International Nuclear Information System (INIS)
A new relativistic formulation of MOND is advanced, involving two metrics as independent degrees of freedom: the MOND metric gμν, to which alone matter couples, and an auxiliary metric g-circumflexμν. The main idea hinges on the fact that we can form tensors from the difference of the Levi-Civita connections of the two metrics, Cβγα=Γβγα-Γ-circumflexβγα, and these act like gravitational accelerations. In the context of MOND, we can form dimensionless 'acceleration' scalars and functions thereof (containing only first derivatives) from contractions of a0-1Cβγα. I look at a subclass of bimetric MOND theories governed by the action I=-(16πG)-1∫[βg1/2R+αg-circumflex1/2R-circumflex-2(gg-circumflex)1/4f(κ)a02 M(Υ-tilde/a02)]d4x+IM(gμν,ψi)+I-circumflexM(g-circumflexμν,χi), with Υ-tilde as a scalar quadratic in the Cβγα, κ=(g/g-circumflex)1/4, IM as the matter action, and allow for the existence of twin matter that couples to g-circumflexμν alone. Thus, gravity is modified not by modifying the elasticity of the space-time in which matter lives, but by the interaction between that space-time and the auxiliary one. In particular, I concentrate on the interesting and simple choice Υ-tilde∝gμν(CμλγCνγλ-CμνγCλγλ). This theory introduces only one new constant, a0; it tends simply to general relativity (GR) in the limit a0→0 and to a phenomenologically valid MOND theory in the nonrelativistic limit. The theory naturally gives MOND and 'dark energy' effects from the same term in the action, both controlled by the MOND constant a0. In regards to gravitational lensing by nonrelativistic systems-a holy grail for relativistic MOND theories-the theory predicts that the same potential that controls massive-particle motion also dictates lensing in the same way as in GR: Lensing and massive-particle probing of galactic fields will require the same 'halo' of dark matter to explain the departure of the present theory from GR. This
Milgrom, Mordehai
2009-01-01
A new relativistic formulation of MOND is advanced, involving two metrics as independent degrees of freedom: the MOND metric g_mn, to which alone matter couples, and an auxiliary metric g*_mn. The main idea hinges on the fact that we can form tensors from the difference, C^a_bc, of the Levi-Civita connections of the two metrics, and these act like gravitational accelerations. In the context of MOND we can form dimensionless `acceleration' scalars, and functions thereof, from contractions of C^a_bc/a0. I look at a class of bimetric MOND theories governed by an action with the gravitational Lagrangian density b sqrt(g)R+a sqrt(g*) R* -2(gg*)^{1/4}f(k)a0^2M(U/a0^2), and with matter actions I(g_mn,psi)+I*(g*_mn,chi), with U a scalar quadratic in the C^a_bc, k=(g/g*)^{1/4}, and allowing for the existence of twin matter, chi, that couples to g*_mn alone. In particular, I concentrate on one interesting and simple choice of the scalar U. This theory introduces only one new constant, a0; it tends simply to General Rel...
Milgrom, Mordehai
2009-01-01
A new relativistic formulation of MOND is advanced, involving two metrics as independent degrees of freedom: the MOND metric g_mn, to which alone matter couples, and an auxiliary metric g*_mn. The main idea hinges on the fact that we can form tensors from the difference, C^a_bc, of the Levi-Civita connections of the two metrics, and these act like gravitational accelerations. In the context of MOND we can form dimensionless `acceleration' scalars, and functions thereof, from contractions of C...
MOND and its bimetric formulation
Milgrom, Mordehai
2013-01-01
I first give a succinct account of the MOND paradigm--emphasizing the centrality of scale invariance in the nonrelativistic, deep-MOND limit--and describing rudiments of its phenomenology. I then present my credo, and some generalities, concerning existing MOND theories. Then I concentrate on one relativistic formulation of MOND in the form of a bimetric theory (BIMOND). I describe its various limits: the weak field, with application to gravitational waves, the nonrelativistic limit, and their further deep-MOND (low acceleration) limits, which are scale invariant. Other aspects of BIMOND that have been explored are aspects of cosmology, matter fluctuations in cosmology, and matter-twin-matter interactions. BIMOND remains largely unexplored, despite its promise in several regards: It tends to GR for a0 goes to 0 (a0 is the MOND constant); it has a simple nonrelativistic limit; it describes gravitational lensing correctly; and, it has a generic appearance of a cosmological-constant term that is of order a0^2/c^...
Cosmological fluctuation growth in bimetric MOND
International Nuclear Information System (INIS)
I begin to look at the growth of weak density inhomogeneities of nonrelativistic matter, in bimetric-MOND (BIMOND) cosmology. Far from making an exhaustive study, I concentrate on one attractive cosmological scenario, which employs matter-twin-matter-symmetric versions of BIMOND, and, furthermore, assumes that, on average, the universe is symmetrically populated in the two sectors. MOND effects are totally absent in an exactly symmetric universe, apart from the significant possible appearance of a cosmological constant, Λ∼(a0/c)2. MOND effects--local and cosmological--do enter when density inhomogeneities that differ in the two sectors appear and develop. MOND later takes its standard form in systems that are islands dominated by pure matter, as are presumably the well scrutinized systems such as galaxies. I derive the nonrelativistic (weak-field-slow-motion) equations governing small-scale fluctuation growth. The equations split into two uncoupled systems, one for the sum, the other for the difference, of the fluctuations in the two sectors. The former is governed strictly by Newtonian dynamics, and describes standard growth of fluctuations. The latter is governed by MOND dynamics, which entails stronger gravity, and nonlinearity even for the smallest of perturbations. These cause the difference to grow faster than the sum, leading to anticorrelated perturbations, conducing to matter-twin-matter segregation (which continues for high overdensities). The nonlinearity also causes interaction between nested perturbations on different scales. Because matter and twin matter (TM) repel each other in the MOND regime, matter inhomogeneities grow not only by their own self-gravity, but also through shepherding by flanking twin matter overdensities (and vice versa). The relative importance of gravity and pressure in the MOND system (analog of the Jeans criterion), depends also on the strength of the perturbation. MOND gravity, which scales as the square root of the
No consistent bimetric gravity?
Deser, S.; Sandora, M.; Waldron, A
2013-01-01
We discuss the prospects for a consistent, nonlinear, partially massless (PM), gauge symmetry of bimetric gravity (BMG). Just as for single metric massive gravity, we show that consistency of BMG relies on it having a PM extension; we then argue that it cannot.
No consistent bimetric gravity?
Deser, S; Waldron, A
2013-01-01
We discuss the prospects for a consistent, nonlinear, partially massless (PM), gauge symmetry of bimetric gravity (BMG). Just as for single metric massive gravity, ultimate consistency of both BMG and the putative PM BMG theory relies crucially on this gauge symmetry. We argue, however, that it does not exist.
Bimetric gravity and dark matter
Bernard, Laura; Heisenberg, Lavinia
2015-01-01
We review some recent proposals for relativistic models of dark matter in the context of bimetric gravity. The aim is to solve the problems of cold dark matter (CDM) at galactic scales, and to reproduce the phenomenology of the modified Newtonian dynamics (MOND), while still being in agreement with the standard cosmological model $\\Lambda$-CDM at large scales. In this context a promising alternative is dipolar dark matter (DDM) in which two different species of dark matter particles are separately coupled to the two metrics of bigravity and are linked together by an internal vector field. The phenomenology of MOND then results from a mechanism of gravitational polarization. Probably the best formulation of the model is within the framework of recently developed massive bigravity theories. Then the gravitational sector of the model is safe by construction, but a ghostly degree of freedom in the decoupling limit is still present in the dark matter sector. Future work should analyse the cosmological solutions of...
Massive gravity as a limit of bimetric gravity
Martin-Moruno, Prado; Baccetti, Valentina; Visser, Matt
2013-01-01
Massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure can lead to an interesting interplay between the "background" and "foreground" metrics in a cosmological context. The fact that in bimetric theories one always has two sets of metric equations of motion continues to have an effect even in the massive gravity limit. Thus, solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statem...
Higher Derivative Gravity and Conformal Gravity from Bimetric and Partially Massless Bimetric Theory
Hassan, Sayed; Schmidt-May, Angnis; Strauss, Mikael von
2015-01-01
In this paper, we establish the correspondence between ghost-free bimetric theory and a class of higher derivative gravity actions, including conformal gravity and new massive gravity. We also characterize the relation between the respective equations of motion and classical solutions. We illustrate that, in this framework, the spin-2 ghost of higher derivative gravity at the linear level is an artifact of the truncation to a four-derivative theory. The analysis also gives a relation between ...
Bimetric gravity is cosmologically viable
Directory of Open Access Journals (Sweden)
Yashar Akrami
2015-09-01
Full Text Available Bimetric theory describes gravitational interactions in the presence of an extra spin-2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, Mf, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin-2 interaction scale. This provides a late-time expansion history which is extremely close to ΛCDM, but with a technically-natural value for the cosmological constant. We find Mf should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales.
On Higuchi Ghosts and Gradient Instabilities in Bimetric Gravity
Könnig, Frank
2015-01-01
We discuss the conditions to satisfy the Higuchi bound and to avoid gradient instabilities in the scalar sector for cosmological solutions in singly coupled bimetric gravity theories. We find that in expanding universes the ratio of the scale factors of the reference and observable metric has to increase at all times. This automatically implies a ghost-free helicity-2 sector and enforces a phantom Dark Energy. Furthermore, the condition for the absence of gradient instabilities in the scalar sector will be analyzed. Finally, we discuss whether cosmological solutions, including exotic evolutions like bouncing cosmologies, can exist, in which both the Higuchi ghost and scalar instabilities are absent at all times.
Entropic-gravity derivation of MOND
Klinkhamer, F. R.
2012-01-01
A heuristic entropic-gravity derivation has previously been given of the gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is shown that also another characteristic of MOND can be recovered, namely, the external field effect (implying a violation of the Strong Equivalence Principle). In fact, the derivation gives precisely the modified Poisson equation which Bekenstein and Milgrom proposed as a consistent nonrelativistic theory of MOND.
No-go theorem for bimetric gravity with positive and negative mass
Hohmann, Manuel
2009-01-01
We argue that the most conservative geometric extension of Einstein gravity describing both positive and negative mass sources and observers is bimetric gravity and contains two copies of standard model matter which interact only gravitationally. Matter fields related to one of the metrics then appear dark from the point of view of an observer defined by the other metric, and so may provide a potential explanation for the dark universe. In this framework we consider the most general form of linearized field equations compatible with physically and mathematically well-motivated assumptions. Using gauge-invariant linear perturbation theory, we prove a no-go theorem ruling out all bimetric gravity theories that, in the Newtonian limit, lead to precisely opposite forces on positive and negative test masses.
Primordial fluctuations from inflation in dRGT bimetric theory of gravity
Sakakihara, Yuki
2016-01-01
We investigate primordial gravitational waves and curvature perturbations in de Rham-Gabadadze-Tolley (dRGT) bimetric gravity. We evaluate the power-spectra in the leading order in slow roll. Taking into account the decay of massive graviton, we find that the action up to the second order reduces to the Einstein theory with a non-minimally coupled scalar field, which is simplified to a minimally coupled model by conformal transformation. We also find that the tensor to scalar ratio for large field inflation with power law potential is larger than the general relativity counterpart for any choice of parameters in dRGT bimetric gravity. In addition, we confirm that the usual consistency relation holds and we have a steeper spectrum for the gravitational waves.
Note on the relationship between the speed of light and gravity in the bi-metric theory of gravity
Kopeikin, Sergei
2005-01-01
Relationship between the speed of gravity c_g and the speed of light c_e in the bi-metric theory of gravity is discussed. We reveal that the speed of light is a function of the speed of gravity which is a primary fundamental constant. Thus, experimental measurement of relativistic bending of light propagating in time-dependent gravitational field directly compares the speed of gravity versus the speed of light and tests if there is any aether associated with the gravitational field considered...
General virial theorem for modified-gravity MOND
Milgrom, Mordehai
2014-01-01
An important and useful relation is known to hold in two specific MOND theories. It pertains to low-acceleration, isolated systems of pointlike masses, m_p, at positions r_p, subject to gravitational forces F_p. It reads sum_p r_p.F_p=-(2/3)(Ga0)^{1/2}[(\\sum_p m_p)^{3/2}-\\sum_p m_p^{3/2}]; a0 is the MOND acceleration constant. Here I show that this relation holds in the nonrelativistic limit of any modified-gravity MOND theory. It follows from only the basic tenets of MOND (as applied to such theories): departure from standard dynamics at accelerations below a0, and space-time scale invariance in the nonrelativistic, low-acceleration limit. This implies space-dilatation invariance of the static, gravitational-field equations, which, in turn, leads to the above point-mass virial relation. Thus, the various MOND predictions and tests based on this relation hold in any modified-gravity MOND theory. Since we do not know that any of the existing MOND theories point in the right direction, it is important to identi...
Nonhomogeneous Cooling, Entropic Gravity and MOND Theory
Neto, Jorge Ananias
2011-11-01
In this paper, by using the holographic principle, a modified equipartition theorem where we assume that below a critical temperature the energy is not equally divided on all bits, and the Unruh temperature, we derive MOND theory and a modified Friedmann equation compatible with MOND theory. Furthermore, we rederive a modified Newton's law of gravitation by employing an adequate redefinition of the numbers of bits.
Nonhomogeneous Cooling, Entropic Gravity and MOND Theory
Neto, Jorge Ananias
2010-01-01
In this paper, by using the holographic principle, a modified equipartition theorem where we assume that below a critical temperature the energy is not equally divided on all bits, and the Unruh temperature, we derive MOND theory and a modified Friedmann equation compatible with MOND theory. Furthermore, we rederive a modified Newton's law of gravitation by employing an adequate redefinition of the numbers of bits.
Cosmological Solutions in Biconnection and Bimetric Gravity Theories
Sergiu I. Vacaru
2013-01-01
We show how generic off--diagonal cosmological solutions depending, in general, on all spacetime coordinates can be constructed in massive gravity using the anholonomic frame deformation method. Such metrics describe the late time acceleration due to effective cosmological terms induced by nonlinear off--diagonal interactions and graviton mass and include matter, graviton mass and other effective sources modelling nonlinear gravitational and matter fields interactions with polarization of phy...
Bimetric Gravity From Adjoint Frame Field In Four Dimensions
Guo, Zhi-Qiang
2015-01-01
We provide a novel model of gravity by using adjoint frame fields in four dimensions. It has a natural interpretation as a gravitational theory of a complex metric field, which describes interactions between two real metrics. The classical solutions establish three appealing features. The spherical symmetric black hole solution has an additional hair, which includes the Schwarzschild solution as a special case. The de Sitter solution is realized without introducing a cosmological constant. The constant flat background breaks the Lorentz invariance spontaneously, although the Lorentz breaking effect can be localized to the second metric while the first metric still respects the Lorentz invariance.
General virial theorem for modified-gravity MOND
Milgrom, Mordehai
2013-01-01
An important and useful relation is known to hold in two specific MOND theories. It pertains to low-acceleration, isolated systems of pointlike masses, m_p, at positions r_p, subject to gravitational forces F_p. It reads sum_p r_p.F_p=-(2/3)(Ga0)^{1/2}[(\\sum_p m_p)^{3/2}-\\sum_p m_p^{3/2}]; a0 is the MOND acceleration constant. Here I show that this relation holds in the nonrelativistic limit of any modified-gravity MOND theory. It follows from only the basic tenets of MOND (as applied to such...
Stable and unstable cosmological models in bimetric massive gravity
Könnig, Frank; Amendola, Luca; Motta, Mariele; Solomon, Adam R
2014-01-01
Nonlinear, ghost-free massive gravity has two tensor fields; when both are dynamical, the mass of the graviton can lead to cosmic acceleration that agrees with background data, even in the absence of a cosmological constant. Here the question of the stability of linear perturbations in this theory is examined. Instabilities are presented for several classes of models, and simple criteria for the cosmological stability of massive bigravity are derived. In this way, we identify a particular self-accelerating bigravity model, infinite-branch bigravity (IBB), which exhibits both viable background evolution and stable linear perturbations. We discuss the modified gravity parameters for IBB, which do not reduce to the standard $\\Lambda$CDM result at early times, and compute the combined likelihood from measured growth data and type Ia supernovae. IBB predicts a present matter density $\\Omega_{m0}=0.18$ and an equation of state $w(z)=-0.79+0.21z/(1+z)$. The growth rate of structure is well-approximated at late times...
Einstein equations and MOND theory from Debye entropic gravity
International Nuclear Information System (INIS)
Verlinde's proposal on the entropic origin of gravity is based strongly on the assumption that the equipartition law of energy holds on the holographic screen induced by the mass distribution of the system. However, from the theory of statistical mechanics we know that the equipartition law of energy does not hold in the limit of very low temperature. Inspired by the Debye model for the equipartition law of energy in statistical thermodynamics and adopting the viewpoint that gravitational systems can be regarded as a thermodynamical system, we modify Einstein field equations. We also perform the study for Poisson equation and modified Newtonian dynamics (MOND). Interestingly enough, we find that the origin of the MOND theory can be understood from Debye entropic gravity perspective. Thus our study may fill in the gap existing in the literature understanding the theoretical origin of MOND theory. In the limit of high temperature our results reduce to their respective standard gravitational equations
Gordon and Kerr-Schild ansatze in massive and bimetric gravity
Baccetti, Valentina; Visser, Matt
2012-01-01
We develop the "generalized Gordon ansatz" for the ghost-free versions of both massive and bimetric gravity, an ansatz which is general enough to include almost all spacetimes commonly considered to be physically interesting, and restricted enough to greatly simplify calculations. The ansatz allows explicit calculation of the matrix square root gamma = sqrt{g^{-1} f} appearing as a central feature of the ghost-free analysis. In particular, this ansatz automatically allows us to write the effective stress-energy tensor as that corresponding to a perfect fluid. A qualitatively similar "generalized Kerr-Schild ansatz" can also be easily considered, now leading to an effective stress-energy tensor that corresponds to a null fluid. Cosmological implications are considered, as are consequences for black hole physics. Finally we have a few words to say concerning the null energy condition in the framework provided by these ansatze.
Recovering MOND from extended metric theories of gravity
International Nuclear Information System (INIS)
We show that the Modified Newtonian Dynamics (MOND) regime can be fully recovered as the weak-field limit of a particular theory of gravity formulated in the metric approach. This is possible when Milgrom's acceleration constant is taken as a fundamental quantity which couples to the theory in a very consistent manner. As a consequence, the scale invariance of the gravitational interaction is naturally broken. In this sense, Newtonian gravity is the weak-field limit of general relativity and MOND is the weak-field limit of that particular extended theory of gravity. We also prove that a Noether's symmetry approach to the problem yields a conserved quantity coherent with this relativistic MONDian extension. (orig.)
MOND-like acceleration in integrable Weyl geometric gravity
Scholz, Erhard
2014-01-01
In a Weyl geometric scalar tensor theory of gravity we replace the quadratic kinetic Lagrangian of the scalar field by a cubic term, similar to the one of Bekenstein and Milgrom's first relativistic MOND theory (AQUAL). In Einstein-scalar field gauge of the Weylian metric, the scale connection expresses an additional acceleration adding to the (Riemannian) metrical component known from Einstein gravity. It becomes MOND-like in the static weak field approximation, while the Riemannian component remains Newtonian. Near mass centers the energy-momentum tensor of the scalar field acquires spatial inhomogeneities containing a considerable amount of energy. These inhomogeneities have consequences comparable to the ones attributed to dark matter, as far as cluster dynamics and gravitational lensing are concerned.
Modified gravity, Dark Energy and MOND
Navarro, Ignacio; Van Acoleyen, Karel
2005-01-01
We propose a class of actions for the spacetime metric that introduce corrections to the Einstein-Hilbert Lagrangian depending on the logarithm of some curvature scalars. We show that for some choices of these invariants the models are ghost free and modify Newtonian gravity below a characteristic acceleration scale given by a_0 = c\\mu, where c is the speed of light and \\mu is a parameter of the model that also determines the late-time Hubble constant: H_0 \\sim \\mu. In these models, besides t...
Modified gravity, Dark Energy and MOND
Navarro, I; Acoleyen, Karel Van; Navarro, Ignacio
2006-01-01
We propose a class of actions for the spacetime metric that introduce corrections to the Einstein-Hilbert Lagrangian depending on the logarithm of some curvature scalars. We show that for some choices of these invariants the models are ghost free and modify Newtonian gravity below a characteristic acceleration scale given by a_0 = c\\mu, where c is the speed of light and \\mu is a parameter of the model that also determines the late-time Hubble constant: H_0 \\sim \\mu. In these models, besides the massless spin two graviton, there is a scalar excitation of the spacetime metric whose mass depends on the background curvature. This dependence is such that this scalar, although almost massless in vacuum, becomes massive and effectively decouples when one gets close to any source and we recover an acceptable weak field limit at short distances. There is also a (classical) ``running'' of Newton's constant with the distance to the sources and gravity is easily enhanced at large distances by a large ratio. We comment on...
On the gauge and global symmetries of the candidate partially massless bimetric gravity
Apolo, Luis; Lundkvist, Anders
2016-01-01
In this paper we investigate a particular ghost-free bimetric theory that exhibits the partially massless (PM) symmetry at quadratic order. At this order the global SO(1,4) symmetry of the theory is enhanced to SO(1,5). We show that this global symmetry becomes inconsistent at cubic order, in agreement with a previous calculation. Furthermore, we find that the PM symmetry of this theory cannot be extended beyond cubic order in the PM field. More importantly, it is shown that the PM symmetry cannot be extended to quartic order in any theory with one massless and one massive spin-2 fields.
Testing MOND gravity in the shell galaxy NGC 3923
Bilek, Michal; Jilkova, Lucie; Ebrova, Ivana; Bartoskova, Katerina; Krizek, Miroslav
2013-01-01
Context. The elliptical galaxy NGC 3923 is surrounded by numerous stellar shells that are concentric arcs centered on the galactic core. They are very likely a result of a minor merger and they consist of stars in nearly radial orbits. For a given potential, the shell radii at a given time after the merger can be calculated and compared to observations. The Modified Newtonian Dynamics (MOND) is a theory that aims to solve the missing mass problem by modifying the laws of classical dynamics in the limit of small accelerations. Hernquist & Quinn(1987) claimed that the shell distribution of NGC 3923 contradicted MOND, but Milgrom(1988) found several substantial insufficiencies in their work. Aims. We test whether the observed shell distribution in NGC 3923 is consistent with MOND using the current observational knowledge of the shell number and positions and of the host galaxy surface brightness profile, which supersede the data available in the 1980s when the last (and negative) tests of MOND viability were...
Testing MOND gravity in the shell galaxy NGC 3923
Bílek, M.; Jungwiert, B.; Jílková, L.; Ebrová, I.; Bartošková, K.; Křížek, M.
2013-11-01
Context. The elliptical galaxy NGC 3923 is surrounded by numerous stellar shells that are concentric arcs centered on the Galactic core. They are very likely a result of a minor merger and they consist of stars in nearly radial orbits. For a given potential, the shell radii at a given time after the merger can be calculated and compared to observations. The MOdified Newtonian Dynamics (MOND) is a theory that aims to solve the missing mass problem by modifying the laws of classical dynamics in the limit of small accelerations. Hernquist & Quinn (1987, ApJ, 312, 1) claimed that the shell distribution of NGC 3923 contradicted MOND, but Milgrom (1988, ApJ, 332, 86) found several substantial insufficiencies in their work. Aims: We test whether the observed shell distribution in NGC 3923 is consistent with MOND using the current observational knowledge of the shell number and positions and of the host galaxy surface brightness profile, which supersede the data available in the 1980s when the last (and negative) tests of MOND viability were performed on NGC 3923. Methods: Using the 3.6 μm bandpass image of NGC 3923 from the Spitzer space telescope we construct the mass profile of the galaxy. The evolution of shell radii in MOND is then computed using analytical formulae. We use 27 currently observed shells and allow for their multi-generation formation, unlike the Hernquist & Quinn one-generation model that used the 18 shells known at the time. Results: Our model reproduces the observed shell radii with a maximum deviation of ~5% for 25 out of 27 known shells while keeping a reasonable formation scenario. A multi-generation nature of the shell system, resulting from successive passages of the surviving core of the tidally disrupted dwarf galaxy, is one of key ingredients of our scenario supported by the extreme shell radial range. The 25 reproduced shells are interpreted as belonging to three generations.
Post-Newtonian constraints on Lorentz-violating gravity theories with a MOND phenomenology
Bonetti, Matteo; Barausse, Enrico
2015-01-01
We study the post-Newtonian expansion of a class of Lorentz-violating gravity theories that reduce to khronometric theory (i.e. the infrared limit of Horava gravity) in high-acceleration regimes, and reproduce the phenomenology of the modified Newtonian dynamics (MOND) in the low-acceleration, non-relativistic limit. Like in khronometric theory, Lorentz symmetry is violated in these theories by introducing a dynamical scalar field (the "khronon") whose gradient is enforced to be timelike. As ...
Soares, D. S. L.
1995-01-01
Binary galaxies are modeled as point-masses obeying the non-Newtonian MOND and Mannheim-Kazanas (MKG) theories of gravity. Random samples of such systems are generated by means of Monte Carlo simulations of binary orbits. Model pairs have total masses and mass ratios similar to pairs in the cataloged sample used in the analysis. General features of synthetic samples are derived from a comparison with observed data of galaxy pairs in $R \\times \\Delta V/(L_1+L_2)^{1/2} $ space. Both MOND and Ma...
Field-theoretical formulations of MOND-like gravity
International Nuclear Information System (INIS)
Modified Newtonian dynamics (MOND) is a possible way to explain the flat galaxy rotation curves without invoking the existence of dark matter. It is, however, quite difficult to predict such a phenomenology in a consistent field theory, free of instabilities and admitting a well-posed Cauchy problem. We examine critically various proposals of the literature, and underline their successes and failures both from the experimental and the field-theoretical viewpoints. We exhibit new difficulties in both cases, and point out the hidden fine-tuning of some models. On the other hand, we show that several published no-go theorems are based on hypotheses which may be unnecessary, so that the space of possible models is a priori larger. We examine a new route to reproduce the MOND physics, in which the field equations are particularly simple outside matter. However, the analysis of the field equations within matter (a crucial point which is often forgotten in the literature) exhibits a deadly problem, namely, that they do not remain always hyperbolic. Incidentally, we prove that the same theoretical framework provides a stable and well-posed model able to reproduce the Pioneer anomaly without spoiling any of the precision tests of general relativity. Our conclusion is that all MOND-like models proposed in the literature, including the new ones examined in this paper, present serious difficulties: Not only they are unnaturally fine-tuned, but they also fail to reproduce some experimental facts or are unstable or inconsistent as field theories. However, some frameworks, notably the tensor-vector-scalar one of Bekenstein and Sanders, seem more promising than others, and our discussion underlines in which directions one should try to improve them
Testing MOND gravity in the shell galaxy NGC 3923
Bilek, Michal; Jungwiert, Bruno; Jilkova, Lucie; Ebrova, Ivana; Bartoskova, Katerina; Krizek, Miroslav
2013-01-01
Context. The elliptical galaxy NGC 3923 is surrounded by numerous stellar shells that are concentric arcs centered on the galactic core. They are very likely a result of a minor merger and they consist of stars in nearly radial orbits. For a given potential, the shell radii at a given time after the merger can be calculated and compared to observations. The Modified Newtonian Dynamics (MOND) is a theory that aims to solve the missing mass problem by modifying the laws of classical dynamics in...
Dark energy, MOND and sub-millimeter tests of gravity
Navarro, I
2006-01-01
We consider modifications of General Relativity obtained by adding the logarithm of some curvature invariants to the Einstein-Hilbert action. These non-linear actions can explain the late-time acceleration of the universe giving an expansion history that differs from that of a pure cosmological constant. We show that they also modify the Newtonian potential below a fixed acceleration scale given by the late-time Hubble constant times the speed of light. This is exactly what is required in MOND, a phenomenological modification of the Newtonian potential that is capable of explaining galactic rotation curves without the need to introduce dark matter. We show that this kind of modification also predicts short distance deviations of Newton's law at the sub-mm scale and an anomalous shift in the precession of the Moon's orbit around the Earth, both effects of a size that is less than an order of magnitude below current bounds.
Cosmology with moving bimetric fluids
García-García, Carlos; Maroto, Antonio L.; Martín-Moruno, Prado
2016-01-01
We study cosmological implications of bigravity and massive gravity solutions with non-simultaneously diagonal metrics by considering the generalized Gordon and Kerr-Schild ansatzes. The scenario that we obtain is equivalent to that of General Relativity with additional non-comoving perfect fluids. We show that the most general ghost-free bimetric theory generates three kinds of effective fluids whose equations of state are fixed by a function of the ansatz. Different choices of such function...
Drummond, I T
2016-01-01
We study, as a model of Lorentz symmetry breaking, the quantisation and renormalisation of an extension of QED in a flat spacetime where the photons and electrons propagate differently and do not share the same lightcone. We will refer to this model as Bimetric QED (BIMQED). As a preliminary we discuss the formulation of electrodynamics in a pre-metric formalism showing nevertheless that there is, on the basis of a simple criteron, a preferred metric. Arising from this choice of metric is a Weyl-like tensor (WLT). The Petrov classification of the WLT gives rise to a corresponding classification of Lorentz symmetry breaking. We do not impose any constraint on the strength of the symmetry breaking and are able to obtain explicit dispersion relations for photon propagation in each of the Petrov classes. The associated birefringence appears in some cases as two distinct polarisation dependent lightcones and in other cases as a a more complicated structure that cannot be disentangled in a simple way. We show how i...
Stoeger, W. R.
1978-01-01
Since Rosen's bimetric theory of gravity provides at present a worthy devil's advocate for the black hole hypothesis, it is important for eventual observational work to elaborate the astrophysical consequences and possibilities peculiar to it. This work is begun by deriving the orbital topography of the spherically symmetric solution to Rosen's field equations - which is relevant to the behavior of relativistic axisymmetric accretion flows - and calculating predicted accretion disk efficiencies, which can be as much as 2.5 times higher than for a disk in Schwarzschild. Thereafter, a brief treatment of the shortest kinematic time scale and the time dilations for in-falling material is given. Finally it is shown that Birkhoff's theorem does not hold in Rosen's theory, and, therefore, that genuine gravitational monopole radiation is possible. The energy it carries, however, is not positive definite.
Bimetric Extension of General Relativity and Phenomenology of Dark Matter
Bernard, Laura
2014-01-01
We propose a relativistic model of dark matter reproducing at once the concordance cosmological model $\\Lambda$-Cold-Dark-Matter ($\\Lambda$-CDM) at cosmological scales, and the phenomenology of the modified Newtonian dynamics (MOND) at galactic scales. To achieve this we postulate a non-standard form of dark matter, consisting of two different species of particles coupled to gravity via a bimetric extension of general relativity, and linked together through an internal vector field (a "graviphoton") generated by the mass of these particles. We prove that this dark matter behaves like ordinary cold dark matter at the level of first order cosmological perturbation, while a pure cosmological constant plays the role of dark energy. The MOND equation emerges in the non-relativistic limit through a mechanism of gravitational polarization of the dark matter medium in the gravitational field of ordinary matter. Finally we show that the model is viable in the solar system as it predicts the same parametrized post-Newt...
Testing MOG/Non-local/MOND gravity with rotation curve of dwarf galaxies
Haghighi, M H Zhoolideh
2016-01-01
The MOdified Gravity (MOG) and Non-local Gravity are two different alternative theories to General Relativity where in the limit of weak filed approximation behave almost in similarly way and are able to play the role of dark matter and explain the rotation curve of spiral galaxies and cluster of galaxies (Moffat & Rahvar 2013, 2014, Rahvar & Mashhoon 2014). The effective gravitational potential in these theories compose of two terms, (i) Newtonian gravity with an enhanced gravitational constant and (ii) the second term with Yukawa type repulsive force which is defined with the length scale of $1/\\mu$. In this work we analysis the rotation curve of dwarf galaxies in the LITTLE THINGS catalog and compare them with MOG/Non-local gravity and Modified Newtonian Dynamics (MOND). We obtain almost the same $\\alpha$ factor as in our analysis of the spiral galaxy and cluster of galaxies, however we need a smaller length scale of ${\\mu} =2.77 kpc^{-1}$ to describe the rotation curve of dwarf galaxies compare to...
Emergence of cosmic space, Gauss-Bonnet gravity, MOND theory and nonextensive considerations
Abreu, Everton M C; Mendes, Albert C R; Souza, Daniel O
2015-01-01
In this paper, by using Verlinde's formalism and a modified Padmanabhan's prescription, we have obtained the lowest order quantum correction to the gravitational acceleration and MOND-type theory by considering a nonzero difference between the number of bits of the holographic screen and the number of bits of the holographic screen that satisfy the equipartition theorem (the bulk). We will also carry out an analysis for the pure and an asymptotic (actual) de Sitter Universe considering the holographic principle. We had also used nonextensive concepts into the theory and we accomplished a $N$-dimensional generalization of our results. Some physical consequences of the nonextensive ideas in Gauss-Bonnet (GB) gravity theory were analyzed also. We have obtained the $q$-parameter as a function of the GB coefficient and some physical aspects were discussed.
Nipoti, Carlo; Londrillo, Pasquale; Ciotti, Luca
2007-01-01
We present the results of N-body simulations of dissipationless galaxy merging in Modified Newtonian Dynamics (MOND). For comparison, we also studied Newtonian merging between galaxies embedded in dark matter halos, with internal dynamics equivalent to the MOND systems. We found that the merging timescales are significantly longer in MOND than in Newtonian gravity with dark matter, suggesting that observational evidence of rapid merging could be difficult to explain in MOND. However, when two...
Milgrom, Mordehai
2002-01-01
I discuss open theoretical questions pertaining to the modified dynamics (MOND)--a proposed alternative to dark matter, which posits a breakdown of Newtonian dynamics in the limit of small accelerations. In particular, I point the reasons for thinking that MOND is an effective theory--perhaps, despite appearance, not even in conflict with GR. I then contrast the two interpretations of MOND as modified gravity and as modified inertia. I describe two mechanical models that are described by pote...
Interacting Galaxies with MOND
Tiret, O
2007-01-01
We compare N-body simulations performed in MOND with analogs in Newtonian gravity with dark matter (DM). We have developed a code which solves the Poisson equation in both gravity models. It is a grid solver using adaptive mesh refinement techniques, allowing us to study isolated galaxies as well as interacting galaxies. Galaxies in MOND are found to form bars faster and stronger than in the DM model. In Newton dynamics, it is difficult to reproduce the observed high frequency of strong bars, while MOND appears to fit better the observations. Galaxy interactions and mergers, such as the Antennae, are also simulated with Newton and MOND dynamics. In the latter, dynamical friction is much weaker, and merging time-scales are longer. The formation of tidal dwarf galaxies in tidal tails are also compared in MOND and Newton+DM models.
Quantum statistical modified entropic gravity as a theoretical basis for MOND
Pazy, E.
2013-01-01
Considering the quantum statistics of the degrees of freedom on the holographic screen it is shown that the ratio of the number of excited bulk degrees of freedom to the number of excited surface degrees of freedom, is given by the MOND interpolating function {\\mu}. This relationship is shown to hold also in AQUAL, and in the extension of MOND to de Sitter space. Based on the relationship between the entropy, and the number of degrees of freedom on the holographic screen, a simple expression,...
Particular Solutions in Bimetric Theory and Their Implications
Hassan, S F; von Strauss, Mikael
2014-01-01
Ghost-free bimetric theory can describe gravity in the presence of an extra spin-2 field. We study certain aspects of dynamics in this theory: (1) It is shown that if either of the metrics is an Einstein solution then the other is always forced to be Einstein, too. For a class of bimetric models this constraint is stronger and as soon as one metric is Einstein, the other metric is forced to be proportional to it. As a consequence, the models in this class avoid a branch of pathological solutions that exhibit determinant singularities or nonlinear ghosts. These constraints persists in a generalized form when sources are included, but are destroyed in the massive gravity limit of the theory. (2) For another class of bimetric models, we show the existence of solutions that do not admit a massive gravity limit. A bimetric model that could exhibit a nonlinear version of "partially massless" symmetry belongs to both these classes. It is argued that if such a model exits, its symmetry will not survive in the massive...
Barrientos, E
2016-01-01
We construct a relativistic metric description of MOND using the Palatini formalism following the \\( f(\\chi)=\\chi^b \\) description of \\citet{mendozatula}. We show that in order to recover the non-relativistic MOND regime where, for circular orbits the Tully-Fisher law replaces Kepler's third law, the value of the parameter $ b = 3/2 $, which is coincident with the value found using a pure metric formalism Capozziello et al. (2011). Unlike the pure metric formalism, which yields 4th order field equations, the Palatini approach yields second order field equations, which is a desirable requirement from a theoretical perspective. Thus, the phenomenology associated to astrophysical phenomena with Tully-Fisher scalings can be accounted for using this proposal, without the need to introduce any non-baryonic dark matter particles.
Cosmology with moving bimetric fluids
García-García, Carlos; Martín-Moruno, Prado
2016-01-01
We study cosmological implications of bigravity and massive gravity solutions with non-simultaneously diagonal metrics by considering the generalized Gordon and Kerr-Schild ansatzes. The scenario that we obtain is equivalent to that of General Relativity with additional non-comoving perfect fluids. We show that the most general ghost-free bimetric theory generates three kinds of effective fluids whose equations of state are fixed by a function of the ansatz. Different choices of such function allow to reproduce the behaviour of different dark fluids. In particular, the Gordon ansatz is suitable for the description of various kinds of slowly-moving fluids, whereas the Kerr-Schild one is shown to describe a null dark energy component. The motion of those dark fluids with respect to the CMB is shown to generate, in turn, a relative motion of baryonic matter with respect to radition which contributes to the CMB anisotropies. CMB dipole observations are able to set stringent limits on the dark sector described by ...
