Tests of Gravitational Symmetries with Pulsar Binary J1713+0747

TL;DR

This paper tests key aspects of the strong equivalence principle using pulsar binary data, providing new constraints on gravitational theories and symmetry violations in strongly self-gravitating systems.

Contribution

It presents the first direct tests of UFF and $ ilde{eta}_3$ using pulsar binaries, improving constraints on gravitational symmetries beyond Solar system limits.

Findings

Constraint on the variation of G: $rac{\dot{G}}{G} = (-0.1 \\pm 0.9) \times 10^{-12}$ yr$^{-1}$

Bounds on UFF violation: $|\Delta| < 0.002$

Limits on $ ilde{eta}_3$: $-3 \times 10^{-20} < \hat{\alpha}_3 < 4 \times 10^{-20}$

Abstract

Symmetries play an important role in modern theories of gravity. The strong equivalence principle (SEP) constitutes a collection of gravitational symmetries which are all implemented by general relativity. Alternative theories, however, are generally expected to violate some aspects of SEP. We test three aspects of SEP using observed change rates in the orbital period and eccentricity of binary pulsar J1713+0747: 1. the gravitational constant's constancy as part of locational invariance of gravitation; 2. the post-Newtonian parameter $\hat{\alpha}_3$ in gravitational Lorentz invariance; 3. the universality of free fall (UFF) for strongly self-gravitating bodies. Based on the pulsar timing result of the combined dataset from the North American Nanohertz Gravitational Observatory (NANOGrav) and the European Pulsar Timing Array (EPTA), we find $\dot{G}/G = (-0.1 \pm 0.9) \times 10^{-12}\,{\rm yr}^{-1}$, which is weaker than Solar system limits, but applies for strongly self-gravitating objects. Furthermore, we obtain the constraints $|\Delta|< 0.002$ for the UFF test and $-3\times10^{-20} < \hat{\alpha}_3 < 4\times10^{-20}$ at 95% confidence. These are the first direct UFF and $\hat{\alpha}_3$ tests based on pulsar binaries, and they overcome various limitations of previous tests.