Gravitational Radiation in Horava Gravity

TL;DR

This paper investigates how gravitational wave emission in Horava gravity differs from General Relativity, revealing modifications in energy-loss formulas and setting constraints on the theory using binary pulsar observations.

Contribution

It derives the modified energy-loss formula for gravitational waves in Horava gravity, including scalar and tensor mode effects, and constrains the theory with pulsar data.

Findings

Quadrupole contribution is altered due to different tensor mode speed.

A monopole contribution arises from an extra scalar degree of freedom.

Constraints on Horava gravity parameters are established from binary pulsar observations.

Abstract

We study the radiation of gravitational waves by self-gravitating binary systems in the low-energy limit of Horava gravity. We find that the predictions for the energy-loss formula of General Relativity are modified already for Newtonian sources: the quadrupole contribution is altered, in part due to the different speed of propagation of the tensor modes; furthermore, there is a monopole contribution stemming from an extra scalar degree of freedom. A dipole contribution only appears at higher post-Newtonian order. We use these findings to constrain the low-energy action of Horava gravity by comparing them with the radiation damping observed for binary pulsars. Even if this comparison is not completely appropriate - since compact objects cannot be described within the post-Newtonian approximation - it represents an order of magnitude estimate. In the limit where the post-Newtonian metric coincides with that of General Relativity, our energy-loss formula provides the strongest constraints for Horava gravity at low-energies.