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
Milgrom, Mordehai
2010-01-01
I look at the growth of weak density inhomogeneities of nonrelativistic matter, in bimetric-MOND (BIMOND) cosmology. I concentrate on matter-twin-matter-symmetric versions of BIMOND, and assume that, on average, the universe is symmetrically populated in the two sectors. MOND effects are absent in an exactly symmetric universe, apart from the appearance of a cosmological constant, Lambda~(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. I derive the nonrelativistic 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. The latter is governed by MOND dynamics, which entails stronger gravity, and nonlinearity even for the smallest of perturbations. These ...
Cosmological fluctuation growth in bimetric MOND
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...
Growth histories in bimetric massive gravity
We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless and massive scalar gravitational fluctuations. Matter perturbations then evolve like in Einstein gravity. We perturb the future de Sitter regime by the ratio of matter to dark energy, producing quasi-de Sitter space. In this more general setting the massive and massless fluctuations mix. We argue that in the quasi-de Sitter regime, the growth of structure in bimetric gravity differs from that of Einstein gravity
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
Akrami, Yashar; Hassan, S. F.; Könnig, Frank; Schmidt-May, Angnis; Solomon, Adam R.
2015-09-01
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.
Bimetric gravity is cosmologically viable
Akrami, Yashar; Könnig, Frank; Schmidt-May, Angnis; Solomon, Adam R
2015-01-01
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, $M_f$, 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 $\\Lambda$CDM, but with a technically-natural value for the cosmological constant. We find $M_f$ should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis.
Bimetric gravity is cosmologically viable
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.
Spherically Symmetric Solution in Bi-metric theory of Gravity
E, Anoop Narayanan P; Suresh, P. K.
2014-01-01
The possibility of spherically symmetric solutions in bi-metric theory of gravity is examined. It is shown that two possible black hole type solutions exists in the model. Spherically symmetric solution of general theory of relativity is recovered in the absence of the second metric. The result is compared with other bi-metric models as well as general theory of relativity.
Gravitational waves in ghost free bimetric gravity
We obtain a set of exact gravitational wave solutions for the ghost free bimetric theory of gravity. With a flat reference metric, the theory admits the vacuum Brinkmann plane wave solution for suitable choices of the coefficients of different terms in the interaction potential. An exact gravitational wave solution corresponding to a massive scalar mode is also admitted for arbitrary choice of the coefficients with the reference metric being proportional to the spacetime metric. The proportionality factor and the speed of the wave are calculated in terms of the parameters of the theory. We also show that a F(R) extension of the theory admits similar solutions but in general is plagued with ghost instabilities
Viable cosmological solutions in massive bimetric gravity
We find the general conditions for viable cosmological solution at the background level in bigravity models. Furthermore, we constrain the parameters by comparing to the Union 2.1 supernovae catalog and identify, in some cases analytically, the best fit parameter or the degeneracy curve among pairs of parameters. We point out that a bimetric model with a single free parameter predicts a simple relation between the equation of state and the density parameter, fits well the supernovae data and is a valid and testable alternative to ΛCDM. Additionally, we identify the conditions for a phantom behavior and show that viable bimetric cosmologies cannot cross the phantom divide
Bimetric renormalization group flows in quantum Einstein gravity
Research highlights: → Gravitational Effective Action in the bimetric truncation. → First study of the full gravitational flow with a bimetric structure. → The non-trivial gravitational RG fixed point persists under bimetric truncations. → Second non-trivial fixed point emerges, which may control the IR behavior of the theory. - Abstract: The formulation of an exact functional renormalization group equation for quantum Einstein gravity necessitates that the underlying effective average action depends on two metrics, a dynamical metric giving the vacuum expectation value of the quantum field, and a background metric supplying the coarse graining scale. The central requirement of 'background independence' is met by leaving the background metric completely arbitrary. This bimetric structure entails that the effective average action may contain three classes of interactions: those built from the dynamical metric only, terms which are purely background, and those involving a mixture of both metrics. This work initiates the first study of the full-fledged gravitational RG flow, which explicitly accounts for this bimetric structure, by considering an ansatz for the effective average action which includes all three classes of interactions. It is shown that the non-trivial gravitational RG fixed point central to the asymptotic safety program persists upon disentangling the dynamical and background terms. Moreover, upon including the mixed terms, a second non-trivial fixed point emerges, which may control the theory's IR behavior.
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.
Cosmological solutions in bimetric gravity and their observational tests
We obtain the general cosmological evolution equations for a classically consistent theory of bimetric gravity. Their analytic solutions are demonstrated to generically allow for a cosmic evolution starting out from a matter dominated FLRW universe and relaxing towards a de Sitter (anti-de Sitter) phase at late cosmic time. In particular, we examine a subclass of models which contain solutions that are able to reproduce the expansion history of the cosmic concordance model inspite of the nonlinear couplings of the two metrics. This is demonstrated explicitly by fitting these models to observational data from Type Ia supernovae, Cosmic Microwave Background and Baryon Acoustic Oscillations. In the appendix we comment on the relation to massive gravity
Visser's Massive Gravity Bimetric Theory Revisited
de Roany, Alain; Pacheco, J A de Freitas
2011-01-01
A massive gravity theory was proposed by Visser in the late nineties. This theory, based on a backgroung metric $b_{\\alpha \\beta}$ and on an usual dynamical metric $g_{\\alpha \\beta}$ has the advantage of being free of ghosts as well as discontinuities present in other massive theories proposed in the past. In the present investigation, the equations of Visser's theory are revisited with a particular care on the related conservation laws.\\ It will be shown that a multiplicative factor is missing in the graviton tensor originally derived by Visser, which has no incidence on the weak field approach but becomes important in the strong field regime when, for instance, cosmological applications are considered. In this case, contrary to some previous claims found in the literature, we conclude that a non-static background metric is required in order to obtain a solution able to mimic the $\\Lambda$CDM cosmology.
