Double Binary Pulsar Test of Dynamical Chern-Simons Modified Gravity

TL;DR

This paper uses observations of the double binary pulsar PSR J0737-3039A/B to place stringent constraints on non-dynamical Chern-Simons modified gravity, significantly surpassing previous Solar System tests.

Contribution

It calculates Chern-Simons corrections to binary orbital evolution and applies pulsar data to tightly constrain the theory's coupling parameter.

Findings

Chern-Simons corrections scale quadratically with semi-major axis

Binary pulsars are highly effective for testing this gravity modification

Constraints on the coupling parameter exceed Solar System bounds by a factor of 10^11

Abstract

Chern-Simons modified gravity is a string-theory and loop-quantum-gravity inspired effective theory that modifies General Relativity by adding a parity-violating Pontryagin density to the Einstein-Hilbert action multiplied by a coupling scalar. We strongly constrain non-dynamical Chern-Simons modified gravity with a timelike Chern-Simons scalar through observations of the double binary pulsar PSR J0737-3039A/B. We first calculate Chern-Simons corrections to the orbital evolution of binary systems. We find that the ratio of the correction to periastron precession to the general relativistic prediction scales quadratically with the semi-major axis and inversely with the square of the object's radius. Binary pulsar systems are thus ideal to test this theory, since periastron precession can be measured with sub-degree accuracies and the semi-major axis is millions of times larger than the stellar radius. Using data from PSR J0737-3039A/B we dramatically constrain the non-dynamical Chern-Simons coupling to $M_{\CS} := 1/|\dot{\vartheta}| > 33 {\textrm{meV}}$, approximately a hundred billion times better than current Solar System tests.