PostNewtonian constraints on Lorentzviolating gravity theories with a MOND phenomenology
Abstract
We study the postNewtonian expansion of a class of Lorentzviolating gravity theories that reduce to khronometric theory (i.e. the infrared limit of Hořava gravity) in highacceleration regimes and reproduce the phenomenology of modified Newtonian dynamics (MOND) in the lowacceleration, nonrelativistic 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 highacceleration regime, the postNewtonian expansion breaks down at low accelerations, and the theory becomes strongly coupled. Nevertheless, we identify a sizeable region of the parameter space where the postNewtonian expansion remains perturbative for all accelerations, and the theory passes both Solar System and pulsar gravity tests, besides producing a MOND phenomenology for the rotation curves of galaxies. We illustrate this explicitly with a toy model of a system containing only baryonic matter but no dark matter.
 Publication:

Physical Review D
 Pub Date:
 April 2015
 DOI:
 10.1103/PhysRevD.91.084053
 arXiv:
 arXiv:1502.05554
 Bibcode:
 2015PhRvD..91h4053B
 Keywords:

 95.35.+d;
 04.50.Kd;
 Dark matter;
 Modified theories of gravity;
 General Relativity and Quantum Cosmology;
 Astrophysics  Astrophysics of Galaxies;
 High Energy Physics  Phenomenology
 EPrint:
 17 pages, 2 figures