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...
Yang-Mills theory as bimetrical gravity: Polarization effects and finite-energy gluon clusters
Pavlovsky, Oleg V
2002-01-01
In this report a gravity representation of Yang-Mills theory is given. Using this approach, one obtains new information on solutions of classical YM theory. Singular solutions (black-hole-like solutions) of the YM equations are discussed in connection with bimetrical gravity. The behaviour of these solutions in a theory with a 'cosmological' Lambda-part is also investigated. A physical interpretation of such solutions is given. Using an effective field theory approach we try to show that quantum fluctuations and vacuum polarization effects lead to the generation of finite-energy objects in QCD.
Yang-Mills theory as bimetrical gravity: Polarization effects and finite-energy gluon clusters
In this report a gravity representation of Yang-Mills theory is given. Using this approach, one obtains new information on solutions of classical YM theory. Singular solutions (black-hole-like solutions) of the YM equations are discussed in connection with bimetrical gravity. The behaviour of these solutions in a theory with a 'cosmological' Lambda-part is also investigated. A physical interpretation of such solutions is given. Using an effective field theory approach we try to show that quantum fluctuations and vacuum polarization effects lead to the generation of finite-energy objects in QCD
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
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...
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...
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.
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
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
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.)
Corda, Christian
2008-01-01
Recently, some papers in the literature have shown that, from a bimetric theory of gravity, it is possible to produce massive gravitational waves which generate a longitudinal component in a particular polarization of the wave. After a review of previous works, in this paper the longitudinal response function of interferometers for this particular polarization of the wave is computed in two different gauges, showing the gauge invariance, and in its full frequency dependence, with specific app...
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 MOND, extended gravity and non-geodesic motion
Benedetto, Elmo; Corda, Christian
2014-01-01
Starting from the origin of Einstein general relativity (GR) the request of Mach on the theory's structure has been the core of the foundational debate. That problem is strictly connected with the nature of the mass-energy equivalence. It is well known that this is exactly the key point that Einstein used to realize a metric theory of gravitation having an unequalled beauty and elegance. On the other hand, the current requirements of particle physics and the open questions within extended gravity theories request a better understanding of Equivalence Principle (EP). The MOND theory by Milgrom proposes a modify of Newtonian dynamics and a variation of the ratio m_{i}/m_{g}, to be tested, at least, within the solar system. In this paper we attack this important issue from the general point of view of a weak modification of GR which considers a direct coupling between the Ricci curvature scalar and the matter Lagrangian. It is shown that a non geodesic ratio m_{i}/m_{g} can be fixed and that Milgrom acceleration...
Recent developments in bimetric theory
Schmidt-May, Angnis; von Strauss, Mikael
2016-05-01
This review is dedicated to recent progress in the field of classical, interacting, massive spin-2 theories, with a focus on ghost-free bimetric theory. We will outline its history and its development as a nontrivial extension and generalisation of nonlinear massive gravity. We present a detailed discussion of the consistency proofs of both theories, before we review Einstein solutions to the bimetric equations of motion in vacuum as well as the resulting mass spectrum. We introduce couplings to matter and then discuss the general relativity and massive gravity limits of bimetric theory, which correspond to decoupling the massive or the massless spin-2 field from the matter sector, respectively. More general classical solutions are reviewed and the present status of bimetric cosmology is summarised. An interesting corner in the bimetric parameter space which could potentially give rise to a nonlinear theory for partially massless spin-2 fields is also discussed. Relations to higher-curvature theories of gravity are explained and finally we give an overview of possible extensions of the theory and review its formulation in terms of vielbeins.
Recent developments in bimetric theory
This review is dedicated to recent progress in the field of classical, interacting, massive spin-2 theories, with a focus on ghost-free bimetric theory. We will outline its history and its development as a nontrivial extension and generalisation of nonlinear massive gravity. We present a detailed discussion of the consistency proofs of both theories, before we review Einstein solutions to the bimetric equations of motion in vacuum as well as the resulting mass spectrum. We introduce couplings to matter and then discuss the general relativity and massive gravity limits of bimetric theory, which correspond to decoupling the massive or the massless spin-2 field from the matter sector, respectively. More general classical solutions are reviewed and the present status of bimetric cosmology is summarised. An interesting corner in the bimetric parameter space which could potentially give rise to a nonlinear theory for partially massless spin-2 fields is also discussed. Relations to higher-curvature theories of gravity are explained and finally we give an overview of possible extensions of the theory and review its formulation in terms of vielbeins. (topical review)
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
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.
Palatini approach to modified f(R) gravity and its bi-metric structure
Santos, Janilo; 10.1063/1.4756822
2012-01-01
f(R) gravity theories in the Palatini formalism has been recently used as an alternative way to explain the observed late-time cosmic acceleration with no need of invoking either dark energy or extra spatial dimension. However, its applications have shown that some subtleties of these theories need a more profound examination. Here we are interested in the conformal aspects of the Palatini approach in extended theories of gravity. As is well known, extremization of the gravitational action a la Palatini, naturally "selects" a new metric h related to the metric g of the subjacent manifold by a conformal transformation. The related conformal function is given by the derivative of f(R). In this work we examine the conformal symmetries of the flat (k=0) FLRW spacetime and find that its Conformal Killing Vectors are directly linked to the new metric h and also that each vector yields a different conformal function.
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...
Post-Newtonian constraints on khronometric gravity theories with a MOND phenomenology
Bonetti, Matteo
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 a result, hypersurfaces of constant khronon define a preferred foliation of the spacetime, and the khronon can be thought of as a physical absolute time. The MOND phenomenology arises as a result of the presence, in the action, of terms depending on the acceleration of the congruence orthogonal to the preferred foliation. We find that if the theory is forced to reduce exactly to General Relativity (rather than to khronometric theory) in the high-acceleration regime, the post-Newtonian expansion breaks down at low accelerati...
