Lorentz-Violating Vector Fields Slow the Universe Down

TL;DR

This paper explores how a Lorentz-violating vector field influences cosmic expansion and Newtonian gravity, showing it slows the universe's rate of expansion and constrains its parameters using primordial nucleosynthesis data.

Contribution

It introduces a fixed-norm Lorentz-violating vector field in cosmology, analyzing its effects on gravitational dynamics and providing observational constraints.

Findings

The vector field rescaled Newton's constant in cosmology and Newtonian limits.

It causes the universe to expand more slowly for a given matter content.

Constraints suggest the vector field's norm is below the Planck scale by an order of magnitude.

Abstract

We consider the gravitational effects of a single, fixed-norm, Lorentz-violating timelike vector field. In a cosmological background, such a vector field acts to rescale the effective value of Newton's constant. The energy density of this vector field precisely tracks the energy density of the rest of the universe, but with the opposite sign, so that the universe experiences a slower rate of expansion for a given matter content. This vector field similarly rescales Newton's constant in the Newtonian limit, although by a different factor. We put constraints on the parameters of the theory using the predictions of primordial nucleosynthesis, demonstrating that the norm of the vector field should be less than the Planck scale by an order of magnitude or more.