regular lattice of the plane (such as $\\Z^2$ for example), one defines it instead on a well-chosen "random planar lattice". Doing so corresponds to studying the model in its {\\it quantum gravity} form. In the case of percolation, the appropriate choice of random lattice matches with ...
Spin Foam Models For Quantum Gravity
Pérez, A
2001-01-01
The definition of a quantum theory of gravity is explored following Feynman's path-integral approach. The aim is to construct a well defined version of the Wheeler-Misner- Hawking “sum over four geometries” formulation of quantum general relativity (GR). This is done by means of exploiting the similarities between the formulation of GR in terms of tetrad-connection variables (Palatini formulation) and a simpler theory called BF theory. One can go from BF theory to GR by imposing certain constraints on the BF-theory configurations. BF theory contains only global degrees of freedom (topological theory) and it can be exactly quantized á la Feynman introducing a discretization of the manifold. Using the path integral for BF theory we define a path integration for GR imposing the BF-to-GR constraints on the BF measure. The infinite degrees of freedom of gravity are restored in the process, and the restriction to a single discretization introduces a cut- off in the summed-over configu...
New ground state for quantum gravity
Magueijo, Joao
2012-01-01
In this paper we conjecture the existence of a new "ground" state in quantum gravity, supplying a wave function for the inflationary Universe. We present its explicit perturbative expression in the connection representation, exhibiting the associated inner product. The state is chiral, dependent on the Immirzi parameter, and is the vacuum of a second quantized theory of graviton particles. We identify the physical and unphysical Hilbert sub-spaces. We then contrast this state with the perturbed Kodama state and explain why the latter can never describe gravitons in a de Sitter background. Instead, it describes self-dual excitations, which are composites of the positive frequencies of the right-handed graviton and the negative frequencies of the left-handed graviton. These excitations are shown to be unphysical under the inner product we have identified. Our rejection of the Kodama state has a moral tale to it: the semi-classical limit of quantum gravity can be the wrong path for making contact with reality (w...
Quantum Gravity and the Algebra of Tangles
Baez, J C
1993-01-01
In Rovelli and Smolin's loop representation of nonperturbative quantum gravity in 4 dimensions, there is a space of solutions to the Hamiltonian constraint having as a basis isotopy classes of links in R^3. The physically correct inner product on this space of states is not yet known, or in other words, the *-algebra structure of the algebra of observables has not been determined. In order to approach this problem, we consider a larger space H of solutions of the Hamiltonian constraint, which has as a basis isotopy classes of tangles. A certain algebra T, the ``tangle algebra,'' acts as operators on H. The ``empty state'', corresponding to the class of the empty tangle, is conjectured to be a cyclic vector for T. We construct simpler representations of T as quotients of H by the skein relations for the HOMFLY polynomial, and calculate a *-algebra structure for T using these representations. We use this to determine the inner product of certain states of quantum gravity associated to the Jones polynomial (or m...
Quantum gravity from descriptive set theory
Energy Technology Data Exchange (ETDEWEB)
El Naschie, M.S
2004-03-01
We start from Hilbert's criticism of the axioms of classical geometry and the possibility of abandoning the Archimedean axiom. Subsequently we proceed to the physical possibility of a fundamental limitation on the smallest length connected to certain singular points in spacetime and below which measurements become meaningless, Finally we arrive at the conclusion that maximising the Hawking-Bekenstein informational content of spacetime makes the existence of a transfinite geometry for physical 'spacetime' not only plausible but probably inevitable. The main part of the paper is then concerned with a proposal for a mathematical description of a transfinite, non-Archimedean geometry using descriptive set theory. Nevertheless, and despite all abstract mathematics, we remain quite close to similar lines of investigation initiated by physicists like A. Wheeler, D. Finkelstein and G. 'tHooft. In particular we introduce a logarithmic gauge transformation linking classical gravity with the electro weak via a version of informational entropy. That way we may claim to have accomplished an important step towards a general theory of quantum gravity using {epsilon}{sup ({infinity}}{sup )} and complexity theory and finding that {alpha}{sub G}=(2){sup {alpha}}{sup -bar{sub ew-1}} congruent with (1.7)(10){sup 38} where {alpha}{sub G} is the dimensionless Newton gravity constant, and {alpha}{sub ew}{approx_equal}128 is the fine structure constant at the electro weak scale.
Mobile quantum gravity sensor with unprecedented stability
Freier, Christian; Schkolnik, Vladimir; Leykauf, Bastian; Schilling, Manuel; Wziontek, Hartmut; Scherneck, Hans-Georg; Müller, Jürgen; Peters, Achim
2015-01-01
Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of $\\mathrm{39\\,nm/s^2}$ and long-term stability of $\\mathrm{0.5\\,nm/s^2}$ short-term noise of $96\\,\\mathrm{nm/s^2/\\sqrt{Hz}}$. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrum...
Non-perturbative quantum gravity: a conformal perspective
Budd, T.G.
2012-01-01
The construction of meaningful observables in models of quantum gravity is a highly non-trivial task, but necessary in order to study their continuum physics. In this thesis several such observables are identified in lattice models of quantum gravity. In dynamical triangulations in two dimensions wi
The relation between Euclidean and Lorentzian 2D quantum gravity
Ambjørn, J.; Correia, J.; Kristjansen, C.; Loll, R.
2006-01-01
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 (gen
An Adynamical, Graphical Approach to Quantum Gravity and Unification
Stuckey, W. M.; Silberstein, Michael; McDevitt, Timothy
We use graphical field gradients in an adynamical, background independent fashion to propose a new approach to quantum gravity (QG) and unification. Our proposed reconciliation of general relativity (GR) and quantum field theory (QFT) is based on a modification of their graphical instantiations, i.e. Regge calculus and lattice gauge theory (LGT), respectively, which we assume are fundamental to their continuum counterparts. Accordingly, the fundamental structure is a graphical amalgam of space, time, and sources (in parlance of QFT) called a "space-time source element". These are fundamental elements of space, time, and sources, not source elements in space and time. The transition amplitude for a space-time source element is computed using a path integral with discrete graphical action. The action for a space-time source element is constructed from a difference matrix K and source vector J on the graph, as in lattice gauge theory. K is constructed from graphical field gradients so that it contains a non-trivial null space and J is then restricted to the row space of K, so that it is divergence-free and represents a conserved exchange of energy-momentum. This construct of K and J represents an adynamical global constraint (AGC) between sources, the space-time metric, and the energy-momentum content of the element, rather than a dynamical law for time-evolved entities. In this view, one manifestation of quantum gravity becomes evident when, for example, a single space-time source element spans adjoining simplices of the Regge calculus graph. Thus, energy conservation for the space-time source element includes contributions to the deficit angles between simplices. This idea is used to correct proper distance in the Einstein-de Sitter (EdS) cosmology model yielding a fit of the Union2 Compilation supernova data that matches ΛCDM without having to invoke accelerating expansion or dark energy. A similar modification to LGT results in an adynamical account of quantum
Quantum Interactive Dualism: The Libet and Einstein-Podolsky-RosenCausal Anomalies
Energy Technology Data Exchange (ETDEWEB)
Stapp, Henry P.
2006-02-20
The "free will" data of Benjamin Libet and the predictionsof quantum theory considered by Einstein, Podolsky,and Rosen, both posepuzzles within aconceptual framework that, simultaneously, is compatiblewith the theory of relativity and allows human subjects to freely choosehow they will act. The quantum theoretic resolutions of these puzzles aredescribed.
A Model for Macroscopic Quantum Tunneling of Bose-Einstein Condensate with Attractive Interaction
Institute of Scientific and Technical Information of China (English)
YAN Ke-Zhu; TAN Wei-Han
2000-01-01
Based on the numerical wave function solutions of neutral atoms with attractive interaction in a harmonic trap, we propose an exactly solvable model for macroscopic quantum tunneling of a Bose condensate with attractive interaction. We calculate the rate of macroscopic quantum tunneling from a metastable condensate state to the collapse state and analyze the stability of the attractive Bose-Einstein condensation.
Exact analytical solution for quantum spins mixing in spin-1 Bose-Einstein condensates
Institute of Scientific and Technical Information of China (English)
Chen Ai-Xi; Qiu Wan-Ying; Wang Zhi-Ping
2008-01-01
This paper solves exactly a set of fully quantized coupled equations describing the quantum dynamics of quantum spins mixing in spin-1 Bose-Einstein condensates by deriving the exact explicit analytical expressions for the evolution of creation and annihilation operators.
Conformal invariance and renormalization group in quantum gravity near two dimensions
Aida, T; Kawai, H; Ninomiya, M
1994-01-01
We study quantum gravity in 2+\\epsilon dimensions in such a way to preserve the volume preserving diffeomorphism invariance. In such a formulation, we prove the following trinity: the general covariance, the conformal invariance and the renormalization group flow to Einstein theory at long distance. We emphasize that the consistent and macroscopic universes like our own can only exist for matter central charge 0
Fixed points and infrared completion of quantum gravity
Christiansen, Nicolai; Pawlowski, Jan M; Rodigast, Andreas
2012-01-01
The phase diagram of four-dimensional Einstein-Hilbert gravity is studied using Wilson's renormalization group. Smooth trajectories connecting the ultraviolet fixed point at short distances with attractive infrared fixed points at long distances are derived from the non-perturbative graviton propagator. Implications for the asymptotic safety conjecture and further results are discussed.
Intersecting Quantum Gravity with Noncommutative Geometry - a Review
Directory of Open Access Journals (Sweden)
Johannes Aastrup
2012-03-01
Full Text Available We review applications of noncommutative geometry in canonical quantum gravity. First, we show that the framework of loop quantum gravity includes natural noncommutative structures which have, hitherto, not been explored. Next, we present the construction of a spectral triple over an algebra of holonomy loops. The spectral triple, which encodes the kinematics of quantum gravity, gives rise to a natural class of semiclassical states which entail emerging fermionic degrees of freedom. In the particular semiclassical approximation where all gravitational degrees of freedom are turned off, a free fermionic quantum field theory emerges. We end the paper with an extended outlook section.