Dark Matter via Massive (bi-)Gravity
Blanchet, Luc
2015-01-01
In this work we investigate the existence of relativistic models for dark matter in the context of bimetric gravity, used here to reproduce the modified Newtonian dynamics (MOND) at galactic scales. For this purpose we consider two different species of dark matter particles that separately couple to the two metrics of bigravity. These two sectors are linked together \\textit{via} an internal $U(1)$ vector field, and some effective composite metric built out of the two metrics. Among possible models only certain class of kinetic and interaction terms are allowed without invoking ghost degrees of freedom. Along these lines we explore the number of allowed kinetic terms in the theory and point out the presence of ghosts in a previous model. Finally, we propose a promising class of ghost-free candidate theories that could provide the MOND phenomenology at galactic scales while reproducing the standard cold dark matter (CDM) model at cosmological scales.
A general theory of linear cosmological perturbations: bimetric theories
Lagos, Macarena
2016-01-01
We implement the method developed in [1] to construct the most general parametrised action for linear cosmological perturbations of bimetric theories of gravity. Specifically, we consider perturbations around a homogeneous and isotropic background, and identify the complete form of the action invariant under diffeomorphism transformations, as well as the number of free parameters characterising this cosmological class of theories. We discuss, in detail, the case without derivative interactions, and compare our results with those found in massive bigravity.
Interacting Galaxies with MOND
Tiret, O; Combes, F
2007-01-01
We compare N-body simulations performed in MOND with analogs in Newtonian gravity with dark matter (DM). We have developed a code which solves the Poisson equation in both gravity models. It is a grid solver using adaptive mesh refinement techniques, allowing us to study isolated galaxies as well as interacting galaxies. Galaxies in MOND are found to form bars faster and stronger than in the DM model. In Newton dynamics, it is difficult to reproduce the observed high frequency of strong bars,...
MOND cosmology from entropic force
Zhang, Hongsheng; Li, Xin-Zhou
2011-01-01
We derive the MOND cosmology which is uniquely corresponding to the original MOND at galaxy scales via entropic gravity method. It inherits the key merit of MOND, that is, it reduces the baryonic matter and non-baryonic dark matter into baryonic matter only. For the first time we obtain the critical parameter in MOND, i.e., the transition acceleration $a_c$ at cosmological scale. We thus solve the long-standing coincidence problem $a_c\\sim cH_{0}$. More interestingly, a term like age-graphic ...
Extended Weyl Invariance in a Bimetric Model
Hassan, S F; von Strauss, Mikael
2015-01-01
We revisit a particular ghost-free bimetric model which is related to both partial masslessness as well conformal gravity. Its equations of motion can be recast in the form of a perturbative series in derivatives which exhibits a remarkable amount of structure. In a perturbative (but fully nonlinear) analysis, we demonstrate that the equations are invariant under scalar gauge transformations up to six orders in derivatives, the lowest-order term being a local Weyl scaling of the metrics. More specifically, we develop a procedure for constructing terms in the gauge transformations order by order in the perturbative framework. This allows us to derive sufficient conditions for the existence of a gauge symmetry at the nonlinear level. It is explicitly demonstrated that these conditions are satisfied at the first relevant order and, consequently, the equations are gauge invariant up to six orders in derivatives. We furthermore show that the model propagates six instead of seven degrees of freedom not only around ...
Milgrom, Mordehai
2014-01-01
A general account of MOND theory is given. I start with the basic tenets of MOND, which posit departure from standard dynamics in the limit of low acceleration -- below an acceleration constant a0 -- where dynamics become scale invariant. I list some of the salient predictions of these tenets. The special role of a0 and its significance are then discussed. In particular, I stress its coincidence with cosmologically relevant accelerations. The deep-MOND limit and the consequences of its scale ...
MOND cosmology from entropic force
International Nuclear Information System (INIS)
We derive the MOND cosmology which is uniquely corresponding to the original MOND at galaxy scales via entropic gravity method. It inherits the key merit of MOND, that is, it reduces the baryonic matter and non-baryonic dark matter into baryonic matter only. For the first time we obtain the critical parameter in MOND, i.e., the transition acceleration ac at cosmological scale. We thus solve the long-standing coincidence problem ac∼cH0. More interestingly, a term like age-graphic dark energy emerges naturally. In the frame of this MOND cosmology, we only need baryonic matter to describe both dark matter and dark energy in standard cosmology.
Bimetric Killing vectors and generation laws in bimetric theories of gravitation
Energy Technology Data Exchange (ETDEWEB)
Israelit, M. (Haifa Univ. (Israel). School of Education of the Kibbutz Movement)
1981-06-01
The concept of bimetric Killing vectors is introduced. The set of these vectors allows one to define global mechanical integrals for matter and field separately, and to get conservation laws for the matter quantities and generation laws for the field quantities. It is possible to predict what physical spaces of high mobility are contained in a certain variant of a bimetric theory. The procedure is developed in the framework of Rosen's bimetric theories of gravitation, but it may be applied to a wide class of bimetric theories.
Viable cosmology in bimetric theory
De Felice, Antonio; Mukohyama, Shinji; Tanahashi, Norihiro; Tanaka, Takahiro
2014-01-01
We study cosmological perturbations in bimetric theory with two fluids each of which is coupled to one of the two metrics. Focusing on a healthy branch of background solutions, we clarify the stability of the cosmological perturbations. For this purpose, we extend the condition for the absence of the so-called Higuchi ghost, and show that the condition is guaranteed to be satisfied on the healthy branch. We also calculate the squared propagation speeds of perturbations and derive the conditions for the absence of the gradient instability. To avoid the gradient instability, we find that the model parameters are weakly constrained.
Reconciling MOND and dark matter?
International Nuclear Information System (INIS)
Observations of galaxies suggest a one-to-one analytic relation between the inferred gravity of dark matter at any radius and the enclosed baryonic mass, a relation summarized by Milgrom's law of modified Newtonian dynamics (MOND). However, present-day covariant versions of MOND usually require some additional fields contributing to the geometry, as well as an additional hot dark matter component to explain cluster dynamics and cosmology. Here, we envisage a slightly more mundane explanation, suggesting that dark matter does exist but is the source of MOND-like phenomenology in galaxies. We assume a canonical action for dark matter, but also add an interaction term between baryonic matter, gravity, and dark matter, such that standard matter effectively obeys the MOND field equation in galaxies. We show that even the simplest realization of the framework leads to a model which reproduces some phenomenological predictions of cold dark matter (CDM) and MOND at those scales where these are most successful. We also devise a more general form of the interaction term, introducing the medium density as a new order parameter. This allows for new physical effects which should be amenable to observational tests in the near future. Hence, this very general framework, which can be furthermore related to a generalized scalar-tensor theory, opens the way to a possible unification of the successes of CDM and MOND at different scales
Vertical dynamics of disk galaxies in MOND
Nipoti, Carlo; Londrillo, Pasquale; Zhao, HongSheng; Ciotti, Luca
2007-01-01
We investigate the possibility of discriminating between Modified Newtonian Dynamics (MOND) and Newtonian gravity with dark matter, by studying the vertical dynamics of disk galaxies. We consider models with the same circular velocity in the equatorial plane (purely baryonic disks in MOND and the same disks in Newtonian gravity embedded in spherical dark matter haloes), and we construct their intrinsic and projected kinematical fields by solving the Jeans equations under the assumption of a t...
Milgrom, Mordehai
2008-01-01
I review briefly different aspects of the MOND paradigm, with emphasis on phenomenology, epitomized here by many MOND laws of galactic motion--analogous to Kepler's laws of planetary motion. I then comment on the possible roots of MOND in cosmology, possibly the deepest and most far reaching aspect of MOND. This is followed by a succinct account of existing underlying theories. I also reflect on the implications of MOND's successes for the dark matter (DM) paradigm: MOND predictions imply tha...
Combes, F
2009-01-01
We review galaxy formation and dynamics under the MOND hypothesis of modified gravity, and compare to similar galaxies in Newtonian dynamics with dark matter. The aim is to find peculiar predictions both to discriminate between various hypotheses, and to make the theory progress through different constraints, touching the interpolation function, or the fundamental acceleration scale. Galaxy instabilities, forming bars and bulges at longer term, evolve differently in the various theories, and help to bring constraints, together with the observations of bar frequency. Dynamical friction and the predicted merger rate could be a sensitive test of theories. The different scenarios of galaxy formation are compared within the various theories and observations.
International Nuclear Information System (INIS)
Gravitational potentials in the cosmos are deeper than expected from observed visible objects, a phenomenon usually attributed to dark matter, presumably in the form of a new fundamental particle. Until such a particle is observed, the jury remains out on dark matter, and modified gravity models must be considered. The class of models reducing to modified Newtonian dynamics (MOND) in the weak field limit does an excellent job fitting the rotation curves of galaxies, predicting the relation between baryonic mass and velocity in gas-dominated galaxies, and explaining the properties of the local group. Several of the initial challenges facing MOND have been overcome, while others remain. Here we point out the most severe challenge facing MOND.
MOND - Particularly as Modified Inertia
International Nuclear Information System (INIS)
After a succinct review of the MOND paradigm - with its phenomenology, and its various underlying theories - I concentrate on so-called modified inertia (MI) formulations of MOND, which have so far received only little attention. These share with all MOND theories the salient MOND predictions, such as asymptotically flat rotation curves, and the universal mass-asymptotic-speed relation. My emphasis here is, however, on the fact that MI theories can differ substantially from their '' modified-gravity '' (MG) kin in predicting other phenomena. Because MI theories are nonlocal in time, MOND effects depend on the full trajectory of a system, not only on its instantaneous state, as in MG theories. This may lead to rather different predictions for, e.g., the external-field effect (EFE): A subsystem, such as a globular cluster or a dwarf galaxy, moving in the field of a mother galaxy, or a galaxy in a cluster, may be subject to an EFE that depends on the accelerations all along its orbit, not only on the instantaneous value. And, it is even possible to construct MI theories with practically no EFE. Other predictions that may differ are also discussed. Since we do not yet have a full fledged, modified-inertia formulation, simple, heuristic models have been used to demonstrate these points. (author)
The Search for Dark Matter, Einstein's Cosmology and MOND
Cline, David B.
2005-01-01
The discovery of dark matter particles would conclusively reject the MOND theory. MOND may violate Einstein's Strong Equivalence principle. However, as we show, there is already evidence that MOND is likely not required. MOND was invented to explain the rotation velocities of stars far into the galactic halos. Dark Matter also explains this same effect. These both use a gravity probe of the I/R^2 law. We show that non gravity probes determine the same value for the amount of dark matter that ...
MOND virial theorem applied to a galaxy cluster
International Nuclear Information System (INIS)
Large values for the mass-to-light ratio (Υ) in self-gravitating systems is one of the most important evidences of dark matter. We propose a expression for the mass-to-light ratio in spherical systems using MOND. Results for the COMA cluster reveal that a modification of the gravity, as proposed by MOND, can reduce significantly this value. (author)
MOND virial theorem applied to a galaxy cluster
Fabris, J. C.; Velten, H. E. S.
2009-01-01
Large values for the mass-to-light ratio (") in self-gravitating systems is one of the most important evidences of dark matter. We propose a expression for the mass-to-light ratio in spherical systems using MOND. Results for the COMA cluster reveal that a modification of the gravity, as proposed by MOND, can reduce significantly this value.
Finslerian MOND versus the Strong Gravitational Lensing of the Early-type Galaxies
Chang, Zhe; Li, Ming-Hua; Li, Xin; Lin, Hai-Nan(Institute of High Energy Physics, Chinese Academy of Sciences, 100049, Beijing, China); Wang, Sai
2013-01-01
The gravitational lensing of Bullet Clusters and early-type galaxies pose serious challenges on the validity of MOND. Recently, Finslerian MOND, a generalization of MOND in the framework of Finsler gravity, has been proposed to explain the mass discrepancy problem of Bullet Cluster 1E 0657\\ 558. In this paper, we check the validity of the Finslerian MOND in describing the strong gravitational lensing of early-type galaxies. The investigation on ten strong lenses of the CASTLES samples shows t...
Testing MOND with Ultra-Compact Dwarf Galaxies
Scarpa, Riccardo
2005-01-01
The properties of the recently discovered Ultra-Compact Dwarf Galaxies (UCDs) show that their internal acceleration of gravity is everywhere above a0, the MOdified Newtonian Dynamics (MOND) constant of gravity. MOND therefore makes the strong prediction that no mass discrepancy should be observed for this class of objects. This is confirmed by the few UCDs for which virial masses were derived. We argue that UCD galaxies represent a suitable test-bench for the theory, in the sense that even a ...
Sanders, R. H.
2005-01-01
I review various ideas on MOND cosmology and structure formation beginning with non-relativistic models in analogy with Newtonian cosmology. I discuss relativistic MOND cosmology in the context of Bekenstein's theory and propose an alternative biscalar effective theory of MOND in which the acceleration parameter is identified with the cosmic time derivative of a matter coupling scalar field. Cosmic CDM appears in this theory as scalar field oscillations of the auxiliary "coupling strength" fi...
Famaey, Benoit; Bruneton, Jean-Philippe; Zhao, HongSheng
2007-01-01
We present a new test of modified Newtonian dynamics (MOND) on galactic scales, based on the escape speed in the solar neighbourhood. This test is independent from other empirical successes of MOND at reproducing the phenomenology of galactic rotation curves. The galactic escape speed in MOND is entirely determined by the baryonic content of the Galaxy and the external field in which it is embedded. We estimate that the external field in which the Milky Way must be embedded to produce the obs...
Ciotti, L.; Nipoti, C.; Londrillo, P.
2007-01-01
Dissipationless collapses in Modified Newtonian Dynamics (MOND) have been studied by using our MOND particle-mesh N-body code, finding that the projected density profiles of the final virialized systems are well described by Sersic profiles with index m
Hiding Lorentz invariance violation with MOND
International Nuclear Information System (INIS)
Horava-Lifshitz gravity is an attempt to construct a renormalizable theory of gravity by breaking the Lorentz invariance of the gravitational action at high energies. The underlying principle is that Lorentz invariance is an approximate symmetry and its violation by gravitational phenomena is somehow hidden to present limits of observational precision. Here I point out that a simple modification of the low-energy limit of Horava-Lifshitz gravity in its nonprojectable form can effectively camouflage the presence of a preferred frame in regions where the Newtonian gravitational field gradient is higher than cH0; this modification results in the phenomenology of modified Newtonian dynamics (MOND) at lower accelerations. As a relativistic theory of MOND, this modified Horava-Lifshitz theory presents several advantages over its predecessors.
International Nuclear Information System (INIS)
An account is given of the development, and the status, of the modified dynamics (MOND) - a proposed alternative to dark matter, which posits a breakdown of Newtonian dynamics in the limit of small accelerations. (author)
MOND and the Universal Rotation Curve: similar phenomenologies
Gentile, Gianfranco
2008-01-01
The Modified Newtonian Dynamics (MOND) and the Universal Rotation Curve (URC) are two ways to describe the general properties of rotation curves, with very different approaches concerning dark matter and gravity. Phenomenological similarities between the two approaches are studied by looking for properties predicted in one framework that are also reproducible in the other one. First, we looked for the analogous of the URC within the MOND framework. Modifying in an observationally-based way th...
Ignatiev, A Yu
2014-01-01
MOND is one of the most popular alternatives to Dark Matter (DM). While efforts to directly detect DM in laboratories have been steadily pursued over the years, the proposed Earth-based tests of MOND are still in their infancy. Some proposals recently appeared in the literature are briefly reviewed, and it is argued that collaborative efforts of theorists and experimenters are needed to move forward in this exciting new area. Possible future directions are outlined.
Cardone, V F; Diaferio, A; Tortora, C; Molinaro, R
2010-01-01
Modified Newtonian Dynamics (MOND) has been shown to be able to fit spiral galaxy rotation curves as well as giving a theoretical foundation for empirically determined scaling relations, such as the Tully - Fisher law, without the need for a dark matter halo. As a complementary analysis, one should investigate whether MOND can also reproduce the dynamics of early - type galaxies (ETGs) without dark matter. As a first step, we here show that MOND can indeed fit the observed central velocity dispersion $\\sigma_0$ of a large sample of ETGs assuming a simple MOND interpolating functions and constant anisotropy. We also show that, under some assumptions on the luminosity dependence of the Sersic n parameter and the stellar M/L ratio, MOND predicts a fundamental plane for ETGs : a log - linear relation among the effective radius $R_{eff}$, $\\sigma_0$ and the mean effective intensity $\\langle I_e \\rangle$. However, we predict a tilt between the observed and the MOND fundamental planes.
Relativistic MOND as an alternative to the dark matter paradigm
International Nuclear Information System (INIS)
Milgrom's Modified Newtonian dynamics (MOND) provides an efficient way to summarize phenomenology of galaxies which does not lean on the notion of dark matter; it has great predictive power. Here I briefly review MOND as well as its implementation as a nonrelativistic modified gravity theory, AQUAL. Gravitational lensing and cosmology call for a relativistic gravity theory different from general relativity if dark matter is to be avoided. In recent years such a theory, TeVeS, has emerged from the marriage of AQUAL with the timelike vector field of Sanders. I discuss its structure and some of its successes and shortcomings.
Relativistic MOND as an alternative to the dark matter paradigm
Bekenstein, Jacob D.
2009-08-01
>Milgrom's Modified Newtonian dynamics (MOND) provides an efficient way to summarize phenomenology of galaxies which does not lean on the notion of dark matter; it has great predictive power. Here I briefly review MOND as well as its implementation as a nonrelativistic modified gravity theory, AQUAL. Gravitational lensing and cosmology call for a relativistic gravity theory different from general relativity if dark matter is to be avoided. In recent years such a theory, TeVeS, has emerged from the marriage of AQUAL with the timelike vector field of Sanders. I discuss its structure and some of its successes and shortcomings.
Relativistic MOND as an alternative to the dark matter paradigm
Bekenstein, Jacob D
2009-01-01
Milgrom's Modified Newtonian dynamics (MOND) provides an efficient way to summarize phenomenology of galaxies which does not lean on the notion of dark matter; it has great predictive power. Here I briefly review MOND as well as its implementation as a nonrelativistic modified gravity theory, AQUAL. Gravitational lensing and cosmology call for a relativistic gravity theory different from general relativity if dark matter is to be avoided. In recent years such a theory, T$e$V$e$S, has emerged from the marriage of AQUAL with the timelike vector field of Sanders. I discuss its structure and some of its successes and shortcomings.
Milgrom, Mordehai
1995-01-01
Gerhard had recently analyzed the data on seven dwarf spheroidals, and concluded that these disagree with the predictions of MOND. We contend that this conclusion is anything but correct. With new data for three of the dwarfs the observations of all dwarfs are in compelling agreement with the predictions of MOND. Gerhard found MOND M/L values that fall around a few solar units, as expected if MOND is a valid alternative to dark matter. His sole cause for complaint was that some of his MOND M/...
Finslerian MOND versus the strong gravitational lensing of the early-type galaxies
Energy Technology Data Exchange (ETDEWEB)
Chang, Zhe; Li, Xin [Chinese Academy of Sciences, Institute of High Energy Physics, Beijing (China); Chinese Academy of Sciences, Theoretical Physics Center for Science Facilities, Beijing (China); Li, Ming-Hua; Lin, Hai-Nan; Wang, Sai [Chinese Academy of Sciences, Institute of High Energy Physics, Beijing (China)
2013-08-15
The gravitational lensing of Bullet Clusters and early-type galaxies pose serious challenges on the validity of MOND. Recently, Finslerian MOND, a generalization of MOND in the framework of Finsler gravity, has been proposed to explain the mass discrepancy problem of Bullet Cluster 1E0657-558. In this paper, we check the validity of the Finslerian MOND in describing the strong gravitational lensing of early-type galaxies. The investigation on ten strong lenses of the CASTLES samples shows that there is no strong evidence for the existence of dark matter. (orig.)
Finslerian MOND versus the strong gravitational lensing of the early-type galaxies
International Nuclear Information System (INIS)
The gravitational lensing of Bullet Clusters and early-type galaxies pose serious challenges on the validity of MOND. Recently, Finslerian MOND, a generalization of MOND in the framework of Finsler gravity, has been proposed to explain the mass discrepancy problem of Bullet Cluster 1E0657-558. In this paper, we check the validity of the Finslerian MOND in describing the strong gravitational lensing of early-type galaxies. The investigation on ten strong lenses of the CASTLES samples shows that there is no strong evidence for the existence of dark matter. (orig.)
Spherically symmetric fields in Rosen's bimetric theories of gravitation
Energy Technology Data Exchange (ETDEWEB)
Israelit, M. (University of Haifa, School of Education of the Kibbutz Movement, Oranim, P.O. Kiryat Tivon, Israel)
1981-07-01
By means of bimetric Killing vectors two spherically symmetric fields are investigated: (i) the time-dependent one in Rosen's flat-background bimetric theory; and (ii) the energy-preserving in Rosen's cosmological-background bimetric theory with k = 1. In the first case a wave behavior of the field is present. In the second case a time evolution is obtained for fields, created by insular systems of constant energy. These phenomena are typical for bimetric theories of gravitation.
Four principles for quantum gravity
Smolin, Lee
2016-01-01
Four principles are proposed to underlie the quantum theory of gravity. We show that these suffice to recover the Einstein equations. We also suggest that MOND results from a modification of the classical equivalence principle, due to quantum gravity effects.
Magnetized cosmological models in bimetric theory of gravitation
Indian Academy of Sciences (India)
S D Katore; R S Rane
2006-08-01
Bianchi type-III magnetized cosmological model when the field of gravitation is governed by either a perfect fluid or cosmic string is investigated in Rosen's [1] bimetric theory of gravitation. To complete determinate solution, the condition, viz., = (), where is a constant, between the metric potentials is used. We have assumed different equations of state for cosmic string [2] for the complete solution of the model. Some physical and geometrical properties of the exhibited model are discussed and studied.
Macleod, Alasdair
2007-01-01
MOND is a phenomenological theory with no apparent physical justification which seems to undermine some of the basic principles that underpin established theoretical physics. It is nevertheless remarkably successful over its sphere of application and this suggests MOND may have some physical basis. It is shown here that two simple axioms pertaining to fundamental principles will reproduce the characteristic behaviour of MOND, though the axioms are in conflict with general relativistic cosmology.
Hiding Lorentz Invariance Violation with MOND
Sanders, R H
2011-01-01
Ho\\v{r}ava gravity is a attempt to construct a renormalizable theory of gravity by breaking the Lorentz Invariance of the gravitational action at high energies. The underlying principle is that Lorentz Invariance is an approximate symmetry and its violation by gravitational phenomena is somehow hidden to present limits of observational precision. Here I point out that a simple modification of the low energy limit of Ho\\v{r}ava gravity in its non-projectable form can effectively camouflage the presence of a preferred frame in regions where the Newtonian gravitational field gradient is higher than $cH_0$; this modification results in the phenomenology of MOND at lower accelerations.
The velocity field in MOND cosmology
Candlish, G. N.
2016-01-01
The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAyMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAyMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evol...
A generic problem with purely metric formulations of MOND
International Nuclear Information System (INIS)
We give a simple argument to show that no purely metric-based, relativistic formulation of Milgrom's Modified Newtonian Dynamics (MOND) whose energy functional is stable (in the sense of being quadratic in perturbations) can be consistent with the observed amount of gravitational lensing from galaxies. An important part of the argument is the fact that reproducing the MOND force law requires any completely stable, metric-based theory of gravity to become conformally invariant in the weak field limit. We discuss the prospects for a formulation with a very weak instability
MOND laws of galactic dynamics
Milgrom, Mordehai
2012-01-01
MOND predicts a number of laws that galactic systems should obey irrespective of their complicated, haphazard, and mostly unknowable histories -- as Kepler's laws are obeyed by planetary systems. The main purpose of this work is to show how, and to what extent, these MOND laws follow from only the paradigm's basic tenets: departure from standard dynamics at accelerations a
Combined Solar System and rotation curve constraints on MOND
Hees, A; Angus, G W; Gentile, G
2015-01-01
The Modified Newtonian Dynamics (MOND) paradigm generically predicts that the external gravitational field in which a system is embedded can produce effects on its internal dynamics. In this communication, we first show that this External Field Effect can significantly improve some galactic rotation curves fits by decreasing the predicted velocities of the external part of the rotation curves. In modified gravity versions of MOND, this External Field Effect also appears in the Solar System and leads to a very good way to constrain the transition function of the theory. A combined analysis of the galactic rotation curves and Solar System constraints (provided by the Cassini spacecraft) rules out several classes of popular MOND transition functions, but leaves others viable. Moreover, we show that LISA Pathfinder will not be able to improve the current constraints on these still viable transition functions.
Combined Solar system and rotation curve constraints on MOND
Hees, Aurélien; Famaey, Benoit; Angus, Garry W.; Gentile, Gianfranco
2016-01-01
The Modified Newtonian Dynamics (MOND) paradigm generically predicts that the external gravitational field in which a system is embedded can produce effects on its internal dynamics. In this communication, we first show that this external field effect (EFE) can significantly improve some galactic rotation curves fits by decreasing the predicted velocities of the external part of the rotation curves. In modified gravity versions of MOND, this EFE also appears in the Solar system and leads to a very good way to constrain the transition function of the theory. A combined analysis of the galactic rotation curves and Solar system constraints (provided by the Cassini spacecraft) rules out several classes of popular MOND transition functions, but leaves others viable. Moreover, we show that Laser Interferometer Space Antenna Pathfinder will not be able to improve the current constraints on these still viable transition functions.
Gauge-covariant bimetric theory of gravitation and electromagnetism
Energy Technology Data Exchange (ETDEWEB)
Israelit, M.; Rosen, N.
1983-10-01
The Weyl theory of gravitation and electromagnetism, as modified by Dirac, contains a gauge-covariant scalar ..beta.. which has no geometric significance. This is a flaw if one is looking for a geometric description of gravitation and electromagnetism. A bimetric formalism is therefore introduced which enables one to replace ..beta.. by a geometric quantity. The formalism can be simplified by the use of a gauge-invariant physical metric. The resulting theory agrees with the general relativity for phenomena in the solar system.
Deser, S; Ong, Y C; Waldron, A
2014-01-01
The method of characteristics is a key tool for studying consistency of equations of motion; it allows issues such as predictability, maximal propagation speed, superluminality, unitarity and acausality to be addressed without requiring explicit solutions. We review this method and its application to massive gravity theories to show the limitations of these models' physical viability: Among their problems are loss of unique evolution, superluminal signals, matter coupling inconsistencies and micro-acausality (propagation of signals around local closed timelike/causal curves). We extend previous no-go results to the entire three-parameter range of massive gravity theories. It is also argued that bimetric models suffer a similar fate.
Roger, Philippe
2015-01-01
Jean Grémillon emploie la voix dans ses films de manière très différente de ses collègues. C’est l’ensemble du sonore – bruits, voix et musique – qu’il imagine de façon originale. Son traitement s’inscrit dans une vision du monde : Grémillon conçoit le cinématographe comme un biographe, une écriture de la vie. Cette vie est comprise sur deux plans : celui de l’homme et celui de l’univers. La voix selon Grémillon serait le reflet dans l’homme d’un macrocosme perçu comme énigme (le bruit) ou ré...
Famaey, Benoit
2013-01-01
The Lambda-CDM cosmological model is succesful at reproducing various independent sets of observations concerning the large-scale Universe. This model is however currently, and actually in principle, unable to predict the gravitational field of a galaxy from it observed baryons alone. Indeed the gravitational field should depend on the relative contribution of the particle dark matter distribution to the baryonic one, itself depending on the individual assembly history and environment of the galaxy, including a lot of complex feedback mechanisms. However, for the last thirty years, Milgrom's formula, at the heart of the MOND paradigm, has been consistently succesful at predicting rotation curves from baryons alone, and has been resilient to all sorts of observational tests on galaxy scales. We show that the few individual galaxy rotation curves that have been claimed to be highly problematic for the predictions of Milgrom's formula, such as Holmberg II or NGC 3109, are actually false alarms. We argue that the...
Milgrom, M
2001-01-01
An account is given of the development, and the status, of the modified dynamics (MOND)--a proposed alternative to dark matter, which posits a breakdown of Newtonian dynamics in the limit of small accelerations.
Repulsive gravity model for dark energy
Hohmann, Manuel; Wohlfarth, Mattias N. R.
2010-01-01
We construct a multimetric gravity theory containing N >= 3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector, and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N = 2 cannot be extended beyond the bimetric case. We apply our theory...
Quantum Gravity and Dark Matter
Ho, Chiu Man; Ng, Y Jack
2011-01-01
We propose a connection between global physics and local galactic dynamics via quantum gravity. The salient features of cold dark matter (CDM) and modified Newtonian dynamics (MOND) are combined into a unified scheme by introducing the concept of MONDian dark matter which behaves like CDM at cluster and cosmological scales but emulates MOND at the galactic scale.
Mass eigenstates in bimetric theory with matter coupling
Schmidt-May, Angnis
2015-01-01
In this paper we study the ghost-free bimetric action extended by a recently proposed coupling to matter through a composite metric. The equations of motion for this theory are derived using a method which avoids varying the square-root matrix that appears in the matter coupling. We make an ansatz for which the metrics are proportional to each other and find that it can solve the equations provided that one parameter in the action is fixed. In this case, the proportional metrics as well as the effective metric that couples to matter solve Einstein's equations of general relativity including a matter source. Around these backgrounds we derive the quadratic action for perturbations and diagonalize it into generalized mass eigenstates. It turns out that matter only interacts with the massless spin-2 mode whose equation of motion has exactly the form of the linearized Einstein equations, while the field with Fierz-Pauli mass term is completely decoupled. Hence, bimetric theory, with one parameter fixed such that proportional solutions exist, is degenerate with general relativity up to linear order around these backgrounds.
The velocity field in MOND cosmology
Candlish, G N
2016-01-01
The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAyMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAyMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to $\\Lambda$CDM, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard $\\Lambda$CDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAyMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field ...
Loss of mass and stability of galaxies in MOND
Wu, Xufen; Famaey, Benoit; Gentile, G; Tiret, O; Combes, F; Angus, G W; Robin, A C
2007-01-01
The self-binding energy and stability of a galaxy in MOND-based gravity are curiously decreasing functions of its center of mass acceleration towards neighbouring mass concentrations. A tentative indication of this breaking of the Strong Equivalence Principle in field galaxies is the RAVE-observed escape speed in the Milky Way. Another consequence is that satellites of field galaxies will move on nearly Keplerian orbits at large radii (100 - 500 kpc), with a declining speed below the asymptotically constant naive MOND prediction. But consequences of an environment-sensitive gravity are even more severe in clusters, where member galaxies accelerate fast: no more Dark-Halo-like potential is present to support galaxies, meaning that extended axisymmetric disks of gas and stars are likely unstable. These predicted reappearance of asymptotic Keplerian velocity curves and disappearance of "stereotypic galaxies" in clusters are falsifiable with targeted surveys.
International Nuclear Information System (INIS)
The Universe on large scales is well described by the ΛCDM cosmological model. There however remain some heavy clouds on our global understanding, especially on galaxy scales, which we review here. While some of these clouds might perhaps disappear through small compensatory adjustments of the model, such as changing the mass of the dark matter particles or accounting better for baryonic physics, others should rather be taken as strong indications that the physics of the dark sector is, at the very least, much richer and complex than currently assumed, and that our understanding of gravity and dynamics might also be at play. For instance, the empirically well-tested MOND phenomenology in galaxies, whatever its final explanation, should be understood in any model of galaxy formation and dynamics. Current alternatives to ΛCDM however bring with them many unsolved questions and challenges.
Testing of MOND with Local Group Timing
Shi, Yan-Chi
2009-01-01
The timing of the Local Group is used to test Modified Newtonian Dynamics (MOND). The result shows that the masses predicted by MOND are well below the baryonic contents of the Milky Way and Andromeda galaxies.
NEWTON's trajectories versus MOND's trajectories
Gozzi, Ennio
2016-01-01
MOND dynamics consists of a deformation of the acceleration with respect to the one provided by Newtonian mechanics. In this paper we study the issue of whether the above deformation can be derived from a velocity-dependent deformation of the coordinates of the system.
Pazy, Ehoud
2013-01-01
Modified Newtonian dynamics (MOND) can be obtained by modifying the entropic formulation of gravity, this is achieved by considering the quantum statistical nature of the degrees of freedom on the holographic screen. Through this frame work, we find some constraints on a cosmological extension for MOND, with no additional auxiliary fields. The connections between MOND to conformal gravity and Rindler force gravity are examined. These two alternative gravity theories are subsequently considere...
Fine tuning and MOND in a metamaterial multiverse
Smolyaninov, Igor I
2016-01-01
We consider the recently suggested model of a multiverse based on a ferrofluid. When the ferrofluid is subjected to a modest external magnetic field, the nanoparticles inside the ferrofluid form small hyperbolic metamaterial domains, which from the electromagnetic standpoint behave as individual Minkowski universes exhibiting different laws of physics, such as different strength of effective gravity, different versions of MOND and different radiation lifetimes. When the ferrofluid multiverse is populated with atomic or molecular species, and these species are excited using an external laser source, the radiation lifetimes of atoms and molecules in these universes depend strongly on the individual physical properties of each universe via the Purcell effect. Some universes are better fine-tuned than others to sustain the excited states of these species. Thus, the ferrofluid-based metamaterial multiverse may be used to study models of MOND and to illustrate the fine-tuning mechanism in cosmology.
Bulge formation in disk galaxies with MOND
Combes, F
2014-01-01
The formation of galaxies and their various components can be stringent tests of dark matter models and of gravity theories. In the standard cold dark matter (CDM) model, spheroids are formed through mergers in a strongly hierarchical scenario, and also in the early universe through dynamical friction in clumpy galaxies. More secularly, pseudo-bulges are formed by the inner vertical resonance with bars. The high efficiency of bulge formation is in tension with observations in the local universe of a large amount of bulge-less spiral galaxies. In the present work, the formation of bulges in very gas-rich galaxies, as those in the early universe, is studied in the Milgrom's MOdified Newtonian Dynamics (MOND), through multi-grid simulations of the non-linear gravity, including the gas dissipation, star formation and feedback. Clumpy disks are rapidly formed, as in their Newtonian equivalent systems. However, the dynamical friction is not as efficient, in the absence of dark matter halos, and the clumps have no t...
Energy Technology Data Exchange (ETDEWEB)
Becker, D., E-mail: BeckerD@thep.physik.uni-mainz.ded; Reuter, M., E-mail: reuter@thep.physik.uni-mainz.de
2014-11-15
non-invariant functional RG equation. As an application, we compute the scale dependent spectral dimension which governs the fractal properties of the effective QEG spacetimes at the bi-metric level. Earlier tests of the Asymptotic Safety conjecture almost exclusively employed ‘single-metric truncations’ which are blind towards the difference between quantum and background fields. We explore in detail under which conditions they can be reliable, and we discuss how the single-metric based picture of Asymptotic Safety needs to be revised in the light of the new results. We shall conclude that the next generation of truncations for quantitatively precise predictions (of critical exponents, for instance) is bound to be of the bi-metric type. - Highlights: • The Asymptotic Safety scenario in quantum gravity is explored. • A bi-metric generalization of the Einstein–Hilbert truncation is investigated. • We find that Background Independence can coexist with Asymptotic Safety. • RG trajectories restoring (background-quantum) split-symmetry are constructed. • The degree of validity of single-metric truncations is critically assessed.
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
Relativistic MOND from modified energetics
International Nuclear Information System (INIS)
We begin to investigate the question of what modifications in the energy-momentum tensor can yield the correct MOND regime. As a starting study, we refrain from insisting on an action principle and focus exclusively on the equations of motion. The present work, despite the absence of an explicit action functional, can be regarded to extend Milgrom's modified inertia approach to relativistic domain. Our results show that a proper MOND limit arises if the energy-momentum tensor is modified to involve the determinant of the metric tensor in reference to the flat metric, where the latter is dynamically generated as in the gravitational Higgs mechanism. This modified energy-momentum tensor is conserved in both Newtonian and MONDian regimes. (orig.)
Relativistic MOND from modified energetics
Energy Technology Data Exchange (ETDEWEB)
Demir, Durmus Ali; Karahan, Canan Nurhan [izmir Institute of Technology, izmir (Turkey)
2014-12-01
We begin to investigate the question of what modifications in the energy-momentum tensor can yield the correct MOND regime. As a starting study, we refrain from insisting on an action principle and focus exclusively on the equations of motion. The present work, despite the absence of an explicit action functional, can be regarded to extend Milgrom's modified inertia approach to relativistic domain. Our results show that a proper MOND limit arises if the energy-momentum tensor is modified to involve the determinant of the metric tensor in reference to the flat metric, where the latter is dynamically generated as in the gravitational Higgs mechanism. This modified energy-momentum tensor is conserved in both Newtonian and MONDian regimes. (orig.)
MOND habitats within the solar system
Bekenstein, Jacob; Magueijo, Joao
2006-01-01
MOdified Newtonian Dynamics (MOND) is an interesting alternative to dark matter in extragalactic systems. We here examine the possibility that mild or even strong MOND behavior may become evident well inside the solar system, in particular near saddle points of the total gravitational potential. Whereas in Newtonian theory tidal stresses are finite at saddle points, they are expected to diverge in MOND, and to remain distinctly large inside a sizeable oblate ellipsoid around the saddle point....
NGC 2419 does not challenge MOND
Sanders, R. H.
2011-01-01
I show that, in the context of MOND, non-isothermal models, approximated by high order polytropic spheres, are consistent with the observations of the radial distribution of the line-of-sight velocity dispersion in the distant globular cluster, NGC 2419. This calls into question the claim by Ibata et al. that the object constitutes a severe challenge for MOND. In general, the existence and properties of globular clusters are more problematic for LCDM than for MOND.
