Strong field effects on binary systems in Einstein-aether theory

TL;DR

This paper investigates how strong field effects near neutron stars influence binary pulsar dynamics within Einstein-aether theory, finding that small coupling constants make the theory compatible with current observations.

Contribution

It extends previous work by incorporating strong field effects via an effective point particle approach and derives post-Newtonian equations of motion and radiation damping rates.

Findings

Strong field effects are negligible for couplings less than ~0.01.

A one-parameter family of theories passes current observational tests.

Precise constraints require further calculation of sensitivities.

Abstract

"Einstein-aether" theory is a generally covariant theory of gravity containing a dynamical preferred frame. This article continues an examination of effects on the motion of binary pulsar systems in this theory, by incorporating effects due to strong fields in the vicinity of neutron star pulsars. These effects are included through an effective approach, by treating the compact bodies as point particles with nonstandard, velocity dependent interactions parametrized by dimensionless "sensitivities". Effective post-Newtonian equations of motion for the bodies and the radiation damping rate are determined. More work is needed to calculate values of the sensitivities for a given fluid source, so precise constraints on the theory's coupling constants cannot yet be stated. It is shown, however, that strong field effects will be negligible given current observational uncertainties if the dimensionless couplings are less than roughly 0.01 and two conditions that match the PPN parameters to those of pure general relativity are imposed. In this case, weak field results suffice and imply one further condition on the couplings. Thus, there exists a one-parameter family of Einstein-aether theories with "small-enough" couplings that passes all current observational tests. No conclusion can yet be reached for large couplings.