Testing Loop Quantum Gravity and Electromagnetic Dark Energy in Superconductors
de Matos, Clovis Jacinto
2008-01-01
In 1989 Cabrera and Tate reported an anomalous excess of mass of the Cooper pairs in rotating thin Niobium rings. So far, this experimental result never received a proper theoretical explanation in the context of superconductor's physics. In the present work we argue that what Cabrera and Tate interpreted as an anomalous excess of mass can also be associated with a deviation from the classical gravitomagnetic Larmor theorem due to the presence of dark energy in the superconductor, as well as with the discrete structure of the area of the superconducting Niobium ring as predicted by Loop Quantum Gravity. From Cabrera and Tate measurements we deduce that the quantization of spacetime in superconducting circular rings occurs at the Planck-Einstein scale $l_{PE} = (\\hbar G/c^3 \\Lambda)^{1/4}\\sim 3.77\\times 10 ^{-5} m$, instead of the Planck scale $l_{P} =(\\hbar G / c^3)^{1/2}=1.61 \\times 10 ^{-35} m$, with an Immirzi parameter which depends on the specific critical temperature of the superconducting material and ...
Towards self dual Loop Quantum Gravity
Achour, Jibril Ben
2015-01-01
In this PhD thesis, we introduced a new strategy to investigate the kinematical and physical predictions of self dual Loop Quantum Gravity (LQG) and by-passed the old problem of implementing quantum mechanically the so called reality conditions inherent to the self dual Ashtekar's phase space. We first review the loop quantization of the spherically isolated horizon and the computation of its micro-canonical entropy. Then we present the so called gas of punctures model for the quantum horizon, discussing its results in the canonical and grand-canonical ensembles and its limits. The fourth chapter is devoted to studying to what extend the loop quantization based on the self dual variables could cure those problems. We introduce a new strategy, based on an analytic continuation of the degeneracy from $\\gamma \\in R$ to $\\gamma = \\pm i$. We review in details the construction of the procedure, and present the results. At the leading term, we recover exactly the Bekenstein-Hawking area law. The fifth chapter is dev...
Testing the effects of gravity and motion on quantum entanglement in space-based experiments
Bruschi, David Edward; White, Angela; Baccetti, Valentina; Oi, Daniel K L; Fuentes, Ivette
2013-01-01
We propose an experiment to test the effects of gravity and acceleration on quantum entanglement in space-based setups. We show that the entanglement between transverse excitations of two Bose-Einstein condensates is degraded after one of them undergoes a change in the gravitational field strength. This prediction can be tested if the condensates are initially entangled in two separate satellites while being in the same orbit and then one of them moves to a different orbit. We show that the effect is observable in a typical orbital manoeuvre of nanosatellites like CanX4 and CanX5.
A note on the dimensional regularization of the Standard Model coupled with Quantum Gravity
Anselmi, D
2004-01-01
In flat space, gamma5 and the epsilon tensor break the dimensionally continued Lorentz symmetry in such a way that the propagators have fully Lorentz invariant denominators. When the Standard Model is coupled with quantum gravity gamma5 breaks the continued local Lorentz symmetry. I show how to deform the Einstein lagrangian and gauge-fix the residual local Lorentz symmetry so that the propagators of the graviton, the ghosts and the BRST auxiliary fields have fully Lorentz invariant denominators. This makes the calculation of Feynman diagrams more efficient.
A note on the dimensional regularization of the Standard Model coupled with quantum gravity
Anselmi, Damiano
2004-08-01
In flat space, γ5 and the epsilon tensor break the dimensionally continued Lorentz symmetry, but propagators have fully Lorentz invariant denominators. When the Standard Model is coupled with quantum gravity γ5 breaks the continued local Lorentz symmetry. I show how to deform the Einstein Lagrangian and gauge-fix the residual local Lorentz symmetry so that the propagators of the graviton, the ghosts and the BRST auxiliary fields have fully Lorentz invariant denominators. This makes the calculation of Feynman diagrams more efficient.
Loop quantum gravity and black hole entropy quantization
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Using the spin networks and the asymptotic quasinormal mode frequencies of black holes given by loop quantum gravity,the minimum horizon area gap is obtained.Then the quantum area spectrum of black holes is derived and the black hole entropy is a realized quantization.The results show that the black hole entropy given by loop quantum gravity is in full accord with the Bekenstein-Hawking entropy with a suitable Immirzi.
Loop quantum gravity and black hole entropy quantization
Institute of Scientific and Technical Information of China (English)
LI ChuanAn; JIANG JiJian; SU JiuQing
2009-01-01
Using the spin networks and the asymptotic quasinormal mode frequencies of black holes given by loop quantum gravity, the minimum horizon area gap is obtained. Then the quantum area spectrum of black holes is derived and the black hole entropy is a realized quantization. The results show that the black hole entropy given by loop quantum gravity is in full accord with the Bekenstein-Hawking entropy with a suitable Immirzi.
Yazadjiev, S
2012-01-01
We present a new solution in 5D Einstein-Maxwell-dilaton gravity describing an equilibrium configuration of extremal rotating black holes with lens space horizon topologies. The basic properties of the solution are investigated and the basic physical quantities are calculated. It is shown that the black hole horizons are superconducting in the sense that they expel the magnetic flux lines.
Spin foam models for quantum gravity
Perez, Alejandro
The definition of a quantum theory of gravity is explored following Feynman's path-integral approach. The aim is to construct a well defined version of the Wheeler-Misner- Hawking ``sum over four geometries'' formulation of quantum general relativity (GR). This is done by means of exploiting the similarities between the formulation of GR in terms of tetrad-connection variables (Palatini formulation) and a simpler theory called BF theory. One can go from BF theory to GR by imposing certain constraints on the BF-theory configurations. BF theory contains only global degrees of freedom (topological theory) and it can be exactly quantized á la Feynman introducing a discretization of the manifold. Using the path integral for BF theory we define a path integration for GR imposing the BF-to-GR constraints on the BF measure. The infinite degrees of freedom of gravity are restored in the process, and the restriction to a single discretization introduces a cut- off in the summed-over configurations. In order to capture all the degrees of freedom a sum over discretization is implemented. Both the implementation of the BF-to-GR constraints and the sum over discretizations are obtained by means of the introduction of an auxiliary field theory (AFT). 4-geometries in the path integral for GR are given by the Feynman diagrams of the AFT which is in this sense dual to GR. Feynman diagrams correspond to 2-complexes labeled by unitary irreducible representations of the internal gauge group (corresponding to tetrad rotation in the connection to GR). A model for 4-dimensional Euclidean quantum gravity (QG) is defined which corresponds to a different normalization of the Barrett-Crane model. The model is perturbatively finite; divergences appearing in the Barrett-Crane model are cured by the new normalization. We extend our techniques to the Lorentzian sector, where we define two models for four-dimensional QG. The first one contains only time-like representations and is shown to be
Revisiting the quantum scalar field in spherically symmetric quantum gravity
Borja, Enrique F; Strobel, Eckhard
2012-01-01
We extend previous results in spherically symmetric gravitational systems coupled with a massless scalar field within the loop quantum gravity framework. As starting point, we take the Schwarzschild spacetime. The results presented here rely on the uniform discretization method. We are able to minimize the associated discrete master constraint using a variational method. The trial state for the vacuum consists of a direct product of a Fock vacuum for the matter part and a Gaussian centered around the classical Schwarzschild solution. This paper follows the line of research presented by Gambini, Pullin and Rastgoo and a comparison between their result and the one given in this work is made.
Quantum Fluctuations of Low Dimensional Bose-Einstein ...
African Journals Online (AJOL)
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detecting and imaging them. Besides ... ideal playground to test correlations between light and mesoscopic objects, to understand the underlying ..... Collective atomic recoil in a moving Bose-Einstein condensate: From Superradiance to.
Revisiting the quantum scalar field in spherically symmetric quantum gravity
Borja, Enrique F.; Garay, Iñaki; Strobel, Eckhard
2012-07-01
We extend previous results in spherically symmetric gravitational systems coupled with a massless scalar field within the loop quantum gravity framework. As a starting point, we take the Schwarzschild spacetime. The results presented here rely on the uniform discretization method. We are able to minimize the associated discrete master constraint using a variational method. The trial state for the vacuum consists of a direct product of a Fock vacuum for the matter part and a Gaussian centered around the classical Schwarzschild solution. This paper follows the line of research presented by Gambini et al (2009 Class. Quantum Grav. 26 215011 (arXiv:0906.1774v1)) and a comparison between their result and the one given in this work is made.
Desai, Shantanu; Popławski, Nikodem J.
2016-04-01
The coupling between spin and torsion in the Einstein-Cartan-Sciama-Kibble theory of gravity generates gravitational repulsion at very high densities, which prevents a singularity in a black hole and may create there a new universe. We show that quantum particle production in such a universe near the last bounce, which represents the Big Bang, gives the dynamics that solves the horizon, flatness, and homogeneity problems in cosmology. For a particular range of the particle production coefficient, we obtain a nearly constant Hubble parameter that gives an exponential expansion of the universe with more than 60 e-folds, which lasts about ∼10-42 s. This scenario can thus explain cosmic inflation without requiring a fundamental scalar field and reheating. From the obtained time dependence of the scale factor, we follow the prescription of Ellis and Madsen to reconstruct in a non-parametric way a scalar field potential which gives the same dynamics of the early universe. This potential gives the slow-roll parameters of cosmic inflation, from which we calculate the tensor-to-scalar ratio, the scalar spectral index of density perturbations, and its running as functions of the production coefficient. We find that these quantities do not significantly depend on the scale factor at the Big Bounce. Our predictions for these quantities are consistent with the Planck 2015 observations.
Desai, Shantanu
2015-01-01
The coupling between spin and torsion in the Einstein-Cartan-Sciama-Kibble theory of gravity generates gravitational repulsion at very high densities, which prevents a singularity in a black hole and may create there a new universe. We show that quantum particle production in such a universe near the last bounce, which represents the Big Bang gives the dynamics that solves the horizon, flatness, and homogeneity problems in cosmology. For a particular range of the particle production coefficient, we obtain a nearly constant Hubble parameter that gives an exponential expansion of the universe with more than 60 $e$-folds, which lasts about $\\sim 10^{-42}$ s. This scenario can thus explain cosmic inflation without requiring a fundamental scalar field and reheating. From the obtained time dependence of the scale factor, we follow the prescription of Ellis and Madsen to reconstruct in a non-parametric way a scalar field potential which gives the same dynamics of the early universe. This potential gives the slow-rol...