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...
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,...
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.
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 ...
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
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
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.
Daniel CEFAÏ
2015-01-01
Le concept de monde social, avant d’être thématisé par Anselm Strauss, Tamotsu Shibutani et Howard Becker, avait une longue histoire dans la sociologie de Chicago. L’objectif de ce texte est de réélaborer une perspective écologique sur les mondes sociaux en relisant certains textes de George H. Mead et en explorant son héritage dans la génération d’après 1945, d’ordinaire qualifiée de seconde école de sociologie de Chicago. Ce sont ainsi des concepts d’expérience, de monde, de communication e...
Reconciling MOND and dark matter?
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.
Dodelson, Scott
2011-01-01
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 I point out the most severe challenge facing MOND.
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
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
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 ...
Cardone, V. F.; Angus, G.; 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 di...
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
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.
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...
An alternative to the dark matter paradigm: relativistic MOND gravitation
Jacob D. Bekenstein
2004-01-01
MOND, invented by Milgrom, is a phenomenological scheme whose basic premise is that the visible matter distribution in a galaxy or cluster of galaxies alone determines its dynamics. MOND fits many observations surprisingly well. Could it be that there is no dark matter in these systems and we witness rather a violation of Newton's universal gravity law ? If so, Einstein's general relativity would also be violated. For long conceptual problems have prevented construction of a consistent relati...
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
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.
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
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
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
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.
Magnetized cosmological models in bimetric theory of gravitation
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.
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.
Nonlocal Metric Realizations of MOND
Woodard, R. P.
2014-01-01
I discuss relativistic extensions of MOND in which the metric couples normally to matter. I argue that MOND might be a residual effect from the vacuum polarization of infrared gravitons produced during primordial inflation. If so, MOND corrections to the gravitational field equations would be nonlocal. Nonocality also results when one constructs metric field equations which reproduce the Tully-Fisher relation, along with sufficient weak lensing. I give the full field equations for the simples...
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.
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
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
RAyMOND: An N-body and hydrodynamics code for MOND
Candlish, G N; Fellhauer, M
2014-01-01
The LCDM concordance cosmological model is supported by a wealth of observational evidence, particularly on large scales. At galactic scales, however, the model is poorly constrained and recent observations suggest a more complex behaviour in the dark sector than may be accommodated by a single cold dark matter component. Furthermore, a modification of the gravitational force in the very weak field regime may account for at least some of the phenomenology of dark matter. A well-known example of such an approach is MOdified Newtonian Dynamics (MOND). While this idea has proven remarkably successful in the context of stellar dynamics in individual galaxies, the effects of such a modification of gravity on galaxy interactions and environmental processes deserves further study. To explore this arena we modify the parallel adaptive mesh refinement code RAMSES to use two formulations of MOND. We implement both the fully non-linear aquadratic Lagrangian (AQUAL) formulation as well as the simpler quasi-linear formula...
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
Fussman, Gérard
2014-01-01
Les indianistes doivent cesser de se définir par la seule référence à l’Inde et se penser aussi en termes de disciplines : l’indianisme n’est que l’application des sciences humaines à une région déterminée du monde. Pour faire œuvre d’historien de l’Inde ancienne, la connaissance du sanskrit demeure toutefois fondamentale : sans elle, pas de contact intime avec la culture de cet immense pays, pas de lecture possible des documents dans leur langue originale. Mais le sanskrit n’est pas toute l’...
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.
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.
Gauge-covariant bimetric theory of gravitation and electromagnetism
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.
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...
2004-01-01
"C'est l'histoire d'une aventure humaine, scientifique, international qui a vu le jour il y a cinquante ans, aux confins de la Suisse et du département de l'Ain. Le plus grand laboratoire de physique des particules du monde, le Cern, a été fondé en 1954. Les festivités organisées à l occasion de cet anniversaire connaîtront leur point d'orgue le 16 octobre prochain, avec portes-ouvertes, accueil de personallités et inauguration d'un monumnet spécifique, le Globe de l'innovation" (2 pages)
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.
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.
Mass eigenstates in bimetric theory with matter coupling
Schmidt-May, Angnis, E-mail: angnis.schmidt-may@fysik.su.se [Department of Physics and The Oskar Klein Centre, Stockholm University, AlbaNova University Centre, Stockholm, SE-106 91 Sweden (Sweden)
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.
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.
Andrea Moorhead
2012-10-01
Full Text Available L’Américaine Andrea Moorhead explique comment elle en est venue à écrire en français alors qu’elle est native de Buffalo, près des chutes du Niagara. Elle interroge les différentes dispositions et dispositifs poétiques en français et en anglais, et souligne en particulier le rôle de l’inconscient et de l’enfance. Écrire en français, selon l’auteur, n’est pas la traduction d’un état anglais : c’est un mouvement intérieur qui répond aux exigences de l’esprit, car le regard, le lien avec soi et avec les autres, l’énoncé lui-même sont différents. Écrire en anglais porte la franchise des Saxons et la mélancolie des Celtes, alors qu’écrire en français laisse entrer le murmure du subconscient et la douleur du monde. L’auteur montre que l’anglais est une langue à la fois poétique et pragmatique et qu’en français, la tension vient plutôt de l’abstraction et de la finesse du regard. Le bilinguisme poétique représente à ses yeux la foi dans une humanité planétaire.