Dwarf Galaxies, MOND, and Relativistic Gravitation
Arthur Kosowsky
2010-01-01
MOND is a phenomenological modification of Newton's law of gravitation which reproduces the dynamics of galaxies, without the need for additional dark matter. This paper reviews the basics of MOND and its application to dwarf galaxies. MOND is generally successful at reproducing stellar velocity dispersions in the Milky Way's classical dwarf ellipticals, for reasonable values of the stellar mass-to-light ratio of the galaxies; two discrepantly high mass-to-light ratios may be explained by tid...
Scale Invariance at low accelerations (aka MOND) and the dynamical anomalies in the Universe
Milgrom, Mordehai
2016-01-01
Galactic systems, and the Universe at large, exhibit large dynamical anomalies: The observed matter in them falls very short of providing enough gravity to account for their dynamics. The mainstream response to this conundrum is to invoke large quantities of `dark matter' -- which purportedly supplies the needed extra gravity -- and also of `dark energy', to account for further anomalies in cosmology, such as the observed, accelerated expansion. The MOND paradigm offers a different solution: ...
On Bianchi-I cosmic strings coupled with Maxwell ﬁelds in bimetric relativity
Indian Academy of Sciences (India)
V Mahurpawar; S D Deo
2003-10-01
Axially symmetric Bianchi-I model is studied with source cosmic cloud strings coupled with electromagnetic ﬁeld in Rosen’s bimetric theory of relativity and observed that there is no contribution from cosmic strings and Maxwell ﬁelds in this theory.
Evolution of spiral galaxies in modified gravity
Tiret, O; Combes, F
2007-01-01
We compare N-body simulations of isolated galaxies performed in both frameworks of modified Newtonian dynamics (MOND) and Newtonian gravity with dark matter (DM). We have developed a multigrid code able to efficiently solve the modified Poisson equation derived from the Lagrangian formalism AQUAL. We take particular care of the boundary conditions that are a crucial point in MOND. The 3-dimensional dynamics of initially identical stellar discs is studied in both models. In Newtonian gravity t...
Generalizing the MOND description of rotation curves
Costa, Sandro S. e; Opher, R.
2001-01-01
We present new mathematical alternatives for explaining rotation curves of spiral galaxies in the MOND context. For given total masses, it is shown that various mathematical alternatives to MOND, while predicting flat rotation curves for large galactic radii, predict curves with different peculiar features for smaller radii. They are thus testable against observational data.
MOND, dark matter, and conservation of energy
Shariati, Ahmad; Jafari, Nosratollah
2007-01-01
The MOND equation $m \\vec a \\mu(a) = \\vec F$ could be transformed to the equivalent form $m \\vec a = \\vec{F'}$, where $\\Vec{F'}$ is a transformed force. Using this transformation we argue that MOND could not avoid introducing dark matter, and introduces nonconservative terms to the equations of motion.
A Primer to Relativistic MOND Theory
Bekenstein, J.D..; Sanders, R. H.
2005-01-01
Abstract: We first review the nonrelativistic lagrangian theory as a framework for the MOND equation. Obstructions to a relativistic version of it are discussed leading up to TeVeS, a relativistic tensor-vector-scalar field theory which displays both MOND and Newtonian limits. The whys for its particular structure are discussed and its achievements so far are summarized.
The velocity field in MOND cosmology
Candlish, G. N.
2016-08-01
The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAYMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAYMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to Λcold dark matter, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard ΛCDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAYMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field is likely an unavoidable consequence of the gravitational modification implemented in MOND, and may represent a clear observational signature of such a modification. It is further suggested that such a signal may be clearest in intermediate-density regions such as cluster outskirts and filaments.
THE MOND LIMIT FROM SPACETIME SCALE INVARIANCE
International Nuclear Information System (INIS)
The modified Newtonian dynamics (MOND) limit is shown to follow from a requirement of spacetime scale invariance of the equations of motion for nonrelativistic, purely gravitational systems, i.e., invariance of the equations of motion under (t, r) → (λt, λr) in the limit a 0 → ∞. It is suggested that this should replace the definition of the MOND limit based on the low-acceleration behavior of a Newtonian-MOND interpolating function. In this way, the salient, deep-MOND results-asymptotically flat rotation curves, the mass-rotational-speed relation (baryonic Tully-Fisher relation), the Faber-Jackson relation, etc.,-follow from a symmetry principle. For example, asymptotic flatness of rotation curves reflects the fact that radii change under scaling, while velocities do not. I then comment on the interpretation of the deep-MOND limit as one of 'zero mass': rest masses, whose presence obstructs scaling symmetry, become negligible compared to the 'phantom', dynamical masses-those that some would attribute to dark matter. Unlike the former masses, the latter transform in a way that is consistent with the symmetry. Finally, I discuss the putative MOND-cosmology connection in light of another, previously known symmetry of the deep-MOND limit. In particular, it is suggested that MOND is related to the asymptotic de Sitter geometry of our universe. It is conjectured, for example that in an exact de Sitter cosmos, deep-MOND physics would exactly apply to local systems. I also point out, in this connection, the possible relevance of a de Sitter-conformal-field-theory (dS/CFT) duality.
Iorio, Lorenzo
2009-01-01
We numerically investigate the features of typical orbits occurring in the Oort cloud (r\\approx 50-150 kAU) in the low-acceleration regime of the MOdified Newtonian Dynamics (MOND). We take into account the so-called External Field Effect (EFE) because the solar system is embedded in the Milky Way. In the framework of MOND this does matter since the gravitational acceleration of Galactic origin felt by the solar system is of the same order of magnitude of the characteristic MOND acceleration ...
New Cosmologies on the Horizon. Cosmology and Holography in bigravity and massive gravity
Energy Technology Data Exchange (ETDEWEB)
Tolley, Andrew James [Case Western Reserve Univ., Cleveland, OH (United States)
2013-03-31
The goal of this research program is to explore the cosmological dynamics, the nature of cosmological and black hole horizons, and the role of holography in a new class of infrared modified theories of gravity. This will capitalize of the considerable recent progress in our understanding of the dynamics of massive spin two fields on curved spacetimes, culminating in the formulation of the first fully consistent theories of massive gravity and bigravity/bimetric theories.
Atlani-Duault, Laëtitia (ed.); Dufoix, Stéphane; Wieviorka, Michel
2014-01-01
Figure 1 Immanuel Wallerstein Socio : Nous traversons depuis quelques années une période où le mot « crise » est sur toutes les lèvres : crise de l’euro et de l’Europe, crise financière… On sait que le thème de la crise des sciences sociales est récurrent depuis au moins les années 1950. Estimez-vous que les sciences sociales sont, elles aussi, actuellement en crise ou qu’elles connaissent plutôt une période d’épanouissement ? Immanuel Wallerstein : La crise générale du système-monde dans le...
On the election of the flat metric in the bimetric theory of gravitation
International Nuclear Information System (INIS)
The problem of the form of the flat metric in the Rosen bimetric theory is examined in the following work. It is shown, on concrete examples, how necessary it is to write down the flat metric and solve the problem of finding the gravitational field in arbitrary non-inertial frame. It is shown also how to separate the pure gravitational effects from those connected with non-inertiality of the frame by way of comparing both metrics. (orig.)
On the relationship between MOND and DM
Dunkel, Jörn
2004-01-01
Numerous astrophysical observations have shown that classical Newtonian dynamics fails on galactic scales and beyond, if only visible matter is taken into account. The two most popular theoretical concepts dealing with this problem are Dark Matter (DM) and Modified Newtonian Dynamics (MOND). In the first part of this paper it is demonstrated that a generalized MOND equation can be derived in the framework of Newtonian Dark Matter theory. For systems satisfying a fixed relationship between the...
Reconciliation of MOND and Dark Matter theory
Chan, Man Ho
2013-01-01
I show that Modified Newtonian Dynamics (MOND) is equivalent to assuming an isothermal dark matter density profile, with its density related to the enclosed total baryonic mass. This density profile can be deduced by physical laws if a dark matter core exists and if the baryonic component is spherically-symmetric, isotropic and isothermal. All the usual predictions of MOND, as well as the universal constant $a_0$, can be derived in this model. Since the effects of baryonic matter are larger i...
Global Deep-MOND Parameter as a Theory Discriminant
Milgrom, Mordehai
2012-01-01
Different formulations of MOND predict somewhat different rotation curves for the same mass distribution. Here I consider a global attribute of the rotation curve that might provide a convenient discriminant between theories when applied to isolated, pure-disk galaxies that are everywhere deep in the MOND regime. This parameter is Q=/V0^2, where is the mean squared rotational speed of the galaxy, and V0 is the asymptotic (constant) rotational speed. The comparison between the observed and predicted values of Q is oblivious to the distance, the inclination, the mass, and the size of the disk, and to the form of the interpolating function. For the known modified-gravity theories Q is predicted to be a universal constant (independent of the mass distribution in the disk): Q=2/3. The predicted Q value for modified-inertia theories does depend on the mass distribution. However, surprisingly, I find here that it varies only little among a very wide range of mass distributions, Q=0.73+-0.01. While the difference be...
Directory of Open Access Journals (Sweden)
Hélène Thiollet
2004-09-01
Full Text Available L’étude des migrations contemporaines des Érythréens vers le Yémen au tournant des années quatre-vingt-dix permet d’observer les transformations des dynamiques régionales à l’œuvre dans le monde arabe. Les migrations sont un phénomène sensible aux différents aspects (politiques, économiques, culturels, géographiques de l’intégration régionale. Celle si est envisagée dans cet article à travers une approche doublement marginale : -la marginalité géographique de l’Érythrée arabo-africaine et du Yémen, économiquement isolé dans la péninsule Arabique, -l’étude des migrations formelles et informelles, élément souvent marginal dans l’étude des institutions et des échanges qui constituent un système régional intégré. Cette étude est fondée sur une série d’entretiens menés au Yémen entre février et avril 2002 auprès des administrations yéménites et de la population érythréenne.
Acosta, R.; Tuiran, E.; Molina Redondo, U.
2015-02-01
The basic principles that originated the Modified Newtonian Dynamics MOND, are shown, as well as a description of the fundamentals aspects of the theory: modification of gravity and modification of inertia. Also, it is considered the behaviour of the movement equations under space-temporal scale transformations of the movement equations, that is, transformations that have the form (t, r) --> (lambda*t, r). It was observed in this way that the MOND regime comes from the requirement of the invariance of the movement equations with respect to this transformations.
Massive Nordstr\\"om Scalar (Density) Gravities from Universal Coupling
Pitts, J Brian
2010-01-01
Both particle physics and the 1890s Seeliger-Neumann modification of Newtonian gravity suggest considering a "mass term" for gravity, yielding a finite range due to an exponentially decaying Yukawa potential. Unlike Nordstr\\"{o}m's "massless" theory, massive scalar gravities are strictly Special Relativistic, being invariant under the Poincar\\'{e} group but not the conformal group. Geometry is a poor guide to understanding massive scalar gravities: matter sees a conformally flat metric, but gravity also sees the rest of the flat metric, barely, in the mass term. Infinitely many theories exhibit this bimetric 'geometry,' all with the total stress-energy's trace as source. All are new except the Freund-Nambu theory. The smooth massless limit indicates underdetermination of theories by data between massless and massive scalar gravities. The ease of accommodating electrons, protons and other fermions using density-weighted Ogievetsky-Polubarinov spinors in scalar gravity is noted.
Galaxy interactions: dark matter vs. Modified Newtonian dynamics (MOND)
Bílek, Michal
2016-01-01
(doctoral thesis of Michal Bilek, finished on June 19, 2015) MOND is an observational rule for predicting the acceleration of stars and galaxies from the distribution of the visible matter. It possibly stems from a new law of physics. I list the theoretical aspects of MOND, its achievements and problems. MOND has been tested mainly in disc galaxies so far. Its tests in elliptical galaxies are rare because the MOND effects are small for them in the parts observable by the conventional methods....
Cold dark matter with MOND scaling
International Nuclear Information System (INIS)
We provide a holographic dual description of Milgrom's scaling associated with galactic rotation curves. Our argument is partly based on the recent entropic reinterpretation of Newton's laws of motion. We propose a duality between cold dark matter and modified Newtonian dynamics (MOND). We introduce the concept of MONDian dark matter, and discuss some of its phenomenological implications. At cluster as well as cosmological scales, the MONDian dark matter would behave as cold dark matter, but at the galactic scale, the MONDian dark matter would act as MOND.
Wat gebeurt er als je consumenten beloont voor mond tot mond reclame?
Tuk, Mirjam; Verlegh, Peter; Smidts, Ale; Wigboldus, Daniel
2009-01-01
textabstractMond tot mond communicatie heeft veel invloed op productkeuzes en aankoopbeslissingen van consumenten. Omdat dit zo veel invloed heeft, proberen marketeers deze communicatie te stimuleren, bijvoorbeeld door consumenten te belonen voor een aanbeveling. In dit onderzoek richten we ons op de vraag hoe de ontvanger van een beloonde aanbeveling hier op reageert. We argumenteren dat de introductie van een beloning als gevolg heeft dat een aanbeveling zowel aspecten krijgt van een vriend...
MOND: time for a change of mind?
Milgrom, Mordehai
2009-01-01
This is a semi-popular account of the MOND paradigm and its comparison with the competing Newtonian-dynamics-plus-CDM paradigm. It was published recently in the online magazine of the Israel Physical Society in the IYA 2009 issue.
Dwarf Galaxies, MOND, and Relativistic Gravitation
Directory of Open Access Journals (Sweden)
Arthur Kosowsky
2010-01-01
Certain limits of these theories can also give the accelerating expansion of the Universe. The standard dark matter cosmology boasts numerous manifest triumphs; however, alternatives should also be pursued as long as outstanding observational issues remain unresolved, including the empirical successes of MOND on galaxy scales and the phenomenology of dark energy.
Cosmology with modified Newtonian dynamics (MOND)
Sanders, R. H.
1998-01-01
It is well known that the application of Newtonian dynamics to an expanding spherical region leads to the correct relativistic expression (the Friedmann equation) for the evolution of the cosmic scalefactor. Here, the cosmological implications of Milgrom's modified Newtonian dynamics (MOND) are cons
Gravitational polarization and the phenomenology of MOND
International Nuclear Information System (INIS)
The modified Newtonian dynamics (MOND) has been proposed as an alternative to the dark matter paradigm; the philosophy behind is that there is no dark matter and we witness a violation of the Newtonian law of dynamics. In this paper, we interpret the phenomenology sustaining MOND differently, as resulting from an effect of 'gravitational polarization', of some cosmic fluid made of dipole moments, aligned in the gravitational field, and representing a new form of dark matter. We invoke an internal force, of non-gravitational origin, in order to hold together the microscopic constituents of the dipole. The dipolar particles are weakly influenced by the distribution of ordinary matter; they are accelerated not by the gravitational field, but by its gradient or tidal gravitational field
Prigent, François
2008-01-01
Intellectuel éclectique à revisiter, Augustin Hamon émerge à la fin du XIXe siècle, inséré dans les cercles anarchistes parisiens. Traducteur français de Shaw, figurant parmi les fondateurs de la psychologie sociale française, ce bâtisseur de la SFIO en Bretagne multiplie les formes d’engagements. Ainsi, explorer « les mondes d’Augustin Hamon », c’est analyser d’une position intellectuelle originale d’ouverture sur le monde s’appuyant sur un réseau étoffé de relations à l’échelle européenne. ...
Manfroid, J.
2005-02-01
Ultrasons solaires, GMT, Caméra infrarouge géante, Mars, Titan et Dioné, Japet, les anneaux, Mimas, Huygens sur Titan, découverte d'un nouveau monde, Swift débute, pulsar 3C58, Jeunes galaxies, 2004 MN4 near miss, volcans martiens, Et de cinq Champs magnétiques et nébuleuses planétaires,
Testing MOND in the Solar System
Blanchet, Luc; Novak, Jerome
2011-01-01
The Modified Newtonian Dynamics (MOND) generically predicts a violation of the strong version of the equivalence principle. As a result the gravitational dynamics of a system depends on the external gravitational field in which the system is embedded. This so-called external field effect is shown to imply the existence of an anomalous quadrupolar correction, along the direction of the external galactic field, in the gravitational potential felt by planets in the Solar System. We compute this ...
The road to MOND--a novel perspective
Milgrom, Mordehai
2015-01-01
Accepting that galactic mass discrepancies are due to modified dynamics, I show why it is specifically the MOND paradigm that is pointed to cogently. MOND is thus discussed here as a special case of a larger class of modified dynamics theories whereby galactic systems with large mass discrepancies are described by scale-invariant dynamics. This is a novel presentation that uses more recent, after-the-fact insights and data (largely predicted beforehand by MOND). Starting from a purist set of ...
Oppenheimer-Volkoff Equation in Relativistic MOND Theory
Jin, Xing-Hua; Li, Xin-Zhou
2006-01-01
In this paper, we discuss the internal and external metric of the semi-realistic stars in relativistic MOND theory. We show the Oppenheimer-Volkoff equation in relativistic MOND theory and get the metric and pressure inside the stars to order of post-Newtonian corrections. We study the features of motion around the static, spherically symmetric stars by Hamilton-Jacobi mothod, and find there are only some small corrections in relativistic MOND theory.
Modified gravitational collapse, or the wonders of the MOND
Golovnev, Alexey; Masalaeva, Natalia
2013-01-01
There are many hot discussions in the literature about two competing paradigms in galactic and extra-galactic astronomy and cosmology, namely the Dark Matter and the Modified Newtonian Dynamics (MOND). It is very difficult to challenge MOND from the cosmological side because a full relativistic realisation is needed in the first place, and any failure can then be attributed to a particular model, and not to the MOND itself. We propose to study non-relativistic stages of gravitational collapse...
Scale Invariance at low accelerations (aka MOND) and the dynamical anomalies in the Universe
Milgrom, Mordehai
2016-01-01
Galactic systems, and the Universe at large, exhibit large dynamical anomalies: The observed matter in them falls very short of providing enough gravity to account for their dynamics. The mainstream response to this conundrum is to invoke large quantities of `dark matter' (DM) -- which purportedly supplies the needed extra gravity -- and also of `dark energy' (DE), to account for further anomalies in cosmology, such as the observed, accelerated expansion. The MOND paradigm offers a different solution: a breakdown of standard dynamics (gravity and/or inertia) in the limit of low accelerations -- below some acceleration $a_0$. In this limit, dynamics become space-time scale invariant, and is controlled by a gravitational constant $\\mathcal{A}_0\\equiv Ga_0$, which replaces Newton's $G$. With the new dynamics, the various detailed manifestations of the anomalies in galaxies disappear with no need for DM. The cosmological anomalies could, but need not have to do with small accelerations. For example, the need for ...
The MOND limit from space-time scale invariance
Milgrom, Mordehai
2008-01-01
The MOND limit is shown to follow from a requirement of space-time scale invariance of the equations of motion for nonrelativistic, purely gravitational systems; i.e., invariance of the equations of motion under (t,r) goes to (qt,qr), in the limit a0 goes to infinity. It is suggested that this should replace the definition of the MOND limit based on the low-acceleration behavior of a Newtonian-MOND interpolating function. In this way, the salient, deep-MOND results--asymptotically flat rotati...
An Accelerating Solution for N-Body MOND Simulation with FPGA-SoC
Directory of Open Access Journals (Sweden)
Bo Peng
2016-01-01
Full Text Available As a modified-gravity proposal to handle the dark matter problem on galactic scales, Modified Newtonian Dynamics (MOND has shown a great success. However, the N-body MOND simulation is quite challenged by its computation complexity, which appeals to acceleration of the simulation calculation. In this paper, we present a highly integrated accelerating solution for N-body MOND simulations. By using the FPGA-SoC, which integrates both FPGA and SoC (system on chip in one chip, our solution exhibits potentials for better performance, higher integration, and lower power consumption. To handle the calculation bottleneck of potential summation, on one hand, we develop a strategy to simplify the pipeline, in which the square calculation task is conducted by the DSP48E1 of Xilinx 7 series FPGAs, so as to reduce the logic resource utilization of each pipeline; on the other hand, advantages of particle-mesh scheme are taken to overcome the bottleneck on bandwidth. Our experiment results show that 2 more pipelines can be integrated in Zynq-7020 FPGA-SoC with the simplified pipeline, and the bandwidth requirement is reduced significantly. Furthermore, our accelerating solution has a full range of advantages over different processors. Compared with GPU, our work is about 10 times better in performance per watt and 50% better in performance per cost.
Cosmology in bimetric theory with an effective composite coupling to matter
Gumrukcuoglu, A Emir; Mukohyama, Shinji; Tanahashi, Norihiro
2015-01-01
We study the cosmology of bimetric theory with a composite matter coupling. We find two possible branches of background evolution. We investigate the question of stability of cosmological perturbations. For the tensor and vector perturbations, we derive conditions on the absence of ghost and gradient instabilities. For the scalar modes, we obtain conditions for avoiding ghost degrees. In the first branch, we find that one of the scalar modes becomes a ghost at the late stages of the evolution. Conversely, this problem can be avoided in the second branch. However, we also find that the constraint for the second branch prevents the doubly coupled matter fields from being the standard ingredients of cosmology. We thus conclude that a realistic and stable cosmological model requires additional minimally coupled matter fields.
Modified Newtonian Dynamics (MOND: Observational Phenomenology and Relativistic Extensions
Directory of Open Access Journals (Sweden)
Stacy S. McGaugh
2012-09-01
Full Text Available A wealth of astronomical data indicate the presence of mass discrepancies in the Universe. The motions observed in a variety of classes of extragalactic systems exceed what can be explained by the mass visible in stars and gas. Either (i there is a vast amount of unseen mass in some novel form - dark matter - or (ii the data indicate a breakdown of our understanding of dynamics on the relevant scales, or (iii both. Here, we first review a few outstanding challenges for the dark matter interpretation of mass discrepancies in galaxies, purely based on observations and independently of any alternative theoretical framework. We then show that many of these puzzling observations are predicted by one single relation - Milgrom's law - involving an acceleration constant a_0 (or a characteristic surface density Σ_† = a_0∕G on the order of the square-root of the cosmological constant in natural units. This relation can at present most easily be interpreted as the effect of a single universal force law resulting from a modification of Newtonian dynamics (MOND on galactic scales. We exhaustively review the current observational successes and problems of this alternative paradigm at all astrophysical scales, and summarize the various theoretical attempts (TeVeS, GEA, BIMOND, and others made to effectively embed this modification of Newtonian dynamics within a relativistic theory of gravity.
Repulsive gravity model for dark energy
Hohmann, Manuel
2010-01-01
We construct a multimetric gravity theory containing N >= 3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector, and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N = 2 cannot be extended beyond the bimetric case. We apply our theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way dark energy can be explained simply by dark copies of the well-understood standard model.
Repulsive gravity model for dark energy
Hohmann, Manuel; Wohlfarth, Mattias N. R.
2010-05-01
We construct a multimetric gravity theory containing N≥3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N=2 cannot be extended beyond the bimetric case. We apply our theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way dark energy can be explained simply by dark copies of the well-understood standard model.
MOND rotation curves of very low mass spiral galaxies
Milgrom, Mordehai; Sanders, Robert H.
2006-01-01
We present MOND analysis for several of the lowest mass disc galaxies currently amenable to such analysis--with (baryonic) masses below 4x10^8 solar masses. The agreement is good, extending the validity of MOND and its predicted mass velocity relation, to such low masses.
MOND and the fundamental plane of elliptical galaxies
Scarpa, Riccardo
2003-01-01
It is shown that the MOdified Newtonian Dynamics (MOND) explains the tilt of the fundamental plane of elliptical galaxies without the need of non-baryonic dark matter. Results found for elliptical galaxies extends to globular clusters and galaxy clusters, showing that MOND agrees with observations over 7 order of magnitude in acceleration.
Manfroid, J.
2006-09-01
Les Pégasides; Titan; L'étrange danse d'Encelade; Encelade et l'anneau E; Mimas et l'anneau G; Les deux Taches Rouges; Itokawa; Une seconde Lune; L'axe du monde vacille; Trois disques pour une étoile; Vénus; La vie sur Mars; Molécules interstellaires; Poussières et supernovae; Mirage quintuple; La structure spirale de la galaxie d'Andromède; Distances cosmiques (I); Distances cosmiques (II); Planémo; Renflement lunaire; DEN0255-4700; TNOs; Comète en mille morceaux; Naines et géante
A review on success and problem of MOND on globular cluster scale
Zhao, HongSheng
2005-01-01
Many past attempts to kill MOND have only strengthened the theory. Better data on galaxy velocity curves clearly favor MOND (without fine-tuning) over cold dark matter. The usual critism on the incompleteness of classical MOND has spurred a Modified Relativity (MR) by Bekenstein. After outlining cosmology and lensing in MOND, we review MOND on small scales. We point out some potential problems of MOND in two-body relaxation and tidal truncation. We argue that the tidal field in any MOND-like ...
Spacetime structure of MOND with Tully-fisher relation and lorentz invariance violation
International Nuclear Information System (INIS)
It is believed that the modification of Newtonian dynamics (MOND) is a possible alternative for dark matter hypothesis. Although Bekenstein's TeVeS supplies a relativistic version of MOND, one may still wish for a more concise covariant formulism of MOND. In this paper, within covariant geometrical framework, we present another version of MOND. We show the spacetime structure of MOND with properties of Tully-Fisher relation and Lorentz invariance violation. (authors)
The spacetime structure of MOND with Tully-Fisher relation and Lorentz invariance violation
Li, Xin; Chang, Zhe
2012-01-01
It is believed that the modification of Newtonian dynamics (MOND) is possible alternate for dark matter hypothesis. Although Bekenstein's TeVeS supplies a relativistic version of MOND, one may still wish a more concise covariant formulism of MOND. In this paper, within covariant geometrical framwork, we present another version of MOND. We show the spacetime structure of MOND with properties of Tully-Fisher relation and Lorentz invariance violation.
ANDROMEDA DWARFS IN LIGHT OF MOND. II. TESTING PRIOR PREDICTIONS
International Nuclear Information System (INIS)
We employ recently published measurements of the velocity dispersions in the newly discovered dwarf satellite galaxies of Andromeda to test our previously published predictions of this quantity. The data are in good agreement with our specific predictions for each dwarf made a priori with modified Newtonian dynamics (MOND), with reasonable stellar mass-to-light ratios, and no dark matter, while Newtonian dynamics point to quite large mass discrepancies in these systems. MOND distinguishes between regimes where the internal field of the dwarf, or the external field of the host, dominates. The data appear to recognize this distinction, which is a unique feature of MOND not explicable in ΛCDM
ANDROMEDA DWARFS IN LIGHT OF MOND. II. TESTING PRIOR PREDICTIONS
Energy Technology Data Exchange (ETDEWEB)
McGaugh, Stacy [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States); Milgrom, Mordehai [Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel)
2013-10-01
We employ recently published measurements of the velocity dispersions in the newly discovered dwarf satellite galaxies of Andromeda to test our previously published predictions of this quantity. The data are in good agreement with our specific predictions for each dwarf made a priori with modified Newtonian dynamics (MOND), with reasonable stellar mass-to-light ratios, and no dark matter, while Newtonian dynamics point to quite large mass discrepancies in these systems. MOND distinguishes between regimes where the internal field of the dwarf, or the external field of the host, dominates. The data appear to recognize this distinction, which is a unique feature of MOND not explicable in ΛCDM.
Andromeda Dwarfs in Light of MOND. II. Testing Prior Predictions
McGaugh, Stacy
2013-01-01
We employ recently published measurements of the velocity dispersions in the newly discovered dwarf satellite galaxies of Andromeda to test our previously published predictions of this quantity. The data are in good agreement with our specific predictions for each dwarf made a priori with MOND, with reasonable stellar mass-to-light ratios, and no dark matter, while Newtonian dynamics point to quite large mass discrepancies in these systems. MOND distinguishes between regimes where the internal field of the dwarf, or the external field of the host, dominates. The data appear to recognize this distinction, which is a unique feature of MOND not explicable in LCDM.
A nonlocal metric formulation of MOND
International Nuclear Information System (INIS)
We study a class of nonlocal, but causal, covariant and conserved field equations for the metric. Although nonlocal, these equations do not seem to possess extra graviton solutions in weak field perturbation theory. Indeed, the equations reduce to those of general relativity when the Ricci scalar vanishes throughout spacetime. When a static matter source is present, we show how these equations can be adjusted to reproduce Milgrom's modified Newtonian dynamics in the weak field regime, while reducing to general relativity for strong fields. We compute the angular deflection of light in the weak field regime and demonstrate that it is the same as for general relativity, resulting in far too little lensing if no dark matter is present. We also study the field equations for a general Robertson-Walker geometry. An interesting feature of our equations is that they become conformally invariant in the MOND (modified nonrelativistic dynamics) limit
Les danses du monde. Exemples musicaux
Giurchescu, Anca
2011-01-01
En publiant son coffret Les danses du monde, Hugo Zemp s’est attelé à la tâche périlleuse de fournir un maximum d’informations sur la danse, mode visuel d’expression humaine intimement lié à la musique. Gravitant autour de la relation étroite et compliquée qui unit la musique à la danse, les exemples parviennent à illustrer de façon équilibrée la grande diversité de l’expression vocale et instrumentale, sa richesse rythmique et dynamique, ainsi que la variété des formes de la danse et du voca...
Entretiens sur la multitude du monde
Damour, Thibault
2014-01-01
L'un est un écrivain et un scénariste célèbre. L'autre est un physicien et un chercheur mondialement connu. Une même interrogation les porte. Comment penser le monde après un siècle de bouleversements scientifiques ? Jean- Claude Carrière et Thibault Damour nous entraînent ici dans un dialogue lumineux, qui met l'esprit au défi de lui- même et où la clarté rivalise avec le gai savoir. La matière éternelle, l'espace et le temps absolus, l 'unique réalité : en ce début de troisième millénaire, toutes ces grandes notions du passé n'ont plus qu'une valeur d'illu- sions. Il n'y a plus d'histoire prédéterminée, inexorable, li- vrée à des forces mécaniques. L'univers se révèle léger, instable, multiple dans la superposition d'une infinité d'his- toires possibles dont nous ne percevons qu'un mince fais- ceau. C'est à la découverte de cette multitude du monde, laissant loin derrière les récits de science-fiction, que nous invitent Jean-Claude Carrière et Thibault Damour. Un voyage p...
Knelpunten bestrijding mond- en klauwzeer en klassieke varkenspest
Bergevoet, R.H.M.; Bondt, N.; Asseldonk, van, N.
2014-01-01
Dit onderzoek inventariseert de belangrijkste knelpunten tijdens de uitbraakfase van Mond- en klauwzeer en Klassieke Varkenspest die voortkomen uit de geldende regelgeving en/of uit de structuur van veehouderijsectoren, en beschrijft de mogelijke oplossingsrichtingen.
Systemische reacties op in de mond toegepaste metaallegeringen
A.J. Feilzer; C.J. Kleverlaan; C. Prahl; J. Muris
2013-01-01
In de mond toegepaste metaallegeringen kunnen ongewenste lichamelijke effecten veroorzaken. Daarbij wordt onderscheid gemaakt tussen lokale en systemische reacties en toxische en immuunreacties. Een gepresenteerde casus illustreert de problematiek. In deze casus is waarschijnlijk het aanbrengen van
How Dark Energy Affects the MOND Theory in Clusters
Man Ho Chan
2012-01-01
Modified Newtonian Dynamics (MOND) is one of the successful theories to explain the dark matter problem in galaxies. However, the data from clusters and the cosmic microwave background (CMB) indicate some dark matter should exist in larger scales. In addition, recent dynamical studies of clusters show that the effect of dark energy should not be ignored in cluster scale. In this article, I will demonstrate how dark energy affects the cluster mass calculation by using MOND. Also, I will show t...
MOND predictions of "halo" phenomenology in disc galaxies
Milgrom, Mordehai; Sanders, Robert H.
2004-01-01
We examine two corollaries of MOND pertaining to the properties of the equivalent dark-matter halo. MOND predicts for pure exponential discs a tight relation involving the halo and disc scale lengths and the mean acceleration in the disc, which we find to test favorably against the Verheijen sample of Ursa Major galaxies. A correlation between halo and disc length scales is also apparent when the "maximum disc" contribution is assumed, but we demonstrate that this follows from the more genera...
Indian Academy of Sciences (India)
S D Katore; R S Rane; K S Wankhade
2011-04-01
Bianchi type-I massive string cosmological model for perfect ﬂuid distribution in the presence of magnetic ﬁeld is investigated in Rosen’s [Gen. Relativ. Gravit. 4, 435 (1973)] bimetric theory of gravitation. To obtain the deterministic model in terms of cosmic time, we have used the condition $A = (B C)^n$, where n is a constant, between the metric potentials. The magnetic ﬁeld is due to the electric current produced along the -axis with inﬁnite electrical conductivity. Some physical and geometrical properties of the exhibited model are discussed and studied.
Galaxy interactions: dark matter vs. Modified Newtonian dynamics (MOND)
Bílek, Michal
2016-01-01
(doctoral thesis of Michal Bilek, finished on June 19, 2015) MOND is an observational rule for predicting the acceleration of stars and galaxies from the distribution of the visible matter. It possibly stems from a new law of physics. I list the theoretical aspects of MOND, its achievements and problems. MOND has been tested mainly in disc galaxies so far. Its tests in elliptical galaxies are rare because the MOND effects are small for them in the parts observable by the conventional methods. In the thesis, I explain the methods and ideas I developed for testing MOND in the ellipticals using stellar shells. Moreover, the shells enable us to test MOND for stars in radial orbits for the first time. The shells are results of galactic interactions. I discuss the shell formation mechanisms and summarize the findings from shell observations and simulations. The thesis contains as yet unpublished results mainly in: 1) the introduction of Sect. 3 (the expected differences in the shell morphology in the Newtonian dyna...
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. PMID:19892973
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.
Alternatives to dark matter: Modified gravity as an alternative to dark matter
Bekenstein, Jacob D
2010-01-01
The premier alternative to the dark matter paradigm is modified gravity. Following an introduction to the relevant phenomenology of galaxies, I review the MOND paradigm, an effective summary of the observations which any theory must reproduce. A simple nonlinear modified gravity theory does justice to MOND at the nonrelativistic level, but cannot be elevated to the relativistic level in a unique way. I go in detail into the covariant tensor-vector-theory (TeVeS) which not only recovers MOND but can also deal in detail with gravitational lensing and cosmology. Problems with MOND and TeVeS at the level of clusters of galaxies are given attention. I also summarize the status of TeVeS cosmology.
Tensor-vector-scalar-modified gravity: from small scale to cosmology
Bekenstein, Jacob D
2012-01-01
The impressive success of the standard cosmological model has suggested to many that its ingredients are all one needs to explain galaxies and their systems. I summarize a number of known problems with this program. They might signal the failure of standard gravity theory on galaxy scales. The requisite hints as to the alternative gravity theory may lie with the MOND paradigm which has proved an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the nonrelativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first sidestepped with the formulation of TeVeS, a covariant modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in face of galaxy phenomenology. I also summarize features of TeVeS cosmology and describe the confrontation with data from strong and weak gravitational lensing
A Closer Look at the Mond No-Go Statement for Purely Metric Formulations
Soussa, Marc
2003-01-01
We reexamine the assumptions made in arriving at a no-go statement for purely metric formulations of MOND. Removing the requirement of gravitational stability at appropriate scales gives life to the possibility of a purely metric theory of MOND.
Lopsidedness of cluster galaxies in modified gravity
International Nuclear Information System (INIS)
We point out an interesting theoretical prediction for elliptical galaxies residing inside galaxy clusters in the framework of modified Newtonian dynamics (MOND), that could be used to test this paradigm. Apart from the central brightest cluster galaxy, other galaxies close enough to the centre experience a strong gravitational influence from the other galaxies of the cluster. This influence manifests itself only as tides in standard Newtonian gravity, meaning that the systematic acceleration of the centre of mass of the galaxy has no consequence. However, in the context of MOND, a consequence of the breaking of the strong equivalence principle is that the systematic acceleration changes the own self-gravity of the galaxy. We show here that, in this framework, initially axisymmetric elliptical galaxies become lopsided along the external field's direction, and that the centroid of the galaxy, defined by the outer density contours, is shifted by a few hundreds parsecs with respect to the densest point
Marie-Monique Robin, Le monde selon Monsanto
Duchemin , Eric
2008-01-01
Silent Spring, écrit par la biologiste Rachel Carson et publié en septembre 1962, provoqua une prise de conscience du public des problèmes liés aux pesticides et à la pollution de l'environnement. Ce livre est aussi largement reconnu pour avoir contribué à lancer le mouvement écologiste dans le monde occidental. Le monde selon Monsato reprend la critique sociale initiée par Silent Spring et alerte sur les agissements du premier semencier mondial qui était déjà visé par le livre de Rachel Cars...
Suivre les acteurs vers un monde sans voiture
Rigal, Alexandre; Rudler, Jade
2015-01-01
Nous vivons dans un monde de voitures, agencé pour les voitures. Pourtant peu à peu le nombre d'automobilistes à temps partiel et de non-automobilistes augmente. L'attractivité de la voiture semble diminuer. Il s'agit donc de saisir ses nouveaux désirs, les nouvelles mobilités des acteurs qui refusent le monde du tout voiture individuelle. Pour exposer les potentiels qu'ils ont mis en acte et les potentiels dont bien d'autres disposent, des visualisations nous aideront à rendre compte de leur...