Area Law from Loop Quantum Gravity
Hamma, Alioscia; Marciano, Antonino; Zhang, Mingyi
2015-01-01
We explore the constraints following from requiring the Area Law in the entanglement entropy in the context of loop quantum gravity. We find a unique solution to the single link wave-function in the large j limit, believed to be appropriate in the semi-classical limit. We then generalize our considerations to multi-link coherent states, and find that the area law is preserved very generically using our single link wave-function as a building block. Finally, we develop the framework that generates families of multi-link states that preserve the area law while avoiding macroscopic entanglement, the space-time analogue of "Schroedinger cat". We note that these states, defined on a given set of graphs, are the ground states of some local Hamiltonian that can be constructed explicitly. This can potentially shed light on the construction of the appropriate Hamiltonian constraints in the LQG framework.
Inflationary cosmology from quantum Conformal Gravity
Jizba, Petr; Scardigli, Fabio
2014-01-01
We analyze the functional integral for quantum Conformal Gravity and show that with the help of a Hubbard-Stratonovich transformation, the action can be broken into a local quadratic-curvature theory coupled to a scalar field. A one-loop effective action calculation reveals that strong fluctuations of the metric field are capable of spontaneously generating a dimensionally transmuted parameter which in the weak-field sector of the broken phase induces a Starobinsky-type f(R)-model with a gravi-cosmological constant. A resulting non-trivial relation between Starobinsky'sparameter and the cosmological constant is highlighted and implications for cosmic inflation are briefly discussed and compared with recent PLANCK and BICEP2 data.
Chiral vacuum fluctuations in quantum gravity
Magueijo, Joao
2010-01-01
We examine tensor perturbations around a deSitter background within the framework of Ashtekar's variables and cousins parameterized by the Immirzi parameter $\\gamma$. At the classical level we recover standard cosmological perturbation theory, with illuminating insights. Quantization leads to real novelties. In the low energy limit we find a second quantized theory of gravitons which displays different vacuum fluctuations for right and left gravitons. Nonetheless right and left gravitons have the same (positive) energies, resolving a number of paradoxes suggested in the literature. The right-left asymmetry of the vacuum fluctuations depends on $\\gamma$ and the ordering of the Hamiltonian constraint, and it would leave a distinctive imprint in the polarization of the cosmic microwave background, thus opening quantum gravity to observational test.
Inflationary cosmology from quantum conformal gravity
Energy Technology Data Exchange (ETDEWEB)
Jizba, Petr [Czech Technical University in Prague, FNSPE, Praha 1 (Czech Republic); Freie Universitaet Berlin, ITP, Berlin (Germany); Kleinert, Hagen [Freie Universitaet Berlin, ITP, Berlin (Germany); Scardigli, Fabio [American University of the Middle East, Department of Mathematics, College of Engineering, P.O. Box 220, Dasman (Kuwait); Politecnico di Milano, Dipartimento di Matematica, Milan (Italy)
2015-06-15
We analyze the functional integral for quantum conformal gravity and show that, with the help of a Hubbard-Stratonovich transformation, the action can be broken into a local quadratic-curvature theory coupled to a scalar field. A one-loop effective-action calculation reveals that strong fluctuations of the metric field are capable of spontaneously generating a dimensionally transmuted parameter which, in the weak-field sector of the broken phase, induces a Starobinsky-type f(R)-model with a gravi-cosmological constant. A resulting non-trivial relation between Starobinsky's parameter and the gravi-cosmological constant is highlighted and implications for cosmic inflation are briefly discussed and compared with the recent PLANCK and BICEP2 data. (orig.)
Chiral Vacuum Fluctuations in Quantum Gravity
Magueijo, João; Benincasa, Dionigi M. T.
2011-03-01
We examine tensor perturbations around a de Sitter background within the framework of Ashtekar’s variables and its cousins parameterized by the Immirzi parameter γ. At the classical level we recover standard cosmological perturbation theory, with illuminating insights. Quantization leads to real novelties. In the low energy limit we find a second quantized theory of gravitons which displays different vacuum fluctuations for right and left gravitons. Nonetheless right and left gravitons have the same (positive) energies, resolving a number of paradoxes suggested in the literature. The right-left asymmetry of the vacuum fluctuations depends on γ and the ordering of the Hamiltonian constraint, and it would leave a distinctive imprint in the polarization of the cosmic microwave background, thus opening quantum gravity to observational test.
Diffeomorphism invariant cosmological symmetry in full quantum gravity
Beetle, Christopher; Engle, Jonathan S.; Hogan, Matthew E.; Mendonça, Phillip
2016-06-01
This paper summarizes a new proposal to define rigorously a sector of loop quantum gravity at the diffeomorphism invariant level corresponding to homogeneous and isotropic cosmologies, thereby enabling a detailed comparison of results in loop quantum gravity and loop quantum cosmology. The key technical steps we have completed are (a) to formulate conditions for homogeneity and isotropy in a diffeomorphism covariant way on the classical phase-space of general relativity, and (b) to translate these conditions consistently using well-understood techniques to loop quantum gravity. Some additional steps, such as constructing a specific embedding of the Hilbert space of loop quantum cosmology into a space of (distributional) states in the full theory, remain incomplete. However, we also describe, as a proof of concept, a complete analysis of an analogous embedding of homogeneous and isotropic loop quantum cosmology into the quantum Bianchi I model of Ashtekar and Wilson-Ewing. Details will appear in a pair of forthcoming papers.
Diffeomorphism invariant cosmological symmetry in full quantum gravity
Beetle, Christopher; Hogan, Matthew E; Mendonca, Phillip
2016-01-01
This paper summarizes a new proposal to define rigorously a sector of loop quantum gravity at the diffeomorphism invariant level corresponding to homogeneous and isotropic cosmologies, thereby enabling a detailed comparison of results in loop quantum gravity and loop quantum cosmology. The key technical steps we have completed are (a) to formulate conditions for homogeneity and isotropy in a diffeomorphism covariant way on the classical phase space of general relativity, and (b) to translate these conditions consistently using well-understood techniques to loop quantum gravity. Some additional steps, such as constructing a specific embedding of the Hilbert space of loop quantum cosmology into a space of (distributional) states in the full theory, remain incomplete. However, we also describe, as a proof of concept, a complete analysis of an analogous embedding of homogeneous and isotropic loop quantum cosmology into the quantum Bianchi I model of Ashtekar and Wilson-Ewing. Details will appear in a pair of fort...
Rotating black holes in Einstein-Dilaton-Gauss-Bonnet gravity with finite coupling
Maselli, Andrea; Gualtieri, Leonardo; Ferrari, Valeria
2015-01-01
Among various strong-curvature extensions to General Relativity, Einstein-Dilaton-Gauss-Bonnet gravity stands out as the only nontrivial theory containing quadratic curvature corrections while being free from the Ostrogradsky instability to any order in the coupling parameter. We derive an approximate stationary and axisymmetric black-hole solution of this gravitational theory in closed form, which is quadratic in the black-hole spin angular momentum and of seventh order in the coupling parameter of the theory. This extends previous work that obtained the corrections to the metric only at the leading order in the coupling parameter, and allows us to consider values of the coupling parameter close to the maximum permitted by theoretical constraints. We compute some geometrical properties of this solution, such as the dilaton charge, the moment of inertia and the quadrupole moment, and its geodesic structure, including the innermost-stable circular orbit and the epicyclic frequencies for massive particles. The ...
Primordial massive gravitational waves from Einstein-Chern-Simons-Weyl gravity
Energy Technology Data Exchange (ETDEWEB)
Myung, Yun Soo; Moon, Taeyoon, E-mail: ysmyung@inje.ac.kr, E-mail: tymoon@inje.ac.kr [Institute of Basic Sciences and Department of Computer Simulation, Inje University, Gimhae 621-749 (Korea, Republic of)
2014-08-01
We investigate the evolution of cosmological perturbations during de Sitter inflation in the Einstein-Chern-Simons-Weyl gravity. Primordial massive gravitational waves are composed of one scalar, two vector and four tensor circularly polarized modes. We show that the vector power spectrum decays quickly like a transversely massive vector in the superhorizon limit z → 0. In this limit, the power spectrum coming from massive tensor modes decays quickly, leading to the conventional tensor power spectrum. Also, we find that in the limit of m{sup 2} → 0 (keeping the Weyl-squared term only), the vector and tensor power spectra disappear. It implies that their power spectra are not gravitationally produced because they (vector and tensor) are decoupled from the expanding de Sitter background, as a result of conformal invariance.
Non-Singular Spherically Symmetric Solution in Einstein-Scalar-Tensor Gravity
Moffat, J W
2007-01-01
A static spherically symmetric metric in Einstein-scalar-tensor gravity theory with a scalar field potential is non-singular for all real values of the coordinates. It does not have a black hole event horizon and there is no essential singularity at the origin of coordinates. The weak energy condition $\\rho > 0$ is satisfied but the strong energy condition $\\rho+3p > 0$ is violated by a scalar field ``dark energy'' vacuum contribution with pressure $p_\\phi < -{1/3}\\rho_\\phi$. The collapse of a star with zero normal matter pressure and uniform matter density is solved for an interior constant scalar field vacuum energy and leads to a finite singularity free collapsed object called a ``grey star'' with a non-singular exterior gravitational field. The properties of hydrostatic stability of a grey star are obtained and compared to the black hole Schwarzschild solution in general relativity.
Bouncing dynamics of Bose-Einstein condensates under the effects of gravity
Sekh, Golam Ali
2017-03-01
Bouncing dynamics of quasi-one dimensional Bose-Einstein condensates (BECs) falling under gravity on delta-function potentials is investigated. First, we consider a single component BEC in the presence of cubic-quintic nonlinearity and study dynamical behavior of different parameters of the system using variational and numerical approaches. We see that the quintic nonlinearity plays a dominant role over cubic nonlinear interaction to extend the bouncing dynamics in the non-linear regime. We find that a matter-wave performs bouncing motion only for certain discrete values of initial position above the reflecting potential. We then consider bouncing dynamics of binary BECs. It is shown that the pair of matter-waves bounces together if inter-species interaction is attractive. However, their pairing breaks down if the inter-species interaction is made repulsive.
