Prospects for axion searches with Advanced LIGO through binary mergers

TL;DR

This paper explores how gravitational wave observations from binary neutron star mergers can be used to detect or constrain axions, a candidate for new physics beyond the Standard Model, by analyzing their effects on orbital dynamics and gravitational waveforms.

Contribution

It provides the first post-Newtonian calculations of axion effects on binary mergers and forecasts Advanced LIGO's potential to constrain axion parameters.

Findings

Advanced LIGO can potentially exclude axions with mass less than 10^{-11} eV.

Constraints on axion decay constant f_a in the range 10^{14} to 10^{17} GeV.

Complementary probes include binary pulsars, black hole superradiance, and laboratory experiments.

Abstract

The observation of gravitational waves from a binary neutron star merger by LIGO/VIRGO and the associated electromagnetic counterpart provides a high precision test of orbital dynamics, and therefore a new and sensitive probe of extra forces and new radiative degrees of freedom. Axions are one particularly well-motivated class of extensions to the Standard Model leading to new forces and sources of radiation, which we focus on in this paper. Using an effective field theory (EFT) approach, we calculate the first post-Newtonian corrections to the orbital dynamics, radiated power, and gravitational waveform for binary neutron star mergers in the presence of an axion. This result is applicable to many theories which add an extra massive scalar degree of freedom to General Relativity. We then perform a detailed forecast of the potential for Advanced LIGO to constrain the free parameters of the EFT, and map these to the mass $m_a$ and decay constant $f_a$ of the axion. At design sensitivity, we find that Advanced LIGO can potentially exclude axions with $m_a \lesssim 10^{-11} \ {\rm eV}$ and $f_a \sim (10^{14} - 10^{17}) \ {\rm GeV}$. There are a variety of complementary observational probes over this region of parameter space, including the orbital decay of binary pulsars, black hole superradiance, and laboratory searches. We comment on the synergies between these various observables.