Damour, Thibault
2016-01-01
Avec Bob et son chien, Rick, embarquez pour une joyeuse épopée dans les mystères du monde quantique ! La physique quantique est partout autour de nous, tant dans l'infiniment grand que dans l'infiniment petit. Mais ce qu'elle dit du monde qui nous entoure diffère de manière vertigineuse de ce qu'on observe et ressent au quotidien. Partez à la rencontre de ceux qui ont théorisé et créé la physique quantique : Planck, Einstein, le prince de Broglie, Heisenberg, Schrödinger, Bohr, Born, Everett…
Immanuel Maurice Wallerstein, Comprendre le monde. Introduction à l'analyse des systèmes-monde
Cotelette, Patrick
2011-01-01
Immanuel Wallerstein - un des rares sociologues étasuniens lu en France - propose dans la réédition de son ouvrage Comprendre le monde (World-Systems Analysis. An Introduction. 2004) une introduction à l'analyse des systèmes-monde, comme l'indique le sous-titre du livre. Le projet est ambitieux : « réunir en un seul volume tout ce [que Wallerstein entend] par « analyse des systèmes-monde » tout en s'adressant à « trois types de lecteurs à la fois » (p.8), les débutants, les étudiants en docto...
Institute of Scientific and Technical Information of China (English)
N. P. Gaikwad; M. S. Borkar; S. S. Charjan
2011-01-01
@@ We investigate the Bianchi type-I massive string magnetized barotropic perfect fluid cosmological model in Rosen's bimetric theory of gravitation with and without a magnetic field by applying the techniques used by Latelier(1979,1980) and Stachel(1983).To obtain a deterministic model of the universe, it is assumed that the universe is filled with barotropic perfect fluid distribution.The physical and geometrical significance of the model are discussed.By comparing our model with the model of Bali et al.(2007), it is realized that there are no big-bang and big-crunch singularities in our model and T＝0 is not the time of the big bang, whereas the model of Bali et al.starts with a big bang at T=0.Further, our model is in agreement with Bali et al.(2007) as time increases in the presence, as well as in the absence, of a magnetic field.
Star formation triggered by galaxy interactions in modified gravity
Renaud, Florent; Famaey, Benoit; Kroupa, Pavel
2016-09-01
Together with interstellar turbulence, gravitation is one key player in star formation. It acts both at galactic scales in the assembly of gas into dense clouds, and inside those structures for their collapse and the formation of pre-stellar cores. To understand to what extent the large scale dynamics govern the star formation activity of galaxies, we present hydrodynamical simulations in which we generalise the behaviour of gravity to make it differ from Newtonian dynamics in the low acceleration regime. We focus on the extreme cases of interacting galaxies, and compare the evolution of galaxy pairs in the dark matter paradigm to that in the Milgromian Dynamics (MOND) framework. Following up on the seminal work by Tiret & Combes, this paper documents the first simulations of galaxy encounters in MOND with a detailed Eulerian hydrodynamical treatment of baryonic physics, including star formation and stellar feedback. We show that similar morphologies of the interacting systems can be produced by both the dark matter and MOND formalisms, but require a much slower orbital velocity in the MOND case. Furthermore, we find that the star formation activity and history are significantly more extended in space and time in MOND interactions, in particular in the tidal debris. Such differences could be used as observational diagnostics and make interacting galaxies prime objects in the study of the nature of gravitation at galactic scales.
Towards a $C$-function in 4D quantum gravity
Becker, Daniel
2014-01-01
We develop a generally applicable method for constructing functions, $C$, which have properties similar to Zamolodchikov's $C$-function, and are geometrically natural objects related to the theory space explored by non-perturbative functional renormalization group (RG) equations. Employing the Euclidean framework of the Effective Average Action (EAA), we propose a $C$-function which can be defined for arbitrary systems of gravitational, Yang-Mills, ghost, and bosonic matter fields, and in any number of spacetime dimensions. It becomes stationary both at critical points and in classical regimes, and decreases monotonically along RG trajectories provided the breaking of the split-symmetry which relates background and quantum fields is sufficiently weak. Within the Asymptotic Safety approach we test the proposal for Quantum Einstein Gravity in $d>2$ dimensions, performing detailed numerical investigations in $d=4$. We find that the bi-metric Einstein-Hilbert truncation of theory space introduced recently is gene...
Femme dans un monde d’hommes musiciens
Buscatto, Marie
2007-01-01
L’enquête ethnographique menée dans le monde du jazz français depuis juin 1998 nous avait permis de constater une double hiérarchisation sexuée à l’œuvre dans ce monde et d’identifier ses processus sociaux de production et de légitimation (Buscatto, 2003). Adoptant une position réflexive, cet article discute les multiples manières dont notre « genre » a aussi bien affecté les possibilités de l’enquête ethnographique, que favorisé le renouvellement, l’affinement ou la transformation de nos a...
The First Compact Objects in the MOND Model
International Nuclear Information System (INIS)
We trace the evolution of a spherically symmetric density perturbation in the MOdified Newtonian Dynamics (MOND) model. The background cosmological model is a Λ-dominated, low-Ωb Friedmann model with no Cold Dark Matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that the first density perturbations which collapse to form luminous objects have mass ∼ 105 Mo. The time of the final collapse of these objects depends mainly on the value of the MOND acceleration a0 and also on the baryon density Ωb. For the ''standard'' value a0=1.2x10-8 cm/s2 the collapse starts at redshift z∼160 for Ωb = 0.05 and z∼110 for Ωb=0.02. (author)
可凸化因子与Mond-Weir型对偶%Convexifactors and the Mond-Weir Duality
Institute of Scientific and Technical Information of China (English)
周厚春; 杨正豪
2003-01-01
利用可凸化因子的定义和性质,建立了一类不可微数学规划的Mond-Weir型对偶,在广义凸性条件下,证明了弱对偶定理和强对偶定理,并通过具体例子说明,本文建立的对偶模型不能被简化为传统形式.
Mond-Weir Duality Theorems of Nonsmooth Generalized Convexity Programming%非光滑广义凸规划的Mond-Weir对偶定理
Institute of Scientific and Technical Information of China (English)
姚元金
2002-01-01
把可微规划的Mond-Weir对偶推广到非光滑规划的广义Mond-Weir对偶,然后在广义η-严格伪凸函数,广义η-伪凸函数、广义η-拟凸函数和广义η-弱拟凸函数四类广义凸函数条件下,讨论了该非光滑规划的广义Mond-Weir对偶,得到了相应的弱对偶定理、直接对偶定理和严格逆对偶定理.
An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos
Zhao, HongSheng
2008-01-01
Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as opposite frameworks, e.g. in the debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid...
An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos
International Nuclear Information System (INIS)
Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as antagnising frameworks, e.g. in the muddled debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It is timely to consider an interdisciplinary approach across all semantic boundaries of dark sectors, treating the dark stress as one identity, hence accounts for several 'coincidences' naturally.
MOND rotation curves for spiral galaxies with Cepheid-based distances
Bottema, R; Pestana, JLG; Rothberg, B; Sanders, RH
2002-01-01
Rotation curves for four spiral galaxies with recently determined Cepheid-based distances are reconsidered in terms of modified Newtonian dynamics (MOND). For two of the objects, NGC 2403 and NGC 7331, the rotation curves predicted by MOND are compatible with the observed curves when these galaxies
Le tennis dans le monde: état et prospective
Directory of Open Access Journals (Sweden)
Pierre DUMOLARD
1989-06-01
Full Text Available Le tennis est peu ou prou pratiqué dans tous les pays du monde, mais avec de considérables variations d'intensité. Actuellement, ses points d'ancrage se situent dans les pays développés occidentaux et dans l'ancienne sphère d'influence britannique. En tenant compte de l'évolution démographique et économique possible des nations, des projections de pénétration de ce sport sont établies pour l'horizon 2000.
Directory of Open Access Journals (Sweden)
Claudia de Rham
2014-08-01
Full Text Available We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP, cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alternative and related models of massive gravity such as new massive gravity, Lorentz-violating massive gravity and non-local massive gravity.
Marriage \\`a-la-MOND: Baryonic dark matter in galaxy clusters and the cooling flow puzzle
Milgrom, Mordehai
2007-01-01
I start with a brief introduction to MOND phenomenology and its possible roots in cosmology--a notion that may turn out to be the most far reaching aspect of MOND. Next I discuss the implications of MOND for the dark matter (DM) doctrine: MOND's successes imply that baryons determine everything. For DM this would mean that the puny tail of leftover baryons in galaxies wags the hefty DM dog. This has to occur in many intricate ways, and despite the haphazard construction history of galaxies--a very tall order. I then concentrate on galaxy clusters in light of MOND, which still requires some yet undetected cluster dark matter, presumably in some baryonic form (CBDM). This CBDM might contribute to the heating of the x-ray emitting gas and thus alleviate the cooling-flow puzzle. MOND, qua theory of dynamics, does not directly enter the microphysics of the gas; however, it does force a new outlook on the role of DM in shaping the cluster gasdynamics: MOND tells us that the cluster DM is not cold dark matter, is no...
Confrontation of MOND with the rotation curves of early-type disc galaxies
Sanders, R. H.; Noordermeer, E.
2007-01-01
We extend the MOND analysis to a sample of 17 high surface brightness, early-type disc galaxies with rotation curves derived from a combination of 21cm HI line observations and optical spectroscopic data. A number of these galaxies have asymptotic rotation velocities between 250 and 350 km/s making them among the most massive systems (in terms of baryonic mass) considered in the context of MOND. We find that the general MOND prediction for such galaxies -- a rotation curve which gradually dec...
GRANDE VENTE DE NOEL - MAGASIN DU MONDE MEYRIN - French version only
Groupe Magasin du Monde Meyrin
2002-01-01
Mercredi 4 décembre de 10h. à 14h.30 Bâtiment principal, devant le restaurant no1 Vous y trouverez des produits alimentaires tels que miel, café, chocolat, sucre, quinoa, épices, etc, bref un riche assortiment des produits du commerce équitable porteurs du label Max Havelaar garantissant un meilleur revenu aux producteurs du Tiers Monde. Egalement à votre disposition des produits de l'artisanat des quatre coins du monde et des idées de cadeaux pour Noël. Groupe Magasin du Monde Meyrin
LHC 2008 lectures "Une nouvelle vision du monde"
2008-01-01
The history of the science of the Universe and the science of matter have been marked by a small number of "revolutions" that have turned our understanding of the infinitesimally large and the infinitesimally small on its head. New ways of looking at the world have come about sometimes through conceptual advances and sometimes through innovations in scientific instrumentation. How do things stand at the beginning of the 21st century? Will today’s large-scale machine projects like the LHC and gravitational wave detectors pave the way for a new scientific revolution? Thursday, 15 May 2008 at 8.00 p.m. Une nouvelle vision du monde Jean-Pierre Luminet, Research Director at the CNRS The Globe, first floor No specialist knowledge required. Entrance free. To reserve call + 41 (0) 22 767 76 76 http://www.cern.ch/globe
The dynamics of face-on galaxies in MOND
Angus, Garry W.
2016-05-01
We present an overview of the dynamical analysis using the DiskMass Survey’s measurements of vertical velocity dispersions of nearly face-on galaxy disks in both MOND and the standard model of cosmology. We found that the only, even partly realistic, solution is to have galaxy disks that are twice as thin as current surveys suggest. In the standard theory, with cold dark matter, after improving upon the original analysis we found the typical mass-to-light ratios to be less than 0.1 for almost half the sample. This is unrealistically low compared to the 0.6 found by stellar evolution models. Both these issues would disappear if the stellar vertical velocity dispersions were incorrectly measured and are actually 30% larger.
Festivals de cinéma dans le monde arabe
Directory of Open Access Journals (Sweden)
Jean-Michel Frodon
2013-12-01
Full Text Available Alors que les deux grands festivals « historiques » du monde arabe, Carthage (JCC et Le Caire, sont entrés en décadence, on assiste depuis le début des années 2000 à une véritable explosion du phénomène festivalier dans le monde arabe. Le pays le plus en pointe est le Maroc, quoique de manière contrastée, avec une manifestation de prestige à Marrakech, et une nuée de petites manifestations. Dans les émirats du Golfe, la multiplication des festivals traduit une stratégie de communication plutôt qu’une volonté de développement culturel. Cette stratégie est fragilisée par la concurrence que se livrent les différents acteurs. Dans les autres pays arabes, on trouve une grande variété de situations sous le signe de la dispersion. Pourtant, l’accumulation de festivals (une centaine dans la région finit par avoir des effets d’ensemble, au-delà des buts, moyens et limites de chacun d’eux. Le phénomène festivalier, bien qu’inscrit dans des agendas locaux ou nationaux, génère de manière plus vaste des réseaux générationnels, financiers, de procédures d’expertise, de processus d’interrelation, géographiques mais aussi entre le cinéma et les autres arts ou médias.
Quantum Gravitational Correction and MOND Theory in the Holographic Equipartition Scenario
Abreu, Everton M C; Mendes, Albert C R
2014-01-01
In this paper, by using Verlinde's formalism and a modified Padmanabhan's prescription, we have obtained the lowest order quantum correction to the gravitational acceleration and MOND-type theory by considering a nonzero difference between the number of bits of the holographic screen and number of bits of the holographic screen that satisfy the equipartition theorem. We will also carry out a phase transition and critical phenomena analysis in MOND-type theory where critical exponents are obtained.
K-MOND (with "Dark Matter" as a distinction between Inertial and Gravitational Mass)
Pankovic, Vladan; Kapor, Darko
2010-01-01
In this work we definitely prove a possibility that Milgrom's modified Newtonian dynamics, MOND, can be consistently interpreted as a theory with the modified kinetic terms of the usual Newtonain dynamics, simply called k-MOND. Precisely, we suggest only a functional dependence between inertial and gravitational mass tending toward identity in the limit of large accelerations (characteristic for Newtonian dynamics and its relativistic generalizations) but which behaves as a principal non-iden...
Low-mass disc galaxies and the issue of stability: MOND versus dark matter
Sánchez-Salcedo, F. J.; Martínez-Gómez, E.; Aguirre-Torres, V. M.; Hernández-Toledo, H. M.
2016-11-01
We analyse the rotation curves and gravitational stability of a sample of six bulgeless galaxies for which detailed images reveal no evidence for strong bars. We explore two scenarios: Newtonian dark matter models and MOdified Newtonian Dynamics (MOND). By adjusting the stellar mass-to-light ratio, dark matter models can match simultaneously both the rotation curve and bar-stability requirements in these galaxies. To be consistent with stability constraints, in two of these galaxies, the stellar mass-to-light ratio is a factor of ˜1.5-2 lower than the values suggested from galaxy colours. In contrast, MOND fits to the rotation curves are poor in three galaxies, perhaps because the gas tracer contains non-circular motions. The bar stability analysis provides a new observational test to MOND. We find that most of the galaxies under study require abnormally high levels of random stellar motions to be bar stable in MOND. In particular, for the only galaxy in the sample for which the line-of-sight stellar velocity dispersion has been measured (NGC 6503), the observed velocity dispersion is not consistent with MOND predictions because it is far below the required value to guarantee bar stability. Precise measurements of mass-weighted velocity dispersions in (unbarred and bulgeless) spiral galaxies are crucial to test the consistency of MOND.
MOND impact of the recently updated mass-discrepancy-acceleration relation
Milgrom, Mordehai
2016-01-01
McGaugh et al. (2016) have used their extensive SPARC sample to update the well-known mass-discrepancy-acceleration relation (MDAR), which is one of the major predicted "MOND laws". This is not a newly discovered relation. Rather, it improves on the many previous studies of it, with more and better data. Like its precedents, it bears crucial ramifications for the observed dynamical anomalies in disc galaxies, and, in particular, on their resolution by the MOND paradigm. Their result, indeed, constitute a triumph for MOND. However, unlike previous analyses of the MDAR, McGaugh et al. have chosen to obfuscate the MOND roots of their analysis, and its connection with, and implications for, this paradigm. For example, the fitting formula they use, seemingly as a result of some unexplained inspiration, follows in its salient properties from the basic tenets of MOND, and has already been used in the past in several MOND analyses. No other possible origin for such a function is known. Given that this formula had alr...
Star formation triggered by galaxy interactions in modified gravity
Renaud, Florent; Kroupa, Pavel
2016-01-01
Together with interstellar turbulence, gravitation is one key player in star formation. It acts both at galactic scales in the assembly of gas into dense clouds, and inside those structures for their collapse and the formation of pre-stellar cores. To understand to what extent the large scale dynamics govern the star formation activity of galaxies, we present hydrodynamical simulations in which we generalise the behaviour of gravity to make it differ from Newtonian dynamics in the low acceleration regime. We focus on the extreme cases of interacting galaxies, and compare the evolution of galaxy pairs in the dark matter paradigm to that in the Milgromian Dynamics (MOND) framework. Following up on the seminal work by Tiret & Combes, this paper documents the first simulations of galaxy encounters in MOND with a detailed Eulerian hydrodynamical treatment of baryonic physics, including star formation and stellar feedback. We show that similar morphologies of the interacting systems can be produced by both the ...
Sneddon, Andrew
2013-01-01
Gravity is a cross-disciplinary research project in Fine Art at Sheffield Institute of the Arts (SIA) in partnership with Sheffield Galleries and Museums. Gravity is led by Penny McCarthy, Dr Becky Shaw and Andrew Sneddon. Gravity begins with a series of lectures designed to examine the wider context of practice and discourse. Gravity examines the contemporary condition of the art object or artefact, and the relations between maker, medium, site of production and systems of dissemination. ...
Claudia de Rham
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
Liouville gravity from Einstein gravity
Grumiller, D.; Jackiw, R.
2007-01-01
We show that Liouville gravity arises as the limit of pure Einstein gravity in 2+epsilon dimensions as epsilon goes to zero, provided Newton's constant scales with epsilon. Our procedure - spherical reduction, dualization, limit, dualizing back - passes several consistency tests: geometric properties, interactions with matter and the Bekenstein-Hawking entropy are as expected from Einstein gravity.
Marriage à-la-MOND: Baryonic dark matter in galaxy clusters and the cooling flow puzzle
Milgrom, Mordehai
2008-05-01
I start with a brief introduction to MOND phenomenology and its possible roots in cosmology—a notion that may turn out to be the most far reaching aspect of MOND. Next I discuss the implications of MOND for the dark matter (DM) doctrine: MOND's successes imply that baryons determine everything. For DM this would mean that the puny tail of leftover baryons in galaxies wags the hefty DM dog. This has to occur in many intricate ways, and despite the haphazard construction history of galaxies—a very tall order. I then concentrate on galaxy clusters in light of MOND, which still requires some yet undetected cluster dark matter, presumably in some baryonic form (CBDM). This CBDM might contribute to the heating of the X-ray emitting gas and thus alleviate the cooling flow puzzle. MOND, qua theory of dynamics, does not directly enter the microphysics of the gas; however, it does force a new outlook on the role of DM in shaping the cluster gas dynamics: MOND tells us that the cluster DM is not cold dark matter, is not so abundant, and is not expected in galaxies; it is thus not subject to constraints on baryonic DM in galaxies. The mass in CBDM required in a whole cluster is, typically, similar to that in hot gas, but is rather more centrally concentrated, totally dominating the core. The CBDM contribution to the baryon budget in the universe is thus small. Its properties, deduced for isolated clusters, are consistent with the observations of the "bullet cluster". Its kinetic energy reservoir is much larger than that of the hot gas in the core, and would suffice to keep the gas hot for many cooling times. Heating can be effected in various ways depending on the exact nature of the CBDM, from very massive black holes to cool, compact gas clouds.
SLOWLY ROTATING GAS-RICH GALAXIES IN MODIFIED NEWTONIAN DYNAMICS (MOND)
Energy Technology Data Exchange (ETDEWEB)
Sanchez-Salcedo, F. J.; Martinez-Garcia, E. E. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, 04510 Mexico City (Mexico); Hidalgo-Gamez, A. M., E-mail: jsanchez@astro.unam.mx [Departamento de Fisica, Escuela Superior de Fisica y Matematicas, IPN, U.P. Adolfo Lopez Mateos, C.P. 07738, Mexico City (Mexico)
2013-03-15
We have carried out a search for gas-rich dwarf galaxies that have lower rotation velocities in their outskirts than MOdified Newtonian Dynamics (MOND) predicts, so that the amplitude of their rotation curves cannot be fitted by arbitrarily increasing the mass-to-light ratio of the stellar component or by assuming additional undetected matter. With presently available data, the gas-rich galaxies UGC 4173, Holmberg II, ESO 245-G05, NGC 4861, and ESO 364-G029 deviate most from MOND predictions and, thereby, provide a sample of promising targets in testing the MOND framework. In the case of Holmberg II and NGC 4861, we find that their rotation curves are probably inconsistent with MOND, unless their inclinations and distances differ significantly from the nominal ones. The galaxy ESO 364-G029 is a promising target because its baryonic mass and rotation curve are similar to Holmberg II but presents a higher inclination. Deeper photometric and H I observations of ESO 364-G029, together with further decreasing systematic uncertainties, may provide a strong test to MOND.
SLOWLY ROTATING GAS-RICH GALAXIES IN MODIFIED NEWTONIAN DYNAMICS (MOND)
International Nuclear Information System (INIS)
We have carried out a search for gas-rich dwarf galaxies that have lower rotation velocities in their outskirts than MOdified Newtonian Dynamics (MOND) predicts, so that the amplitude of their rotation curves cannot be fitted by arbitrarily increasing the mass-to-light ratio of the stellar component or by assuming additional undetected matter. With presently available data, the gas-rich galaxies UGC 4173, Holmberg II, ESO 245-G05, NGC 4861, and ESO 364-G029 deviate most from MOND predictions and, thereby, provide a sample of promising targets in testing the MOND framework. In the case of Holmberg II and NGC 4861, we find that their rotation curves are probably inconsistent with MOND, unless their inclinations and distances differ significantly from the nominal ones. The galaxy ESO 364-G029 is a promising target because its baryonic mass and rotation curve are similar to Holmberg II but presents a higher inclination. Deeper photometric and H I observations of ESO 364-G029, together with further decreasing systematic uncertainties, may provide a strong test to MOND.
Testing the MOND paradigm of modified dynamics with galaxy-galaxy gravitational lensing.
Milgrom, Mordehai
2013-07-26
The MOND paradigm of modified dynamics predicts that the asymptotic gravitational potential of an isolated, bounded (baryonic) mass, M, is ϕ(r)=(MGa0)1/2ln(r). Relativistic MOND theories predict that the lensing effects of M are dictated by ϕ(r) as general-relativity lensing is dictated by the Newtonian potential. Thus MOND predicts that the asymptotic Newtonian potential deduced from galaxy-galaxy gravitational lensing will have (1) a logarithmic r dependence, and (2) a normalization (parametrized standardly as 2σ2) that depends only on M: σ=(MGa0/4)1/4. I compare these predictions with recent results of galaxy-galaxy lensing, and find agreement on all counts. For the “blue”-lenses subsample (“spiral” galaxies) MOND reproduces the observations well with an r′-band M/Lr′∼(1–3)(M/L)⊙, and for “red” lenses (“elliptical” galaxies) with M/Lr′∼(3–6)(M/L)⊙, both consistent with baryons only. In contradistinction, Newtonian analysis requires, typically, M/Lr′∼130(M/L)⊙, bespeaking a mass discrepancy of a factor ∼40. Compared with the staple, rotation-curve tests, MOND is here tested in a wider population of galaxies, through a different phenomenon, using relativistic test objects, and is probed to several-times-lower accelerations–as low as a few percent of a0. PMID:23931350
Testing MOND over a wide acceleration range in x-ray ellipticals.
Milgrom, Mordehai
2012-09-28
The gravitational fields of two isolated ellipticals, NGC 720 and NGC 1521, have been recently measured to very large galactic radii (~100 and ~200 kpc), assuming hydrostatic balance of the hot gas enshrouding them. They afford, for the first time to my knowledge, testing modified Newtonian dynamics (MOND) in ellipticals with force and quality that, arguably, approach those of rotation-curve tests in disk galaxies. In the context of MOND, it is noteworthy that the measured accelerations span a wide range, from more than 10a(0) to about 0.1a(0), unprecedented in individual ellipticals. I find that MOND predicts correctly the measured dynamical mass runs (apart from a possible minor tension in the inner few kpc of NGC 720, which might be due to departure from hydrostatic equilibrium): The predicted mass discrepancy increases outward from none near the center, to ~10 at the outermost radii. The implications for the MOND-versus-dark-matter controversy go far beyond the simple fact of two more galaxies conforming to MOND. PMID:23030078
Critical take on "Mass models of disk galaxies from the DiskMass Survey in MOND''
Milgrom, Mordehai
2015-01-01
Angus et al.(2015) have recently faulted MOND as follows: Studying thirty disc galaxies from the DiskMass survey, they derive the profiles of velocity dispersion perpendicular to the discs as predicted by MOND, call them $\\sigma_M(r)$. These are then compared with the dispersion profiles, $\\sigma(r)$, measured as part of the DiskMass project. This is a (theory dependent) test of MOND, different from rotation-curve analysis. A nontrivial accomplishment of MOND -- not discussed by Angus et al. -- is that $\\eta(r)\\equiv\\sigma_M(r)/\\sigma(r)$ is well consistent with being $r$-independent (while $\\sigma$ and $\\sigma_M$ are strongly $r$ dependent). The fault found with MOND was that $\\eta$ is systematically above 1 (with an average of about 1.4). I have suggested to Angus et al. that the fault may lie with the DiskMass dispersions, which may well be $\\sim 30\\%$ too low for the purpose at hand: Being based on population-integrated line profiles, they may be overweighed by younger populations, known to have much smal...
Modified Gravity Theories: Alternatives To The Missing Mass And Missing Energy Problems
Soussa, M E
2005-01-01
Modified theories of gravity are examined and shown to be alternative possibilities to the standard paradigms of dark matter and dark energy in explaining the currently observed cosmological phenomenology. Special consideration is given to the relativistic extension of Modified Newtonian Dynamics (MOND) in supplanting the need for dark matter. A specific modification of the Einstein-Hilbert action (whereby an inverse power of the Ricci scalar is added) is shown to serve as an alternative to dark energy.
A Tale of Two Paradigms: the Mutual Incommensurability of LCDM and MOND
McGaugh, Stacy S
2014-01-01
The concordance model of cosmology, LCDM, provides a satisfactory description of the evolution of the universe and the growth of large scale structure. Despite considerable effort, this model does not at present provide a satisfactory description of small scale structure and the dynamics of bound objects like individual galaxies. In contrast, MOND provides a unique and predictively successful description of galaxy dynamics, but is mute on the subject of cosmology. Here I briefly review these contradictory world views, emphasizing the wealth of distinct, interlocking lines of evidence that went into the development of LCDM while highlighting the practical impossibility that it can provide a satisfactory explanation of the observed MOND phenomenology in galaxy dynamics. I also briefly review the baryon budget in groups and clusters of galaxies where neither paradigm provides an entirely satisfactory description of the data. Relatively little effort has been devoted to the formation of structure in MOND; I revie...
Some clues to understand MOND and the accelerated expansion of the universe
Tank, Hasmukh K.
2011-12-01
This letter points out that the values of `critical-acceleration' of MOND, and the `accelerated-expansion' of the universe are just two of the fourteen strikingly equal values of accelerations recurring in different physical situations. Some of them could be explained by a new law of equality of potential-energy and energy-of-mass of reasonably-independent systems (Tank in Astrophys. Space Sci. 330:203-205, 2010; Tank in Adv. Stud. Theor. Phys. 5:45-55, 2011). This new conservation-law, of equality of potential-energy, energy-of-mass and `kinetic-energy' may be a clue to understand MOND, and the `accelerated-expansion' of the universe. Alternative expressions for the cosmological red-shift, the `critical-acceleration' of MOND and Newton's law of universal gravitation are also presented for comparison of three different accelerations.
MOND Prediction for the Velocity Dispersion of the `Feeble Giant' Crater II
McGaugh, Stacy S
2016-01-01
Crater II is an unusual object among the dwarf satellite galaxies of the Local Group in that it has a very large size for its small luminosity. This provides a strong test of MOND, as Crater II should be in the deep MOND regime ($g_{in} \\approx 34\\;\\mathrm{km}^2\\,\\mathrm{s}^{-2}\\,\\mathrm{kpc}^{-1} \\ll a_0 = 3700\\;\\mathrm{km}^2\\,\\mathrm{s}^{-2}\\,\\mathrm{kpc}^{-1}$). Despite its great distance ($\\approx 120$ kpc) from the Milky Way, the external field of the host ($g_{ex} \\approx 282\\; \\mathrm{km}^2\\,\\mathrm{s}^{-2}\\,\\mathrm{kpc}^{-1}$) comfortably exceeds the internal field. Consequently, Crater II should be subject to the external field effect, a feature unique to MOND. This leads to the prediction of a very low velocity dispersion: $\\sigma_{efe} = 2.1^{+0.9}_{-0.6}\\;\\mathrm{km}\\,\\mathrm{s}^{-1}$.
Can MOND type hypotheses be tested in a free fall laboratory environment?
Das, Saurya
2013-01-01
The extremely small accelerations of objects required for the the onset of modified Newtonian dynamics, or MOND, makes testing the hypothesis in conventional terrestrial laboratories virtually impossible. This is due to the large background acceleration of Earth, which is transmitted to the acceleration of test objects within an apparatus. We show however, that it may be possible to test MOND-type hypotheses with experiments using a conventional apparatus capable of tracking very small accelerations of its components, but performed in locally inertial frames such as artificial satellites and other freely falling laboratories. For example, experiments involving an optical interferometer or a torsion balance in these laboratories would show nonlinear dynamics, and displacement amplitudes larger than expected. These experiments may also be able to test potential violations of the strong equivalence principle by MOND and to distinguish between its two possible interpretations (modified inertia and modified gravit...
Pitts, J Brian
2015-01-01
Klein-Gordon gravity, 1920s-30s particle physics, and 1890s Neumann-Seeliger modified gravity suggest a "graviton mass term" *algebraic* in the potential. Unlike Nordstr\\"om's "massless" theory, massive scalar gravity is invariant under the Poincar\\'e group but not the 15-parameter conformal group. It thus exhibits the whole Minkowski space-time structure, indirectly for volumes. Massive scalar gravity is plausible as a field theory, but violates Einstein's principles of general covariance, general relativity, equivalence, and Mach. Geometry is a poor guide: matter sees a conformally flat metric due to universal coupling, but gravity sees the rest of the flat metric (on long distances) in the mass term. What is the `true' geometry, in line with Poincar\\'e's modal conventionality argument? Infinitely many theories exhibit this bimetric `geometry,' all with the total stress-energy's trace as source; geometry does not explain the field equations. The irrelevance of the Ehlers-Pirani-Schild construction to conven...
Einstein Gravity from Conformal Gravity
Maldacena, Juan
2011-01-01
We show that that four dimensional conformal gravity plus a simple Neumann boundary condition can be used to get the semiclassical (or tree level) wavefunction of the universe of four dimensional asymptotically de-Sitter or Euclidean anti-de Sitter spacetimes. This simple Neumann boundary condition selects the Einstein solution out of the more numerous solutions of conformal gravity. It thus removes the ghosts of conformal gravity from this computation. In the case of a five dimensional pure ...
Institute of Scientific and Technical Information of China (English)
雨墨
2005-01-01
爱马仕Le Monde d Hermes杂志中文版面世了。Le Monde d Hermes杂志同时是爱马仕新款产品的样本和生活艺术的杂志，书中尽显爱马仕公司的创意设计。艺术家、摄影家或作家才华横溢的杰作．更在此彰显其价值。
Institute of Scientific and Technical Information of China (English)
马丽; 王其林; 解军; 胡晓丽
2013-01-01
讨论了约束集值优化问题的一类二阶Mond-Weir型对偶,获得了广义二阶合成相依上图导数的一个新的性质,利用广义二阶合成相依上图导数构建了约束集值优化问题的一类二阶Mond-Weir型对偶,并建立了相应的弱对偶、强对偶和逆对偶定理.
广义凸非光滑规划的Mond-Weir对偶%Mond-Weir duality for generalized convex and nonsmooth programming
Institute of Scientific and Technical Information of China (English)
姚元金
2003-01-01
建立了非光滑Lipschitz规划的两种Mond-Weir对偶形式,然后利用Clarke广义梯度定义的Lipschitz函数的广义凸性条件,证明了相应的弱对偶、强对偶和严格逆对偶定理,所得结果涵盖并推广了有关已知的对偶性定理.
群体多目标规划的联合Mond-Weir对偶%JOINT MOND-WEIR TYPE DUALITY FOR GROUP MULTIOBJECTIVE PROGRAMMING
Institute of Scientific and Technical Information of China (English)
胡毓达; 王晓敏
2003-01-01
对于目标和约束均为不对称的群体多目标规划问题,本文研究它的联合有效解类的Mond-Weir型对偶性,得到了相应的弱对偶定理、直接对偶定理和逆对偶定理.
Can TeVeS be a viable theory of gravity?
International Nuclear Information System (INIS)
Among modified gravitational theories, the Tensor–Vector–Scalar (TeVeS) occupies a special place – it is a covariant theory of gravity that produces the modified Newtonian dynamics (MOND) in the nonrelativistic weak field limit and explains the astrophysical data at scales larger than that of the Solar System, without the need of an excessive amount of invisible matter. We show that, in contrast to other modified theories, TeVeS is free from ghosts. These achievements make TeVeS (and its nonrelativistic limit) a viable theory of gravity. A speculative outlook on the emergence of TeVeS from a quantum theory is presented
Can TeVeS be a viable theory of gravity?
Energy Technology Data Exchange (ETDEWEB)
Chaichian, Masud, E-mail: masud.chaichian@helsinki.fi [Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki (Finland); Klusoň, Josef, E-mail: klu@physics.muni.cz [Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37, Brno (Czech Republic); Oksanen, Markku, E-mail: markku.oksanen@helsinki.fi [Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki (Finland); Tureanu, Anca, E-mail: anca.tureanu@helsinki.fi [Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki (Finland)
2014-07-30
Among modified gravitational theories, the Tensor–Vector–Scalar (TeVeS) occupies a special place – it is a covariant theory of gravity that produces the modified Newtonian dynamics (MOND) in the nonrelativistic weak field limit and explains the astrophysical data at scales larger than that of the Solar System, without the need of an excessive amount of invisible matter. We show that, in contrast to other modified theories, TeVeS is free from ghosts. These achievements make TeVeS (and its nonrelativistic limit) a viable theory of gravity. A speculative outlook on the emergence of TeVeS from a quantum theory is presented.
Slowly rotating gas-rich galaxies in modified Newtonian dynamics (MOND)
Sanchez-Salcedo, F J; Martinez-Garcia, Eric E
2013-01-01
We have carried out a search for gas-rich dwarf galaxies that have lower rotation velocities in their outskirts than MOdified Newtonian Dynamics (MOND) predicts, so that the amplitude of their rotation curves cannot be fitted by arbitrarily increasing the mass-to-light ratio of the stellar component or by assuming additional undetected matter. With presently available data, the gas-rich galaxies UGC 4173, Holmberg II, ESO 245-G05, NGC 4861 and ESO 364-G029 deviate most from MOND predictions and, thereby, provide a sample of promising targets in testing the MOND framework. In the case of Holmberg II and NGC 4861, we find that their rotation curves are probably inconsistent with MOND, unless their inclinations and distances differ significantly from the nominal ones. The galaxy ESO 364-G029 is a promising target because its baryonic mass and rotation curve are similar to Holmberg II but presents a higher inclination. Deeper photometric and HI observations of ESO 364-G029, together with further decreasing system...
Low-mass disc galaxies and the issue of stability: MOND vs dark matter
Sanchez-Salcedo, F J; Aguirre-Torres, V M; Hernandez-Toledo, H M
2016-01-01
We analyse the rotation curves and gravitational stability of a sample of six bulgeless galaxies for which detailed images reveal no evidence for strong bars. We explore two scenarios: Newtonian dark matter models and MOdified Newtonian Dynamics (MOND). By adjusting the stellar mass-to-light ratio, dark matter models can match simultaneously both the rotation curve and bar-stability requirements in these galaxies. To be consistent with stability constraints, in two of these galaxies, the stellar mass-to-light ratio is a factor of ~1.5-2 lower than the values suggested from galaxy colours. In contrast, MOND fits to the rotation curves are poor in three galaxies, perhaps because the gas tracer contains noncircular motions. The bar stability analysis provides a new observational test to MOND. We find that most of the galaxies under study require abnormally-high levels of random stellar motions to be bar stable in MOND. In particular, for the only galaxy in the sample for which the line-of-sight stellar velocity ...
Milgrom, Mordehai
2016-01-01
I derive a new MOND relation for pure-disc galaxies: The `dynamical' central surface density, $\\Sigma^0_D$, deduced from the measured velocities, is a universal function of only the true, `baryonic' central surface density, $\\Sigma^0_B$: $\\Sigma^0_D=\\Sigma_M \\mathcal{S}(\\Sigma^0_B/\\Sigma_M)$, where $\\Sigma_M\\equiv a_0/2\\pi G$ is the MOND surface density constant. This surprising result is shown to hold in both existing, nonrelativistic MOND theories (the nonlinear Poisson formulation, and QUMOND). $\\mathcal{S}(y)$ is derived, giving in the two limits: $\\Sigma^0_D=\\Sigma^0_B$ for very high arguments, and $\\Sigma^0_D=(4\\Sigma_M\\Sigma^0_B)^{1/2}$ for $\\Sigma^0_B/\\Sigma_M\\ll 1$. This study was prompted by the recent finding of a correlation between related attributes in a large sample of disc galaxies by Lelli et al. (2016). The MOND relation is shown to agree very well with these results.
Lujan, Richard E.
2001-01-01
A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.
Reichhardt, Tony
1994-03-01
Mariner 10 traveled to Mercury by using Venus' gravity to bend its course in toward the sun, a correction that would otherwise required vast amounts of rocket fuel. For the first time, an interplanetary spacecraft changed course not with rocket fuel but by using a planet's gravitational field. That maneuver stands, along with the development of the rocket engine, as one of the keys that opened the solar system for exploration. The Pioneer, Voyager, and Galileo missions all used gravity assist, and in fact would not have been possible otherwise. Gravity assist is the most efficient form of space propulsion known. Various aspects of the developmental history of the gravity assist technique and the dispute over who should receive credit for inventing the technique are discussed.