Vacuum energy in Einstein-Gauss-Bonnet AdS gravity
Kofinas, G; Kofinas, Georgios; Olea, Rodrigo
2006-01-01
A finite action principle for Einstein-Gauss-Bonnet AdS gravity is presented. The boundary term, which is different for even and odd dimensions, is a functional of the boundary metric, intrinsic curvature and extrinsic curvature. For even dimensions, the boundary term corresponds to the maximal Chern form of the spacetime, and the asymptotic AdS condition for the curvature suffices for the well-posedness of this action. For odd dimensions, the action is stationary under a boundary condition on the variation of the extrinsic curvature. The background-independent Noether charges associated to asymptotic symmetries are found and the Euclidean continuation of the action correctly describes the black hole thermodynamics in the canonical ensemble. In particular, this procedure leads to a covariant formula for the vacuum energy in odd-dimensional asymptotically AdS spacetimes.
Dark Matter as a Relativistic Inertial Effect in Einstein Canonical Gravity?
Lusanna, Luca
2010-01-01
After the study of non-inertial frames in special relativity with emphasis on the problem of clock synchronization (i.e. of how to define 3-space), an overview is given of Einstein canonical gravity in the York canonical basis and of its Hamiltonian Post-Minkowskian (PM) linearization in 3-orthogonal gauges. It is shown that the York time (the trace of the extrinsic curvature of 3-spaces) is the inertial gauge variable describing the general relativistic remnant of the clock synchronization gauge freedom. The dark matter implied by the rotation curves of galaxies can be explained with a choice of the York time implying a PM extension of the Newtonian celestial frame ICRS.
Bu, Yanyan; Sharon, Amir
2015-01-01
Relativistic hydrodynamics dual to Einstein-Gauss-Bonnet gravity in asymptotic $\\textrm{AdS}_5$ space is under study. To linear order in the amplitude of the fluid velocity and temperature, we derive the fluid's stress-energy tensor via an all-order resummation of the derivative terms. Each order is accompanied by new transport coefficients, which all together could be compactly absorbed into two functions of momenta, referred to as viscosity functions. Via inverse Fourier transform, these viscosities appear as memory functions in the constitutive relation between components of the stress-energy tensor. We discover that for arbitrary small Gauss-Bonnet coefficient, these memory functions have support in the future, suggesting causality violation in the theory.
Reduction of entanglement degradation and teleportation improvement in Einstein-Gauss-Bonnet gravity
Esfahani, Bahram Nasr; Soltani, Morteza
2010-01-01
Bipartite entanglement for states of a non-interacting bosonic or fermionic field in the spacetime of a spherically symmetric black hole of Einstein-Gauss-Bonnet gravity, is investigated. Although the initial state is chosen to be maximally entangled as the Bell states, the Hawking-Unruh effect causes the state to be mixed and the entanglement degrades, but with different asymptotic behaviors for the fermionic and bosonic fields. The Gauss-Bonnet term with positive $\\alpha$ can play an anti-gravitation role and so this causes to decrease the Hawking-Unruh effect and consequently reduces the entanglement degradation. On the other hand, the suggested higher dimensions for the spacetime, lead to more entanglement degradation by increasing the dimension. There is a dramatic difference between the behaviors of the entanglement in terms of the radius of the horizon for a five-dimensional black hole and that for higher dimensional black holes.
Towards a quantum gravity; Vers une gravitation quantique
Energy Technology Data Exchange (ETDEWEB)
Romney, B.; Barrau, A.; Vidotto, F.; Le Meur, H.; Noui, K.
2011-12-15
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{sup -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.)
Electric hyperscaling violating solutions in Einstein-Maxwell-dilaton gravity with R^2 corrections
O'Keeffe, Daniel K
2013-01-01
In the context of holography applied to condensed matter physics, we study Einstein-Maxwell-dilaton theory with curvature squared corrections. This theory has three couplings eta_i for the three R^2 invariants and two theory functions: a dilaton potential V(phi) and a dilaton-dependent gauge coupling f(phi). We find hyperscaling violating solutions of this theory, parametrized by dynamical critical exponent z and HSV parameter theta. We obtain restrictions on the form of the theory functions required to support HSV-type solutions using three physical inputs: the null energy condition, causality z $\\leq$ 1, and d_eff = d - theta lying in the range 0 < d_eff $\\leq$ d. The NEC constraints are linear in the eta_i and (quartic) polynomial in d,z,theta. The allowed ranges of z,theta change depending on the signs of eta_i. For the case of Einstein-Weyl gravity, we further narrow down the theory functions and solution parameters required for crossover solutions interpolating between HSV, AdS_d+2 near the boundary,...
Thermodynamics of (2 +1 )-dimensional black holes in Einstein-Maxwell-dilaton gravity
Dehghani, M.
2017-08-01
In this paper, the linearly charged three-dimensional Einstein's theory coupled to a dilatonic field has been considered. It has been shown that the dilatonic potential must be considered in a form of generalized Liouville-type potential. Two new classes of charged dilatonic black hole solutions, as the exact solutions to the Einstein-Maxwell-dilaton (EMd) gravity, have been obtained and their properties have been studied. The conserved charge and mass related to both of the new EMd black holes have been calculated. Through comparison of the thermodynamical extensive quantities (i.e., temperature and entropy) obtained from both, the geometrical and the thermodynamical methods, the validity of first law of black hole thermodynamics has been investigated for both of the new black holes we just obtained. At the final stage, making use of the canonical ensemble method and regarding the black hole heat capacity, the thermal stability or phase transition of the new black hole solutions have been analyzed. It has been shown that there is a specific range for the horizon radius in such a way that the black holes with the horizon radius in that range are locally stable. Otherwise, they are unstable and may undergo type one or type two phase transitions to be stabilized.
Lorentz covariance of loop quantum gravity
Rovelli, Carlo
2010-01-01
The kinematics of loop gravity can be given a manifestly Lorentz-covariant formulation: the conventional SU(2)-spin-network Hilbert space can be mapped to a space K of SL(2,C) functions, where Lorentz covariance is manifest. K can be described in terms of a certain subset of the "projected" spin networks studied by Livine, Alexandrov and Dupuis. It is formed by SL(2,C) functions completely determined by their restriction on SU(2). These are square-integrable in the SU(2) scalar product, but not in the SL(2,C) one. Thus, SU(2)-spin-network states can be represented by Lorentz-covariant SL(2,C) functions, as two-component photons can be described in the Lorentz-covariant Gupta-Bleuler formalism. As shown by Wolfgang Wieland in a related paper, this manifestly Lorentz-covariant formulation can also be directly obtained from canonical quantization. We show that the spinfoam dynamics of loop quantum gravity is locally SL(2,C)-invariant in the bulk, and yields states that are preciseley in K on the boundary. This c...
The Variation of Photon Speed with Photon Frequency in Quantum Gravity
Dubey, Anuj Kumar; Nath, Sonarekha
2016-01-01
Einstein's special relativity is Lorentz invariance; the postulate that all observers measure exactly the same speed of light in vacuum, independent of photon frequency. There is a fundamental scale the Planck scale, at which quantum effects are expected to strongly affect the nature of space-time. The commonly used ideas of space-time should break down at or before the Planck length is reached. It is then natural to question the exactness of the Lorentz invariance that is pervasive in all macroscopic theories. Quantum gravity effect could be seen from the dispersion relations violating Lorentz invariance, because the motivation for the Lorentz invariance violation is quantum gravity. Then it is expected that the energy-momentum dispersion relation could be modified to include the dependence on the ratio of the particle's energy and the quantum gravity energy. In the present work, we have derived an expression of Planck mass or Planck energy by equating the Compton wavelength with Kerr gravitational radius of...
Quantum gravity and Standard-Model-like fermions
Eichhorn, Astrid
2016-01-01
We discover that chiral symmetry does not act as an infrared attractor of the renormalization group flow under the impact of quantum gravity fluctuations. Thus, observationally viable quantum gravity models must respect chiral symmetry. In our truncation, asymptotically safe gravity does, as a chiral fixed point exists. A second non-chiral fixed point with massive fermions provides a template for models with dark matter. This fixed point disappears for more than 10 fermions, suggesting that an asymptotically safe ultraviolet completion for the standard model plus gravity enforces chiral symmetry.
Quantum gravity and Standard-Model-like fermions
Eichhorn, Astrid; Lippoldt, Stefan
2017-04-01
We discover that chiral symmetry does not act as an infrared attractor of the renormalization group flow under the impact of quantum gravity fluctuations. Thus, observationally viable quantum gravity models must respect chiral symmetry. In our truncation, asymptotically safe gravity does, as a chiral fixed point exists. A second non-chiral fixed point with massive fermions provides a template for models with dark matter. This fixed point disappears for more than 10 fermions, suggesting that an asymptotically safe ultraviolet completion for the standard model plus gravity enforces chiral symmetry.
"Long live effrontery!" Albert Einstein and the birth of Quantum Theory
Giulini, D
2005-01-01
From its very beginning, Quantum Theory developed contrary to the intentions of its creators. For Max Planck it marks the failure of a long-term research program, in which he tried to understand the 2nd law of thermodynamics deterministically in terms of mechanics and electrodynamics. For Albert Einstein it meant a refutation of his scientific credo. I describe parts of the early stages of this most remarkable development, up to Einstein's light-quantum hypotheis and its unfavourable reception by most other physicists.
Hu, Ya-Peng; Wu, Xiao-Ning
2014-01-01
Using the gravity/fluid correspondence in our paper, we investigate the holographic fluid at finite cutoff surface in the Einstein gravity. After constructing the first order perturbative solution of the Schwarzschild-AdS black brane solution in the Einstein gravity, we focus on the stress-energy tensor of the dual fluid with transport coefficients at the finite cutoff surface. Besides the pressure and energy density of dual fluid are obtained, the shear viscosity is also obtained. The most important results are that we find that if we adopt different conditions to fix the undetermined parameters contained in the stress-energy tensor of the dual fluid, the pressure and energy density of the dual fluid can be perturbed. Particularly, the bulk viscosity of the dual fluid can also be given in this case.
Ivanov, A. N.; Wellenzohn, M.
