New Graviton Mass Bound from Binary Pulsars

TL;DR

This paper uses observations of binary pulsars to set new upper limits on the mass of the graviton, providing constraints on modified gravity theories involving Galileon fields.

Contribution

It introduces a novel bound on the graviton mass from binary pulsar data and explores future prospects for testing cubic Galileon theories with pulsar-black hole systems.

Findings

Graviton mass bound: $m_g \,\lesssim 2 \times 10^{-28}$ eV/c^2

Corresponding Compton wavelength: $\lambda_g \gtrsim 7 \times 10^{21}$ m

Potential for future tests with pulsars near black holes

Abstract

In Einstein's general relativity, gravity is mediated by a massless metric field. The extension of general relativity to consistently include a mass for the graviton has profound implications for gravitation and cosmology. Salient features of various massive gravity theories can be captured by Galileon models, the simplest of which is the cubic Galileon. The presence of the Galileon field leads to additional gravitational radiation in binary pulsars where the Vainshtein mechanism is less suppressed than its fifth-force counterpart, which deserves a detailed confrontation with observations. We prudently choose fourteen well-timed binary pulsars, and from their intrinsic orbital decay rates we put a new bound on the graviton mass, $m_g \lesssim 2 \times 10^{-28}\,{\rm eV}/c^2$ at the 95% confidence level, assuming a flat prior on $\ln m_g$. It is equivalent to a bound on the graviton Compton wavelength $\lambda_g \gtrsim 7 \times 10^{21}\,{\rm m}$. Furthermore, we extensively simulate times of arrival for pulsars in orbit around stellar-mass black holes and the supermassive black hole at the Galactic center, and investigate their prospects in probing the cubic Galileon theory in the near future.