Equations of motion in Rosen's bimetric theory of gravitation
The paper contains an investigation of Rosen's bimetric theory of gravitation (Gen. Relativ. Gravitation; 4: 435 (1973) and Ann. Phys. N.Y.; 84: 455 (1974)) in the case of slow velocities and weak fields. Newtonian and post-Newtonian approximations are obtained. The post-Newtonian equation of motion is integrated for an insular system of spherical bodies that move translationally at large mutual distances. It appears that the post-Newtonian law of motion obtained in this way contains terms that depend on the self-energy of the test body (a self-influence phenomenon). It is proved that in Einsteinian gravitation this influence is also present, but it can be cancelled out from the post-Newtonian law of motion if one takes into account the de Donder conditions. The self-influence discovered here seems to be a general gravitation phenomenon, which usually appears in theories of gravitation in the post-Newtonian approximation. (author)
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...
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.
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
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...
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
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.
Relativistic MOND from modified energetics
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
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: ...
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...
On Bianchi-I cosmic strings coupled with Maxwell ﬁelds in bimetric relativity
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.
A Primer to Relativistic MOND Theory
Bekenstein, Jacob D.; Sanders, Robert H.
2005-01-01
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.
Road to MOND: A novel perspective
Milgrom, Mordehai
2015-08-01
Accepting that galactic mass discrepancies are due to modified dynamics, I show why it is specifically the Modified Newtonian dynamics (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 tenets, I follow the path that leads specifically to the MOND basic tenets. The main signposts are as follows: (i) Space-time scale invariance underlies the dynamics of systems with large mass discrepancies. (ii) In these dynamics, G must be replaced by a single "scale-invariant" gravitational constant, Q0 (in MOND, Q0=A0=G a0, where a0 is MOND's acceleration constant). (iii) Universality of free fall points to the constant q0≡Q0/G as the boundary between the G -controlled, standard dynamics, and the Q0-controlled, scale-invariant dynamics (in MOND, q0=a0). (iv) Data clinch the case for q0 being an acceleration (MOND).
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.
Analysis of recent G experiments by a differential version of MOND theory
Klein, Norbert
2015-01-01
The discrepancy between two recently reported experimental values of the gravitational constant G was analysed within a differential version of MOND theory. In contrast to the most commonly accepted interpretation of MOND theory, it is assumed that only the relative gravitational acceleration between a test mass and an array of source masses determines the magnitude of post Newtonian corrections at small magnitudes of acceleration. The analysis was applied to one of the most recent Cavendish-type gravitational force experiments, which showed a significant deviation of the measured gravitational constant from the current CODATA value. A remarkable agreement between the observed G discrepancy and MOND fits to galaxy rotation curves was revealed by a consistent extrapolation within the framework of this model. The differential approach suggests that gravity-induced alterations of the space-time-curvature may define the magnitude of corrections to Newton's law.
New Cosmologies on the Horizon. Cosmology and Holography in bigravity and massive gravity
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.
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
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 ...
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...
Bigravity : A bimetric model of the Universe. Positive and negative gravitational lensings
Petit, Jean-Pierre
2008-01-01
After a short summary of our bimetric model of the Universe, an exact nonlinear solution is built, which demonstrates the existence of solutions for our two coupled field equations system. In addition to the classical positive gravitational lensing, this solution is shown to also lead to negative gravitational lensing, a phenomenon previously described in 1995 (Astrophysics and Space Science). Such negative lensing provides an alternative interpretation for the observed faint magnitudes of high redshift galaxies, so far considered as dwarf galaxies.
On the election of the flat metric in the bimetric theory of gravitation
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.)
Geologie der terrestrischen Planeten und Monde.
Stöffler, D.
Contents: 1. Inhalt und Aufgabe der Planetologie. 2. Aufbau des Sonnensystems. 3. Methoden der Exploration und Analyse der Planeten und Monde. 4. Geologische Grundprozesse auf den terrestrischen Planeten und Monden. 5. Geologische Formationen der planetaren Oberflächen. 6. Gesteine und Mineralien der planetaren Krusten. 7. Der innere Aufbau der terrestrischen planetaren Körper. 8. Vergleichende geologische Entwicklungsgeschichte der terrestrischen Planeten und des Mondes. 9. Ursprung und Entstehung der terrestrischen planetaren Körper.
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...
Deser, S.; Izumi, K.; Ong, Y. C.; Waldron, A.
2015-01-01
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 (mGR) 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 time-like curves (CTCs)/closed causal curves (CCCs)). We extend previous no-go results to the entire three-parameter range of mGR theories. It is also argued that bimetric models suffer a similar fate.
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...
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.
The thickness of HI in galactic discs under MOND: theory and application to the Galaxy
Sánchez-Salcedo, F J; Narayan, C A
2007-01-01
The outskirts of galaxies are a very good laboratory for testing the nature of the gravitational field at low accelerations. By assuming that the neutral hydrogen gas is in hydrostatic equilibrium in the gravitational potential of the host galaxy, the observed flaring of the gas layer can be used to test modified gravities. For the first time we construct a simple framework to derive the scaleheight of the neutral hydrogen gas disc in the MOND scenario and apply this to the Milky Way. It is shown that using a constant gas velocity dispersion of ~9 km/s, MOND is able to give a very good fit to the observed HI flaring beyond a galactocentric distance of 17 kpc up to the last measured point (~40 kpc). Between 10 and 16 kpc, however, the observed scaleheight is about 40% more than what MOND predicts for the standard interpolating function and 70% for the form suggested by Famaey & Binney. Given the uncertainties in the non-thermal pressure support by cosmic rays and magnetic fields, MOND seems to be a plausib...
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
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.