2016-09-01
We analyse the Einstein-Cartan gravity in its standard form { R }=R+{{ K }}2, where { R } {and} R are the Ricci scalar curvatures in the Einstein-Cartan and Einstein gravity, respectively, and {{ K }}2 is the quadratic contribution of torsion in terms of the contorsion tensor { K }. We treat torsion as an external (or background) field and show that its contribution to the Einstein equations can be interpreted in terms of the torsion energy-momentum tensor, local conservation of which in a curved spacetime with an arbitrary metric or an arbitrary gravitational field demands a proportionality of the torsion energy-momentum tensor to a metric tensor, a covariant derivative of which vanishes owing to the metricity condition. This allows us to claim that torsion can serve as an origin for the vacuum energy density, given by the cosmological constant or dark energy density in the universe. This is a model-independent result that may explain the small value of the cosmological constant, which is a long-standing problem in cosmology. We show that the obtained result is valid also in the Poincaré gauge gravitational theory of Kibble, where the Einstein-Hilbert action can be represented in the same form: { R }=R+{{ K }}2.
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
On the integrability of Einstein-Maxwell-(A)dS gravity in presence of Killing vectors
Klemm, Dietmar; Rabbiosi, Marco
2015-01-01
We study some symmetry and integrability properties of four-dimensional Einstein-Maxwell gravity with nonvanishing cosmological constant in the presence of Killing vectors. First of all, we consider stationary spacetimes, which lead, after a timelike Kaluza-Klein reduction followed by a dualization of the two vector fields, to a three-dimensional nonlinear sigma model coupled to gravity, whose target space is a noncompact version of $\\mathbb{C}\\text{P}^2$ with SU(2,1) isometry group. It is shown that the potential for the scalars, that arises from the cosmological constant in four dimensions, breaks three of the eight SU(2,1) symmetries, corresponding to the generalized Ehlers and the two Harrison transformations. This leaves a semidirect product of a one-dimensional Heisenberg group and a translation group $\\mathbb{R}^2$ as residual symmetry. We show that, under the additional assumptions that the three-dimensional manifold is conformal to a product space $\\mathbb{R}\\times\\Sigma$, and all fields depend only ...
Conserved charges of black holes in Weyl and Einstein-Gauss-Bonnet gravities
Energy Technology Data Exchange (ETDEWEB)
Peng, Jun-Jin [SEEE, Wuhan Textile University, Institute of Technical Physics, Wuhan, Hubei (China); Chinese Academy of Sciences, Kavli Institute for Theoretical Physics China, Institute of Theoretical Physics, P.O. Box 2735, Beijing (China)
2014-11-15
An off-shell generalization of the Abbott-Deser-Tekin (ADT) conserved charge was recently proposed by Kim et al. They achieved this by introducing off-shell Noether currents and potentials. In this paper, we construct the crucial off-shell Noether current by the variation of the Bianchi identity for the expression of EOM, with the help of the property of Killing vector. Our Noether current, which contains an additional term that is just one half of the Lie derivative of a surface term with respect to the Killing vector, takes a different form in comparison with the one in their work. Then we employ the generalized formulation to calculate the quasi-local conserved charges for the most general charged spherically symmetric and the dyonic rotating black holes with AdS asymptotics in four-dimensional conformal Weyl gravity, as well as the charged spherically symmetric black holes in arbitrary dimensional Einstein-Gauss-Bonnet gravity coupled to Maxwell or nonlinear electrodynamics in AdS spacetime. Our results confirm those obtained through other methods in the literature. (orig.)
Bouncing dynamics of Bose–Einstein condensates under the effects of gravity
Energy Technology Data Exchange (ETDEWEB)
Sekh, Golam Ali, E-mail: golamali.sekh@ba.infn.it [Department of Physics, University of Kashmir, Hazratbal, Srinagar-190006, J & K (India); Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Bari, I-70126 Bari (Italy)
2017-03-03
Bouncing dynamics of quasi-one dimensional Bose–Einstein condensates (BECs) falling under gravity on delta-function potentials is investigated. First, we consider a single component BEC in the presence of cubic-quintic nonlinearity and study dynamical behavior of different parameters of the system using variational and numerical approaches. We see that the quintic nonlinearity plays a dominant role over cubic nonlinear interaction to extend the bouncing dynamics in the non-linear regime. We find that a matter-wave performs bouncing motion only for certain discrete values of initial position above the reflecting potential. We then consider bouncing dynamics of binary BECs. It is shown that the pair of matter-waves bounces together if inter-species interaction is attractive. However, their pairing breaks down if the inter-species interaction is made repulsive. - Highlights: • Single and coupled BECs • Effects of inter-component interaction and gravity • Periodic and quasi-periodic dynamics • Fermi-type acceleration.
Modified Einstein-Gauss-Bonnet gravity: Riemann-Cartan and Pseudo-Riemannian cases
Özer, Hatice; Delice, Özgür
2016-01-01
A modified Einstein-Gauss-Bonnet gravity in four dimensions where the quadratic Gauss-Bonnet term is coupled to a scalar field is considered. The field equations of the model are obtained by variational methods by making use of the constrained-first order formalism covering both pseudo-Riemannian and non-Riemannian cases. In the pseudo-Riemannian case, the Lagrange multiplier forms, which impose the vanishing torsion constraint, are eliminated in favor of the remaining fields and the resulting metric field equations are expressed in terms of the double-dual curvature 2-form. In the non-Riemannian case with torsion, the field equations are expressed in terms of the pseudo-Riemannian quantities by a perturbative scheme valid for a weak coupling constant. It is shown that, for both cases, the model admits a maximally symmetric de-Sitter solution with nontrivial scalar field. Minimal coupling of a Dirac spinor to the Gauss-Bonnet modified gravity is also discussed briefly.
A practitioner's view on quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Loll, Renate [Radboud University, Nijmegen (Netherlands)
2016-07-01
Quantum gravity is a subject difficult to grasp for outsiders. Which lofty ideas of exotic structures at the Planck scale will turn out to be right? Do theorists agree on what ''quantum gravity'' means and what questions such a theory should answer? How far are we from obtaining answers? My collaborators and I show by explicit construction that understanding nonperturbative quantum gravity does not require hitherto unseen symmetries, dimensions, strings, loops or branes, which appear to lead us ever further away from a unique theory. Staying within the framework of quantum field theory, but adapting it to the situation where spacetime itself is dynamical, Quantum Gravity from Causal Dynamical Triangulations (CDT) is a promising candidate theory of this type. It is a gravitational analogue of obtaining nonperturbative QCD as the scaling limit of a lattice theory, and is unique in producing evidence of a good semiclassical limit. Not only may this approach lead us to the correct theory of quantum gravity, it also provides a concrete and extremely useful computational framework to study fundamental questions. One example is the recent demonstration that a renormalization group analysis can be set up and performed in CDT quantum gravity despite its background-free character.
Emergence of a classical Universe from quantum gravity and cosmology.
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.
An introduction to spherically symmetric loop quantum gravity black holes
Energy Technology Data Exchange (ETDEWEB)
Gambini, Rodolfo [Instituto de Física, Facultad de Ciencias, Iguá 4-225, esq. Mataojo, 11400 Montevideo (Uruguay); Pullin, Jorge [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)
2015-03-26
We review recent developments in the treatment of spherically symmetric black holes in loop quantum gravity. In particular, we discuss an exact solution to the quantum constraints that represents a black hole and is free of singularities. We show that new observables that are not present in the classical theory arise in the quantum theory. We also discuss Hawking radiation by considering the quantization of a scalar field on the quantum spacetime.
Observables in Loop Quantum Gravity with a cosmological constant
Dupuis, Maïté
2013-01-01
An open issue in loop quantum gravity (LQG) is the introduction of a non-vanishing cosmological constant $\\Lambda$. In 3d, Chern-Simons theory provides some guiding lines: $\\Lambda$ appears in the quantum deformation of the gauge group. The Turaev-Viro model, which is an example of spin foam model is also defined in terms of a quantum group. By extension, it is believed that in 4d, a quantum group structure could encode the presence of $\\Lambda\
Bounce Loop Quantum Cosmology Corrected Gauss-Bonnet Gravity
Haro, J; Myagky, A N; Odintsov, S D; Oikonomou, V K
2015-01-01
We develop a Gauss-Bonnet extension of Loop Quantum Cosmology, by introducing holonomy corrections in modified $F(\\mathcal{G})$ theories of gravity. Within the context of our formalism, we provide a perturbative expansion in the critical density, a parameter characteristic of Loop Quantum Gravity theories, and we result in having leading order corrections to the classical $F(\\mathcal{G})$ theories of gravity. After extensively discussing the formalism, we present a reconstruction method that makes possible to find the Loop Quantum Cosmology corrected $F(\\mathcal{G})$ theory that can realize various cosmological scenarios. Specifically, we studied exponential and power-law bouncing cosmologies, emphasizing on the behavior near the bouncing point and in some cases, the behavior for all the values of the cosmic time is obtained. We exemplify our theoretical constructions by using bouncing cosmologies, and we investigate which Loop Quantum Cosmology corrected Gauss-Bonnet modified gravities can successfully reali...
The new spin foam models and quantum gravity
Perez, Alejandro
2012-01-01
In this article we give a systematic definition of the recently introduced spin foam models for four dimensional quantum gravity reviewing the main results on their semiclassical limit on fixed discretizations.
Stability of the Einstein static universe in f(R, T) gravity
Energy Technology Data Exchange (ETDEWEB)
Shabani, Hamid [University of Sistan and Baluchestan, Physics Department, Faculty of Sciences, Zahedan (Iran, Islamic Republic of); Ziaie, Amir Hadi [Kahnooj Branch, Islamic Azad University, Department of Physics, Kerman (Iran, Islamic Republic of)
2017-01-15
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.)
Renormalization of 3d quantum gravity from matrix models
Ambjørn, Jan; Loll, R
2004-01-01
Lorentzian simplicial quantum gravity is a non-perturbatively defined theory of quantum gravity which predicts a positive cosmological constant. Since the approach is based on a sum over space-time histories, it is perturbatively non-renormalizable even in three dimensions. By mapping the three-dimensional theory to a two-matrix model with ABAB interaction we show that both the cosmological and the (perturbatively) non-renormalizable gravitational coupling constant undergo additive renormalizations consistent with canonical quantization.
Quantum-gravity phenomenology with primordial black holes
Vidotto, Francesca; Bolliet, Boris; Shutten, Marrit; Weimer, Celine
2016-01-01
Quantum gravity may allow black holes to tunnel into white holes. If so, the lifetime of a black hole could be shorter than the one given by Hawking evaporation, solving the information paradox. More interestingly, this could open to a new window for quantum-gravity phenomenology, in connection with the existence of primordial black holes. We discuss in particular the power of the associated explosion and the possibility to observe an astrophysical signal in the radio and in the gamma wavelengths.
