The Geometry Of Modified Newtonian Dynamics

Abstract

Modified Newtonian Dynamics is an empirical modification to Poisson's equation which has had success in accounting for the `gravitational field' $\Phi$ in a variety of astrophysical systems. The field $\Phi$ may be interpreted in terms of the weak field limit of a variety of spacetime geometries. Here we consider three of these geometries in a more comprehensive manner and look at the effect on timelike and null geodesics. In particular we consider the Aquadratic Lagrangian (AQUAL) theory, Tensor-Vector-Scalar (TeVeS) theory and Generalized Einstein-Æther (GEA) theory. We uncover a number of novel features, some of which are specific to the theory considered while others are generic. In the case of AQUAL and TeVeS theories, the spacetime exhibits an excess (AQUAL) or deficit (TeVeS) solid angle akin to the case of a Barriola-Vilenkin global monopole. In the case of GEA, a disformal symmetry of the action emerges in the limit of $\gradΦ\rightarrow 0$. Finally, in all theories studied, massive particles can never reach spatial infinity while photons can do so only after experiencing infinite redshift.

18 pages

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Cited by in corpus (6)

• Modified Gravity and Cosmology
• Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions
• Galactic rotation curves, the baryon-to-dark-halo-mass relation and space-time scale invariance
• Challenges for Lambda-CDM and MOND
• Scalar-tensor black holes in an expanding universe
• Tests of Modified Gravity Theories in the Solar System