Marc Ouimet
2011-03-01
Full Text Available Cette étude vise à établir les variations du taux d’homicides entre les pays du monde et à examiner les facteurs qui y sont liés. L’analyse porte sur 167 pays pour lesquels nous disposons en 2004 d’une estimation fiable du taux d’homicides. Les données sur l’homicide proviennent de l’Organisation mondiale de la santé et les données pour les variables explicatives proviennent de sources variées. Les analyses statistiques préliminaires portent sur les caractéristiques populationnelles, économiques, environnementales, sociales, identitaires et politiques des pays. La modélisation statistique finale montre que trois grands facteurs expliquent les variations du taux d’homicides, soit le pourcentage de jeunes dans la population, le niveau de vie tel que mesuré par le PIB et le degré d’inégalité de la redistribution des revenus. En discussion sont abordés les thèmes de la composition de la population, de la situation économique et du système politique.The homicide rate varies greatly from one country to the other. The current study aims at describing the variations in the homicide rate in 2004 for 167 countries for which a valid estimate is available. Data for homicide comes from the World Health Organization and exploratory data have been coded from various sources. Bivariate analysis are conducted on the following dimensions : demographic composition of the population, economic indicators, environmental factors, ethnic composition and the political situation. A set of multiple regression analyses show that three main dimensions are important in explaining the variation in the homicide rate : the percentage of youths in the population, general wealth as measured by the GNP and the inequality of income distribution. A general discussion is provided.
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...
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
Dwarf Galaxies, MOND, and Relativistic Gravitation
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.
Explaining the Formation of Bulges with MOND
Combes, Françoise
In the cold dark matter (CDM) paradigm, bulges easily form through galaxy mergers, either major or minor, or through clumpy discs in the early universe, where clumps are driven to the center by dynamical friction. Also pseudobulges, with a more discy morphology and kinematics, can form more slowly through secular evolution of a bar, where resonant stars are elevated out of the plane, in a peanut/box shape. As a result, in CDM cosmological simulations, it is very difficult to find a bulgeless galaxy, while they are observed very frequently in the local universe. A different picture emerges in alternative models of the missing mass problem. In MOND (MOdified Newtonian Dynamics), galaxy mergers are much less frequent, since the absence of dark matter halos reduces the dynamical friction between two galaxies. Also, while clumpy galaxies lead to rapid classical bulge formation in CDM, the inefficient dynamical friction with MOND in the early-universe galaxies prevents the clumps to coalesce together in the center to form spheroids. This leads to less frequent and less massive classical bulges. Bars in MOND are more frequent and stronger, and have a more constant pattern speed, which modifies significantly the pseudobulge morphology. The fraction of pseudobulges is expected to be dominant in MOND.
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.
Testing MOND gravity in the shell galaxy NGC 3923
Bílek, Michal; Jungwiert, Bruno; Jílková, L.; Ebrová, Ivana; Bartošková, Kateřina; Křížek, Miroslav
2013-01-01
Roč. 559, November (2013), A110/1-A110/8. ISSN 0004-6361 Institutional support: RVO:67985815 Keywords : gravitation * elliptical and lenticular galaxies Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.479, year: 2013
Gravitational polarization and the phenomenology of MOND
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. ...
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 ...
Cold Dark Matter with MOND Scaling
Ho, Chiu Man; Minic, Djordje; Ng, Y. Jack
2010-01-01
We provide a holographic dual description of Milgrom's scaling associated with galactic rotation curves. Our argument is 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 ...
Modified gravitational collapse, or the wonders of the MOND
Golovnev, Alexey
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 in MOND which, we argue, is a relevant task for this competition. Spherically symmetric dust cloud collapse and intrinsic unavoidable non-linearities of the deep MOND regime are discussed. We conclude that complicated, both numerical and {\\it analytic}, studies of modified gravitational dynamics are needed in order to assess the viability of MOND.
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 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...
An Accelerating Solution for N-Body MOND Simulation with FPGA-SoC
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.
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...
Does a scalar meson field represent an irrotational perfect fluid in bimetric theory?
The problems of homogeneous plane symmetric perfect fluid and massive scalar field are investigated in Rosen's bimetric theory. It is shown that a macro cosmological model represented by perfect fluid distribution does not exist and only a vacuum model can be constructed whereas in case of a micro cosmological model represented by a scalar meson field exist and the model is obtained. Moreover it is shown that the massive scalar field cannot be equivalent to irrotational perfect fluid neither through the identification of the the corresponding eigenvalues of their energy momentum tensors nor through the transformation as in the case of Tiwary et all and Tabensky and Taub respectively in general theory of relativity. (authors)
Modified Newtonian Dynamics (MOND: Observational Phenomenology and Relativistic Extensions
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.
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
Nous, Médecins du Monde, refusons…
Brigaud, Thierry
2013-01-01
Face à la situation tragique en Syrie, Médecins du Monde a lancé en août dernier un appel pour réaffirmer que, dans ce pays comme ailleurs, il existe des règles de droit international que tous les acteurs au conflit se doivent de respecter. Depuis, le conflit dure sans perspectives d’arrêt des violences, alors que nos équipes apportent assistance aux réfugiés et aux déplacés. Depuis son lancement, cet appel a atteint plus d’un million de relais sur les réseaux sociaux.
Explaining the formation of bulges with MOND
Combes, F
2015-01-01
In the cold dark matter (CDM) paradigm, bulges easily form through galaxy mergers, either major or minor, or through clumpy disks in the early universe, where clumps are driven to the center by dynamical friction. Also pseudo-bulges, with a more disky morphology and kinematics, can form more slowly through secular evolution of a bar, where resonant stars are elevated out of the plane, in a peanut/box shape. As a result, in CDM cosmological simulations, it is very difficult to find a bulgeless galaxy, while they are observed very frequently in the local universe. A different picture emerges in alternative models of the missing mass problem. In MOND (MOdified Newtonian Dynamics), galaxy mergers are much less frequent, since the absence of dark matter halos reduces the dynamical friction between two galaxies. Also, while clumpy galaxies lead to rapid classical bulge formation in CDM, the inefficient dynamical friction with MOND in the early-universe galaxies prevents the clumps to coalesce together in the center...