Determining Cosmology for a Nonlocal Realization of MOND
Kim, M; Sayeb, M; Tan, L; Woodard, R P; Xu, B
2016-01-01
We numerically determine the cosmological branch of the free function in a nonlocal metric-based modification of gravity which provides a relativistic generalization of Milgrom's Modified Newtonian Dynamics. Although we are not able to get exact agreement with $\\Lambda$CDM cosmology for the range $0 \\leq z < 0.0880$ the deviation is interesting in that it makes the current value of the Hubble parameter about 4.5% larger than in the $\\Lambda$CDM model. This may resolve the tension between inferences of $H_0$ which are based on data from large redshift and inferences based on Hubble plots.
THE GLOBULAR CLUSTER NGC 2419: A CRUCIBLE FOR THEORIES OF GRAVITY
International Nuclear Information System (INIS)
We present the analysis of a kinematic data set of stars in the globular cluster NGC 2419, taken with the DEep Imaging Multi-Object Spectrograph at the Keck II telescope. Combined with a reanalysis of deep Hubble Space Telescope and Subaru Telescope imaging data, which provide an accurate luminosity profile of the cluster, we investigate the validity of a large set of dynamical models of the system, which are checked for stability via N-body simulations. We find that isotropic models in either Newtonian or Modified Newtonian Dynamics (MOND) are ruled out with extremely high confidence. However, a simple Michie model in Newtonian gravity with anisotropic velocity dispersion provides an excellent representation of the luminosity profile and kinematics of the cluster. The anisotropy profiles of these models ensure an isotropic center to the cluster, which progresses to extreme radial anisotropy toward the outskirts. In contrast, with MOND we find that Michie models that reproduce the luminosity profile either overpredict the velocity dispersion on the outskirts of the cluster if the mass-to-light ratio (M/L) is kept at astrophysically motivated values or else they underpredict the central velocity dispersion if the M/L is taken to be very small. We find that the best Michie model in MOND is a factor of ∼104 less likely than the Newtonian model that best fits the system. A likelihood ratio of 350 is found when we investigate more general models by solving the Jeans equation with a Markov Chain Monte Carlo scheme. We verified with N-body simulations that these results are not significantly different when the MOND external field effect is accounted for. If the assumptions that the cluster is in dynamical equilibrium, spherical, not on a peculiar orbit, and possesses a single dynamical tracer population of constant M/L are correct, we conclude that the present observations provide a very severe challenge for MOND.
Institute of Scientific and Technical Information of China (English)
刘海军; 陈国庆
2006-01-01
利用向量泛函的不变凸性,改进了Mond-Weir型对偶,给出并证明了弱对偶定理和强对偶定理.%An improved Mond-Weir type dual for a class of multiobjective optimal control problems is constructed. Under vector functional invexity assumption, a number of weak and strong duality theorems are given and proved.
Mond-Weir duality for a class of multiobjective semi-infinite programming%一类多目标半无限规划的Mond-Weir型对偶
Institute of Scientific and Technical Information of China (English)
王荣波; 冯强
2012-01-01
在广义一致局部连通凸函数的约束下,讨论了一类多目标半无限规划的Mond-Weir型对偶,得到了相应的弱对偶、强对偶和逆对偶定理.%Some weak duality, strong duality and converse duality theorems of Mond-Weir for the multiobjective semi-infnite programming are given under the generalized uniform locally connected functions.
Celada, Mariano; Montesinos, Merced
2016-01-01
$BF$ gravity comprises all the formulations of gravity that are based on deformations of $BF$ theory. Such deformations consist of either constraints or potential terms added to the topological $BF$ action that turn some of the gauge degrees of freedom into physical ones, particularly giving rise to general relativity. The $BF$ formulations have provided new and deep insights into many classical and quantum aspects of the gravitational field, setting the foundations for the approach to quantum gravity known as spinfoam models. In this review, we present a self-contained and unified treatment of the $BF$ formulations of $D$-dimensional general relativity and other related models, focusing on the classical aspects of them and including some new results.
Celada, Mariano; González, Diego; Montesinos, Merced
2016-11-01
BF gravity comprises all the formulations of gravity that are based on deformations of BF theory. Such deformations consist of either constraints or potential terms added to the topological BF action that turn some of the gauge degrees of freedom into physical ones, particularly giving rise to general relativity. The BF formulations have provided new and deep insights into many classical and quantum aspects of the gravitational field, setting the foundations for the approach to quantum gravity known as spinfoam models. In this review, we present a self-contained and unified treatment of the BF formulations of D-dimensional general relativity and other related models, focusing on the classical aspects of them and including some new results.
Quantitative Shisha—Mond Type Theorem of Probability Expression of （C0） Semigroups of Operators
Institute of Scientific and Technical Information of China (English)
陈文忠; 曾晓明
1993-01-01
In this paper we set up quanttative shisha-Mond type theorem of probability expression of (C0)-semigroup of opertors and we give an example by introducing S-λ probability distribution to ob-tain corresponding quantitative estimation.
Davis, Hyman R.; Long, R. H.; Simone, A. A.
1979-01-01
Solids are separated from a liquid in a gravity settler provided with inclined solid intercepting surfaces to intercept the solid settling path to coalesce the solids and increase the settling rate. The intercepting surfaces are inverted V-shaped plates, each formed from first and second downwardly inclined upwardly curved intersecting conical sections having their apices at the vessel wall.
Pipinos, Savas
2010-01-01
This article describes one classroom activity in which the author simulates the Newtonian gravity, and employs the Euclidean Geometry with the use of new technologies (NT). The prerequisites for this activity were some knowledge of the formulae for a particle free fall in Physics and most certainly, a good understanding of the notion of similarity…
Newton's second law versus modified-inertia MOND: A test using the high-latitude effect
International Nuclear Information System (INIS)
The modified-inertia MOND is an approach that proposes a change in Newton's second law at small accelerations as an alternative to dark matter. Recently it was suggested that this approach can be tested in terrestrial laboratory experiments. One way of doing the test is based on the static high-latitude equinox modified-inertia effect: around each equinox date, 2 spots emerge on the Earth where static bodies experience spontaneous displacement due to the violation of Newton's second law required by the modified-inertia MOND. Here, a detailed theory of this effect is developed and estimates of the magnitude of the signal due to the effect are obtained. The expected displacement of a mirror in a gravitational-wave interferometer is found to be about 10-14 m. Some experimental aspects of the proposal are discussed
New Physics at Low Accelerations (MOND): an Alternative to Dark Matter
Milgrom, Mordehai
2009-01-01
I describe the MOND paradigm, which posits a departure from standard physics below a certain acceleration scale. This acceleration as deduced from the dynamics in galaxies is found mysteriously to agree with the cosmic acceleration scales defined by the present day expansion rate and by the density of `dark energy'. I put special emphasis on phenomenology and on critical comparison with the competing paradigm based on classical dynamics plus cold dark matter. I also describe briefly nonrelati...
La faim et la sécurité alimentaire dans le monde (extrait)
SERAGELDIN, Ismail
2011-01-01
Ismail Serageldin, Économiste en éducation et ressources humaines, directeur de la Bibliothèque d’Alexandrie, a donné sa leçon inaugurale le 18 novembre 2010. Son cours intitulé « La faim et la sécurité alimentaire dans le monde » commençera le 5 janvier 2011.
Low-mass disc galaxies and the issue of stability: MOND vs dark matter
Sanchez-Salcedo, F. J.; Martinez-Gomez, E. (Estrella); Aguirre-Torres, V. M.; Hernandez-Toledo, H. M.
2016-01-01
We analyse the rotation curves and gravitational stability of a sample of six bulgeless galaxies for which detailed images reveal no evidence for strong bars. We explore two scenarios: Newtonian dark matter models and MOdified Newtonian Dynamics (MOND). By adjusting the stellar mass-to-light ratio, dark matter models can match simultaneously both the rotation curve and bar-stability requirements in these galaxies. To be consistent with stability constraints, in two of these galaxies, the stel...
N-body simulations of the Carina dSph in MOND
Angus, G. W.; Gentile, G.; Diaferio, A.; Famaey, B.; van der Heyden, K. J.
2014-05-01
The classical dwarf spheroidals (dSphs) provide a critical test for Modified Newtonian Dynamics (MOND) because they are observable satellite galactic systems with low internal accelerations and low, but periodically varying, external acceleration. This varying external gravitational field is not commonly found acting on systems with low internal acceleration. Using Jeans modelling, Carina in particular has been demonstrated to require a V-band mass-to-light ratio greater than 5, which is the nominal upper limit for an ancient stellar population. We run MOND N-body simulations of a Carina-like dSph orbiting the Milky Way to test if dSphs in MOND are stable to tidal forces over the Hubble time and if those same tidal forces artificially inflate their velocity dispersions and therefore their apparent mass-to-light ratio. We run many simulations with various initial total masses for Carina and Galactocentric orbits (consistent with proper motions), and compare the simulation line-of-sight velocity dispersions (losVDs) with the observed losVDs of Walker et al. We find that the dSphs are stable, but that the tidal forces are not conducive to artificially inflating the losVDs. Furthermore, the range of mass-to-light ratios that best reproduces the observed losVDs of Carina is 5.3 to 5.7 and circular orbits are preferred to plunging orbits. Therefore, some tension still exists between the required mass-to-light ratio for the Carina dSph in MOND and those expected from stellar population synthesis models. It remains to be seen whether a careful treatment of the binary population or triaxiality might reduce this tension.
Clewett, Paul
2016-01-01
New volume Just Work? Migrant Workers’ Struggles Today , edited by Aziz Choudry and Mondli Hlatshwayo, gives a platform to the struggles of migrant workers propping up economies in the Global North and South through grounded, optimistic analysis built on first-hand experience. Paul Clewett finds this collection both a fascinating read and a welcome antidote to migration scholarship that has hitherto disproportionately focused on the West.
Global deep-MOND parameter as a theory discriminant.
Milgrom, Mordehai
2012-12-21
Different formulations of modified Newtonian dynamics predict somewhat different rotation curves for the same mass distribution. Here I consider a global attribute of the rotation curve that might provide a convenient discriminant between theories when applied to isolated, pure-disk galaxies that are everywhere deep in the modified Newtonian dynamics regime. This parameter is Q ≡ V(2)/V(∞)(2), where V(2) ≡ M(-1)∫ 2πrΣ(r)V(2)(r)dr, with Σ(r) the disk's surface density, M its total mass, and V∞ the asymptotic (constant) rotational speed. The comparison between the observed and predicted values of Q is oblivious to the distance, the inclination, the mass, and the size of the disk, and to the form of the interpolating function. For the known modified-gravity theories Q is predicted to be a universal constant [independent of Σ(r)]: Q = 2/3. The predicted Q value for modified-inertia theories does depend on the form of Σ. However, surprisingly, I find here that it varies only little among a very wide range of mass distributions, Q ≈ 0.73 ± 0.01. While the difference between the theories amounts to only about 5% in the predicted rms velocity, a good enough sample of galaxies may provide the first discerning test between the two classes of theories. PMID:23368445
The Newtonian and MOND Dynamical Models of NGC 5128: Investigation of the Dark Matter Contribution
Samurović, S.
2016-06-01
We study the well-known nearby early-type galaxy NGC~5128 (Centaurus A) and use the sample of its globular clusters to analyze its dynamics. We study both Newtonian and MOND models assuming three cases of orbital anisotropies: isotropic case, mildly tangentially anisotropic case and the radially anisotropic case based on the literature. We find that there are two regions with different values of the velocity dispersion: interior to ˜ 3 effective radii the value of the velocity dispersion is approximately 150 km/s, whereas beyond ˜ 3 effective radii its value increases to approximately 190 km/s, thus implying the increase of the total cumulative mass which is indicative of the existence of dark matter there in the Newtonian approach: the mass-to-light increases from M/L_B=7 in the inner regions to M/L_B=26 in the outer regions. We found that the Navarro-Frenk-White (NFW) model with dark halo provides good description of the dynamics of NGC~5128. Using three MOND models (standard, simple and toy), we find that they all provide good fits to the velocity dispersion of NGC~5128 and that no additional dark component is needed in MOND.
Multivers mondes possibles de l'astrophysique, de la philosophie et de l'imaginaire
Barrau, Aurélien; Kistler, Max; Uzan, Jean-Philippe
2010-01-01
Et si notre Univers n'était qu un parmi d'autres ? Cette idée d'univers multiples, qui est envisagée depuis l'Antiquité, n'est entrée que récemment - et avec fracas - dans le champ de la science. Si l'hypothèse fascine, elle n'en est pas moins dérangeante : comment se formeraient ces mondes invisibles ? Auraient-ils les mêmes lois physiques ? Peut-on tester et réfuter leur existence ? Une telle hypothèse est-elle vraiment scientifique ? Faut-il en rester aux critères de scientificité traditionnels ou ouvrir la porte aux mondes possibles de l'astrophysique, de la philosophie et de l'imaginaire ? Un cosmologiste, un physicien théoricien, un philosophe et un historien de la science-fiction nous invitent à nous immerger au coeur de la physique théorique, à révolutionner la manière de concevoir ce qu'est une théorie physique signifiante, à extrapoler les lois de la nature pour décrire d'autres univers. Ils nous montrent qu'il y a une multiplicité de «manières de faire des mondes» et que n...
The Newtonian and MOND dynamical models of NGC 5128: Investigation of the dark matter contribution
Directory of Open Access Journals (Sweden)
Samurović S.
2016-01-01
Full Text Available We study the well-known nearby early-type galaxy NGC 5128 (Centaurus A and use the sample of its globular clusters to analyze its dynamics. We study both Newtonian and MOND models assuming three cases of orbital anisotropies: isotropic case, mildly tangentially anisotropic case and the radially anisotropic case based on the literature. We find that there are two regions with different values of the velocity dispersion: interior to ~ 3 effective radii the value of the velocity dispersion is approximately 150 km s−1 , whereas beyond ~ 3 effective radii its value increases to approximately 190 km s−1 , thus implying the increase of the total cumulative mass which is indicative of the existence of dark matter there in the Newtonian approach: the mass-to-light increases from M/LB = 7 in the inner regions to M/LB = 26 in the outer regions. We found that the Navarro-Frenk-White (NFW model with dark halo provides good description of the dynamics of NGC 5128. Using three MOND models (standard, simple and toy, we find that they all provide good fits to the velocity dispersion of NGC 5128 and that no additional dark component is needed in MOND. [Projekat Ministarstva nauke Republike Srbije, br. 176021: Visible and Invisible Matter in Nearby Galaxies: Theory and Observations
MOND and IMF variations in early-type galaxies from $\\rm ATLAS^{3D}$
Tortora, C; Cardone, V F; Napolitano, N R; Jetzer, Ph
2013-01-01
MOdified Newtonian dynamics (MOND) represents a phenomenological alternative to dark matter (DM) for the missing mass problem in galaxies and clusters of galaxies. We analyze the central regions of a local sample of $\\sim 220$ early-type galaxies from the $\\rm ATLAS^{3D}$ survey, to see if the data can be reproduced without recourse to DM. We estimate dynamical masses in the MOND context through Jeans analysis, and compare to $\\rm ATLAS^{3D}$ stellar masses from stellar population synthesis. We find that the observed stellar mass--velocity dispersion relation is steeper than expected assuming MOND with a fixed stellar initial mass function (IMF) and a standard value for the acceleration parameter $a_{\\rm 0}$. Turning from the space of observables to model space, a) fixing the IMF, a universal value for $a_{\\rm 0}$ cannot be fitted, while, b) fixing $a_{\\rm 0}$ and leaving the IMF free to vary, we find that it is "lighter" (Chabrier-like) for low-dispersion galaxies, and "heavier" (Salpeter-like) for high disp...
N-body simulations of the Carina dSph in MOND
Angus, Garry W; Diaferio, Antonaldo; Famaey, Benoit; van der Heyden, Kurt J
2014-01-01
The classical dwarf spheroidals (dSphs) provide a critical test for Modified Newtonian Dynamics (MOND) because they are observable satellite galactic systems with low internal accelerations and low, but periodically varying, external acceleration. This varying external gravitational field is not commonly found acting on systems with low internal acceleration. Using Jeans modelling, Carina in particular has been demonstrated to require a V-band mass-to-light ratio greater than 5, which is the nominal upper limit for an ancient stellar population. We run MOND N-body simulations of a Carina-like dSph orbiting the Milky Way to test if dSphs in MOND are stable to tidal forces over the Hubble time and if those same tidal forces artificially inflate their velocity dispersions and therefore their apparent mass-to-light ratio. We run many simulations with various initial total masses for Carina, and Galactocentric orbits (consistent with proper motions), and compare the simulation line of sight velocity dispersions (l...
Pitts, J. Brian
2016-02-01
What if gravity satisfied the Klein-Gordon equation? Both particle physics from the 1920-30s and the 1890s Neumann-Seeliger modification of Newtonian gravity with exponential decay suggest considering a "graviton mass term" for gravity, which is algebraic in the potential. Unlike Nordström's "massless" theory, massive scalar gravity is strictly special relativistic in the sense of being invariant under the Poincaré group but not the 15-parameter Bateman-Cunningham conformal group. It therefore exhibits the whole of Minkowski space-time structure, albeit only indirectly concerning volumes. Massive scalar gravity is plausible in terms of relativistic field theory, while violating most interesting versions of Einstein's principles of general covariance, general relativity, equivalence, and Mach. Geometry is a poor guide to understanding massive scalar gravity(s): matter sees a conformally flat metric due to universal coupling, but gravity also sees the rest of the flat metric (barely or on long distances) in the mass term. What is the 'true' geometry, one might wonder, in line with Poincaré's modal conventionality argument? Infinitely many theories exhibit this bimetric 'geometry,' all with the total stress-energy's trace as source; thus geometry does not explain the field equations. The irrelevance of the Ehlers-Pirani-Schild construction to a critique of conventionalism becomes evident when multi-geometry theories are contemplated. Much as Seeliger envisaged, the smooth massless limit indicates underdetermination of theories by data between massless and massive scalar gravities-indeed an unconceived alternative. At least one version easily could have been developed before General Relativity; it then would have motivated thinking of Einstein's equations along the lines of Einstein's newly re-appreciated "physical strategy" and particle physics and would have suggested a rivalry from massive spin 2 variants of General Relativity (massless spin 2, Pauli and Fierz
Stochastic gravity: beyond semiclassical gravity
Energy Technology Data Exchange (ETDEWEB)
Verdaguer, E [Departament de Fisica Fonamental and CER en Astrofisica, Fisica de Particules i Cosmologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona (Spain)
2007-05-15
The back-reaction of a classical gravitational field interacting with quantum matter fields is described by the semiclassical Einstein equation, which has the expectation value of the quantum matter fields stress tensor as a source. The semiclassical theory may be obtained from the quantum field theory of gravity interacting with N matter fields in the large N limit. This theory breaks down when the fields quantum fluctuations are important. Stochastic gravity goes beyond the semiclassical limit and allows for a systematic and self-consistent description of the metric fluctuations induced by these quantum fluctuations. The correlation functions of the metric fluctuations obtained in stochastic gravity reproduce the correlation functions in the quantum theory to leading order in an 1/N expansion. Two main applications of stochastic gravity are discussed. The first, in cosmology, to obtain the spectrum of primordial metric perturbations induced by the inflaton fluctuations, even beyond the linear approximation. The second, in black hole physics, to study the fluctuations of the horizon of an evaporating black hole.
Clifton, T; Barrow, John D.
2006-01-01
We consider the possibility of energy being exchanged between the scalar and matter fields in scalar-tensor theories of gravity. Such an exchange provides a new mechanism which can drive variations in the gravitational 'constant' G. We find exact solutions for the evolution of spatially flat Friedman-Roberston-Walker cosmologies in this scenario and discuss their behaviour at both early and late times.
International Nuclear Information System (INIS)
We consider the possibility of energy being exchanged between the scalar and matter fields in scalar-tensor theories of gravity. Such an exchange provides a new mechanism which can drive variations in the gravitational 'constant' G. We find exact solutions for the evolution of spatially flat Friedmann-Robertson-Walker cosmologies in this scenario and discuss their behavior at both early and late times. We also consider the physical consequences and observational constraints on these models
Motion in alternative theories of gravity
Esposito-Farese, Gilles
2009-01-01
Although general relativity (GR) passes all present experimental tests with flying colors, it remains important to study alternative theories of gravity for several theoretical and phenomenological reasons that we recall in these lecture notes. The various possible ways of modifying GR are presented, and we notably show that the motion of massive bodies may be changed even if one assumes that matter is minimally coupled to the metric as in GR. This is illustrated with the particular case of scalar-tensor theories of gravity, whose Fokker action is discussed, and we also mention the consequences of the no-hair theorem on the motion of black holes. The finite size of the bodies modifies their motion with respect to pointlike particles, and we give a simple argument showing that the corresponding effects are generically much larger in alternative theories than in GR. We also discuss possible modifications of Newtonian dynamics (MOND) at large distances, which have been proposed to avoid the dark matter hypothesi...
National Oceanic and Atmospheric Administration, Department of Commerce — The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The...
National Oceanic and Atmospheric Administration, Department of Commerce — This data base (14,559 records) was received in January 1986. Principal gravity parameters include elevation and observed gravity. The observed gravity values are...
THE MASSIVE ELLIPTICAL GALAXY NGC 4649 FROM THE PERSPECTIVE OF EXTENDED GRAVITY
Energy Technology Data Exchange (ETDEWEB)
Jimenez, M. A.; Garcia, G.; Hernandez, X. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-264 C.P. 04510 Mexico D.F. (Mexico); Nasser, L., E-mail: mjimenez@astro.unam.mx [Department of Science and Mathematics, Columbia College, Chicago, 1L 60605 (United States)
2013-05-10
Elliptical galaxies are systems where dark matter is usually less necessary to explain observed dynamics than in the case of spiral galaxies; however, there are some instances where Newtonian gravity and the observable mass are insufficient to explain their observed structure and kinematics. Such is the case of NGC 4649, a massive elliptical galaxy in the Virgo cluster for which recent studies report a high fraction of dark matter, 0.78 at 4 R{sub e} . However, this galaxy has been studied within the MOdified Newtonian Dynamics (MOND) hypothesis, where a good agreement with the observed values of velocity dispersion is found. Using a MONDian gravity force law, here we model this galaxy as a self-consistent gravitational equilibrium dynamical system. This force law reproduces the MOND phenomenology in the a < a{sub 0} regime, and reduces to the Newtonian case when a > a{sub 0}. Within the MONDian a < a{sub 0} scales, centrifugal equilibrium or dispersion velocities become independent of radius, and show a direct proportionality to the fourth root of the total baryonic mass, V {sup 4}{proportional_to}(MGa{sub 0}). We find that the recent detailed observations of the surface brightness profile and the velocity dispersion profile for this galaxy are consistent with the phenomenology expected in MONDian theories of modified gravity, without the need to invoke the presence of any hypothetical dark matter.
Institute of Scientific and Technical Information of China (English)
高颖; 张庆祥
2011-01-01
(p,r)h,ψ-invex and strictly (p,r)h,ψ-invex function were defined. So,the Mond-Weir duality of mul-tiobjective programming are obtained by applying (p,r)-η Invex.%在(p,r)-η不变凸函数的基础上定义了(p,r)h,φ-不变凸函数及严格(p,r)h,φ-不变凸函数的概念,并在此基础上得到了多目标规划的Mond-Weir型对偶性.
Rojas-Niño, Armando; Pichardo, Barbara; Valenzuela, Octavio
2015-01-01
Recent studies have presented evidence that the Milky Way global potential may be nonspherical. In this case, the assembling process of the Galaxy may have left long lasting stellar halo kinematic fossils due to the shape of the dark matter halo, potentially originated by orbital resonances. We further investigate such possibility, considering now potential models further away from $\\Lambda$CDM halos, like scalar field dark matter halos, MOND, and including several other factors that may mimic the emergence and permanence of kinematic groups, such as, a spherical and triaxial halo with an embedded disk potential. We find that regardless of the density profile (DM nature), kinematic groups only appear in the presence of a triaxial halo potential. For the case of a MOND like gravity theory no kinematic structure is present. We conclude that the detection of these kinematic stellar groups could confirm the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.
STRES PRI ZAPOSLENIH NA ODDELKU IGRALNIH MIZ V PODJETJU IZC MOND
Cvetko, Aleksandra
2016-01-01
V diplomskem delu smo obravnavali zelo aktualno temo današnjega časa, stres. Omejili smo se na stres pri zaposlenih na oddelku igralnih miz v Igralniško zabaviščnem centru Mond, ki je poslovna enota družbe Hit d.d.Večina ljudi se sreča s stresom tekom dneva in/ali na delovnem mestu. Nanj smo se navadili in ga pogosto sprejemamo kot samoumevnega. Vendar nam stres lahko povzroča velike zdravstvene težave. Šeke, ko se stresa zavedamo, se lahko lotimo njegovega obvladovanja oziroma premagovanja. ...
Marguerite Yourcenar’s Le Labyrinthe du Monde: autobiography of an absent self?
Directory of Open Access Journals (Sweden)
E. Snyman
2000-05-01
Full Text Available Marguerite Yourcenar’s autobiography Le Labyrinthe du monde surprised readers by its lack of self-representation and by being mainly a lengthy exploration of the genealogy of her ancestors. This article pursues the hypothesis that although Yourcenar is considered an autonomous creator, uninfluenced by the Parisian avant-garde of the sixties and seventies, certain aspects of her practice of self-representation draw on a new approach to historiography of which Michel Foucault, for example, was one of the earliest practitioners.
Gravity and Mirror Gravity in Plebanski Formulation
Bennett, D. L.; Laperashvili, L. V.; Nielsen, H. B.; Tureanu, A.
2012-01-01
We present several theories of four-dimensional gravity in the Plebanski formulation, in which the tetrads and the connections are the independent dynamical variables. We consider the relation between different versions of gravitational theories: Einstenian, dual, 'mirror' gravities and gravity with torsion. According to Plebanski's assumption, our world, in which we live, is described by the self-dual left-handed gravity. We propose that if the Mirror World exists in Nature, then the 'mirror...
Magueijo, J; Magueijo, Joao; Smolin, Lee
2004-01-01
Non-linear special relativity (or doubly special relativity) is a simple framework for encoding properties of flat quantum space-time. In this paper we show how this formalism may be generalized to incorporate curvature (leading to what might be called ``doubly general relativity''). We first propose a dual to non-linear realizations of relativity in momentum space, and show that for such a dual the space-time invariant is an energy-dependent metric. This leads to an energy-dependent connection and curvature, and a simple modification to Einstein's equations. We then examine solutions to these equations. We find the counterpart to the cosmological metric, and show how cosmologies based upon our theory of gravity may solve the ``horizon problem''. We discuss the Schwarzchild solution, examining the conditions for which the horizon is energy dependent. We finally find the weak field limit.
Lombard, John
2016-01-01
We introduce the construction of a new framework for probing discrete emergent geometry and boundary-boundary observables based on a fundamentally a-dimensional underlying network structure. Using a gravitationally motivated action with Forman weighted combinatorial curvatures and simplicial volumes relying on a decomposition of an abstract simplicial complex into realized embeddings of proper skeletons, we demonstrate properties such as a minimal volume-scale cutoff, the necessity of a positive-definite cosmological constant as a regulator for non-degenerate geometries, and naturally emergent simplicial structures from Metropolis network evolution simulations with no restrictions on attachment rules or regular building blocks. We see emergent properties which echo results from both the spinfoam formalism and causal dynamical triangulations in quantum gravity, and provide analytical and numerical results to support the analogy. We conclude with a summary of open questions and intent for future work in develop...
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.
Le corps, instrument de connaissance du monde: la connaissance des Anciens Toltèques
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Mabel Franzone
2009-10-01
Full Text Available Cet article traite le corps comme instrument de la connaissance de l’univers. Le corps s’étend vers des contrées infinies, se prolonge, atteint d’autres règnes, cherche l’unité absolue de ce qu’on appelle l’intention. L’intention est le mot clé pour les Anciens Toltèques, réunissant sous ce mot le visible et l’invisible, la volonté de la Nature et celle de l’univers. Le corps n’est qu’un instrument et pour arriver à le parfaire devons chercher la totalité de nous-mêmes, réussir la communication de deux côtés, droit et gauche, aller à la quête d’autres expériences, inimaginables. Les conditions nécessaires sont d’avoir un corps puissant et d’emmagasiner de l’énergie. Tout l’enseignement des sorciers est fondé dans un vrai changement de conception du monde et de la perception de ce monde. L’objectif final est celui de pouvoir choisir sa propre mort ; la vraie, la seule, l’unique liberté de l’homme.
Ultra-diffuse cluster galaxies as key to the MOND cluster conundrum
Milgrom, Mordehai
2015-01-01
MOND reduces greatly the mass discrepancy in clusters of galaxies, but does leave a consistent global discrepancy of about a factor of two. It has been proposed, within the minimalist and purist MOND, that clusters harbor some indigenous, yet-undetected, cluster baryonic (dark) matter (CBDM). Its total amount has to be comparable with that of the observed hot gas. Following an initial discovery by van Dokkum & al. (2015a), Koda & al. (2015) have recently identified more than a thousand ultra-diffuse galaxy-like objects (UDGs) in the Coma cluster. Robustness of the UDGs to tidal disruption seems to require, within Newtonian dynamics, that they are much more massive than their observed stellar component. Here, I propound that a considerable fraction of the CBDM is internal to UDGs, which endows them with robustness. The rest of the CBDM objects formed in now-disrupted kin of the UDGs, and is dispersed in the intracluster medium. While the discovery of cluster UDGs is not in itself a resolution of the MO...
Vegetation Mapping of the Mond Protected Area of Bushehr Province (South-west Iran)
Institute of Scientific and Technical Information of China (English)
Ahmadreza Mehrabian; Alireza Naqinezhad; Abdolrassoul Salman Mahiny; Hossein Mostafavi; Homan Liaghati; Mohsen Kouchekzadeh
2009-01-01
Add regions of the wodd occupy up to 35% of the earth's surface, the basis of various definitions of climatic conditions,vegetation types or potential for food production. Due to their high ecological value, monitoring of add regions is necessary and modem vegetation studies can help in the conservation and management of these areas. The use of remote sensing for mapping of desert vegetation is difficult due to mixing of the spectral reflectance of bright desert soils with the weak spectral response of sparse vegetation. We studied the vegetation types in the semiarid to arid region of Mond Protected Area, south-west Iran, based on unsupervised classification of the Spot XS bands and then produced updated maps.Sixteen map units covering t2 vegetation types were recognized in the area based on both field works and satellite mapping. Halocnemum strobilaceum and Suaeda fruticosa vegetation types were the dominant types and Ephedra foliata,Salicornia europaaa-Suaeda heterophylla vegetation types were the smallest. Vegetation coverage decreased sharply with the increase in salinity towards the coastal areas of the Persian Gulf. The highest vegetation coverage belonged to the riparian vegetation along the Mond River, which represents the northern boundary of the protected area. The location of vegetation types was studied on the separate soil and habitat diversity maps of the study area, which helped in final refinements of the vegetation map produced.
Agriculture : comment se nourrira un monde réchauffé ?
Directory of Open Access Journals (Sweden)
Sébastien Treyer
2015-01-01
Full Text Available La sécurité alimentaire a été replacée très haut sur l’agenda international depuis les crises alimentaires de 2008. Les systèmes agricoles seront-ils en mesure de répondre à l’augmentation de la demande alimentaire, dans un monde aux ressources limitées soumis au changement climatique ? Cette question est au cœur de controverses très actives entre modèles techniques et politiques contrastés pour la prochaine modernisation agricole. Le pari stratégique sur la forme la plus pertinente de transformation du secteur alimentaire s’instruit de manière très spécifique dans chaque grande région du monde, et il importe de mettre en place les conditions d’un processus d’apprentissage global entre ces différentes expérimentations nationales ou régionales. Comment laisser aux Etats la capacité de décider de la trajectoire de transformation la plus adaptée, dans un contexte d’inévitable accroissement des échanges commerciaux agricoles entre grandes régions ?
The shape of `dark matter' haloes of disc galaxies according to MOND
Milgrom, Mordehai
2001-10-01
Analyses of halo shapes for disc galaxies are said to give conflicting results. I point out that the modified dynamics (MOND) predicts for disc galaxies a distribution of fictitious dark matter that comprises two components: a pure disc and a rounder halo. The former dominates the true disc in regions of small accelerations, where it controls the z-dynamics in the disc (disc flaring etc.); it has a finite total mass. It also dominates the round component near the centre where the geometry is nearly planar. The second component controls motions far from the plane, has a total enclosed mass that diverges linearly with radius, and determines the rotation curve at large radii. Its ellipticity may be appreciable at small radii but vanishes asymptotically. This prediction of MOND differs from what one expects from galaxy formation scenarios with dark matter. Analyses to date, which, as they do, assume one component - usually with a constant ellipticity - perforce give conflicting results for the best value of ellipticity, depending on whether they probe the disc or the sphere, small radii or large ones.
Objectif Express 1 le monde professionnel en français A1/A2
Tauzin, Béatrice
2013-01-01
Avec un nouveau look et des contenus actualisés pour prendre en compte les évolutions du monde de l’entreprise française, la nouvelle édition d'Objectif Express 1 propose une parfaite association entre le français de tous les jours et le français de l'entreprise. 10 unités basées sur des thématiques de l'entreprise : Entrez en contact ; Organisez votre journée ; Trouvez un emploi ... Chaque unité propose : - 4 leçons d'apprentissage (1 leçon = 1 double page) basées sur des tâches concrètes et simples, ancrées dans le monde du travail francophone - 1 double page Outils linguistiques - 1 page Entrainez-vous - 1 page Testez-vous - 2 pages Repères dans chaque unité : des repères culturels et des repères professionnels Toutes les 3 unités, un scénario professionnel pour une mise en œuvre des acquis langagiers et une mobilisation des compétences professionnelles de l'apprenant. Une préparation aux diplômes DFP A2, DELF Pro A1 et A2 et au test BULATS En annexes : des tableaux d...
Cosmological variation of the MOND constant: secular effects on galactic systems
Milgrom, Mordehai
2014-01-01
The proximity of the MOND acceleration constant with cosmological accelerations -- for example, a0~ cH0/2pi -- points to its possibly decreasing with cosmic time. I begin to consider the secular changes induced in galactic systems by such presumed variations, assumed adiabatic. It is important to understand these effects, in isolation from other evolutionary influences, in order to identify or constrain a0 variations by detection of induced effects, or lack thereof. I find that as long as the system is fully in the deep-MOND regime -- as applies to many galactic systems -- the adiabatic response of the system obeys simple scaling laws. For example, in a system that would be stationary for fixed a0, the system expands homologously as a0^{-1/4}, while internal velocities decrease uniformly as a0^{1/4}. If a0 is proportional to cH at all relevant times, this change amounts to a factor of ~ 2.5 since redshift 10. For a system stationary in a rotating frame, the angular frequency decreases as a0^{1/2}. The acceler...
Lineal gravity from planar gravity
Achúcarro, A
1993-01-01
We show how to obtain the two-dimensional black hole action by dimensional reduction of the three-dimensional Einstein action with a non-zero cosmological constant. Starting from the Chern-Simons formulation of 2+1 gravity, we obtain the 1+1 dimensional gauge formulation given by Verlinde. Remarkably, the proposed reduction shares the relevant features of the formulation of Cangemi and Jackiw, without the need for a central charge in the algebra. We show how the Lagrange multipliersin these formulations appear naturally as the remnants of the three dimensional connection associated to symmetries that have been lostin the dimensional reduction. The proposed dimensional reduction involves a shift in the three dimensional connection whose effect is to make the length of the extra dimension infinite.
Institute of Scientific and Technical Information of China (English)
邹水木; 惠晓娣
2004-01-01
本文研究具有Fuzzy约束的非光滑Fuzzy多目标规划(FVP),利用分明多目标规划建立了(FVP)的Mond-Weir型对偶模型,得到了Fuzzy有效解的弱对偶、直接对偶和逆对偶定理.
Institute of Scientific and Technical Information of China (English)
马丽; 王其林; 解军; 胡晓丽
2013-01-01
Abstr act:A second-order Mond-Weir type dual of constrained set-valued optimization problem is discussed . Firstly, a new property of the generalized second-order composed contingent epiderivative is obtained .Secondly, by employing the generalized second-order composed contingent epiderivatives ,a second-order Mond-Weir type dual of constrained set-valued optimization problem is introduced,and the corresponding weak duality , strong duality and converse duality theorems are established .% 讨论了约束集值优化问题的一类二阶Mond-Weir型对偶，获得了广义二阶合成相依上图导数的一个新的性质，利用广义二阶合成相依上图导数构建了约束集值优化问题的一类二阶Mond-Weir型对偶，并建立了相应的弱对偶、强对偶和逆对偶定理。
Oriti, Daniele
2009-03-01
Preface; Part I. Fundamental Ideas and General Formalisms: 1. Unfinished revolution C. Rovelli; 2. The fundamental nature of space and time G. 't Hooft; 3. Does locality fail at intermediate length scales R. Sorkin; 4. Prolegomena to any future quantum gravity J. Stachel; 5. Spacetime symmetries in histories canonical gravity N. Savvidou; 6. Categorical geometry and the mathematical foundations of quantum gravity L. Crane; 7. Emergent relativity O. Dreyer; 8. Asymptotic safety R. Percacci; 9. New directions in background independent quantum gravity F. Markopoulou; Questions and answers; Part II: 10. Gauge/gravity duality G. Horowitz and J. Polchinski; 11. String theory, holography and quantum gravity T. Banks; 12. String field theory W. Taylor; Questions and answers; Part III: 13. Loop Quantum Gravity T. Thiemann; 14. Covariant loop quantum gravity? E. LIvine; 15. The spin foam representation of loop quantum gravity A. Perez; 16. 3-dimensional spin foam quantum gravity L. Freidel; 17. The group field theory approach to quantum gravity D. Oriti; Questions and answers; Part IV. Discrete Quantum Gravity: 18. Quantum gravity: the art of building spacetime J. Ambjørn, J. Jurkiewicz and R. Loll; 19. Quantum Regge calculations R. Williams; 20. Consistent discretizations as a road to quantum gravity R. Gambini and J. Pullin; 21. The causal set approach to quantum gravity J. Henson; Questions and answers; Part V. Effective Models and Quantum Gravity Phenomenology: 22. Quantum gravity phenomenology G. Amelino-Camelia; 23. Quantum gravity and precision tests C. Burgess; 24. Algebraic approach to quantum gravity II: non-commutative spacetime F. Girelli; 25. Doubly special relativity J. Kowalski-Glikman; 26. From quantum reference frames to deformed special relativity F. Girelli; 27. Lorentz invariance violation and its role in quantum gravity phenomenology J. Collins, A. Perez and D. Sudarsky; 28. Generic predictions of quantum theories of gravity L. Smolin; Questions and
Einstein Gravity, Massive Gravity, Multi-Gravity and Nonlinear Realizations
Goon, Garrett; Hinterbichler, Kurt; Joyce, Austin; Trodden, Mark
2014-01-01
The existence of a ghost free theory of massive gravity begs for an interpre-tation as a Higgs phase of General Relativity. We revisit the study of massive gravity as a Higgs phase. Absent a compelling microphysical model of spontaneous symmetry breaking in gravity, we approach this problem from the viewpoint of nonlinear realizations. We employ the coset construction to search for the most restrictive symmetry breaking pattern whose low energy theory will both admit the de Rham-Gabadadze-Tol...