Probing loop quantum gravity with evaporating black holes.
Barrau, A; Cailleteau, T; Cao, X; Diaz-Polo, J; Grain, J
2011-12-16
This Letter aims at showing that the observation of evaporating black holes should allow the usual Hawking behavior to be distinguished from loop quantum gravity (LQG) expectations. We present a full Monte Carlo simulation of the evaporation in LQG and statistical tests that discriminate between competing models. We conclude that contrarily to what was commonly thought, the discreteness of the area in LQG leads to characteristic features that qualify evaporating black holes as objects that could reveal quantum gravity footprints.
Jet Extinction from Non-Perturbative Quantum Gravity Effects
Kilic, Can; Lath, Amitabh; Rose, Keith; Thomas, Scott
2012-01-01
The infrared-ultraviolet properties of quantum gravity suggest on very general grounds that hard short distance scattering processes are highly suppressed for center of mass scattering energies beyond the fundamental Planck scale. If this scale is not too far above the electroweak scale, these non-perturbative quantum gravity effects could be manifest as an extinction of high transverse momentum jets at the LHC. To model these effects we implement an Extinction Monte Carlo modification of the...
Hamiltonian cosmological perturbation theory with loop quantum gravity corrections
Bojowald, M; Kagan, M; Singh, P; Skirzewski, A; Bojowald, Martin; Hern\\'andez, Hector H.; Kagan, Mikhail; Singh, Parampreet; Skirzewski, Aureliano
2006-01-01
Cosmological perturbation equations are derived systematically in a canonical scheme based on Ashtekar variables. A comparison with the covariant derivation and various subtleties in the calculation and choice of gauges are pointed out. Nevertheless, the treatment is more systematic when correction terms of canonical quantum gravity are to be included. This is done throughout the paper for one characteristic modification expected from loop quantum gravity.
A Non-Polynomial Gravity Formulation for Loop Quantum Cosmology Bounce
Directory of Open Access Journals (Sweden)
Stefano Chinaglia
2017-09-01
Full Text Available Recently the so-called mimetic gravity approach has been used to obtain corrections to the Friedmann equation of General Relativity similar to the ones present in loop quantum cosmology. In this paper, we propose an alternative way to derive this modified Friedmann equation via the so-called non-polynomial gravity approach, which consists of adding geometric non-polynomial higher derivative terms to Hilbert–Einstein action, which are nonetheless polynomials and lead to a second-order differential equation in Friedmann–Lemaître–Robertson–Walker space-times. Our explicit action turns out to be a realization of the Helling proposal of effective action with an infinite number of terms. The model is also investigated in the presence of a non-vanishing cosmological constant, and a new exact bounce solution is found and studied.
Chern-Simons expectation values and quantum horizons from loop quantum gravity and the Duflo map.
Sahlmann, Hanno; Thiemann, Thomas
2012-03-16
We report on a new approach to the calculation of Chern-Simons theory expectation values, using the mathematical underpinnings of loop quantum gravity, as well as the Duflo map, a quantization map for functions on Lie algebras. These new developments can be used in the quantum theory for certain types of black hole horizons, and they may offer new insights for loop quantum gravity, Chern-Simons theory and the theory of quantum groups.
Scaling Exponents for Lattice Quantum Gravity in Four Dimensions
Hamber, Herbert W
2015-01-01
In this work nonperturbative aspects of quantum gravity are investigated using the lattice formulation, and some new results are presented for critical exponents, amplitudes and invariant correlation functions. Values for the universal scaling dimensions are compared with other nonperturbative approaches to gravity in four dimensions, and specifically to the conjectured value for the universal critical exponent $\
A note on the gravity screening in quantum systems
Gregori, Andrea
2011-01-01
We discuss how, in the theoretical scenario presented in [1], the gravity screening and the gravity impulse which seem to be produced under certain conditions by high temperature superconductors are expected to be an entropic response to the flow of part of the system into a deeper quantum regime.
Stabilization of 2D quantum gravity by branching interactions
Diego, O
1995-01-01
In this paper the stabilization of 2D quantum Gravity by branching interactions is considered. The perturbative expansion and the first nonperturbative term of the stabilized model are the same than the unbounded matrix model which define pure Gravity, but it has new nonperturbative effects that survives in the continuum limit.
Quantum tunnelling radiation of Einstein-Maxwell-Dilaton-Axion black hole
Institute of Scientific and Technical Information of China (English)
Yang Shu-Zheng; Jiang Qing-Quan; Li Hui-Ling
2005-01-01
By taking the energy conservation and angular momentum conservation into account, the characteristics of the quantum-tunnelling radiation of Einstein-Maxwell-Dilaton-Axion black hole are studied and the result shows that the tunnelling rate of such a black hole is relevant to Bekenstein-Hawking entropy and that the obtained radiation spectrum is not pure thermal.
High-dimension multiparty quantum secret sharing scheme with Einstein-Podolsky-Rosen pairs
Institute of Scientific and Technical Information of China (English)
Chen Pan; Deng Fu-Guo; Long Gui-Lu
2006-01-01
In this paper a high-dimension multiparty quantum secret sharing scheme is proposed by using Einstein-Podolsky-Rosen pairs and local unitary operators. This scheme has the advantage of not only having higher capacity, but also saving storage space. The security analysis is also given.
"Einstein Moon", "Schrodinger Cat", and "Quantity in Phase Space" - About Quantum Measurement (Ⅰ)
Institute of Scientific and Technical Information of China (English)
REN De-Ming
2004-01-01
Generalizing the idea involved in a previous paper [Commun. Theor. Phys. (Beijing, China) 41 (2004)685], "quantity in phase space" is introduced. Thus starting from quantum mechanics, with standard criteria, the disappearing of interference in a macroscopic system is explicitly shown. Then the confusions involved in "the Einstein Moon" and "the Schrodinger Cat" are clarified, at least principally.
Quantum Dynamics of Cooled Atoms in the Presence of Bose-Einstein Condensates
Institute of Scientific and Technical Information of China (English)
YI Xue-Xi; SU Jun-Chen
2001-01-01
Under the Markov approximation, the quantum dynamics of cooled atoms in the presence of Bose-Einstein condensates is studied. A master equation governing the evolution of such a system is derived. Using this master equation, the distribution of the atoms in the excited states at finite temperature and the dynamics of the excited atom at zero temperature are given and discussed.
Weinberg's nonlinear quantum mechanics and the Einstein-Podolsky-Rosen paradox
Polchinski, Joseph
1991-01-01
The constraints imposed on observables by the requirement that transmission not occur in the Einstein-Podolsky-Rosen (EPR) experiment are determined, leading to a different treatment of separated systems from that originally proposed by Weinberg (1989). It is found that forbidding EPR communication in nonlinear quantum mechanics necessarily leads to another sort of unusual communication: that between different branches of the wave function.
Loop Quantum Cosmology, Modified Gravity and Extra Dimensions
Directory of Open Access Journals (Sweden)
Xiangdong Zhang
2016-08-01
Full Text Available Loop quantum cosmology (LQC is a framework of quantum cosmology based on the quantization of symmetry reduced models following the quantization techniques of loop quantum gravity (LQG. This paper is devoted to reviewing LQC as well as its various extensions including modified gravity and higher dimensions. For simplicity considerations, we mainly focus on the effective theory, which captures main quantum corrections at the cosmological level. We set up the basic structure of Brans–Dicke (BD and higher dimensional LQC. The effective dynamical equations of these theories are also obtained, which lay a foundation for the future phenomenological investigations to probe possible quantum gravity effects in cosmology. Some outlooks and future extensions are also discussed.
Quantum cosmology with R + R sup 2 gravity
Sanyal, A K
2002-01-01
Canonical quantization of an action containing a curvature-squared term requires the introduction of an auxiliary variable. Boulware and coworkers prescribed a technique to choose such a variable, by taking the derivative of the action with respect to the highest derivative of the field variable, present in the action. It has been shown that this technique can even be applied in situations where the introduction of auxiliary variables is not required, leading to the wrong Wheeler-De Witt equation. It has also been pointed out that Boulware's prescription should be taken up only after removing all possible total derivative terms from the action. Once this is done only a unique description of quantum dynamics would emerge. For the curvature-squared term this technique yields, for the first time, a quantum mechanical probability interpretation of quantum cosmology, and an effective potential whose extremization leads to Einstein's equation. We conclude that the Einstein-Hilbert action should essentially be modif...
Wave Equations for Discrete Quantum Gravity
Gudder, Stan
2015-01-01
This article is based on the covariant causal set ($c$-causet) approach to discrete quantum gravity. A $c$-causet $x$ is a finite partially ordered set that has a unique labeling of its vertices. A rate of change on $x$ is described by a covariant difference operator and this operator acting on a wave function forms the left side of the wave equation. The right side is given by an energy term acting on the wave function. Solutions to the wave equation corresponding to certain pairs of paths in $x$ are added and normalized to form a unique state. The modulus squared of the state gives probabilities that a pair of interacting particles is at various locations given by pairs of vertices in $x$. We illustrate this model for a few of the simplest nontrivial examples of $c$-causets. Three forces are considered, the attractive and repulsive electric forces and the strong nuclear force. Large models get much more complicated and will probably require a computer to analyze.
Lattice Quantum Gravity and Asymptotic Safety
Laiho, J; Coumbe, D; Du, D; Neelakanta, J T
2016-01-01
We study the nonperturbative formulation of quantum gravity defined via Euclidean dynamical triangulations (EDT) in an attempt to make contact with Weinberg's asymptotic safety scenario. We find that a fine-tuning is necessary in order to recover semiclassical behavior. Such a fine-tuning is generally associated with the breaking of a target symmetry by the lattice regulator; in this case we identify the target symmetry as the Hamiltonian canonical symmetry, which is closely related to, but not identical to, four-dimensional diffeomorphism invariance. After introducing and fine-tuning a non-trivial local measure term, we find no barrier to taking a continuum limit, and we find evidence that four-dimensional, semiclassical geometries are recovered at long distance scales in the continuum limit. We also find that the spectral dimension at short distance scales is consistent with 3/2, a value that could resolve the tension between asymptotic safety and the holographic entropy scaling of black holes. We argue tha...