MD or DM? Modified dynamics at low accelerations vs dark matter
Milgrom, Mordehai
2011-01-01
The MOND paradigm posits a departure from standard Newtonian dynamics, and from General Relativity, in the limit of small accelerations. The resulting modified dynamics aim to account for the mass discrepancies in the universe without non-baryonic dark matter. I briefly review this paradigm with its basic tenets, and its underlying theories--nonrelativistic and relativistic--including a novel, bimetric MOND gravity theory. I also comment on MOND's possible connection to, and origin in, the cosmological state of the universe at large. Some of its main predictions, achievements, and remaining desiderata are listed. I then succinctly pit MOND against the competing paradigm of standard dynamics with cold, dark matter. (Abridged)
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 ...
ANDROMEDA DWARFS IN LIGHT OF MOND. II. TESTING PRIOR PREDICTIONS
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 [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.
Spacetime structure of MOND with Tully-fisher relation and lorentz invariance violation
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.
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...
A nonlocal metric formulation of MOND
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
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...
The two-body problem in Rosen's bimetric theory of gravitation
This is a continuation of a previous paper (Israelit., Gen. Rel. Grav., 7:623 (1976)), in which the field equations in successive approximations and the post-Newtonian equations of motion in Rosen's theory of gravitation were derived. In this paper the energy integral and the center of mass for an insular system with an arbitrary structure are obtained in the post-Newtonian approximation. A many-body system is considered, and in the extreme case of point bodies (particles) the center-of-mass coordinates are found to be identical with the Einsteinian ones. The two-body problem is considered. For a system of two identical neutron stars of mass 1.3 solar mass (a possible model of the Hulse-Taylor binary pulsar system) the trajectory and the perihelion precession are calculated. It is found that the expressions obtained depend on the gravitational self-energy of the stars. The relations deduced from Rosen's bimetric gravitation in the case of small velocities and weak fields are compared with those of general relativity. (author)
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...
Axisymmetric and triaxial MOND density-potential pairs
Ciotti, L.; Londrillo, P.; Nipoti, C.
2005-01-01
We present a simple method, based on the deformation of spherically symmetric potentials, to construct explicit axisymmetric and triaxial MOND density-potential pairs. General guidelines to the choice of suitable deformations, so that the resulting density distribution is nowhere negative, are presented. This flexible method offers for the first time the possibility to study the MOND gravitational field for sufficiently general and realistic density distributions without resorting to sophisti...
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...
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
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...
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
Mass models of disk galaxies from the DiskMass Survey in MOND
Angus, Garry W; Swaters, Robert A; Famaey, Benoit; Diaferio, Antonaldo; McGaugh, Stacy S; van der Heyden, Kurt J
2015-01-01
This article explores the agreement between the predictions of Modified Newtonian Dynamics (MOND) and the rotation curves and stellar velocity dispersion profiles measured by the DiskMass Survey. A bulge-disk decomposition was made for each of the thirty published galaxies, and a MOND Poisson solver was used to simultaneously compute, from the baryonic mass distributions, model rotation curves and vertical velocity dispersion profiles, which were compared to the measured values. The two main free parameters, the stellar disk's mass-to-light ratio ($M/L$) and its exponential scale-height ($h_z$), were estimated by Markov Chain Monte Carlo modelling. The average best-fit K-band stellar mass-to-light ratio was $M/L \\simeq 0.55 \\pm 0.15$. However, to match the DiskMass Survey data, the vertical scale-heights would have to be in the range $h_z=200$ to $400$ pc which is a factor of two lower than those derived from observations of edge-on galaxies with a similar scale-length. The reason is that modified gravity ver...
Modified Newton's gravity in Finsler Space as a possible alternative to dark matter hypothesis
Chang, Zhe; Li, Xin
2008-01-01
A modified Newton's gravity is obtained as the weak field approximation of the Einstein's equation in Finsler space. It is found that a specified Finsler structure makes the modified Newton's gravity equivalent to the modified Newtonian dynamics (MOND). In the framework of Finsler geometry, the flat rotation curves of spiral galaxies can be deduced naturally without invoking dark matter.
Modified Newton's gravity in Finsler space as a possible alternative to dark matter hypothesis
A modified Newton's gravity is obtained as the weak field approximation of the Einstein's equation in Finsler space. It is found that a specified Finsler structure makes the modified Newton's gravity equivalent to the modified Newtonian dynamics (MOND). In the framework of Finsler geometry, the flat rotation curves of spiral galaxies can be deduced naturally without invoking dark matter
Lopsidedness of cluster galaxies in modified gravity
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
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.
Modified Newtonian Dynamics and Induced gravity
Kao, W. F.
2005-01-01
Modified Newtonian dynamics, a successful alternative to the cosmic dark matter model, proposes that gravitational field deviates from the Newtonian law when the field strength $g$ is weaker than a critical value $g_0$. We will show that the dynamics of MOND can be derived from an induced gravity model. New dynamics is shown to be compatible with the spatial deformation of scalar fields coupled to the system. Approximate solutions are shown explicitly for a simple toy model.
Testing modified gravity with globular cluster velocity dispersions
Moffat, J. W.; Toth, V. T.
2007-01-01
Globular clusters (GCs) in the Milky Way have characteristic velocity dispersions that are consistent with the predictions of Newtonian gravity, and may be at odds with Modified Newtonian Dynamics (MOND). We discuss a modified gravity (MOG) theory that successfully predicts galaxy rotation curves, galaxy cluster masses and velocity dispersions, lensing, and cosmological observations, yet produces predictions consistent with Newtonian theory for smaller systems, such as GCs. MOG produces veloc...
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...
How Dark Energy Affects the MOND Theory in Clusters
Man Ho Chan
2012-09-01
Full Text Available 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 that the calculated cluster mass is consistent with the total matter to baryonic matter ratio obtained by the CMB data.
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...
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...
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.