Is nonrelativistic gravity possible?
Kocharyan, A. A.
2009-01-01
We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (anti-)de Sitter black holes of Eins...
Linker, Patrick
2016-01-01
A couple of quantum gravity theories were proposed to make theoretical predictions about the behavior of gravity. The most recent approach to quantum gravity, called E-theory, is proposed mathematical, but there is not formulated much about what dynamics of gravity this theory proposes. This research paper treats the main results of the application of E-theory to General relativity involving conservation laws and scattering of particles in presence of gravity. Also the low-energy limit of thi...
Gravity wave transmission diagram
Tomikawa, Yoshihiro
2016-07-01
A possibility of gravity wave propagation from a source region to the airglow layer around the mesopause has been discussed based on the gravity wave blocking diagram taking into account the critical level filtering alone. This paper proposes a new gravity wave transmission diagram in which both the critical level filtering and turning level reflection of gravity waves are considered. It shows a significantly different distribution of gravity wave transmissivity from the blocking diagram.
Directory of Open Access Journals (Sweden)
Helmut Hostnig
2013-03-01
Full Text Available Helmut Hostnig erläutert einfache Möglichkeiten auditiver Produktion und präsentiert medienpädagogische Vorschläge zur Realisierung eines Märchens im Radio, wobei er das chinesische Märchen "Sonne und Mond" als Beispiel wählt.
International Nuclear Information System (INIS)
It has been recently shown that the cosmic repulsion can have a highly significant influence on the motion of Magellanic Clouds (MC) in the gravitational field of Milky Way, treated in the framework of the Cold Dark Matter (CDM) halo model. However, there is an alternative to the CDM halo explanation of the rotation curves in the periphery of spiral galaxies, based on MOdified Newtonian Dynamics (MOND). Therefore, we study the role of the cosmic repulsion in the framework of the MOND theory applied to determine the MC motion. Our results demonstrate that in the MOND framework the influence of the cosmic repulsion on the motion of both Small and Large MC is also highly significant, but it is of a different character than in the framework of the CDM halo model. Moreover, we demonstrate that the MC motion in the framework of the CDM halo and MOND models is subtantially different and can serve as a test of these fundamentally different approaches to the explanation of the phenomena related to galaxies and the motion of satellite galaxies
Helmut Hostnig
2013-01-01
Helmut Hostnig erläutert einfache Möglichkeiten auditiver Produktion und präsentiert medienpädagogische Vorschläge zur Realisierung eines Märchens im Radio, wobei er das chinesische Märchen "Sonne und Mond" als Beispiel wählt.
Energy Technology Data Exchange (ETDEWEB)
Derakhshani, Kamran, E-mail: kderakhshani@iasbs.ac.ir [Institute for Advanced Studies in Basic Sciences, P. O. Box 45195-1159 Zanjan (Iran, Islamic Republic of)
2014-03-01
In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer parts of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ{sup 2} of surface brightness and velocity dispersion.
International Nuclear Information System (INIS)
In this paper, we investigate the external field effect in the context of the MOdified Newtonian Dynamics (MOND) on the surface brightness and velocity dispersion profiles of globular clusters (GCs). Using N-MODY, which is an N-body simulation code with a MOND potential solver, we show that the general effect of the external field for diffuse clusters, which obey MOND in most of their parts, is that it pushes the dynamics toward the Newtonian regime. On the other hand, for more compact clusters, which are essentially Newtonian in their inner parts, the external field is effective mainly in the outer parts of compact clusters. As a case study, we then choose the remote Galactic GC NGC 2419. By varying the cluster mass, half-light radius, and mass-to-light ratio, we aim to find a model that will reproduce the observational data most effectively, using N-MODY. We find that even if we take the Galactic external field into account, a Newtonian Plummer sphere represents the observational data better than MOND to an order of magnitude in terms of the total χ2 of surface brightness and velocity dispersion.
Energy Technology Data Exchange (ETDEWEB)
Schee, J.; Stuchlík, Z.; Petrásek, M., E-mail: jan.schee@fpf.slu.cz, E-mail: zdenek.stuchlik@fpf.slu.cz, E-mail: martin.petrasek@fpf.slu.cz [Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo nám. 13, CZ-74601 Opava (Czech Republic)
2013-12-01
It has been recently shown that the cosmic repulsion can have a highly significant influence on the motion of Magellanic Clouds (MC) in the gravitational field of Milky Way, treated in the framework of the Cold Dark Matter (CDM) halo model. However, there is an alternative to the CDM halo explanation of the rotation curves in the periphery of spiral galaxies, based on MOdified Newtonian Dynamics (MOND). Therefore, we study the role of the cosmic repulsion in the framework of the MOND theory applied to determine the MC motion. Our results demonstrate that in the MOND framework the influence of the cosmic repulsion on the motion of both Small and Large MC is also highly significant, but it is of a different character than in the framework of the CDM halo model. Moreover, we demonstrate that the MC motion in the framework of the CDM halo and MOND models is subtantially different and can serve as a test of these fundamentally different approaches to the explanation of the phenomena related to galaxies and the motion of satellite galaxies.
Dark matter via massive bigravity
Blanchet, Luc; Heisenberg, Lavinia
2015-05-01
In this work we investigate the existence of relativistic models for dark matter in the context of bimetric gravity, used here to reproduce the modified Newtonian dynamics (MOND) at galactic scales. For this purpose we consider two different species of dark matter particles that separately couple to the two metrics of bigravity. These two sectors are linked together via an internal U (1 ) vector field, and some effective composite metric built out of the two metrics. Among possible models only certain classes of kinetic and interaction terms are allowed without invoking ghost degrees of freedom. Along these lines we explore the number of allowed kinetic terms in the theory and point out the presence of ghosts in a previous model. Finally, we propose a promising class of ghost-free candidate theories that could provide the MOND phenomenology at galactic scales while reproducing the standard cold dark matter model at cosmological scales.
Polar ring galaxies as tests of gravity
Lüghausen, F; Kroupa, P; Angus, G; Combes, F; Gentile, G; Tiret, O; Zhao, H
2013-01-01
Polar ring galaxies are ideal objects with which to study the three-dimensional shapes of galactic gravitational potentials since two rotation curves can be measured in two perpendicular planes. Observational studies have uncovered systematically larger rotation velocities in the extended polar rings than in the associated host galaxies. In the dark matter context, this can only be explained through dark halos that are systematically flattened along the polar rings. Here, we point out that these objects can also be used as very effective tests of gravity theories, such as those based on Milgromian dynamics (MOND). We run a set of polar ring models using both Milgromian and Newtonian dynamics to predict the expected shapes of the rotation curves in both planes, varying the total mass of the system, the mass of the ring with respect to the host, as well as the size of the hole at the center of the ring. We find that Milgromian dynamics not only naturally leads to rotation velocities being typically higher in th...
Approches de gestion durable et démocratique des forêts dans le monde
Gareau, Priscilla
2005-01-01
La déforestation, la dégradation des écosystèmes forestiers et les moyens privilégiés pour y remédier, classés sous le terme générique de gestion durable des forêts, sont devenus des sujets importants dans l’agenda politique international depuis les vingt dernières années. Malgré les piétinements au niveau politique, diverses approches de gestion durable et démocratique des forêts ont été expérimentées à travers le monde. Cet article recense les événements politiques majeurs menant aux pour...
Antjie Krog se vertaling van Henk van Woerden se roman Een mond vol glas
Directory of Open Access Journals (Sweden)
H.P. van Coller
2002-08-01
Full Text Available Antjie Krog’s translation of Henk van Woerden’s novel Een mond vol glas (A mouth full of glass Against a historical backdrop several critical approaches to translational theory are explicated. Traditional criticism seems to imply positioning between the Source Text (ST and the Target Text (TT. A functionalist approach (as propagated among others by Snell-Hornby, Nord and Naaijkens is a descriptive rather than a normative approach that focuses almost exclusively on the ST. This approach is consequently adopted in the evaluation of Krog’s translation; yet even within this more relativistic paradigm, a comparison between ST and TT should not be evaded. In the case of Krog’s translation, this comparison leads to the identification of scores of lexical, grammatical and stylistic errors.
A novel duMond monochromator for high-resolution x-ray diffraction
International Nuclear Information System (INIS)
We discuss the optical principles behind a novel, duMond configuration, beam conditioning monochromator for high resolution X-ray diffraction. The device is capable of being switched extremely rapidly between high intensity and high resolution settings by lateral translation of the elements. It comprises two blocks of silicon each containing two beam channels oriented parallel to and at 17.65 degrees to the (011) planes. In the high intensity mode, with the beam making two asymmetric reflections in each block, the angular divergence and dispersion are comparable to that from a symmetric Ge 022 device. The high resolution setting, where the beam makes four symmetric reflections, while comparable in divergence and dispersion with the 044 Ge device, exploits both σ and π polarisations. We report on the performance of the device and show how this compares with predictions using the dynamical theory of diffraction. 11 refs., 8 figs
DuMond curved crystal spectrometer for in-beam X- and gamma-ray spectroscopy
International Nuclear Information System (INIS)
An in-beam curved crystal spectrometer facility has been installed at the SIN variable energy cyclotron. The radius of curvature is 3.15 m. Using the (110) planes of different bent quartz laminas, diffraction peaks down to Δθ = 5 arcsec FWHM are obtained. The energy resolution is thus ΔE ≅ 0.01 E2/n, where n is the diffraction order, ΔE being expressed in eV and E in keV. The spectrometer has been constructed to cover an angular range of ±100. Transitions in the range 17 to about 350 keV have so far been observed. Measurements have been performed in conventional line source DuMond geometry and in slit geometry. The instrument is being used for the high-resolution observation of X- and gamma-rays induced by proton, helium- and oxygen-ion bombardment. (orig.)
Jérôme Schmidt, Hervé Martin Delpierre, Les mondes manga
Haudot, Jonathan
2013-01-01
Après un premier ouvrage consacré aux mangas qui n’avait pas franchement convaincu, malgré d’intéressantes informations sur les logiques d’importation en France, Jérôme Schmidt revient avec un second livre sur le sujet : Les mondes manga. Collaborant, cette fois-ci, avec le réalisateur et photographe Hervé Martin Delpierre, l’auteur s’attache au manga en présentant des mangaka, des séries emblématiques et certains lieux phares de cette culture. Le tout est visuellement agencé dans une maquett...
Censures et manipulations dans les mondes ibérique et hispano-américain
Champeau, Geneviève
2014-01-01
Ce deuxième volet d’une recherche collective engagée par le CIREMIA (intégré au laboratoire Interactions Culturelles et Discursives, Université François Rabelais de Tours) fait suite à Figures de la censure dans les mondes hispanique et ibéro-américain publié en 2009 chez Indigo. Il réunit 17 articles de chercheurs français, espagnols et anglais, dont 12 sont rédigés en français et cinq en espagnol. Une bibliographie et un index onomastique complètent ce volume dédié à Marie-Aline Barrachina ...
L’âme du monde : Platon, Anaxagore, Empédocle
Karfík, Filip
2015-01-01
Y avait-il un antécédent à la conception platonicienne de l’âme du monde chez les penseurs présocratiques ? Vu l’état fragmentaire de notre corpus, il est plus prudent de se limiter à une question plus étroite : Platon lui-même signale-t-il un tel antécédent ? Deux philosophes présocratiques se prêtent à l’examen : Anaxagore et Empédocle. (1) Dans le Cratyle, Platon identifie l’Intellect anaxagoréen à « l’âme qui ordonne et maintient la nature de toutes les choses ». Dans le Phédon, il reproc...
Modified gravity without dark matter
Sanders, R H
2006-01-01
On an empirical level, the most successful alternative to dark matter in bound gravitational systems is the modified Newtonian dynamics, or MOND, proposed by Milgrom. Here I discuss the attempts to formulate MOND as a modification of General Relativity. I begin with a summary of the phenomenological successes of MOND and then discuss the various covariant theories that have been proposed as a basis for the idea. I show why these proposals have led inevitably to a multi-field theory. I describe in some detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and discuss its successes and shortcomings. This lecture is primarily pedagogical and directed to those with some, but not a deep, background in General Relativity
The Globular Cluster NGC 2419: A Crucible for Theories of Gravity
Ibata, R.; Sollima, A.; Nipoti, C.; Bellazzini, M.; Chapman, S. C.; Dalessandro, E.
2011-09-01
We present the analysis of a kinematic data set of stars in the globular cluster NGC 2419, taken with the DEep Imaging Multi-Object Spectrograph at the Keck II telescope. Combined with a reanalysis of deep Hubble Space Telescope and Subaru Telescope imaging data, which provide an accurate luminosity profile of the cluster, we investigate the validity of a large set of dynamical models of the system, which are checked for stability via N-body simulations. We find that isotropic models in either Newtonian or Modified Newtonian Dynamics (MOND) are ruled out with extremely high confidence. However, a simple Michie model in Newtonian gravity with anisotropic velocity dispersion provides an excellent representation of the luminosity profile and kinematics of the cluster. The anisotropy profiles of these models ensure an isotropic center to the cluster, which progresses to extreme radial anisotropy toward the outskirts. In contrast, with MOND we find that Michie models that reproduce the luminosity profile either overpredict the velocity dispersion on the outskirts of the cluster if the mass-to-light ratio (M/L) is kept at astrophysically motivated values or else they underpredict the central velocity dispersion if the M/L is taken to be very small. We find that the best Michie model in MOND is a factor of ~104 less likely than the Newtonian model that best fits the system. A likelihood ratio of 350 is found when we investigate more general models by solving the Jeans equation with a Markov Chain Monte Carlo scheme. We verified with N-body simulations that these results are not significantly different when the MOND external field effect is accounted for. If the assumptions that the cluster is in dynamical equilibrium, spherical, not on a peculiar orbit, and possesses a single dynamical tracer population of constant M/L are correct, we conclude that the present observations provide a very severe challenge for MOND. Some of the data presented herein were obtained at the W
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (24,284 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
Cadiz, California Gravity Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (32 records) were gathered by Mr. Seth I. Gutman for AridTech Inc., Denver, Colorado using a Worden Prospector gravity meter. This data...
Classical Weyl Transverse Gravity
Oda, Ichiro
2016-01-01
We study various classical aspects of the Weyl transverse (WTDiff) gravity in a general space-time dimension. First of all, we clarify a classical equivalence among three kinds of gravitational theories, those are, the conformally-invariant scalar tensor gravity, Einstein's general relativity and the WTDiff gravity via the gauge fixing procedure. Secondly, we show that in the WTDiff gravity the cosmological constant is a mere integration constant as in unimodular gravity, but it does not receive any radiative corrections unlike the unimodular gravity. A key point in this proof is to construct a covariantly conserved energy-momentum tensor, which is achieved on the basis of this equivalence relation. Thirdly, we demonstrate that the Noether current for the Weyl transformation is identically vanishing, thereby implying that the Weyl symmetry existing in both the conformally-invariant scalar tensor gravity and the WTDiff gravity is a "fake" symmetry. We find it possible to extend this proof to all matter fields,...
... medlineplus.gov/ency/article/003587.htm Urine specific gravity test To use the sharing features on this page, please enable JavaScript. Urine specific gravity is a laboratory test that shows the concentration ...
Northern Oklahoma Gravity Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (710 records) were compiled by Professor Ahern. This data base was received in June 1992. Principal gravity parameters include latitude,...
National Oceanic and Atmospheric Administration, Department of Commerce — The Central Andes gravity data (6,151 records) were compiled by Professor Gotze and the MIGRA Group. This data base was received in April, 1997. Principal gravity...
National Oceanic and Atmospheric Administration, Department of Commerce — The Decade of North American Geology (DNAG) gravity grid values, spaced at 6 km, were used to produce the Gravity Anomaly Map of North America (1987; scale...
AMELINO-CAMELIA, Giovanni
2003-01-01
Comment: 9 pages, LaTex. These notes were prepared while working on an invited contribution to the November 2003 issue of Physics World, which focused on quantum gravity. They intend to give a non-technical introduction (accessible to readers from outside quantum gravity) to "Quantum Gravity Phenomenology"
Ambjorn, Jan
1994-01-01
I discuss recent progress in our understanding of two barriers in quantum gravity: $c > 1$ in the case of 2d quantum gravity and $D > 2$ in the case of Euclidean Einstein-Hilbert gravity formulated in space-time dimensions $D >2$.
Institute of Scientific and Technical Information of China (English)
金鉴禄; 李东升; 陆晶; 刘庆怀
2012-01-01
对一类非光滑广义不变凸多目标优化问题进行了讨论,在一般（F,α,ρ,θ）-d-v-univex不变凸函数下给出了非光滑多目标优化弱有效解的充分条件,并给出了Mond-Weir对偶模型,证明了弱对偶定理和强对偶定理。%sufficient offer the provided. For the optimization of a class of non-smooth generalized invex multi-objective, we give the conditions of the weak effective solutions under the （F,α,ρ, θ）-d-v-univesc functions, and Mond-Weir dual model. The weak duality theorem and strong duality theorem are also
von Grebmer, Klaus; Ringler, Claudia; Rosegrant, Mark W.; Olofinbiyi, Tolulope; Wiesmann, Doris; Fritschel, Heidi; Badiane, Ousmane; Torero, Maximo; Yohannes, Yisehac; Thompson, Jennifer; von Oppeln, Constanze; Rahall, Joseph
2012-01-01
Selon l’Indice de la faim dans le monde 2012 (GHI), la faim dans le monde a quelque peu diminué depuis 1990 mais reste « grave ». La moyenne mondiale masque des écarts importants entre les régions et les pays. A l’échelle régionale, ce sont l’Asie du Sud et l’Afrique subsaharienne qui obtiennent les scores GHI les plus élevés. L’Asie du Sud a considérablement diminué son score GHI entre 1990 et 1996, notamment en réduisant le nombre d’enfants souffrant d’insuffisance pondérale, mais n’a pas p...
Institute of Scientific and Technical Information of China (English)
江孝感; 黄琦炜
2010-01-01
本文主要研究E-凸函数的若干性质,引入E-凸多目标规划的定义,建立E-凸多目标规划的Mond-Weir型对偶问题,并在E.凸条件假设下,证明E-凸多目标规划的弱对偶性、直接对偶性及逆对偶性.
Institute of Scientific and Technical Information of China (English)
刘海军; 苏金梅
2005-01-01
本文在向量泛函不变凸的条件下,对一类多目标优化控制问题建立了Mond-Wier型对偶,给出并证明了原问题和对偶问题之间的弱对偶定理和强对偶定理,推广了该领域早期文献中的一些结果.
Bílek, Michal; a, Ivana Ebrov\\'; a, Kateřina Bartoškov\\'
2014-01-01
CONTEXT. Many ellipticals are surrounded by round stellar shells originating probably from minor mergers. A new method for constraining gravitational potential in elliptical galaxies was recently suggested. It uses the spectral line profiles of these shells to measure the circular velocity at the edge of the shell and the expansion velocity of the shell itself. MOND is an alternative to the dark matter framework aiming to solve the missing mass problem. AIMS. We study how the circular and expansion velocities behave in MOND for large shells. METHODS. The asymptotic behavior for infinitely large shells is derived analytically. The applicability of the asymptotic results for finitely sized shells is studied numerically on a grid galaxies modeled by S\\' ersic spheres. RESULTS. Circular velocity asymptotically settles at a value determined by the baryonic mass of the galaxy forming the baryonic Tully-Fisher relation known for disk galaxies. Shell expansion velocity also becomes asymptotically constant. The expans...
International Nuclear Information System (INIS)
A three-dimensional dynamic DuMond diagram has been constructed, in which the three axes represent the wavelength and vertical and horizontal divergences of an X-ray beam. Such a diagram can be used to analyse successive diffraction of multiple crystals. It is simple and clear cut to use this diagram for the analysis and design of crystal collimators, monochromators and spectrometers involving nearly perfect crystals. (orig.)
Gravity/Fluid Correspondence For Massive Gravity
Pan, Wen-Jian
2016-01-01
In this paper, we investigate the gravity/fluid correspondence in the framework of massive gravity. Treating the gravitational mass terms as an effective energy-momentum tensor and utilizing the Petrov-like boundary condition on a time-like hypersurface, we find that the perturbation effects of massive gravity in bulk can be completely governed by the incompressible Navier-Stokes equation living on the cutoff surface under the near horizon and non-relativistic limit. Furthermore, in our models, we have concisely computed the ratio of dynamical viscosity to entropy density, and shown that it still satisfies KSS bound.
International Nuclear Information System (INIS)
The dynamics of non-spherical systems described by modified Newtonian dynamics (MOND) theories arising from generalizations of the Poisson equation is affected by an extra MONDian quadrupolar potential ϕQ even if they are isolated (no external field effect) and if they are in the deep Newtonian regime. In general MOND theories quickly approaching Newtonian dynamics for accelerations beyond A0, ϕQ is proportional to a coefficient α ∼ 1, while in MOND models becoming Newtonian beyond κA0, κ ≫ 1, it is enhanced by κ2. We analytically work out some orbital effects due to ϕQ in the framework of QUMOND and compare them with the latest observational determinations of Solar System’s planetary dynamics, exoplanets, double lined spectroscopic binary stars and binary radio pulsars. The current admissible range for the anomalous perihelion precession of Saturn −0.5 mas cty−1 ≤Δ π-dot ≤0.8 mas cty−1 yields |κ| ⩽ 3.5 × 103, while the radial velocity of α Cen AB allows us to infer |κ| ⩽ 6.2 × 104 (A) and |κ| ⩽ 4.2 × 104 (B). (paper)
THE BARYONIC TULLY-FISHER RELATION OF GAS-RICH GALAXIES AS A TEST OF ΛCDM AND MOND
International Nuclear Information System (INIS)
The baryonic Tully-Fisher relation (BTFR) is an empirical relation between baryonic mass and rotation velocity in disk galaxies. It provides tests of galaxy formation models in ΛCDM and of alternative theories like modified Newtonian dynamics (MOND). Observations of gas-rich galaxies provide a measure of the slope and normalization of the BTFR that is more accurate (if less precise) than that provided by star-dominated spirals, as their masses are insensitive to the details of stellar population modeling. Recent independent data for such galaxies are consistent with Mb = AV4f with A = 47 ± 6 M☉ km–4 s4. This is equivalent to MOND with a0 = 1.3 ± 0.3 Å s–2. The scatter in the data is consistent with being due entirely to observational uncertainties. It is unclear why the physics of galaxy formation in ΛCDM happens to pick out the relation predicted by MOND. We introduce a feedback efficacy parameter E to relate halo properties to those of the galaxies they host. E correlates with star formation rate and gas fraction in the sense that galaxies that have experienced the least star formation have been most impacted by feedback.
Bílek, M.; Jungwiert, B.; Ebrová, I.; Bartošková, K.
2015-03-01
Context. Many ellipticals are surrounded by round stellar shells probably stemming from minor mergers. A new method for constraining gravitational potential in elliptical galaxies has recently been suggested. It uses the spectral line profiles of these shells to measure the circular velocity at the edge of the shell and the expansion velocity of the shell itself. MOND is an alternative to the dark matter framework aiming to solve the missing mass problem. Aims: We study how the circular and expansion velocities behave in MOND for large shells. Methods: The asymptotic behavior for infinitely large shells is derived analytically. The applicability of the asymptotic results for finitely sized shells is studied numerically on a grid of galaxies modeled with Sérsic spheres. Results: Circular velocity settles asymptotically at a value determined by the baryonic mass of the galaxy forming the baryonic Tully-Fisher relation known for disk galaxies. Shell expansion velocity also becomes asymptotically constant. The expansion velocities of large shells form a multibranched analogy to the baryonic Tully-Fisher relation, together with the galactic baryonic masses. For many - but not all - shell galaxies, the asymptotic values of these two types of velocities are reached under the effective radius. If MOND is assumed to work in ellipticals, then the shell spectra allow many details of the history to be revealed about the formation of the shell system, including its age. The results pertaining to circular velocities apply to all elliptical galaxies, not only those with shells.
Einstein Gravity, Massive Gravity, Multi-Gravity and Nonlinear Realizations
Goon, Garrett; Joyce, Austin; Trodden, Mark
2014-01-01
The existence of a ghost free theory of massive gravity begs for an interpretation as a Higgs phase of General Relativity. We revisit the study of massive gravity as a Higgs phase. Absent a compelling microphysical model of spontaneous symmetry breaking in gravity, we approach this problem from the viewpoint of nonlinear realizations. We employ the coset construction to search for the most restrictive symmetry breaking pattern whose low energy theory will both admit the de Rham--Gabadadze--Tolley (dRGT) potentials and nonlinearly realize every symmetry of General Relativity, thereby providing a new perspective from which to build theories of massive gravity. In addition to the known ghost-free terms, we find a novel parity violating interaction which preserves the constraint structure of the theory, but which vanishes on the normal branch of the theory. Finally, the procedure is extended to the cases of bi-gravity and multi-vielbein theories. Analogous parity violating interactions exist here, too, and may be...
Marco Polo’s 'Devisement dou monde' and Franco-Italian tradition
Directory of Open Access Journals (Sweden)
Alvise Andreose
2015-02-01
Full Text Available The manuscript BNF fr. 1116 (F is the best surviving witness of the Devisement dou monde both for the quality of its reading and because it offers the closest version to the original form of the text. The book was written by Marco Polo, who had travelled for 24 years in Asia in the last quarter of the thirteenth century, and Rustichello da Pisa, an Arthurian romance writer, while both were prisoners in Genoa in 1298. The language in which the work was first written – an Old French heavily sprinkled with morphological as well as lexical Italianisms – is considered as a representative example of «Franco-Italian». The great heterogeneity of the texts usually included within this category, however, might provide an incorrect impression as regards both the original linguistic form of the Devisement and the audience to whom it was originally addressed. The language of the MS BNF fr. 1116 does not display strong similarities to the hybrid language used in Northern Italy for chivalric literature, which is traditionally called «Franco-Italian» or «Franco-Venetan». Some linguistic correspondences enable us to connect the MS BNF fr. 1116 with the group of Old French manuscripts copied by Pisan scribes while incarcerated in Genoa prison, following the battle of Meloria (1284. The fragment of the Devisement recently discovered by C. Concina appears to be very similar to F. Both graphic and phonetic evidences suggest that this witness, too, has to be localised to Tuscany.
Scenarii pour (quasi-) fin du monde traiter les dangers au CERN
Houdart, Sophie
2015-01-01
Au large de Genève court le plus grand dispositif expérimental jamais construit, le LHC, conçu pour comprendre comment s’est aggloméré l’univers. Les physiciens des particules, à l’échelle internationale, y expérimentent les théories physiques les plus avancées sur l’origine et le devenir du monde. Lové 100 mètres sous terre, et donc invisible dans le paysage, cette machine extraordinaire est, en surface, le point de mire de multiples attentions et l’objet de mesures incessantes. Ce dont elle traite (le Big Bang, les trous noirs, l’antimatière…), son envergure, son empreinte territoriale sont propres à nourrir des scénarios catastrophe que le CERN doit scrupuleusement désamorcer à mesure qu’ils surgissent en usant de procédés hétérogènes : mesures techniques, normes juridiques, monitoring de l’environnement.
Smart Grid facets in the world; Les visages de Smart Grid dans le monde
Energy Technology Data Exchange (ETDEWEB)
Marcoux, Benoit; Bauchot, Frederic
2010-09-15
There is a certain consensus on what is the Smart Grid, but priorities vary from one world region to the next. These differences bring business strategies and objectives that vary from one electrical company to the next. However: Smart Grid programs of electrical companies are based on the same elements. -Smart Grid benefits are mainly gained by a greater integration at all levels. -Implementation priorities vary from one region to the next; the regions studied in this paper are the United States, Quebec, France, Denmark and China. [French] Un certain consensus se forme sur ce que constitue le Smart Grid, mais les priorites varient d'une region du monde a l'autre. Ces differences amenent des strategies et des objectifs d'affaires qui varient d'une entreprise d'electricite a l'autre. Cependant : -Les programmes de Smart Grid des entreprises d'electricite se basent sur les memes elements. -Les benefices du Smart Grid passe avant tout par une plus grande integration a tous les niveaux. -Les priorites d'implantation varient d'une region a l'autre; les regions etudiees dans ce papier sont les etats-Unis, le Quebec, la France, le Danemark et la Chine.
An axially symmetric gamma-ray backscatter system for DuMond spectrometry
International Nuclear Information System (INIS)
An axially symmetric spectrometer is described which evolved from a program of measuring Compton profiles with unusually high geometric efficiency. When fitted with a large-volume Ge detector for combined X-ray and γ-ray spectrometry, such as the 51 mm diameter LO-AX detector from EG and G, it allows Compton profiles to be measured at counting rates in excess of 20000 cps. The axially symmetric configuration is also suited to high-efficiency analyses of thick targets by both XRF and Rayleigh/Compton (R/C) ratios. The same spectra permit a competitive binary-system analysis based on the shape of the Compton profile. Both this new analysis, which we call DuMond spectrometry, and R/C analysis are applied to studies of osteoporosis in the calcaneus with promising results. The combination of high intrinsic and geometric detection efficiency makes it practical to use very weak sources (≅ 100 MBq) and unusually low, localized doses (≅ 1 μGy) per reading. (orig.)
High-resolution Laue-type DuMond curved crystal spectrometer
International Nuclear Information System (INIS)
We report on a high-resolution transmission-type curved crystal spectrometer based on the modified DuMond slit geometry. The spectrometer was developed at the University of Fribourg for the study of photoinduced X-ray spectra. K and L X-ray transitions with energies above about 10 keV can be measured with an instrumental resolution comparable to their natural linewidths. Construction details and operational characteristics of the spectrometer are presented. The variation of the energy resolution as a function of the focal distance and diffraction order is discussed. The high sensitivity of the spectrometer is demonstrated via the 2s-1s dipole-forbidden X-ray transition of Gd which could be observed despite its extremely low intensity. The precision of the instrument is illustrated by comparing the sum of the energies of the Au K–L2 and L2–M3 cascading transitions with the energy of the crossover K–M3 transition as well as by considering the energy differences of the Gd Kα1 X-ray line measured at five different diffraction orders. Finally, to demonstrate the versatility of the spectrometer, it is shown that the latter can also be used for in-house extended X-ray absorption fine structure measurements
Risk assessment of desertification using GIS in parts of Mond Basin, Southern Iran
International Nuclear Information System (INIS)
The present paper attempts to evolve a new model by considering various indicators of different types of land degradation desertification, namely water erosion, soil salinity, vegetation degradation, and lowering of ground water table. the Mond river basin, located centrally to this zone, has been selected as a test area to assess the risk and kind of desertification. For this purpose two sub basins of the Payab and Quareh Aghaj have been chosen for detailed study. The thresholds for the severity classes of indicators have been established and then the hazards map for each indicator of types of desertification has been prepared in a GIS. The risk maps of water erosion, soil salinization, lowering of water table, vegetation degradation have been produced for each of the two sub basins. It was possible to distinguish the areas under actual risk from areas under potential risk of desertification types. Also areas under potential risk are classified to subclasses with different probability level to show a statistical picture of risk in future. (Author) 3 refs.
Genesis of the "Critical-Acceleration of MOND" and Its Role in "Formation of Structures"
Directory of Open Access Journals (Sweden)
Tank H. K.
2012-10-01
Full Text Available As an attempt to explain the “flattening of galaxies rotation-curves”, Milgrom proposed a Modification of Newtonian Dynamics MOND, in which he needed a new constant of nature a 0 , termed as “critical-acceleration-of MOND”, in his best-fit empirical formula. But so far it has been an ad-hoc introduction of a new constant. Whereas this article pro- poses: (i a genesis of this constant; (ii explains its recurrences in various physical sit- uations; and (iii its role in determining the size and radii of various structures, like: the electron, the proton, the nucleus-of-atom, the globular-clusters, the spiral-galaxies, the galactic-clusters and the whole universe. In this process we get a new interpretation of “the cosmological-red-shift”, that the linear part of the cosmological-red-shift may not be due to “metric-expansion-of-space”; and even the currently-believed “accelerated- expansion” may be slowing down with time.
Bergshoeff, Eric A; Hohm, Olaf; Merbis, Wout; Townsend, Paul K
2013-01-01
We present a generally-covariant and parity-invariant "zwei-dreibein" action for gravity in three space-time dimensions that propagates two massive spin-2 modes, unitarily, and we use Hamiltonian methods to confirm the absence of unphysical degrees of freedom. We show how zwei-dreibein gravity unifies previous "3D massive gravity" models, and extends them, in the context of the AdS/CFT correspondence, to allow for a positive central charge consistent with bulk unitarity.
Aspects of multimetric gravity
International Nuclear Information System (INIS)
We present a class of gravity theories containing N ≥ 2 metric tensors and a corresponding number of standard model copies. In the Newtonian limit gravity is attractive within each standard model copy, but different standard model copies mutually repel each other. We discuss several aspects of these multimetric gravity theories, including cosmology, structure formation, the post-Newtonian limit and gravitational waves. The most interesting feature we find is an accelerating expansion of the universe that naturally becomes small at late times.
Pirkola, Patrik
2016-01-01
The surface gravity on Mars is smaller than the surface gravity on Earth, resulting in longer falling times. This effect can be simulated on Earth by taking advantage of air resistance and buoyancy, which cause low density objects to fall slowly enough to approximate objects falling on the surface of Mars. We describe a computer simulation based on an experiment that approximates Martian gravity, and verify our numerical results by performing the experiment.
Anderson, James E.; Yoto V. Yotov
2012-01-01
This paper provides striking confirmation of the restrictions of the structural gravity model of trade. Structural forces predicted by theory explain 95% of the variation of the fixed effects used to control for them in the recent gravity literature, fixed effects that in principle could reflect other forces. This validation opens avenues to inferring unobserved sectoral activity and multilateral resistance variables by equating fixed effects with structural gravity counterparts. Our findings...
Anderson, James E.
2010-01-01
The gravity model in economics was until relatively recently an intellectual orphan, unconnected to the rich family of economic theory. This review is a tale of the orphan's reunion with its heritage and the benefits that have flowed from it. Gravity has long been one of the most successful empirical models in economics. Incorporating the theoretical foundations of gravity into recent practice has led to a richer and more accurate estimation and interpretation of the spatial relations describ...
Rovelli Carlo
1997-01-01
The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime, is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (...
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.
Gravity Independent Compressor Project
National Aeronautics and Space Administration — We propose to develop and demonstrate a small, gravity independent, vapor compression refrigeration system using a linear motor compressor which effectively...
Directory of Open Access Journals (Sweden)
Animesh Mukherjee
1991-01-01
Full Text Available Based upon Biot's [1965] theory of initial stresses of hydrostatic nature produced by the effect of gravity, a study is made of surface waves in higher order visco-elastic media under the influence of gravity. The equation for the wave velocity of Stonely waves in the presence of viscous and gravitational effects is obtained. This is followed by particular cases of surface waves including Rayleigh waves and Love waves in the presence of viscous and gravity effects. In all cases the wave-velocity equations are found to be in perfect agreement with the corresponding classical results when the effects of gravity and viscosity are neglected.
Institute of Scientific and Technical Information of China (English)
王荣波; 张庆祥; 冯强
2010-01-01
利用一类新的广义一致Bρ-(p,r)-不变凸函数建立了多目标规划问题的Mond-Weir型对偶,证明了弱对偶,强对偶和逆对偶定理.其结论具有一般性,推广了许多涉及不变凸函数,不变B-凸函数,(p,r)-不变凸以及B-(p,r)-不变凸函数文献的结论.
Institute of Scientific and Technical Information of China (English)
徐义红; 韩倩倩; 涂相求
2013-01-01
在实赋范线性空间中利用锥方向高阶广义邻接导数研究带约束的集值优化在超有效解意义下的高阶Mond-Weir对偶问题.在广义锥-凸假设下,利用锥方向高阶广义邻接导数的性质借助凸集分离定理得到了强对偶定理.利用超有效点的标量化定理得到逆对偶定理.
Institute of Scientific and Technical Information of China (English)
孙玉华
2005-01-01
利用一类新的广义凸函数:B-(p,r)-不变凸函数,建立了多目标规划问题的Mond-Weir型对偶,证明了弱对偶、强对偶和逆对偶定理.其结论具有一般性,推广了许多涉及不变凸函数、不变B-凸函数和(p,r)-不变凸函数的文献的结论.