Quantum field theory II introductions to quantum gravity, supersymmetry and string theory
Manoukian, Edouard B
2016-01-01
This book takes a pedagogical approach to explaining quantum gravity, supersymmetry and string theory in a coherent way. It is aimed at graduate students and researchers in quantum field theory and high-energy physics. The first part of the book introduces quantum gravity, without requiring previous knowledge of general relativity (GR). The necessary geometrical aspects are derived afresh leading to explicit general Lagrangians for gravity, including that of general relativity. The quantum aspect of gravitation, as described by the graviton, is introduced and perturbative quantum GR is discussed. The Schwinger-DeWitt formalism is developed to compute the one-loop contribution to the theory and renormalizability aspects of the perturbative theory are also discussed. This follows by introducing only the very basics of a non-perturbative, background-independent, formulation of quantum gravity, referred to as “loop quantum gravity”, which gives rise to a quantization of space. In the second part the author in...
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Melendez L, L
2004-07-01
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)
Ivanov, A N
2016-01-01
We analyse the Einstein-Cartan gravity in its standard form cal-R = R + cal-K^2, where cal-R and R are the Ricci scalar curvatures in the Einstein-Cartan and Einstein gravity, respectively, and cal-K^2 is the quadratic contribution of torsion in terms of the contorsion tensor cal-K. We treat torsion as an external (or a background) field and show that the contribution of torsion to the Einstein equations can be interpreted in terms of the torsion energy-momentum tensor, local conservation of which in a curved spacetime with an arbitrary metric or an arbitrary gravitational field demands a proportionality of the torsion energy--momentum tensor to a metric tensor, a covariant derivative of which vanishes because of the metricity condition. This allows to claim that torsion can serve as origin for vacuum energy density, given by cosmological constant or dark energy density in the Universe. This is a model-independent result may explain a small value of cosmological constant, which is a long--standing problem of ...
Hendi, S H; Momennia, M
2015-01-01
In this paper, we consider quadratic Maxwell invariant as a correction to the Maxwell theory and study thermodynamic behavior of the black holes in Einstein (EN) and Gauss-Bonnet (GB) gravities. We consider cosmological constant as a thermodynamic pressure to extend phase space. Next, we obtain critical values in case of variation of nonlinearity and GB parameters. We generalized the study by considering the effects of dimensionality on critical values and make comparisons between our models with their special sub classes.
Quantum gravity effects near the null black hole singularity
Bonanno, A; Bonanno, Alfio; Reuter, Martin
1999-01-01
The structure of the Cauchy Horizon singularity of a black hole formed in a generic collapse is studied by means of a renormalization group equation for quantum gravity. It is shown that during the early evolution of the Cauchy Horizon the strength of the classical divergence of the mass function is weakened when quantum fluctuations of the metric are taken into account.
Lorentzian and Euclidean quantum gravity : analytical and numerical results
Ambjørn, J.; Jurkiewicz, J.; Loll, R.
2006-01-01
We review some recent attempts to extract information about the nature of quantum gravity, with and without matter, by quantum field theoretical methods. More specifically, we work within a covariant lattice approach where the individual space-time geometries are constructed from fundamental simplic
Proof of Bekenstein-Mukhanov ansatz in loop quantum gravity
Majhi, Abhishek
2016-01-01
A simple proof of Bekenstein-Mukhanov(BM) ansatz is given within the loop quantum gravity(LQG) framework. The macroscopic area of an equilibrium black hole horizon indeed manifests a linear quantization. The quantum number responsible for this discreteness of the macroscopic area has a physical meaning in the LQG framework, unlike the ad hoc one that remained unexplained in BM ansatz.
Spectral dimension in graph models of causal quantum gravity
Giasemidis, Georgios
2013-01-01
The phenomenon of scale dependent spectral dimension has attracted special interest in the quantum gravity community over the last eight years. It was first observed in computer simulations of the causal dynamical triangulation (CDT) approach to quantum gravity and refers to the reduction of the spectral dimension from 4 at classical scales to 2 at short distances. Thereafter several authors confirmed a similar result from different approaches to quantum gravity. Despite the contribution from different approaches, no analytical model was proposed to explain the numerical results as the continuum limit of CDT. In this thesis we introduce graph ensembles as toy models of CDT and show that both the continuum limit and a scale dependent spectral dimension can be defined rigorously. First we focus on a simple graph ensemble, the random comb. It does not have any dynamics from the gravity point of view, but serves as an instructive toy model to introduce the characteristic scale of the graph, study the continuum li...
The Spin-Foam Approach to Quantum Gravity
Directory of Open Access Journals (Sweden)
Alejandro Perez
2013-02-01
Full Text Available This article reviews the present status of the spin-foam approach to the quantization of gravity. Special attention is payed to the pedagogical presentation of the recently-introduced new models for four-dimensional quantum gravity. The models are motivated by a suitable implementation of the path integral quantization of the Plebanski formulation of gravity on a simplicial regularization. The article also includes a self contained treatment of 2+1 gravity. The simple nature of the latter provides the basis and a perspective for the analysis of both conceptual and technical issues that remain open in four dimensions.
Conformal loop quantum gravity coupled to the standard model
Campiglia, Miguel; Gambini, Rodolfo; Pullin, Jorge
2017-01-01
We argue that a conformally invariant extension of general relativity coupled to the standard model is the fundamental theory that needs to be quantized. We show that it can be treated by loop quantum gravity techniques. Through a gauge fixing and a modified Higgs mechanism particles acquire mass and one recovers general relativity coupled to the standard model. The theory suggests new views with respect to the definition of the Hamiltonian constraint in loop quantum gravity, the semi-classical limit and the issue of finite renormalization in quantum field theory in quantum space-time. It also gives hints about the elimination of ambiguities that arise in quantum field theory in quantum space-time in the calculation of back-reaction.
Hilbert space structure in quantum gravity: an algebraic perspective
Giddings, Steven B
2015-01-01
If quantum gravity respects the principles of quantum mechanics, suitably generalized, it may be that a more viable approach to the theory is through identifying the relevant quantum structures rather than by quantizing classical spacetime. This viewpoint is supported by difficulties of such quantization, and by the apparent lack of a fundamental role for locality. In finite or discrete quantum systems, important structure is provided by tensor factorizations of the Hilbert space. However, even in local quantum field theory properties of the generic type III von Neumann algebras and of long range gauge fields indicate that factorization of the Hilbert space is problematic. Instead it is better to focus on on the structure of the algebra of observables, and in particular on its subalgebras corresponding to regions. This paper suggests that study of analogous algebraic structure in gravity gives an important perspective on the nature of the quantum theory. Significant departures from the subalgebra structure of...
Extended loops a new arena for nonperturbative quantum gravity
Di Bartolo, C; Griego, J R; Pullin, J
1993-01-01
We propose a new representation for gauge theories and quantum gravity. It can be viewed as a generalization of the loop representation. We make use of a recently introduced extension of the group of loops into a Lie Group. This extension allows the use of functional methods to solve the constraint equations. It puts in a precise framework the regularization problems of the loop representation. It has practical advantages in the search for quantum states. We present new solutions to the Wheeler-DeWitt equation that reinforce the conjecture that the Jones Polynomial is a state of nonperturbative quantum gravity.
Linking loop quantum gravity quantization ambiguities with phenomenology
Brahma, Suddhasattwa; Amelino-Camelia, Giovanni; Marciano, Antonino
2016-01-01
Fundamental quantum gravity theories are known to be notoriously difficult to extract viable testable predictions out of. In this paper, we aim to incorporate putative quantum corrections coming from loop quantum gravity in deriving modified dispersion relations for particles on a deformed Minkowski spacetime. We show how different choices of the Immirzi parameter can, in some cases, serendipitously lead to different outcomes for such modifications, depending on the quantization scheme chosen. This allows one to differentiate between these quantization choices via testable phenomenological predictions.
On the critical temperatures of superconductors: a quantum gravity approach
Gregori, Andrea
2010-01-01
We consider superconductivity in the light of the quantum gravity theoretical framework introduced in [1]. In this framework, the degree of quantum delocalization depends on the geometry of the energy distribution along space. This results in a dependence of the critical temperature characterizing the transition to the superconducting phase on the complexity of the structure of a superconductor. We consider concrete examples, ranging from low to high temperature superconductors, and discuss how the critical temperature can be predicted once the quantum gravity effects are taken into account.
Shaken, but not stirred - Potts model coupled to quantum gravity
Ambjørn, Jan; Loll, R; Pushkina, I
2008-01-01
We investigate the critical behaviour of both matter and geometry of the three-state Potts model coupled to two-dimensional Lorentzian quantum gravity in the framework of causal dynamical triangulations. Contrary to what general arguments of the effects of disorder suggest, we find strong numerical evidence that the critical exponents of the matter are not changed under the influence of quantum fluctuations in the geometry, compared to their values on fixed, regular lattices. This lends further support to previous findings that quantum gravity models based on causal dynamical triangulations are in many ways better behaved than their Euclidean counterparts.
Axion experiments to algebraic geometry: Testing quantum gravity via the Weak Gravity Conjecture
Heidenreich, Ben; Reece, Matthew; Rudelius, Tom
2016-06-01
Common features of known quantum gravity theories may hint at the general nature of quantum gravity. The absence of continuous global symmetries is one such feature. This inspired the Weak Gravity Conjecture, which bounds masses of charged particles. We propose the Lattice Weak Gravity Conjecture, which further requires the existence of an infinite tower of particles of all possible charges under both abelian and nonabelian gauge groups and directly implies a cutoff for quantum field theory. It holds in a wide variety of string theory examples and has testable consequences for the real world and for pure mathematics. We sketch some implications of these ideas for models of inflation, for the QCD axion (and LIGO), for conformal field theory, and for algebraic geometry.
Axion Experiments to Algebraic Geometry: Testing Quantum Gravity via the Weak Gravity Conjecture
Heidenreich, Ben; Rudelius, Tom
2016-01-01
Common features of known quantum gravity theories may hint at the general nature of quantum gravity. The absence of continuous global symmetries is one such feature. This inspired the Weak Gravity Conjecture, which bounds masses of charged particles. We propose the Lattice Weak Gravity Conjecture, which further requires the existence of an infinite tower of particles of all possible charges under both abelian and nonabelian gauge groups and directly implies a cutoff for quantum field theory. It holds in a wide variety of string theory examples and has testable consequences for the real world and for pure mathematics. We sketch some implications of these ideas for models of inflation, for the QCD axion (and LIGO), for conformal field theory, and for algebraic geometry.