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. (geophysics, astronomy, and astrophysics)
Distant star clusters of the Milky Way in MOND
Haghi, Hossein; Kroupa, Pavel
2011-01-01
We determine the mean velocity dispersion of six Galactic outer halo globular clusters, AM 1, Eridanus, Pal 3, Pal 4, Pal 15, and Arp 2 in the weak acceleration regime to test classical vs. modified Newtonian dynamics (MOND). Owing to the non-linearity of MOND's Poisson equation, beyond tidal effects, the internal dynamics of clusters is affected by the external field in which they are immersed. For the studied clusters, particle accelerations are much lower than the critical acceleration a_0 of MOND, but the motion of stars is neither dominated by internal accelerations (a_i >> a_e) nor external accelerations (a_e >> a_i). We use the N-body code N-MODY in our analysis, which is a particle-mesh-based code with a numerical MOND potential solver developed by Ciotti, Londrillo, and Nipoti (2006) to derive the line-of-sight velocity dispersion by adding the external field effect. We show that Newtonian dynamics predicts a low-velocity dispersion for each cluster, while in modified Newtonian dynamics the velocity ...
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...
Le Portugal à la rencontre de trois mondes
Martinière, Guy
2014-01-01
Autant, si ce n'est plus que pour l'Espagne, les Grandes découvertes ont été, pour le Portugal, un véritable mythe fondateur. En un siècle et demi, de 1415 aux années 1550 , un pays de dimension modeste (90000 km2) , situé au sud d'une Europe médiévale confrontée en Méditérranée à l'Islam, peuplé d'un peu plus d'un million d'habitants, a mis en relation, de façon directe, grâce à sa maîtrise des routes de la mer océane, cet extrême Occident de l'Ancien Monde avec les "Trois Mondes" d'Afrique,...
The First Compact Objects in the MOND Model
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)
Le document brevet, un passage entre plusieurs mondes
Guyot, Brigitte; Normand, Sylvie
2004-01-01
Linguistique et sociologie de l'information sont convoquées pour étudier la place d'un document dans le secteur de la propriété industrielle, en s'attachant à suivre l'activité d'écriture et de traduction d'un ingénieur-brevet. Elles montrent ce qui est impliqué dans le passage d'un « monde » scientifique à un monde juridique et industriel, par accumulation de signes et de valeurs. Elles montrent également la présence de formes organisationnelles dont est porteur ce « document-activité ». C'e...
Ferreras, Ignacio; Sakellariadou, Mairi; Yusaf, Muhammad Furqaan
2012-01-01
The validity of MOND and TeVeS models of modified gravity has been recently tested by using lensing techniques, with the conclusion that a non-trivial component in the form of dark matter is needed in order to match the observations. In this work those analyses are extended by comparing lensing to stellar masses for a sample of nine strong gravitational lenses that probe galactic scales. The sample is extracted from a recent work that presents the mass profile out to a few effective radii, therefore reaching into regions that are dominated by dark matter in the standard (general relativity) scenario. A range of interpolating functions are explored to test the validity of MOND/TeVeS in these systems. Out of the nine systems, there are five robust candidates with a significant excess (higher that 50%) of lensing mass with respect to stellar mass, irrespective of the stellar initial mass function. One of these lenses (Q0957) is located at the centre of a galactic cluster. This system might be accommodated in MON...
可凸化因子与Mond-Weir型对偶%Convexifactors and the Mond-Weir Duality
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
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
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.
Ultra-diffuse cluster galaxies as key to the MOND cluster conundrum
Milgrom, Mordehai
2015-12-01
Modified Newtonian Dynamics (MOND) reduces greatly the mass discrepancy in clusters of galaxies,but does leave a global discrepancy of about a factor of 2 (epitomized by the structure of the Bullet Cluster). It has been proposed, within the minimalist and purist MOND, that clusters harbour some indigenous, yet undetected, cluster baryonic (dark) matter (CBDM), whose total amount is comparable with that of the observed hot gas. Koda et al. have recently identified more than a thousand ultra-diffuse, galaxy-like objects (UDGs) in the Coma cluster. These, they argue, require, within Newtonian dynamics, that they are much more massive than their observed stellar component. Here, I propound that some 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. The discovery of cluster UDGs is not in itself a resolution of the MOND cluster conundrum, but it lends greater plausibility to CBDM as its resolution. Alternatively, if the UDGs are only now falling into Coma, their large size and very low surface brightness could result from the inflation due to the MOND, variable external-field effect (EFE). I also consider briefly solutions to the conundrum that invoke more elaborate extensions of purist MOND, e.g. that in clusters, the MOND constant takes up larger than canonical values of the MOND constant. Whatever solves the cluster conundrum within MOND might also naturally account for UDGs.
Quelques reflexions sur la conception du monde de Erwin Schrodinger
Pinheiro, M J
2003-01-01
Some personal reflections are made about the philosophical posture of Erwin Schrodinger, as exposed in one of his book "Ma Conception du Monde". It is argued that the Taoist view of the world, as pursued by Schrodinger, although characterized by the dialectical struggle between opposite truths does not contain the temporal dimension, the unique which allows an evolving understanding of phenomena and objects that compose this world in constant evolution. In our point of view, only a genetic view - which is missing in the actual scientific paradigm - will bring a more deep explanation and understanding of Reality.
Le tennis dans le monde: état et prospective
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.
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.
A cosmological dust model with extended f({chi}) gravity
Carranza, D.A.; Mendoza, S.; Torres, L.A. [Universidad Nacional Autonoma de Mexico, Instituto de Astronomia, AP 70-264, Distrito Federal (Mexico)
2013-01-15
Introducing a fundamental constant of nature with dimensions of acceleration into the theory of gravity makes it possible to extend gravity in a very consistent manner. At the non-relativistic level a MOND-like theory with a modification in the force sector is obtained, which is the limit of a very general metric relativistic theory of gravity. Since the mass and length scales involved in the dynamics of the whole universe require small accelerations of the order of Milgrom's acceleration constant a{sub 0}, it turns out that the relativistic theory of gravity can be used to explain the expansion of the universe. In this work it is explained how to use that relativistic theory of gravity in such a way that the overall large-scale dynamics of the universe can be treated in a pure metric approach without the need to introduce dark matter and/or dark energy components. (orig.)