Institute of Scientific and Technical Information of China (English)
邢苗; 张庆祥; 高晔
2014-01-01
在局部Lipschitz函数,Clarke广义梯度和半(E,F)凸函数的基础上,定义了半(E,F)ρ-凸函数和拟半(E,F)ρ-凸函数等几类新的广义凸函数,并研究了涉及这类函数的一类多目标半无限规划的Mond-Weir型对偶问题,得到了若干弱对偶和强对偶定理.
Krasnov, Kirill
2016-01-01
Self-dual gravity is a diffeomorphism invariant theory in four dimensions that describes two propagating polarisations of the graviton and has a negative mass dimension coupling constant. Nevertheless, this theory is not only renormalisable but quantum finite, as we explain. We also collect various facts about self-dual gravity that are scattered across the literature.
Heiss, Jonny
2000-01-01
Assuming the existence of a Multidirectional Homogeneous and Constant Shower of Elementary Particles (MHCSEP) traveling at light speed in space, several basic laws of physics are derived mainly by geometrical considerations. When placing two bodies in space, obstruction of the MHCSEP creates an attractive force among them that coincides, for two bodies, with Newton's law of gravity, generating a mechanical explanation for gravity.
Consistency of orthodox gravity
Energy Technology Data Exchange (ETDEWEB)
Bellucci, S. [INFN, Frascati (Italy). Laboratori Nazionali di Frascati; Shiekh, A. [International Centre for Theoretical Physics, Trieste (Italy)
1997-01-01
A recent proposal for quantizing gravity is investigated for self consistency. The existence of a fixed-point all-order solution is found, corresponding to a consistent quantum gravity. A criterion to unify couplings is suggested, by invoking an application of their argument to more complex systems.
Kan, Nahomi; Maki, Takuya; Shiraishi, Kiyoshi
2016-10-01
We propose a model of gravity in which a General Relativity metric tensor and an effective metric generated from a single scalar formulated in geometric scalar gravity are mixed. We show that the model yields the exact Schwarzschild solution, along with accelerating behavior of scale factors in cosmological solutions.
Topological Aspects of Quantum Gravity
Weis, Morten
1998-01-01
This thesis discusses the topological aspects of quantum gravity, focusing on the connection between 2D quantum gravity and 2D topological gravity. The mathematical background for the discussion is presented in the first two chapters. The possible gauge formulations of 2D topological gravity as a BF or a Super BF theory are presented and compared against 2D quantum gravity in the dynamical triangulation scheme. A new identification between topological gravity in the Super BF formulation and t...
Palsingh, S. (Inventor)
1975-01-01
An educational toy useful in demonstrating fundamental concepts regarding the laws of gravity is described. The device comprises a sphere 10 of radius r resting on top of sphere 12 of radius R. The center of gravity of sphere 10 is displaced from its geometrical center by distance D. The dimensions are so related that D((R+r)/r) is greater than r. With the center of gravity of sphere 10 lying on a vertical line, the device is in equilibrium. When sphere 10 is rolled on the surface of sphere 12 it will return to its equilibrium position upon release. This creates an illusion that sphere 10 is defying the laws of gravity. In reality, due to the above noted relationship of D, R, and r, the center of gravity of sphere 10 rises from its equilibrium position as it rolls a short distance up or down the surface of sphere 12.
La cryptosporidiose zoonosique humaine due à Cryptosporidium felis dans le monde
Directory of Open Access Journals (Sweden)
Raccurt C.P.
2007-03-01
Full Text Available La cryptosporidiose est l’une des principales causes de diarrhée aiguë de l’enfant dans les pays en voie de développement, et de diarrhée chronique chez les sujets immunodéprimés infectés par le virus de l’immunidéficience humaine (VIHj. L’identification de l’espèce est impossible par les méthodes conventionnelles et fait appel aux techniques de biologie moléculaire. La cryptosporidiose humaine est due le plus souvent à Cryptosporidium hominis et à Cryptosporidium parvum. Des espèces et des génotypes spécifiques d’animaux, dont Cryptosporidium felis, parasitent également l’Homme. Une revue systématique des cas humains dus à C. felis publiés dans le monde pjermet d’en décompter 58 dans toutes les régions biogéographiques, excepté l’Australie et l’Océanie. Adultes et enfants sont la cible de ce parasite. Chez ces 58 sujets parasités par C. felis, 83% sont VIH-positifs. Cette zoonose se rencontre également chez des sujets apparemment immunocompétents. Les pays en voie de développement semblent plus concernés probablement à cause d’une transmission environnementale plus présente que dans les pays développés. Cette cryptosporidiose zoonosique demande à être plus largement évaluée dans les pays tropicaux.
Panorama de la recherche sur la montagne en Europe et dans le monde
Directory of Open Access Journals (Sweden)
Axel Borsdorf
2009-06-01
Full Text Available Au cours du siècle dernier, les régions montagneuses et leur système complexe sont sortis de l’ombre. La volonté de protéger ces régions a suscité de nombreuses initiatives dans le monde entier, avec pour objectif d’agir au niveau international et politique, mais également d’unir les forces disponibles pour intensifier l’inter et la transdisciplinarité des travaux scientifiques. Les défis de la recherche sur les montagnes à l’avenir seront de réussir à impliquer plus efficacement les politiciens, les parties prenantes et les habitants des régions montagneuses afin d’atténuer la pression de la mondialisation pour parvenir à un développement régional durable dans les zones montagneuses. Dresser un panorama des institutions qui représentent les régions de montagne de la planète a ainsi l’intérêt de présenter les principales préoccupations de chacune d’entre elles ainsi que les domaines dans lesquels elles travaillent.Within the last century the awareness of mountain regions and their complex system has grown and the motivation to protect these regions has yielded numerous initiatives around the globe with the aim of acting internationally and politically as well as joining forces to intensify inter– and transdisciplinarity in scientific work. The challenges of mountain research in the future will be to involve politicians, stakeholders and the mountain population more effectively in order to mitigate the pressures of globalization towards a sustainable regional development within mountain regions. The significance of providing an overview of institutions representing mountainous regions around the globe lies in showing the main focus of the different institutions and the areas they work in.
Directory of Open Access Journals (Sweden)
Arun Kumar Tripathy
2014-03-01
Full Text Available In this paper, a new class of second order (Φ,ρ-univex and second order (Φ,ρ-pseudo univex function are introduced with example. A pair Mond-Weir type second order mixed symmetric duality for multiobjective nondifferentiable programming is formulated and the duality results are established under the mild assumption of second order (∅,ρ univexity and second order pseudo univexity. Special cases are discussed to show that this study extends some of the known results in related domain.
光明莫斯利安酸奶获第50届Monde Selection银奖
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
近日，光明乳业莫斯利安酸奶产品摘取Monde Selection（世界食品品质评鉴大会）银奖，成为该大会成立50年来唯一获得该世界级大奖的中国企业，其意义不仅提升光明品牌形象，也将有力提振消费者对国产乳品的信心。
Nolwenn Mingant, Hollywood à la conquête du monde. Marchés, stratégies, influences
Robic-Diaz, Delphine
2013-01-01
Nolwenn Mingant is assistant professor in American civilization at the Sorbonne Nouvelle University in Paris and the co-founder of the CinEcoSa (Cinema, Economy and English-Speaking Countries) research group. Her book Hollywood à la conquête du monde. Marchés, stratégies, influences which was published in 2010 by CNRS Publishing (316 pages), is derived from her PhD thesis. Situated at the crossroads of the economic analysis of cinema, of American studies, of geopolitics and of film analysis, ...
Tribunal de los medios: análisis de los editoriales de Le Monde y Folha de S.Paulo
Directory of Open Access Journals (Sweden)
Vinícius Flôres
2015-01-01
Full Text Available [es] Este trabajo tiene como objetivo investigar y comparar la construcción de los editoriales acerca de la Conferencia de las Naciones Unidas sobre el Desarrollo Sostenible, Rio+20, en los diarios Le Monde y Folha de S.Paulo. El enfoque teórico se basa en la teoría del establecimiento periodístico de temas de discusión de McCombs (2009, que determina que los medios de comunicación establecen la agenda para el público cuando destacan algunas perspectivas en vez de otras. Como método, se utiliza el análisis discursivo que mapea las voces y identifica los sentidos (Benetti, 2008. Para el análisis de los editoriales, complementariamente se empleó la lógica de Fausto Neto (1999, que permite caracterizar las voces de los periódicos y sus habilidades. La investigación y comparación de los editoriales acerca de la Conferencia Rio+20 en los diarios Le Monde y Folha de S.Paulo apuntaban la existencia de seis formaciones discursivas que determinan cómo los medios actúan como consultores en la esfera pública (Fausto Neto, 1999. [en] This paper aims to investigate and compare the construction of editorials about the United Nations Conference on Sustainable Development, Rio+20, in the newspapers Le Monde and Folha de S.Paulo. The theorical approach is based on the McCombs’ (2009 Agenda-Setting Theory, which states that the media sets the agenda for the public when highlight some perspectives over others. As a method, it’s used the French Discourse Analysis that seeks a mapping and identification of voices and senses (Benetti, 2008. Additionally the Fausto Neto’s (1999 logic to characteriza the voices of newspapers and their skills was used. The investigation and comparison of editorials about the Rio+20 conference in the newspapers Le Monde and Folha de S.Paulo showed the existence of six discourse formations,and the publications were manifested as consultants in the public sphere (Fausto Neto, 1999
一类非光滑规划问题的Mond Weir和Wolf对偶%Mond Weir Dual and Wolf Dual in a Class of Nonsmooth Programming Problems
Institute of Scientific and Technical Information of China (English)
赵克全; 罗杰; 唐莉萍
2010-01-01
本文考虑带等式和不等式约束的非光滑B-(p,r)单目标规划的对偶问题,研究了函数λf+∑mi=1μigi+∑pj=1vjhj为严格B-(p,r)不变凸性条件下Mond Weri对偶模型的弱对偶、强对偶、逆对偶和严格逆对偶,函数f+∑mi=1μigi+∑pj=1vjhj为B-(p,r)不变凸性条件下Wolf对偶模型的弱对偶和强对偶以及严格B-(p,r)不变凸性条件下限制逆对偶和严格逆对偶.在无约束规格的条件下证明了该类非光滑规划问题的Mond Weir和Wolf对偶模型相应的对偶性结果.本文的结果是对最近一些文献中相应结果的改进与完善.
Setare, M R
2009-01-01
In this paper we study cosmological application of holographic dark energy density in the modified gravity framework. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in spatially flat universe. Our calculation show, taking $\\Omega_{\\Lambda}=0.73$ for the present time, it is possible to have $w_{\\rm \\Lambda}$ crossing -1. This implies that one can generate phantom-like equation of state from a holographic dark energy model in flat universe in the modified gravity cosmology framework. Also we develop a reconstruction scheme for the modified gravity with $f(R)$ action.
International Nuclear Information System (INIS)
We investigate O'Raifeartaigh-type models for F-term supersymmetry breaking in gauge mediation scenarios in the presence of gravity. It is pointed out that the vacuum structure of those models is such that in metastable vacua gravity mediation contribution to scalar masses is always suppressed to the level below 1 percent, almost sufficient for avoiding FCNC problem. Close to that limit, gravitino mass can be in the range 10-100 GeV, opening several interesting possibilities for gauge mediation models, including Giudice-Masiero mechanism for μ and Bμ generation. Gravity sector can include stabilized moduli.
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.
How Zwicky already ruled out modified gravity theories without dark matter
Nieuwenhuizen, Theodorus Maria
2016-01-01
Various theories, such as MOND, MOG, Emergent Gravity and $f(R)$ theories avoid dark matter by assuming a change in General Relativity and/or in Newton's law. Galactic rotation curves are typically described well. Here the application to galaxy clusters is considered, focussed on the good lensing and X-ray data for A1689. As a start, the no-dark-matter case is confirmed to work badly: the need for dark matter starts near the cluster centre, where Newton's law is still supposed to be valid. This leads to the conundrum discovered by Zwicky, which is likely only solvable if the theories assume additional (dark) matter. Neutrinos with eV masses serve well without altering the successes in (dwarf) galaxies.
BRST symmetry of Unimodular Gravity
Upadhyay, S.; Oksanen, M.; Bufalo, R.
2015-01-01
We derive the BRST symmetry for two versions of unimodular gravity, namely, fully diffeomorphism-invariant unimodular gravity and unimodular gravity with fixed metric determinant. The BRST symmetry is generalized further to the finite field-dependent BRST, in order to establish the connection between different gauges in each of the two versions of unimodular gravity.
Toroidal solutions in Horava Gravity
Ghodsi, Ahmad
2009-01-01
Recently a new four-dimensional non relativistic renormalizable theory of gravity was proposed by Horava. This gravity reduces to Einstein gravity at large distances. In this paper by using the new action for gravity we present different toroidal solutions to the equations of motion. Our solutions describe the near horizon geometry with slow rotating parameter.
International Nuclear Information System (INIS)
There exists several modified gravity theories designed to reproduce the empirical Milgrom's formula, modified Newtonian dynamics (MOND). Here we derive analytical results in the context of the static weak-field limit of two of them (bimetric MOND, leading for a given set of parameters to the quasilinear MOND, and Bekenstein's Tensor-Vector-Scalar). In this limit, these theories are constructed to give the same force field for spherical symmetry, but their predictions generally differ out of it. However, for certain realizations of these theories (characterized by specific choices for their free functions), the binding potential-energy of a system is increased, compared to its Newtonian counterpart, by a constant amount independent of the shape and size of the system. In that case, the virial theorem is exactly the same in these two theories, for the whole gravity regime and even outside of spherical symmetry, although the exact force fields are different. We explicitly show this for the force field generated by the two theories inside an elliptical shell. For more general free functions, the virial theorems are, however, not identical in these two theories. We finally explore the consequences of these analytical results for the two-body force.
Janz, Joachim; Cappellari, Michele; Romanowsky, Aaron J.; Ciotti, Luca; Alabi, Adebusola; Forbes, Duncan A.
2016-09-01
The dark matter (DM) haloes around spiral galaxies appear to conspire with their baryonic content: empirically, significant amounts of DM are inferred only below a universal characteristic acceleration scale. Moreover, the discrepancy between the baryonic and dynamical mass, which is usually interpreted as the presence of DM, follows a very tight mass discrepancy acceleration (MDA) relation. Its universality, and its tightness in spiral galaxies, poses a challenge for the DM interpretation and was used to argue in favour of MOdified Newtonian Dynamics (MOND). Here, we test whether or not this applies to early-type galaxies. We use the dynamical models of fast-rotator early-type galaxies by Cappellari et al. based on ATLAS3D and SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) data, which was the first homogenous study of this kind, reaching ˜4 Re, where DM begins to dominate the total mass budget. We find the early-type galaxies to follow an MDA relation similar to spiral galaxies, but systematically offset. Also, while the slopes of the mass density profiles inferred from galaxy dynamics show consistency with those expected from their stellar content assuming MOND, some profiles of individual galaxies show discrepancies.
Milgrom, Mordehai
2016-01-01
Keller and Wadsley (2016) have smugly suggested, recently, that the end of MOND may be in view. This is based on their claim that their highly-restricted sample of $\\Lambda$CDM-simulated galaxies are "consistent" with the observed MOND mass-discrepancy-acceleration relation (MDAR), in particular, with its recent update by McGaugh et al. (2016), based on the SPARC sample. From this they extrapolate to "$\\Lambda$CDM is fully consistent" with the MDAR. I explain why these simulated galaxies do not show that $\\Lambda$CDM accounts for the MDAR. a. Their sample of simulated galaxies contains only 18 high-mass galaxies, within a narrow range of one order of magnitude in baryonic mass, at the very high end of the observed, SPARC sample, which spans 4.5 orders of magnitude in mass. More importantly, the simulated sample has none of the low-mass, low-acceleration galaxies -- abundant in SPARC -- which encapsulate the crux and the nontrivial aspects of the predicted and observed MDAR. The low-acceleration part of the si...
Garland, G D; Wilson, J T
2013-01-01
The Earth's Shape and Gravity focuses on the progress of the use of geophysical methods in investigating the interior of the earth and its shape. The publication first offers information on gravity, geophysics, geodesy, and geology and gravity measurements. Discussions focus on gravity measurements and reductions, potential and equipotential surfaces, absolute and relative measurements, and gravity networks. The text then elaborates on the shape of the sea-level surface and reduction of gravity observations. The text takes a look at gravity anomalies and structures in the earth's crust; interp
Bergshoeff, Eric A.; Hohm, Olaf; Townsend, Paul K.
2012-01-01
We present a brief review of New Massive Gravity, which is a unitary theory of massive gravitons in three dimensions obtained by considering a particular combination of the Einstein-Hilbert and curvature squared terms.
Zinoviev, Yury M
2012-01-01
The equations of the relativistic causal Newton gravity law for the planets of the solar system are studied in the approximation when the Sun rests at the coordinates origin and the planets do not iteract between each other.
Bhattacharya, Swastik
2015-01-01
General theory of relativity (or Lovelock extensions) is a dynamical theory; given an initial configuration on a space-like hypersurface, it makes a definite prediction of the final configuration. Recent developments suggest that gravity may be described in terms of macroscopic parameters. It finds a concrete manifestation in the fluid-gravity correspondence. Most of the efforts till date has been to relate equilibrium configurations in gravity with fluid variables. In order for the emergent paradigm to be truly successful, it has to provide a statistical mechanical derivation of how a given initial static configuration evolves into another. In this essay, we show that the energy transport equation governed by the fluctuations of the horizon-fluid is similar to Raychaudhuri equation and, hence gravity is truly emergent.
Hertog, Thomas; Hollands, Stefan
2005-12-01
We study the stability of designer gravity theories, in which one considers gravity coupled to a tachyonic scalar with anti-de Sitter (AdS) boundary conditions defined by a smooth function W. We construct Hamiltonian generators of the asymptotic symmetries using the covariant phase space method of Wald et al and find that they differ from the spinor charges except when W = 0. The positivity of the spinor charge is used to establish a lower bound on the conserved energy of any solution that satisfies boundary conditions for which W has a global minimum. A large class of designer gravity theories therefore have a stable ground state, which the AdS/CFT correspondence indicates should be the lowest energy soliton. We make progress towards proving this by showing that minimum energy solutions are static. The generalization of our results to designer gravity theories in higher dimensions involving several tachyonic scalars is discussed.
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (65,164 records) were gathered by various governmental organizations (and academia) using a variety of methods. The data base was received...
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (55,907 records) were gathered by various governmental organizations (and academia) using a variety of methods. This data base was received...
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (71 records) were gathered by various governmental organizations (and academia) using a variety of methods. This data base was received in...
National Oceanic and Atmospheric Administration, Department of Commerce — In 1985, Dr. William F. Haxby of the Lamont-Doherty Geological Observatory of Columbia University prepared this data base of free-air gravity anomalies, based on...
Bakker MR; Smit, J.
1993-01-01
We look at gravitational attraction in simplicial gravity using the dynamical triangulation method. On the dynamical triangulation configurations we measure quenched propagators of a free massive scalar field. The masses measured from these propagators show that gravitational attraction is present.
Oda, Ichiro
2016-01-01
We propose a topological model of induced gravity (pregeometry) where both Newton's coupling constant and the cosmological constant appear as integration constants in solving field equations. The matter sector of a scalar field is also considered, and by solving field equations it is shown that various types of cosmological solutions in the FRW universe can be obtained. A detailed analysis is given of the meaning of the BRST transformations, which make the induced gravity be a topological field theory, by means of the canonical quantization analysis, and the physical reason why such BRST transformations are needed in the present formalism is clarified. Finally, we propose a dynamical mechanism for fixing the Lagrange multiplier fields by following the Higgs mechanism. The present study clearly indicates that the induced gravity can be constructed at the classical level without recourse to quantum fluctuations of matter and suggests an interesting relationship between the induced gravity and the topological qu...
De Bakker, B V; Bakker, Bas de; Smit, Jan
1994-01-01
We look at gravitational attraction in simplicial gravity using the dynamical triangulation method. On the dynamical triangulation configurations we measure quenched propagators of a free massive scalar field. The masses measured from these propagators show that gravitational attraction is present.
Bhattacharya, Swastik; Shankaranarayanan, S.
2015-10-01
General theory of relativity (or Lovelock extensions) is a dynamical theory; given an initial configuration on a spacelike hypersurface, it makes a definite prediction of the final configuration. Recent developments suggest that gravity may be described in terms of macroscopic parameters. It finds a concrete manifestation in the fluid-gravity correspondence. Most of the efforts till date has been to relate equilibrium configurations in gravity with fluid variables. In order for the emergent paradigm to be truly successful, it has to provide a statistical mechanical derivation of how a given initial static configuration evolves into another. In this paper, we show that the energy transport equation governed by the fluctuations of the horizon-fluid is similar to Raychaudhuri equation and hence gravity is truly emergent.
Sjogren, William L.
1987-01-01
Work on three different efforts related to gravity data analysis is discussed. The reduction of raw Doppler data from the Apollo 15 subsatellite to produce acceleration profiles as a function of latitude, longitude and altitude; an investigation related to fitting long arcs of Pioneer Venus Orbiter tracking data; and a study of gravity/topography ratios which were found to have a linear trend with longitude are discussed.
Quantum massive conformal gravity
International Nuclear Information System (INIS)
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.)
Quantum massive conformal gravity
Faria, F. F.
2016-01-01
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.
Quantum massive conformal gravity
Faria, F. F.
2016-04-01
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.
Noncommutative Quantum Gravity
Faizal, Mir
2013-01-01
We discuss the BRST and anti-BRST symmetries for perturbative quantum gravity in noncommutative spacetime. In this noncommutative perturbative quantum gravity the sum of the classical Lagrangian density with a gauge fixing term and a ghost term is shown to be invariant the noncommutative BRST and the noncommutative anti-BRST transformations. We analyse the gauge fixing term and the ghost term in both linear as well as non-linear gauges. We also discuss the unitarity evolution of the theory an...
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.)
Emergent Gravity from Noncommutative Spacetime
Yang, Hyun Seok
2006-01-01
We showed before that self-dual electromagnetism in noncommutative (NC) spacetime is equivalent to self-dual Einstein gravity. This result implies a striking picture about gravity: Gravity can emerge from electromagnetism in NC spacetime. Gravity is then a collective phenomenon emerging from gauge fields living in fuzzy spacetime. We elucidate in some detail why electromagnetism in NC spacetime should be a theory of gravity. In particular, we show that NC electromagnetism is realized through ...
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.
Directory of Open Access Journals (Sweden)
Maartens Roy
2004-01-01
Full Text Available The observable universe could be a 1+3-surface (the "brane" embedded in a 1+3+$d$-dimensional spacetime (the "bulk", with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the $d$ extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak ($sim$TeV level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. General relativity cannot describe gravity at high enough energies and must be replaced by a quantum gravity theory, picking up significant corrections as the fundamental energy scale is approached. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review discusses the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall-Sundrum models.
Institute of Scientific and Technical Information of China (English)
万轩; 彭再云
2011-01-01
B-(p,r)-预不变凸函数是一类新的广义凸函数,它是B-(p,r)-不变凸函数的推广,本文对其性质及B-(p,r)-预不变凸多目标规划问题的Mond-Weir型对偶进行了研究.首先,给出了B-(p,r)-预不变凸函数的几个基本性质,表明B-(p,r)-预不变凸函数仍然满足加法,数乘和复合函数运算性质,并举例说明了B-(P,r)-预不变凸函数是B-(P,r)-不变凸函数的真推广.然后,重点讨论了B-(p,r)-预不变凸多目标规划问题及其Mond-Weir型对偶问题的解的情况.分别给出了关于目标函数和约束函数均可微的多目标规划问题(VP)在B-(p,r)-预不变凸型条件下的弱对偶、强对偶和严格逆对偶定理.其结论具有一般性,推广了涉及预不变凸函数、B-预不变凸函数和(p,r)-预不变凸函数的文献的相关结论.%B-(p, r)-pre-invex function is a new generalized convex function and it's a generalization of B-(p, r)-invex functions. In this paper, the property of the B-(p,r) -pre-invex function and its Mond-weir duality of the multi-objective programming problems are considered. First, some basic properties of the B-(p, r)-pre-invex function are introduced to show that the properties of addition, multiplication and composition to the B-(p, r)-pre-invex function are still satisfying, meanwhile, some examples are given to illustrate that the B-(p, r)-pre-invex function is a ture generalization of B-(p, r)-invex function. Second, the multi-objective programming problems of B(p,r)-pre-invex function and the solution for its Mond-weir duality problems are emphasized here. By using the B-(p, r)-pre-invex function, the weak, strong and strict converse duality results are established for multi-objective problems(VP) which concerns about objective function and constraint function. The results extend the corresponding ones in the literature on programming problems with pre-invex function, B-pre-invex function and (p,r)-pre-invex function.
Ensemble Averaged Gravity Theory
Khosravi, Nima
2016-01-01
We put forward the idea that all the theoretically consistent models of gravity have a contribution to the observed gravity interaction. In this formulation each model comes with its own Euclidean path integral weight where general relativity (GR) automatically has the maximum weight in high-curvature regions. We employ this idea in the framework of Lovelock models and show that in four dimensions the result is a specific form of $f(R,G)$ model. This specific $f(R,G)$ satisfies the stability conditions and has self-accelerating solution. Our model is consistent with the local tests of gravity since its behavior is same as GR for high-curvature regimes. In low-curvature regime the gravity force is weaker than GR which can interpret as existence of a repulsive fifth force for very large scales. Interestingly there is an intermediate-curvature regime where the gravity force is stronger in our model than GR. The different behavior of our model in comparison with GR in both low- and intermediate-curvature regimes ...
An Uneven Vacuum Energy Fluid as $\\Lambda$, Dark Matter, MOND and Lens
Zhao, HongSheng
2008-01-01
Various TeVeS-inspired and f(R)-inspired theories of gravity have added an interesting twist to the search for dark matter and vacuum energy, modifying the landscape of astrophysics day by day. These theories can be together called a {\\bf N}on-{\\bf u}niform Dark Energy fluid (a Nu-Lambda fluid or a ${\\mathbf V\\Lambda}$ fluid); a common thread of these theories, according of an up-to-date summary by HZL \\cite{Halle}, is a non-uniform vector field, describing an uneven vacuum energy fluid. The ...
Airborne Gravity: NGS' Gravity Data for CN02 (2013 & 2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Nebraska collected in 2013 & 2014 over 3 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for EN06 (2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Maine, Canada, and the Atlantic Ocean collected in 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for EN08 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Vermont, New Hampshire, Massachusettes, Maine, and Canada collected in 2013 over 1 survey. This data set is part of the Gravity...
Airborne Gravity: NGS' Gravity Data for TS01 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Puerto Rico and the Virgin Islands collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for ES01 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida, the Bahamas, and the Atlantic Ocean collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition...
Airborne Gravity: NGS' Gravity Data for CN03 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Nebraska collected in 2014 over one survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for EN05 (2012)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Minnesota, Wisconsin, and Michigan collected in 2012 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for CS06 (2012 & 2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2012 & 2013 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for AN03 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 and 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for EN04 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Michigan and Lake Huron collected in 2012 over 1 survey. This data set is part of the Gravity for the Re-definition of the American...
Airborne Gravity: NGS' Gravity Data for AS02 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for CS03 (2009)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas and Louisiana collected in 2009 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for EN01 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Canada, and Lake Ontario collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for CS01 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alabama and Florida collected in 2008 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for PN01 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for California and Oregon collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical...
Ortín, Tomás
2015-01-01
Self-contained and comprehensive, this definitive new edition of Gravity and Strings is a unique resource for graduate students and researchers in theoretical physics. From basic differential geometry through to the construction and study of black-hole and black-brane solutions in quantum gravity - via all the intermediate stages - this book provides a complete overview of the intersection of gravity, supergravity, and superstrings. Now fully revised, this second edition covers an extensive array of topics, including new material on non-linear electric-magnetic duality, the electric-tensor formalism, matter-coupled supergravity, supersymmetric solutions, the geometries of scalar manifolds appearing in 4- and 5-dimensional supergravities, and much more. Covering reviews of important solutions and numerous solution-generating techniques, and accompanied by an exhaustive index and bibliography, this is an exceptional reference work.
Jain, Bhuvnesh
2010-01-01
Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. We review recent developments in modified gravity theories, focusing on higher dimensional approaches and chameleon/f(R) theories. We classify these models in terms of the screening mechanisms that enable such theories to approach general relativity on small scales (and thus satisfy solar system constraints). We describe general features of the modified Friedman equation in such theories. The second half of this review describes experimental tests of gravity in light of the new theoretical approaches. We summarize the high precision tests of gravity on laboratory and solar system scales. We describe in some detail tests on astrophysical scales ranging from ~kpc (galaxy scales) to ~Gpc (large-scale structure). These tests rely on the growth and inter-relationship of perturbations in the metric potentials, density and velocity fields which can be measured using gravitational lensi...
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.
Gravity and embryonic development
Young, R. S.
1976-01-01
The relationship between the developing embryo (both plant and animal) and a gravitational field has long been contemplated. The difficulty in designing critical experiments on the surface of the earth because of its background of 1 g, has been an obstacle to a resolution of the problem. Biological responses to gravity (particularly in plants) are obvious in many cases; however, the influence of gravity as an environmental input to the developing embryo is not as obvious and has proven to be extremely difficult to define. In spite of this, over the years numerous attempts have been made using a variety of embryonic materials to come to grips with the role of gravity in development. Three research tools are available: the centrifuge, the clinostat, and the orbiting spacecraft. Experimental results are now available from all three sources. Some tenuous conclusions are drawn, and an attempt at a unifying theory of gravitational influence on embryonic development is made.
Generalizing unimodular gravity
Saez-Gomez, Diego
2016-01-01
The so-called unimodular version of General Relativity is revisited, which assumes the trace-free part of the equations instead of the usual Einstein equations, what leads naturally to a cosmological constant that may compensate the large value of quantum fluctuations. Here we extend such formalism to some extensions of General Relativity that have drawn a lot of attention over the last years, as $f(R)$ gravity (or its equivalent scalar-tensor picture) and Gauss-Bonnet gravity. The corresponding unimodular version of such theories is constructed. From the classical point of view, the unimodular versions of such extensions are completely equivalent to their originals, but an effective cosmological constant arises naturally, what may provide a richer description of the universe evolution. Moreover, conformal transformations within unimodular gravities lead to some corrections that may affect their solutions. Here we analyze the case of Starobisnky inflation and compared with the original one.
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.
Energy Technology Data Exchange (ETDEWEB)
Abele, Hartmut; Bittner, Thomas; Cronenberg, Gunther; Filter, Hanno; Jenke, Tobias; Lemmel, Hartmut; Thalhammer, Martin [Atominstitut TU Wien, Wien (Austria); Geltenbort, Peter [Institut Laue-Langevin, Grenoble (France)
2012-07-01
This talk is about a test of the Newtons Inverse Square Law of Gravity at micron distances by quantum interference with ultra-cold neutrons deep into the theoretically interesting regime. The method is based on a new resonance spectroscopy technique related to Rabi spectroscopy, but it has been adapted to gravitationally bound quantum systems. By coupling such a quantum system to mechanical vibrations, we observe resonant transitions, devoid of electromagnetic interaction. As Newtonian gravity and hypothetical Fifth Forces evolve with different phase information, the experiment has the potential to test the equivalence principle and Newtons gravity law at the micron scale. This experiment can therefore test speculations on large extra dimensions of sub-millimetre size of space-time or the origin of the cosmological constant in the universe, where effects are predicted in the interesting range of this experiment and might give a signal in an improved setup.
Terrestrial gravity data analysis for interim gravity model improvement
1987-01-01
This is the first status report for the Interim Gravity Model research effort that was started on June 30, 1986. The basic theme of this study is to develop appropriate models and adjustment procedures for estimating potential coefficients from terrestrial gravity data. The plan is to use the latest gravity data sets to produce coefficient estimates as well as to provide normal equations to NASA for use in the TOPEX/POSEIDON gravity field modeling program.
1/R gravity and Scalar-Tensor Gravity
Chiba, Takeshi
2003-01-01
We point out that extended gravity theories, the Lagrangian of which is an arbitrary function of scalar curvature $R$, are equivalent to a class of the scalar tensor theories of gravity. The corresponding gravity theory is $\\omega=0$ Brans-Dicke gravity with a potential for the Brans-Dicke scalar field, which is not compatible with solar system experiments if the field is very light: the case when such modifications are important recently.
On the no-gravity limit of gravity
Kowalski-Glikman, J.; Szczachor, M.
2012-01-01
We argue that Relative Locality may arise in the no gravity $G\\rightarrow0$ limit of gravity. In this limit gravity becomes a topological field theory of the BF type that, after coupling to particles, may effectively deform its dynamics. We briefly discuss another no gravity limit with a self dual ground state as well as the topological ultra strong $G\\rightarrow\\infty$ one.
From Classical To Quantum Gravity: Introduction to Loop Quantum Gravity
Giesel, Kristina; Sahlmann, Hanno
2012-01-01
We present an introduction to the canonical quantization of gravity performed in loop quantum gravity, based on lectures held at the 3rd quantum geometry and quantum gravity school in Zakopane in 2011. A special feature of this introduction is the inclusion of new proposals for coupling matter to gravity that can be used to deparametrize the theory, thus making its dynamics more tractable. The classical and quantum aspects of these new proposals are explained alongside the standard quantizati...
Un ordinateur champion du monde d’Échecs : histoire d’un affrontement homme-machine
Rougetet, Lisa
2016-01-01
La victoire du programme Deep Blue sur le champion du monde Garry Kasparov le 11 mai 1997 marque le point final d’une étape importante de l’histoire de la confrontation homme-machine autour du jeu d’Échecs, perçu comme le jeu intelligent par excellence. Cette histoire se divise en trois grandes périodes, qui coïncident avec le niveau atteint par les programmes : durant la première, entre 1950 et 1972, l’ordinateur acquiert un niveau de jeu équivalent à celui d’un lycéen. La seconde, jusqu’en ...
Kieft, Xavier
2011-01-01
Sous ce titre un peu énigmatique se présente une étude originale sur les « fondateurs » (p. 9) de la discipline, partant de l’idée selon laquelle celle-ci se trouve depuis Comte prisonnière d’une conception dualiste, opposant, pour la tradition française, l’ordre physique et l’ordre social ou l’esprit et, pour la sociologie allemande, l’homme et le monde (c’est-à-dire les structures politiques, économiques et sociales). Travaillant à partir de cette perspective une sélection de textes représe...
An application of the swept-current method to a DuMond type magnetic beta ray spectrometer
International Nuclear Information System (INIS)
The ''combination magnetic-Si(Li), swept current electron spectrometer'' method has been applied to a DuMond type magnetic beta ray spectrometer without depriving the spectrometer of the function of high resolution measurements by usual uses. Properties of the system have been examined by observing conversion lines of sup(110m)Ag and good performances of the system have been confirmed. By adopting this method, intensive sources with large area can be used and entire momentum spectra can be obtained rapidly irrespective of the existences of gamma rays and so weak conversion lines can be found more easily. For nuclei with high beta ray backgrounds, the method is not so powerful that an experiment to combine the electron-beta coincidence method with this one is now in progress. (auth.)
Françoise Lavocat (a cura di La théorie littéraire des mondes possibles
Directory of Open Access Journals (Sweden)
Guido Furci
2012-04-01
Full Text Available I testi raccolti ed introdotti da Françoise Lavocat nel suo La théorie littéraire des mondes possibile (2010 ambiscono tutti a colmare una lacuna. Quella causata dal cosiddetto tournant cognitiviste, caratterizzato dal consolidarsi di un dialogo fra scienze umane e scienze esatte – nell’intento, certo, di ridurre lo scarto fra ambiti disciplinari distinti, seppur accomunati da uno stesso interesse per il lascito post-strutturalista –, ma anche promotore di una politica editoriale senza precedenti, destinata ad escludere dal canone contemporaneo buona parte di quei contributi, il cui punto di forza non potesse consistere nell’ulteriore avanzamento della rivoluzione epistemologica in corso.
Crimes et châtiments dans le monde de la finance pendant les années Bush
Régine Hollander
2010-01-01
Le premier mandat de George W. Bush est ébranlé par une série de scandales dans le monde de l’entreprise et de la finance qui provoque une vague de réformes au sein du Congrès et des autorités de réglementation. La loi Sarbanes-Oxley, votée en 2002, a pour but d’accroître les contrôles financiers et de prévenir la fraude. Simultanément un dispositif répressif, destiné à prouver que le crime ne paie pas et à redonner confiance aux petits investisseurs, est mis en place. Les entreprises paient ...
Dietschy Paul, Gastaut Yvan, Mourlane Stéphane, Histoire politique des coupes du monde de football
Directory of Open Access Journals (Sweden)
Gilles Ferréol
2011-03-01
Full Text Available Dès les premières lignes de leur introduction, les auteurs font à juste titre observer que « de l’omniprésence de Benito Mussolini pendant la Coupe du monde en Italie en 1934 au baiser de Jacques Chirac sur le crâne chauve de Fabien Barthez le 12 juillet 1998 au stade de France, la deuxième compétition sportive après les Jeux olympiques d’été en termes d’audience télévisée n’a jamais pu maintenir la position de neutralité absolue et intransigeante qu’aurait voulu respecter son créateur, la fi...
Les mondes imaginaires de Mélanie de Coster, une écrivaine en proie à la fantaisie
Directory of Open Access Journals (Sweden)
Esther Bautista Naranjo
2016-04-01
Full Text Available This interview explores the imaginary worlds created by Mélanie de Coster, a Belgian writer of contemporary fantastic literature. Ever since she published her first book in 2003, De Coster has combined elements from the aesthetics of the fantastic with other genres, thus making this her personal trademark. The fantastic becomes then an approach which is not at the core of the story told, but it rather complements it by adding some features like surprise, anxie-ty or mystery. In her most recent novel, De l’autre côté des mondes, the main plot even includes some social worries. Eventually, the fantastic becomes the leading thread of such a heterogeneous production.