Thermodynamics of AdS Black Holes in Einstein-Scalar Gravity
Lu, H; Wen, Qiang
2014-01-01
We study the thermodynamics of $n$-dimensional static asymptotically AdS black holes in Einstein gravity coupled to a scalar field with a potential admitting a stationary point with an AdS vacuum. Such black holes with non-trivial scalar hair can exist provided that the mass-squared of the scalar field is negative, and above the Breitenlohner-Freedman bound. We use the Wald procedure to derive the first law of thermodynamics for these black holes, showing how the scalar hair (or charge) contributes non-trivially in the expression. We show in general that the black hole mass can be deduced by isolating an integrable contribution to the (non-integrable) variation of the Hamiltonian arising in the Wald construction, and that this is consistent with the mass calculated using the renormalised holographic stress tensor and also, in those cases where it is defined, with the mass calculated using the conformal method of Ashtekar, Magnon and Das. Similar arguments can also be given for the smooth solitonic solutions i...
Charged Rotating Black Branes in anti-de Sitter Einstein-Gauss-Bonnet Gravity
Dehghani, M H
2003-01-01
We present a new class of charged rotating solutions in the Einstein-Gauss-Bonnet gravity with a negative cosmological constant. These solutions may be interpreted as black brane solutions with two inner and outer event horizons or an extreme black brane depending on the value of the mass parameter $m$. We also find that the Killing vectors are the null generators of the event horizon. The physical properties of the brane such as the temperature, the angular velocity, the entropy, the electric charge and potential are computed. We also compute the action and the Gibbs potential as a function of temperature and angular velocity for the uncharged solutions, and compute the angular momentum and the mass of the black brane through the use of Gibbs potential. We show that these thermodynamic quantities satisfy the first law of thermodynamics. We also perform a local stability analysis of the asymptotically AdS uncharged rotating black brane in various dimensions and show that they are locally stable for the whole ...
Classical defects in higher-dimensional Einstein gravity coupled to nonlinear σ -models
Prasetyo, Ilham; Ramadhan, Handhika S.
2017-09-01
We construct solutions of higher-dimensional Einstein gravity coupled to nonlinear σ -model with cosmological constant. The σ -model can be perceived as exterior configuration of a spontaneously-broken SO(D-1) global higher-codimensional "monopole". Here we allow the kinetic term of the σ -model to be noncanonical; in particular we specifically study a quadratic-power-law type. This is some possible higher-dimensional generalization of the Bariola-Vilenkin (BV) solutions with k-global monopole studied recently. The solutions can be perceived as the exterior solution of a black hole swallowing up noncanonical global defects. Even in the absence of comological constant its surrounding spacetime is asymptotically non-flat; it suffers from deficit solid angle. We discuss the corresponding horizons. For Λ >0 in 4 d there can exist three extremal conditions (the cold, ultracold, and Nariai black holes), while in higher-than-four dimensions the extremal black hole is only Nariai. For Λ <0 we only have black hole solutions with one horizon, save for the 4 d case where there can exist two horizons. We give constraints on the mass and the symmetry-breaking scale for the existence of all the extremal cases. In addition, we also obtain factorized solutions, whose topology is the direct product of two-dimensional spaces of constant curvature (M_2, dS_2, or AdS_2) with (D-2)-sphere. We study all possible factorized channels.
Stability of the Einstein static Universe in $f(R,T)$ gravity
Shabani, Hamid
2016-01-01
The Einstein static (ES) universe has played a major role in various emergent scenarios recently proposed in order to cure the problem of initial singularity of the standard model of cosmology. In the herein model, we study the existence and stability of ES universe in the context of $f(R,T)$ modified theories of gravity. Considering specific forms of $f(R,T)$ 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 duty they have 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 a...
Symmetry Reduced Loop Quantum Gravity: A Bird's Eye View
Ashtekar, Abhay
2016-01-01
This is a brief overview of the current status of symmetry reduced models in Loop Quantum Gravity. The goal is to provide an introduction to other more specialized and detailed reviews that follow. Since most of this work is motivated by the physics of the very early universe, I will focus primarily on Loop Quantum Cosmology and discuss quantum aspects of black holes only briefly.
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
Energy Technology Data Exchange (ETDEWEB)
Wamba, Etienne, E-mail: wambaetienne@yahoo.fr [Laboratory of Mechanics, Department of Physics, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé (Cameroon); Department of Physics, Pondicherry University, Puducherry 605014 (India); Porsezian, K., E-mail: ponz.phy@pondiuni.edu.in [Department of Physics, Pondicherry University, Puducherry 605014 (India); Mohamadou, Alidou, E-mail: mohdoufr@yahoo.fr [The Abdus Salam International Centre for Theoretical Physics, P.O. Box 586, Strada Costiera 11, I-34014, Trieste (Italy); Condensed Matter Laboratory, Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157, Douala (Cameroon); Kofané, Timoléon C. [Laboratory of Mechanics, Department of Physics, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé (Cameroon)
2013-01-03
Through a Gross–Pitaevskii equation comprising cubic, quartic, residual, and quintic nonlinearities, we examine the modulational instability (MI) of Bose–Einstein condensates at higher densities in the presence of quantum fluctuations. We obtain an explicit time-dependent criteria for the MI and the instability domains of the condensates. Solitons are generated by suitably exciting the MI, and their stability is analyzed. We find that quantum fluctuations can completely change the instability of condensates by reversing the nature of the effective two-body interactions. The interplay between three-body interactions and quantum fluctuations is shown. Numerical simulations performed agree with analytical predictions.
On the embedding of quantum field theory on curved spacetimes into loop quantum gravity
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Stottmeister, Alexander
2015-07-15
The main theme of this thesis is an investigation into possible connections between loop quantum gravity and quantum field theory on curved spacetimes: On the one hand, we aim for the formulation of a general framework that allows for a derivation of quantum field theory on curved spacetimes in a semi-classical limit. On the other hand, we discuss representation-theoretical aspects of loop quantum gravity and quantum field theory on curved spacetimes as both of the latter presumably influence each other in the aforesaid semi-classical limit. Regarding the first point, we investigate the possible implementation of the Born-Oppenheimer approximation in the sense of space-adiabatic perturbation theory in models of loop quantum gravity-type. In the course of this, we argue for the need of a Weyl quantisation and an associated symbolic calculus for loop quantum gravity, which we then successfully define, at least to a certain extent. The compactness of the Lie groups, which models a la loop quantum gravity are based on, turns out to be a main obstacle to a fully satisfactory definition of a Weyl quantisation. Finally, we apply our findings to some toy models of linear scalar quantum fields on quantum cosmological spacetimes and discuss the implementation of space-adiabatic perturbation theory therein. In view of the second point, we start with a discussion of the microlocal spectrum condition for quantum fields on curved spacetimes and how it might be translated to a background-independent Hamiltonian quantum theory of gravity, like loop quantum gravity. The relevance of this lies in the fact that the microlocal spectrum condition selects a class of physically relevant states of the quantum matter fields and is, therefore, expected to play an important role in the aforesaid semi-classical limit of gravity-matter systems. Following this, we switch our perspective and analyse the representation theory of loop quantum gravity. We find some intriguing relations between the
Formalism locality in quantum theory and quantum gravity
Hardy, Lucien
2008-01-01
We expect a theory of Quantum Gravity to be both probabilistic and have indefinite causal structure. Indefinite causal structure poses particular problems for theory formulation since many of the core ideas used in the usual approaches to theory construction depend on having definite causal structure. For example, the notion of a state across space evolving in time requires that we have some definite causal structure so we can define a state on a space-like hypersurface. We will see that many of these problems are mitigated if we are able to formulate the theory in a "formalism local" (or F-local) fashion. A formulation of a physical theory is said to be F-local if, in making predictions for any given arbitrary space-time region, we need only refer to mathematical objects pertaining to that region. This is a desirable property both on the grounds of efficiency and since, if we have indefinite causal structure, it is not clear how to select some other space-time region on which our calculations may depend. The...
Group Field Theory and Loop Quantum Gravity
Oriti, Daniele
The following sections are included: * GFT from LQG Perspective: The Underlying Ideas * GFT Kinematics: Hilbert Space and Observables * The Quantum Dynamics * The Continuum Limit of Quantum Geometry in GFT * Extracting Effective Continuum Physics from GFTs * Conclusions * References
Einstein was right Proof of absence of spooky state reduction in quantum mechanics
Unnikrishnan, C S
2002-01-01
The present standard interpretation of quantum mechanics invokes nonlocality and state reduction at space-like separated points during measurements on entangled systems. While there is no understanding of the physical mechanism of such nonlocal state reduction, the experimental verifications of quantum correlations different from that predicted by local realistic theories have polarized the physicists' opinion in favour of nonlocality. I show conclusively that there is no such spooky state reduction, vindicating the strong views against nonlocality held by Einstein and Popper. Experimental support to this proof is also discussed. The Bell's inequalities arise due to ignoring the phase information in the correlation function and not due to nonlocality. This result goes against the current belief of quantum nonlocality held by the majority of physicists; yet the proof is transparent and rigorous, and therefore demands a change in the interpretation of quantum mechanics and quantum measurements. The hypothesis o...
Quantum Gravity and Matter: Counting Graphs on Causal Dynamical Triangulations
Benedetti, D
2006-01-01
An outstanding challenge for models of non-perturbative quantum gravity is the consistent formulation and quantitative evaluation of physical phenomena in a regime where geometry and matter are strongly coupled. After developing appropriate technical tools, one is interested in measuring and classifying how the quantum fluctuations of geometry alter the behaviour of matter, compared with that on a fixed background geometry. In the simplified context of two dimensions, we show how a method invented to analyze the critical behaviour of spin systems on flat lattices can be adapted to the fluctuating ensemble of curved spacetimes underlying the Causal Dynamical Triangulations (CDT) approach to quantum gravity. We develop a systematic counting of embedded graphs to evaluate the thermodynamic functions of the gravity-matter models in a high- and low-temperature expansion. For the case of the Ising model, we compute the series expansions for the magnetic susceptibility on CDT lattices and their duals up to orders 6 ...