More about spontaneous Lorentz-violation and infrared modification of gravity

TL;DR

This paper explores a Lorentz-violating gravity model with vector condensates that modifies infrared dispersion laws, alters gravitational behavior at large scales, but does not account for cosmic acceleration.

Contribution

It introduces a ghost- and tachyon-free Lorentz-violating gravity model with modified infrared dispersion laws and analyzes its phenomenological implications.

Findings

Gravity transitions from General Relativity to Fierz-Pauli limit at large scales

Cosmological evolution remains governed by standard Friedmann equations

Model remains phenomenologically acceptable despite low-momentum ghosts and tachyons

Abstract

We consider a model with Lorentz-violating vector field condensates, in which dispersion laws of all perturbations, including tensor modes, undergo non-trivial modification in the infrared. The model is free of ghosts and tachyons at high 3-momenta. At low 3-momenta there are ghosts, and at even lower 3-momenta there exist tachyons. Still, with appropriate choice of parameters, the model is phenomenologically acceptable. Beyond a certain large distance scale and even larger time scale, the gravity of a static source changes from that of General Relativity to that of van Dam--Veltman--Zakharov limit of the Fierz--Pauli theory. Yet the late time cosmological evolution is always determined by the standard Friedmann equation, modulo small correction to the ``cosmological Planck mass'', so the modification of gravity cannot by itself explain the accelerated expansion of the Universe. We argue that the latter property is generic in a wide class of models with condensates.