Constraining MOND Using the Vertical Motion of Stars in the Solar Neighborhood
Margalit, Ben
2015-01-01
Stars with a different vertical motion relative to the galactic disk have a different average acceleration. According to Modified Newtonian Dynamics (MOND) theories they should therefore have a different average orbital velocity while revolving around the Milky Way. We show that this property can be used to constrain MOND theories by studying stars in the local neighborhood. With the Hipparcos dataset we can only place marginal constraints. However, the forthcoming GAIA catalogue with its significantly fainter cutoff should allow placing a stringent constraint. The method cannot be used to prove MOND, since halo stars can contribute a similar signal which would be hard to discern.
Constraints on MOND theory from radio tracking data of the Cassini spacecraft
Hees, A; Jacobson, R A; Park, R S
2014-01-01
The MOdified Newtonian Dynamics (MOND) is an attempt to modify the gravitation theory to solve the Dark Matter problem. This phenomenology is very successful at the galactic level. The main effect produced by MOND in the Solar System is called the External Field Effect parametrized by the parameter $Q_2$. We have used 9 years of Cassini range and Doppler measurements to constrain $Q_2$. Our estimate of this parameter based on Cassini data is given by $Q_2=(3 \\pm 3)\\times 10^{-27} \\ \\rm{s^{-2}}$ which shows no deviation from General Relativity and excludes a large part of the relativistic MOND theories.
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
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.
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
Towards an interpretation of MOND as a modification of inertia
Namouni, Fathi
2015-01-01
We explore the possibility that Milgrom's Modified Newtonian Dynamics (MOND) is a manifestation of the modification of inertia at small accelerations. Consistent with the Tully-Fisher relation, dynamics in the small acceleration domain may originate from a quartic (cubic) velocity-dependence of energy (momentum) whereas gravitational potentials remain linear with respect to mass. The natural framework for this interpretation is Finsler geometry. The simplest static isotropic Finsler metric of a gravitating mass that incorporates the Tully-Fisher relation at small acceleration is associated with a spacetime interval that is either a homogeneous quartic root of polynomials of local displacements or a simple root of a rational fraction thereof. We determine the low energy gravitational equation and find that Finsler spacetimes that produce a Tully-Fisher relation require that the gravitational potential be modified. For an isolated mass, Newton's potential $Mr^{-1}$ is replaced by $Ma_0\\log (r/r_0)$ where $a_0$ ...
Médecins du Monde en Khyber–Pakhtunkhwa, Pakistan
Berdoulet, Marc Tyrant et Stéphane
2011-01-01
Le 18 juin 2009, Médecins du Monde (MdM) démarrait une offre en soins de santé primaire via deux cliniques mobiles dans le district de Swabi, en Kyber-Pakhtunkhwa (KPK, ex-NWFP) au Pakistan. Il s’agissait alors de répondre au plus grand déplacement de population qu’à connu le Pakistan depuis sa création, suite à l’offensive militaire lancée contre les insurgés de la vallée de Swat. Aujourd’hui, cinq équipes mobiles travaillent auprès des personnes affectées par la crise, sur trois districts....
Towards an interpretation of MOND as a modification of inertia
Namouni, Fathi
2015-09-01
We explore the possibility that Milgrom's modified Newtonian dynamics (MOND) is a manifestation of the modification of inertia at small accelerations. Consistent with the Tully-Fisher relation, dynamics in the small acceleration domain may originate from a quartic (cubic) velocity dependence of energy (momentum) whereas gravitational potentials remain linear with respect to mass. The natural framework for this interpretation is Finsler geometry. The simplest static isotropic Finsler metric of a gravitating mass that incorporates the Tully-Fisher relation at small acceleration is associated with a space-time interval that is either a homogeneous quartic root of polynomials of local displacements or a simple root of a rational fraction thereof. We determine the weak field gravitational equation and find that Finsler space-times that produce a Tully-Fisher relation require that the gravitational potential be modified. For an isolated mass, Newton's potential Mr-1 is replaced by Ma0log (r/r0), where a0 is MOND's acceleration scale and r0 is a yet undetermined distance scale. Orbital energy is linear with respect to mass but angular momentum is proportional to M3/4. Asymptotic light deflection resulting from time curvature is similar to that of a singular isothermal sphere implying that space curvature must be the main source of deflection in static Finsler space-times possibly through the presence of the distance scale r0 that appears in the asymptotic form of the gravitational potential. The quartic nature of the Finsler metric hints at the existence of an underlying area metric that describes the effective structure of space-time.
Festivals de cinéma dans le monde arabe
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.
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...
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...
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 ...
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.
Tensor-vector-scalar-modified gravity: from small scale to cosmology.
Bekenstein, Jacob D
2011-12-28
The impressive success of the standard cosmological model has suggested to many that its ingredients are all that one needs to explain galaxies and their systems. I summarize a number of known problems with this programme. 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 modified Newtonian dynamics (MOND) paradigm, which has proved to be an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the non-relativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first side-stepped with the formulation of tensor-vector-scalar theory (TeVeS), a covariant-modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in the face of galaxy phenomenology. I also summarize features of TeVeS cosmology and describe the confrontation with data from strong and weak gravitational lensing. PMID:22084290
SLOWLY ROTATING GAS-RICH GALAXIES IN MODIFIED NEWTONIAN DYNAMICS (MOND)
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)
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.