De Aquino, Fran
2016-01-01
A new type of device for controlling gravity is here proposed. This is a quantum device because results from the behaviour of the matter and energy at subatomic length scale (10 m).-20 From the technical point of view this device is easy to build, and can be used to develop several devices for controlling gravity. Introduction Some years ago I wrote a paper [1] where a correlation between gravitational mass and inertial mass was obtained. In the paper I pointed out that the relationship betwe...
Chiou, Dah-Wei
2015-12-01
This paper 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 paper, 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.
Brans–Dicke gravity theory from topological gravity
International Nuclear Information System (INIS)
We consider a model that suggests a mechanism by which the four dimensional Brans–Dicke gravity theory may emerge from the topological gravity action. To achieve this goal, both the Lie algebra and the symmetric invariant tensor that define the topological gravity Lagrangian are constructed by means of the Lie algebra S-expansion procedure with an appropriate abelian semigroup S
SATELLITE GRAVITY SURVEYING TECHNOLOGY AND RESEARCH OF EARTH'S GRAVITY FIELD
Institute of Scientific and Technical Information of China (English)
Ning Jinsheng
2003-01-01
This is a summarized paper. Two topics are discussed: Firstly, the concept, development and application of four kinds of satellite gravity surveying technology are introduced; Secondly, some problems of theory and method, which must be considered in the study of the Earth's gravity field based on satellite gravity data, are expounded.
Euler Chern Simons Gravity from Lovelock Born Infeld Gravity
Izaurieta, Fernando; Rodriguez, Eduardo; Salgado, Patricio
2004-01-01
In the context of a gauge theoretical formulation, higher dimensional gravity invariant under the AdS group is dimensionally reduced to Euler-Chern-Simons gravity. The dimensional reduction procedure of Grignani-Nardelli [Phys. Lett. B 300, 38 (1993)] is generalized so as to permit reducing D-dimensional Lanczos Lovelock gravity to d=D-1 dimensions.
Gravity separation for oil wastewater treatment
Golomeova, Mirjana; Zendelska, Afrodita; Krstev, Boris; Krstev, Aleksandar
2010-01-01
In this paper, the applications of gravity separation for oil wastewater treatment are presented. Described is operation on conventional gravity separation and parallel plate separation. Key words: gravity separation, oil, conventional gravity separation, parallel plate separation.
Gravity Station Data for Spain
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 28493 records. This data base was received in April 1997. Principal gravity parameters include Free-air Anomalies which have been...
Gravity Data for South America
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (152,624 records) were compiled by the University of Texas at Dallas. This data base was received in June 1992. Principal gravity...
Interior Alaska Gravity Station Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 9416 records. This data base was received in March 1997. Principal gravity parameters include Free-air Anomalies which have been...
Gravity Station Data for Portugal
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 3064 records. This data base was received in April 1997. Principal gravity parameters include Free-air Anomalies which have been...
Scalable Gravity Offload System Project
National Aeronautics and Space Administration — A scalable gravity offload device simulates reduced gravity for the testing of various surface system elements such as mobile robots, excavators, habitats, and...
Diaz, Pablo; Walton, Mark
2016-01-01
With the aim of investigating the relation between gravity and non-locality at the classical level, we study a bilocal scalar field model. Bilocality introduces new (internal) degrees of freedom that can potentially reproduce gravity. We show that the equations of motion of the massless branch of the free bilocal model match those of linearized gravity. We also discuss higher orders of perturbation theory, where there is self-interaction in both gravity and the bilocal field sectors.
Perturbative Quantization of Gravity Theories
Bern, Z.
2001-01-01
We discuss string theory relations between gravity and gauge theory tree amplitudes. Together with $D$-dimensional unitarity, these relations can be used to perturbatively quantize gravity theories, i.e. they contain the necessary information for calculating complete gravity $S$-matrices to any loop orders. This leads to a practical method for computing non-trivial gravity $S$-matrix elements by relating them to much simpler gauge theory ones. We also describe arguments that N=8 D=4 supergrav...
Introduction to Loop Quantum Gravity
Mercuri, Simone
2012-01-01
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.
Localized gravity on FRW branes
Singh, Parampreet; Dadhich, Naresh
2002-01-01
We study the system of Schwarzschild anti de Sitter (S-AdS) bulk and FRW brane for localization of gravity; i.e. zero mass gravitons having ground state on the brane, and thereby recovering the Einstein gravity with high energy correction. It has been known that gravity is not localized on AdS brane with AdS bulk. We prove the general result that gravity is not localized for dynamic branes whenever Lambda_4 0 and black h...
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.
Bueno, Pablo
2016-01-01
We drastically simplify the problem of linearizing a general higher-order theory of gravity. We reduce it to the evaluation of its Lagrangian on a particular Riemann tensor depending on two parameters, and the computation of two derivatives with respect to one of those parameters. We use our method to construct a D-dimensional cubic theory of gravity which satisfies the following properties: 1) it shares the spectrum of Einstein gravity, i.e., it only propagates a transverse and massless graviton on a maximally symmetric background; 2) the relative coefficients of the different curvature invariants involved are the same in all dimensions; 3) it is neither trivial nor topological in four dimensions. Up to cubic order in curvature, the only previously known theories satisfying the first two requirements are the Lovelock ones: Einstein gravity, Gauss-Bonnet and cubic-Lovelock. Of course, the last two theories fail to satisfy requirement 3 as they are, respectively, topological and trivial in four dimensions. We ...
International Nuclear Information System (INIS)
The theoretical basis for gravity-wave astronomy is described, along with the energy and momentum of gravitational fields. Other topics discussed include:- burst and periodic sources of gravitational waves, the cosmological stochastic background, and the detection of gravitational waves. (U.K.)
Bergshoeff, Eric A.; Hohm, Olaf; Rosseel, Jan; Townsend, Paul K.
2011-01-01
The physical modes of a recently proposed D-dimensional "critical gravity'', linearized about its anti-de Sitter vacuum, are investigated. All "log mode'' solutions, which we categorize as "spin-2'' or "Proca'', arise as limits of the massive spin-2 modes of the noncritical theory. The linearized Ei
Banerjee, Rabin; Majhi, Bibhas Ranjan
2010-01-01
Starting from the definition of entropy used in statistical mechanics we show that it is proportional to the gravity action. For a stationary black hole this entropy is expressed as $S = E/ 2T$, where $T$ is the Hawking temperature and $E$ is shown to be the Komar energy. This relation is also compatible with the generalised Smarr formula for mass.
Artificial Gravity Research Plan
Gilbert, Charlene
2014-01-01
This document describes the forward working plan to identify what countermeasure resources are needed for a vehicle with an artificial gravity module (intermittent centrifugation) and what Countermeasure Resources are needed for a rotating transit vehicle (continuous centrifugation) to minimize the effects of microgravity to Mars Exploration crewmembers.
Newburgh, Ronald
2010-01-01
It's both surprising and rewarding when an old, standard problem reveals a subtlety that expands its pedagogic value. I realized recently that the role of gravity in the range equation for a projectile is not so simple as first appears. This realization may be completely obvious to others but was quite new to me.
International Nuclear Information System (INIS)
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)
Sobreiro, R. F.; Tomaz, A. A.; Otoya, V. J. Vasquez
2012-01-01
Pure gauge theories for de Sitter, anti de Sitter and orthogonal groups, in four-dimensional Euclidean spacetime, are studied. It is shown that, if the theory is asymptotically free and a dynamical mass is generated, then an effective geometry may be induced and a gravity theory emerges.
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.
Noncommutative Symmetries and Gravity
Aschieri, P
2006-01-01
Spacetime geometry is twisted (deformed) into noncommutative spacetime geometry, where functions and tensors are now star-multiplied. Consistently, spacetime diffeomorhisms are twisted into noncommutative diffeomorphisms. Their deformed Lie algebra structure and that of infinitesimal Poincare' transformations is defined and explicitly constructed. This allows to construct a noncommutative theory of gravity.
From Classical To Quantum Gravity: Introduction to Loop Quantum Gravity
Giesel, Kristina
2012-01-01
We present an introduction to the canonical quantization of gravity performed in loop quantum gravity, based on lectures held at the 3rd quantum geometry and quantum gravity school in Zakopane in 2011. A special feature of this introduction is the inclusion of new proposals for coupling matter to gravity that can be used to deparametrize the theory, thus making its dynamics more tractable. The classical and quantum aspects of these new proposals are explained alongside the standard quantization of vacuum general relativity in loop quantum gravity.
Even-dimensional topological gravity from Chern-Simons gravity
Merino, N.; Perez, Alfredo; Salgado, P.(Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile)
2009-01-01
It is shown that the topological action for gravity in 2n-dimensions can be obtained from the 2n+1-dimensional Chern-Simons gravity genuinely invariant under the Poincare group. The 2n-dimensional topological gravity is described by the dynamics of the boundary of a 2n+1-dimensional Chern-Simons gravity theory with suitable boundary conditions. The field $\\phi^{a}$, which is necessary to construct this type of topological gravity in even dimensions, is identified with the coset field associat...
Directory of Open Access Journals (Sweden)
A. V. Vikulin
2015-09-01
Full Text Available Gravity phenomena related to the Earth movements in the Solar System and through the Galaxy are reviewed. Such movements are manifested by geological processes on the Earth and correlate with geophysical fields of the Earth. It is concluded that geodynamic processes and the gravity phenomena (including those of cosmic nature are related. The state of the geomedium composed of blocks is determined by stresses with force moment and by slow rotational waves that are considered as a new type of movements [Vikulin, 2008, 2010]. It is shown that the geomedium has typical rheid properties [Carey, 1954], specifically an ability to flow while being in the solid state [Leonov, 2008]. Within the framework of the rotational model with a symmetric stress tensor, which is developed by the authors [Vikulin, Ivanchin, 1998; Vikulin et al., 2012a, 2013], such movement of the geomedium may explain the energy-saturated state of the geomedium and a possibility of its movements in the form of vortex geological structures [Lee, 1928]. The article discusses the gravity wave detection method based on the concept of interactions between gravity waves and crustal blocks [Braginsky et al., 1985]. It is concluded that gravity waves can be recorded by the proposed technique that detects slow rotational waves. It is shown that geo-gravitational movements can be described by both the concept of potential with account of gravitational energy of bodies [Kondratyev, 2003] and the nonlinear physical acoustics [Gurbatov et al., 2008]. Based on the combined description of geophysical and gravitational wave movements, the authors suggest a hypothesis about the nature of spin, i.e. own moment as a demonstration of the space-time ‘vortex’ properties.
Industrial processes influenced by gravity
Ostrach, Simon
1988-01-01
In considering new directions for low gravity research with particular regard to broadening the number and types of industrial involvements, it is noted that transport phenomena play a vital role in diverse processes in the chemical, pharmaceutical, food, and biotech industries. Relatively little attention has been given to the role of gravity in such processes. Accordingly, numerous industrial processes and phenomena are identified which involve gravity and/or surface tension forces. Phase separations and mixing are examples that will be significantly different in low gravity conditions. A basis is presented for expanding the scope of the low gravity research program and the potential benefits of such research is indicated.
Analog Systems for Gravity Duals
Hossenfelder, S.
2014-01-01
We show that analog gravity systems exist for charged, planar black holes in asymptotic Anti-de Sitter space. These black holes have been employed to describe, via the gauge-gravity duality, strongly coupled condensed matter systems on the boundary of AdS-space. The analog gravity system is a different condensed matter system that, in a suitable limit, describes the same bulk physics as the theory on the AdS boundary. This combination of the gauge-gravity duality and analog gravity therefore ...
Quantum gravity from noncommutative spacetime
International Nuclear Information System (INIS)
We review a novel and authentic way to quantize gravity. This novel approach is based on the fact that Einstein gravity can be formulated in terms of a symplectic geometry rather than a Riemannian geometry in the context of emergent gravity. An essential step for emergent gravity is to realize the equivalence principle, the most important property in the theory of gravity (general relativity), from U(1) gauge theory on a symplectic or Poisson manifold. Through the realization of the equivalence principle, which is an intrinsic property in symplectic geometry known as the Darboux theorem or the Moser lemma, one can understand how diffeomorphism symmetry arises from noncommutative U(1) gauge theory; thus, gravity can emerge from the noncommutative electromagnetism, which is also an interacting theory. As a consequence, a background-independent quantum gravity in which the prior existence of any spacetime structure is not a priori assumed but is defined by using the fundamental ingredients in quantum gravity theory can be formulated. This scheme for quantum gravity can be used to resolve many notorious problems in theoretical physics, such as the cosmological constant problem, to understand the nature of dark energy, and to explain why gravity is so weak compared to other forces. In particular, it leads to a remarkable picture of what matter is. A matter field, such as leptons and quarks, simply arises as a stable localized geometry, which is a topological object in the defining algebra (noncommutative *-algebra) of quantum gravity.
Quantum gravity from noncommutative spacetime
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.
DEFF Research Database (Denmark)
Forsberg, René; Sideris, M.G.; Shum, C.K.
2005-01-01
The gravity field of the earth is a natural element of the Global Geodetic Observing System (GGOS). Gravity field quantities are like spatial geodetic observations of potential very high accuracy, with measurements, currently at part-per-billion (ppb) accuracy, but gravity field quantities are also...... unique as they can be globally represented by harmonic functions (long-wavelength geopotential model primarily from satellite gravity field missions), or based on point sampling (airborne and in situ absolute and superconducting gravimetry). From a GGOS global perspective, one of the main challenges...... is to ensure the consistency of the global and regional geopotential and geoid models, and the temporal changes of the gravity field at large spatial scales. The International Gravity Field Service, an umbrella "level-2" IAG service (incorporating the International Gravity Bureau, International Geoid Service...
«Que la vie du monde est infinie»: Montaigne y la tesis de la eternidad del mundo
Directory of Open Access Journals (Sweden)
Jordi Bayod
2010-12-01
Full Text Available Montaigne insère en De la liberté de conscience un commentaire sur la destruction de la culture classique par les chrétiens qui ne peut que nous faire penser au chapitre II, 5 des Discorsi de Machiavel. Or, le problème de fond examiné par le florentin dans ce chapitre, la brièveté de la mémoire humaine comme objection à la thèse de l’éternité du monde, semble avoir intéressé aussi l’auteur des Essais. C’est ce que suggèrent certaines pages de Des coches qui mettent expressément en question l’idée lucrétienne de la naissance et la nouveauté du monde.Ces pages, à leur tour, nous renvoient à une significative digression, ajoutée à l’Apologie de Raymond Sebond après 1588, sur des façons alternatives de concevoir le monde. Dans ces lignes audacieuses Montaigne présente comme vraisemblable un monde régi par une temporalité cyclique et beaucoup plus ancien qu’il n’était traditionnellement admis, peut-être «infini». Dans un autre lieu de l’Apologie nous trouvons, finalement, une péremptoire déclaration, de forte teinture stoïque, sur l’homogénéité de la nature a travers le temps. Son examen confirme, il nous semble, le grand intérêt que Montaigne a eu pour la thèse de l’éternité du monde.Montaigne inserts in “De la liberté de conscience” a commentary on the destruction of pagan culture by Christians that make us think in chapter II, 5 of Machiavelli’s Discorsi. Now, the main question studied by the Florentin in this chapter, the brevity of human memory as an objection to the thesis of the eternity of the world, also seems to have interested the author of the Essays. It is so suggested by certain pages of “Des coches” that call expressly in question the Lucretian idea of the birth and novelty of the world.These pages, in their turn, remit us to a significant digression, added after 1588 to the “Apologie”, about alternative ways of conceiving the world. In these bold lines
Poročilo o doktorskem seminarju »Appropriation et transmission des langues et des cultures du monde«
Directory of Open Access Journals (Sweden)
Jana Zidar Forte
2013-12-01
Full Text Available Od 20. do 22. septembra 2012 je v Londonu potekal Mednarodni doktorski seminar z naslovom »Appropriation et transmission des langues et des cultures du monde« (Usvajanje in prenašanje jezikov in kultur sveta in podnaslovom «Au-delà de la compétence linguistique dans un monde globalisé: action, interaction et médiation interculturelle« (Onkraj jezikovne kompetence v globaliziranem svetu: medkulturno udejstvovanje, interakcija in posredovanje, ki sta ga organizirala francoska inštituta PLIDAM (Pluralité des langues et des identités: didactique, acquisitions, médiations, Paris in INALCO (Institut national des langues et civilisation orientales, Paris v sodelovanju z ustanovo gostiteljico SOAS (School of Oriental and African Studies, University of London, department of Linguistcs, Centre for language Pedagogy.
Le théâtre de Juan Mayorga: de la scène au monde à travers le prisme du langage
Spooner, Claire
2013-01-01
Juan Mayorga signe le retour en force du verbe dans la dramaturgie espagnole contemporaine. Cette thèse pense son œuvre comme une « carte du monde » qui reflète et interroge certaines facettes de la réalité à travers le prisme du langage. L’étude des scènes de langage et du langage de la scène fait appel aux théories de pragmatique du discours. Ensuite, les analyses de la théâtralité de la parole (la manière dont les mots prennent corps et sens sur scène et dans le monde) montrent que chez c...
Directory of Open Access Journals (Sweden)
Christophe Beaurain
2007-02-01
Full Text Available Les mutations récentes du monde rural, pourtant nombreuses depuis quelques années, n’ont pas encore fait, à ce jour, l’objet d’une abondante littérature de portée analytique. La théorie économique abordant l’évolution des choix de localisation des activités économiques et des populations ne s’est que très marginalement intéressée au monde rural, préférant se focaliser sur les espaces urbains. Fruit d’une approche pluridisciplinaire, cet ouvrage vient très heureusement combler cette insuffisan...
« Ecoute, lecteur... » : la représentation de la lecture dans L’Autre monde de Cyrano de Bergerac
Directory of Open Access Journals (Sweden)
Claudine Nédélec
2007-11-01
Full Text Available L'Autre monde, ou les Etats et Empires de la lune de Cyrano de Bergerac s'ouvre sur une conversation : les amis du narrateur s'amusent à proposer des définitions burlesques de la lune ; tout à coup, celui-ci s'écrie :Et moy, [...] je croys sans m'amuser aux imaginations pointuës dont vous chatouillez le temps pour le faire marcher plus viste, que la Lune est un monde comme celuy-ci à qui le nostre sert de Lune.On se moque de lui ; mais il ne renonce pas à son hypothèse :Cette pensée dont la h...
Synthèse: 2015 Indice de la faim dans le monde: Conflict armés et le défi de la faim
von Grebmer, Klaus; Bernstein, Jill; Prasai, Nilam; Yin, Sandra; Yohannes, Yisehac; Towey, Olive; Sonntag, Andrea; Neubauer, Larissa; de Waal, Alex
2015-01-01
L’Indice de la faim dans le monde 2015 (GHI) – le dixième d’une parution annuelle – propose une mesure multidimensionnelle de la faim au niveau national, régional et mondial. Il démontre que le monde a progressé en matière de réduction de la faim depuis 2000, mais qu’il reste encore un long chemin à faire, avec des niveaux de faim « alarmants » ou « graves » dans encore 52 pays. La thématique du rapport de cette année est celle des conflits armés et de la faim. Si l’Histoire a montré que la f...
Akhavan, Amin; Nemati, Azadeh; Shirzad, Ahmad
2016-01-01
We show that the problem of ghosts in critical gravity and its higher dimensional extensions can be resolved by giving dynamics to the symmetric rank two auxiliary field existing in the action of these theories. These New Bi-Gravities, at linear level around the AdS vacuum, are free of Boulware-Deser ghost, kinetic ghost and tachyonic instability within the particular range of parameters. Moreover, we show that the energy and entropy of AdS-Schwarzschild black hole solutions of these new models are positive in the same range of parameters. This may be the sign that these new models are also free of ghost instabilities at the non-linear level.
Murad, P. A.
2003-01-01
Newtonian gravitation adequately predicts planet and satellite motion. Gravitational anomalies and the wish to travel at relativistic speeds, however, imply that gravity should be integrated within a unification framework that may include electricity and magnetism. Thus, new theories are needed that predict currently accepted phenomenon as well as anomalies to prepare the necessary groundwork for experimental validation needed for advanced technology propulsion schemes and far-term missions. A primary deficiency is that we are obviously limited within the confines of our own solar system and a different gravity model may be applicable elsewhere in the cosmos. The model proposed here follows previous ideas proposed by Murad, Dyatlov, and Jefimenko for a universal gravitation model with an intrinsic radial force term coupled with angular momentum. Including angular momentum may explain several spin symmetries seen in some anomalous gyroscopic experiments and throughout the universe regarding planets that orbit around the sun: moons that orbit larger planetary bodies: and the rotation about each planetary axis.
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.
Gravity from Spacetime Thermodynamics
Padmanabhan, T
2002-01-01
The Einstein-Hilbert action (and thus the dynamics of gravity) can be obtained by combining the principle of equivalence, special relativity and quantum theory in the Rindler frame and postulating that the horizon area must be proportional to the entropy. This approach uses the local Rindler frame as a natural extension of the local inertial frame, and leads to the interpretation that the gravitational action represents the free energy of the spacetime geometry. As an aside, one obtains an insight into the peculiar structure of Einstein-Hilbert action and a natural explanation to the questions:(i) Why does the covariant action for gravity contain second derivatives of the metric tensor? (ii) Why is the gravitational coupling constant is positive ? Some geometrical features of gravitational action are clarified.
International Nuclear Information System (INIS)
Superstrings being consistent theories that include gravity have to produce classical gravity within limits provided by unambiguous quantum effects. Through the study of a hard scattering process - clearly provided by string theory - it is shown that infinite genus calculations give indeed rise to a classical limit, when 'large' distances are explored, as well as quantum effects. These are dominant at distances of the order of the string length (related to the Planck length) but may extend much beyond that region hinting indeed to gravitational instabilities. Below the string length even space-time loses meaning as a classical concept. A new position-momentum uncertainty relation is produced that assigns to the string length the meaning of a minimum observable distance. (orig.)
International Nuclear Information System (INIS)
Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem. Furthermore, we
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.
Christiansen, N.; Knorr, B.; Meibohm, J.; Pawlowski, J. M.; Reichert, M.
2015-12-01
We investigate the ultraviolet behavior of quantum gravity within a functional renormalization 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 nontrivial 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 renormalization group flows. We show that momentum locality of graviton correlation functions is nontrivially linked to diffeomorphism invariance, and is realized in the present setup.
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
广义不变凸分式规划的Mond-Weir对偶定理%Mmond-Weir Duality Theorems for Generalized InvexityFractional Programming
Institute of Scientific and Technical Information of China (English)
张钟德; 刘素蓉
2008-01-01
本文对不变凸函数概念推广,引入了一类更为广泛的广义不变凸性概念,并证明了在该类新广义不变凸性条件下,一类非凸非线性分式规划的Mond-Weir对偶的弱对偶、强对偶和逆对偶定理.
International Nuclear Information System (INIS)
Quantum theory and general relativity will only be unified when theory meets experiment. Physics in the 20th century was built on two great revolutions: the general theory of relativity and quantum mechanics. These two theories have profoundly changed the way we think about space, time and the meaning of reality, and both have been verified to extraordinary precision. However, the two theories are also completely incompatible with one another. Three of the four known forces in nature - the electromagnetic, weak and strong interactions - are described by quantum field theories. These theories, which make up the highly successful Standard Model of particle physics, explain fundamental interactions in terms of the exchange of field particles between elementary matter particles. Gravity, on the other hand, does not fit into this framework. Einstein's elegant description of gravity is classical, and gravitational forces result from the curvature of the space-time continuum. But there is something deeply unsettling about this whole picture. Ever since Maxwell unified electricity and magnetism with a single set of equations, finding a general theory that can describe everything that we observe in the physical world has been one of the primary goals in theoretical physics. A unified description of the electromagnetic and weak interactions was achieved in the 1960s, but a true theory of quantum gravity would be a giant step towards this goal. Moreover, a theory of quantum gravity is needed to understand what happens in circumstances when both gravitational and quantum effects are large - such as in the very early universe. (U.K.)
Antimatter gravity with muonium
kaplan, Daniel M.; Fischbach, Ephraim; Kirch, Klaus; Mancini, Derrick C.; Phillips, James D.; Phillips, Thomas J.; Reasenberg, Robert D; Roberts, Thomas J.; Terry, Jeff
2016-01-01
The gravitational acceleration of antimatter, $\\bar{g}$, has never been directly measured and could bear importantly on our understanding of gravity, the possible existence of a fifth force, and the nature and early history of the universe. Three avenues appear feasible for such a measurement: antihydrogen, positronium, and muonium. The muonium measurement requires a novel monoenergetic, low-velocity, horizontal muonium beam directed at an atom interferometer. The precision three-grating inte...
Gravity, Time, and Lagrangians
Huggins, Elisha
2010-01-01
Feynman mentioned to us that he understood a topic in physics if he could explain it to a college freshman, a high school student, or a dinner guest. Here we will discuss two topics that took us a while to get to that level. One is the relationship between gravity and time. The other is the minus sign that appears in the Lagrangian. (Why would one…
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 s...
Dereli, T.; Yetişmişoğlu, C.
2016-06-01
We derive the field equations for topologically massive gravity coupled with the most general quadratic curvature terms using the language of exterior differential forms and a first-order constrained variational principle. We find variational field equations both in the presence and absence of torsion. We then show that spaces of constant negative curvature (i.e. the anti de-Sitter space AdS 3) and constant torsion provide exact solutions.
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.
Covariant Loop Quantum Gravity
Rovelli, Carlo; Vidotto, Francesca
2014-11-01
Preface; Part I. Foundations: 1. Spacetime as a quantum object; 2. Physics without time; 3. Gravity; 4. Classical discretization; Part II. The 3D Theory: 5. 3D Euclidean theory; 6. Bubbles and cosmological constant; Part III. The Real World: 7. The real world: 4D Lorentzian theory; 8. Classical limit; 9. Matter; Part IV. Physical Applications: 10. Black holes; 11. Cosmology; 12. Scattering; 13. Final remarks; References; Index.
Alesci, Emanuele; Cianfrani, Francesco
2015-01-01
Quantum Reduced Loop Gravity provides a promising framework for a consistent characterization of the early Universe dynamics. Inspired by BKL conjecture, a flat Universe is described as a collection of Bianchi I homogeneous patches. The resulting quantum dynamics is described by the scalar constraint operator, whose matrix elements can be analytically computed. The effective semiclassical dynamics is discussed, and the differences with Loop Quantum Cosmology are emphasized.
Aastrup, Johannes; Grimstrup, Jesper M.
2009-01-01
We present a separable version of Loop Quantum Gravity (LQG) based on an inductive system of cubic lattices. We construct semi-classical states for which the LQG operators -- the flux, the area and the volume operators -- have the right classical limits. Also, we present the Hamilton and diffeomorphism constraints as operator constraints and show that they have the right classical limit. Finally, we speculate whether the continuum limit, which these semi-classical states probe, can be defined...
Giribet, Gaston
2014-01-01
Minimal Massive Gravity (MMG) is an extension of three-dimensional Topologically Massive Gravity that, when formulated about Anti-de Sitter space, accomplishes to solve the tension between bulk and boundary unitarity that other models in three dimensions suffer from. We study this theory at the chiral point, i.e. at the point of the parameter space where one of the central charges of the dual conformal field theory vanishes. We investigate the non-linear regime of the theory, meaning that we study exact solutions to the MMG field equations that are not Einstein manifolds. We exhibit a large class of solutions of this type, which behave asymptotically in different manners. In particular, we find analytic solutions that represent two-parameter deformations of extremal Banados-Teitelboim-Zanelli (BTZ) black holes. These geometries behave asymptotically as solutions of the so-called Log Gravity, and, despite the weakened falling-off close to the boundary, they have finite mass and finite angular momentum, which w...
Ashour, Amani; Faizal, Mir; Ali, Ahmed Farag; Hammad, Fayçal
2016-05-01
In this work, we investigate the thermodynamics of black p-branes (BB) in the context of Gravity's Rainbow. We investigate this using rainbow functions that have been motivated from loop quantum gravity and κ -Minkowski non-commutative spacetime. Then for the sake of comparison, we examine a couple of other rainbow functions that have also appeared in the literature. We show that, for consistency, Gravity's Rainbow imposes a constraint on the minimum mass of the BB, a constraint that we interpret here as implying the existence of a black p-brane remnant. This interpretation is supported by the computation of the black p-brane's heat capacity that shows that the latter vanishes when the Schwarzschild radius takes on a value that is bigger than its extremal limit. We found that the same conclusion is reached for the third version of rainbow functions treated here but not with the second one for which only standard black p-brane thermodynamics is recovered.
Granular Superconductors and Gravity
Noever, David; Koczor, Ron
1999-01-01
As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.
Levin, J J
1995-01-01
The union of high-energy particle theories and gravitation often gives rise to an evolving strength of gravity. The standard picture of the earliest universe would certainly deserve revision if the Planck mass, which defines the strength of gravity, varied. A notable consequence is a gravity-driven, kinetic inflation. Unlike standard inflation, there is no potential nor cosmological constant. The unique elasticity in the kinetic energy of the Planck mass provides a negative pressure able to drive inflation. As the kinetic energy grows, the spacetime expands more quickly. The phenomenon of kinetic inflation has been uncovered in both string theory and Kaluza-Klein theories. The difficulty in exiting inflation in these cases is reviewed. General forms of the Planck field coupling are shown to avoid the severity of the graceful exit problem found in string and Kaluza-Klein theories. The completion of the model is foreshadowed with a suggestion for a heating mechanism to generate the hot soup of the big bang.
Energy Technology Data Exchange (ETDEWEB)
Agrawal, Aniket [Indian Institute of Technology Delhi, New Delhi (India)
2012-07-01
Recently, Chiao predicted the quantum incompressibility of a falling Rydberg atom. A Hydrogen-like atom was considered in a very high n,l=m=n-1 state to calculate the effects of tidal gravitational forces on these states. The high values of quantum numbers ensure that gravitational effect is measurable on the *stretch* state. We consider a similar atom and derive the energy of a particular level under the influence of Newtonian gravity. A change in the frequency of observed transition is predicted for a freely falling Hydrogen atom. This change is calculated both in Newtonian gravity and in curved space. We see that the change in energy of the electron under gravity also depends on its principal quantum number. Thus there will be a shift in the frequency of the photon emitted by an electron making an ordinary transition from the state n=100, l=99, m=99 to the state n=99, l=98, m=98. Though this shift is quite less to be observed on Earth, it is measurable in satellites in a highly elliptical orbit about the earth, by spectroscopic methods. A similar result was derived by Chiao recently using a different argument. We conclude that the effect described by Chiao will be masked to a very large extent by the effect calculated above. Such perturbations might be important in emission spectra of white dwarfs and neutron stars.
Polar gravity fields from GOCE and airborne gravity
DEFF Research Database (Denmark)
Forsberg, René; Olesen, Arne Vestergaard; Yidiz, Hasan;
2011-01-01
Airborne gravity, together with high-quality surface data and ocean satellite altimetric gravity, may supplement GOCE to make consistent, accurate high resolution global gravity field models. In the polar regions, the special challenge of the GOCE polar gap make the error characteristics...... of combination models especially sensitive to the correct merging of satellite and surface data. We outline comparisons of GOCE to recent airborne gravity surveys in both the Arctic and the Antarctic. The comparison is done to new 8-month GOCE solutions, as well as to a collocation prediction from GOCE gradients...... in Antarctica. It is shown how the enhanced gravity field solutions improve the determination of ocean dynamic topography in both the Arctic and in across the Drake Passage. For the interior of Antarctica, major airborne gravity programs are currently being carried out, and there is an urgent need...
Gravity Resonance Spectroscopy and Einstein-Cartan Gravity
Abele, Hartmut; Ivanov, Andrei; 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.
Gravity-Matter Entanglement in Regge Quantum Gravity
Paunković, Nikola; Vojinović, Marko
2016-01-01
We argue that Hartle-Hawking states in the Regge quantum gravity model generically contain non-trivial entanglement between gravity and matter fields. Generic impossibility to talk about "matter in a point of space" is in line with the idea of an emergent spacetime, and as such could be taken as a possible candidate for a criterion for a plausible theory of quantum gravity. Finally, this new entanglement could be seen as an additional "effective interaction", which could possibly bring correc...
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 smoot...
Teleparallel Complex Gravity as Foundation for Noncommutative Gravity
Nishino, Hitoshi; Rajpoot, Subhash
2001-01-01
We present a teleparallel complex gravity as the foundation for the formulation of noncommutative gravity theory. The negative energy ghosts in the conventional formulation with U(1,3) local Lorentz connection no longer exists, since the local Lorentz invariance is broken down to U(1,3) global Lorentz symmetry. As desired, our teleparallel complex gravity theory also passes the key classical test of perihelion advance of Mercury. Based on this result, we present a lagrangian for the noncommut...
Geometric scalar theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Novello, M.; Bittencourt, E.; Goulart, E.; Salim, J.M.; Toniato, J.D. [Instituto de Cosmologia Relatividade Astrofisica ICRA - CBPF Rua Dr. Xavier Sigaud 150 - 22290-180 Rio de Janeiro - Brazil (Brazil); Moschella, U., E-mail: novello@cbpf.br, E-mail: eduhsb@cbpf.br, E-mail: Ugo.Moschella@uninsubria.it, E-mail: egoulart@cbpf.br, E-mail: jsalim@cbpf.br, E-mail: toniato@cbpf.br [Università degli Studi dell' Insubria - Dipartamento di Fisica e Matematica Via Valleggio 11 - 22100 Como - Italy (Italy)
2013-06-01
We present a geometric scalar theory of gravity. Our proposal will be described using the ''background field method'' introduced by Gupta, Feynman, Deser and others as a field theory formulation of general relativity. We analyze previous criticisms against scalar gravity and show how the present proposal avoids these difficulties. This concerns not only the theoretical complaints but also those related to observations. In particular, we show that the widespread belief of the conjecture that the source of scalar gravity must be the trace of the energy-momentum tensor — which is one of the main difficulties to couple gravity with electromagnetic phenomenon in previous models — does not apply to our geometric scalar theory. From the very beginning this is not a special relativistic scalar gravity. The adjective ''geometric'' pinpoints its similarity with general relativity: this is a metric theory of gravity. Some consequences of this new scalar theory are explored.
Cascading Gravity is Ghost Free
de Rham, Claudia; Tolley, Andrew J
2010-01-01
We perform a full perturbative stability analysis of the 6D cascading gravity model in the presence of 3-brane tension. We demonstrate that for sufficiently large tension on the (flat) 3-brane, there are no ghosts at the perturbative level, consistent with results that had previously only been obtained in a specific 5D decoupling limit. These results establish the cascading gravity framework as a consistent infrared modification of gravity.
Cosmological tests of modified gravity.
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years. PMID:27007681
Astrophysical aspects of Weyl gravity
Kazanas, Demosthenes
1991-01-01
This paper discusses the astrophysical implications and applications of Weyl gravity, which is the theory resulting from the unique action allowed under the principle of local scale invariance in Einstein gravity. These applications include galactic dynamics, the mass-radius relation, the cosmological constant, and the 'Modified Newtonian Dynamics' proposed by Milgrom (1983). The relation of Weyl gravity to other scale-invariant theories is addressed.
Schwarzschild Solution from WTDiff Gravity
Oda, Ichiro
2016-01-01
We study classical solutions in the Weyl-transverse (WTDiff) gravity. The WTDiff gravity is invariant under both the local Weyl (conformal) transformation and the volume preserving diffeormorphisms (transverse diffeomorphisms) and is known to be equivalent to general relativity at least at the classical level. In particular, we find that in a general space-time dimension, the Schwarzschild metric is a classical solution in the WTDiff gravity when it is expressed in the Cartesian coordinate system.
Conformal Tensors via Lovelock Gravity
Kastor, David
2013-01-01
Constructs from conformal geometry are important in low dimensional gravity models, while in higher dimensions the higher curvature interactions of Lovelock gravity are similarly prominent. Considering conformal invariance in the context of Lovelock gravity leads to natural, higher-curvature generalizations of the Weyl, Schouten, Cotton and Bach tensors, with properties that straightforwardly extend those of their familiar counterparts. As a first application, we introduce a new set of conformally invariant gravity theories in D=4k dimensions, based on the squares of the higher curvature Weyl tensors.
An underlying theory for gravity
International Nuclear Information System (INIS)
A new direction to understand gravity has recently been explored by considering classical gravity to be a derived interaction from an underlying theory. This underlying theory would involve new degrees of freedom at a deeper level, and it would be structurally different from classical gravitation. It may conceivably be a quantum theory or a non-quantum theory. The relation between this underlying theory and Einstein's gravity is similar to the connection between statistical mechanics and thermodynamics. We discuss the apparent lack of evidence of any quantum nature of spacetime and the meaning of quantum gravity in this context
Directory of Open Access Journals (Sweden)
Shan Gao
2011-04-01
Full Text Available The remarkable connections between gravity and thermodynamics seem to imply that gravity is not fundamental but emergent, and in particular, as Verlinde suggested, gravity is probably an entropic force. In this paper, we will argue that the idea of gravity as an entropic force is debatable. It is shown that there is no convincing analogy between gravity and entropic force in Verlinde’s example. Neither holographic screen nor test particle satisfies all requirements for the existence of entropic force in a thermodynamics system. Furthermore, we show that the entropy increase of the screen is not caused by its statistical tendency to increase entropy as required by the existence of entropic force, but in fact caused by gravity. Therefore, Verlinde’s argument for the entropic origin of gravity is problematic. In addition, we argue that the existence of a minimum size of spacetime, together with the Heisenberg uncertainty principle in quantum theory, may imply the fundamental existence of gravity as a geometric property of spacetime. This may provide a further support for the conclusion that gravity is not an entropic force.
Symmetries of Quantum Nonsymmetric Gravity
Mebarki, N; Boudine, A; Benslama, A
1999-01-01
Symmetries of Quantum Nonsymmetric gravity are studied and the corresponding generators are constructed . The related equal time canonical (and non canonical) (anti) commutation relations are established.