Constraining Gravity with LISA Detections of Binaries

TL;DR

This paper develops a framework to use LISA gravitational wave detections of extreme-mass-ratio inspirals to distinguish between General Relativity and dynamical Chern-Simons modified gravity, achieving high precision constraints.

Contribution

It introduces a novel parameter estimation method for EMRIs in DCSMG, enabling tests of gravity theories with upcoming space-based GW detectors.

Findings

LISA can differentiate GR from DCSMG with fractional errors below 5%.

The method constrains the Chern-Simons parameter four orders of magnitude better than current bounds.

The framework uses Fisher matrix analysis in a 15-dimensional parameter space.

Abstract

General Relativity (GR) describes gravitation well at the energy scales which we have so far been able to achieve or detect. However, we do not know whether GR is behind the physics governing stronger gravitational field regimes, such as near neutron stars or massive black-holes (MBHs). Gravitational-wave (GW) astronomy is a promising tool to test and validate GR and/or potential alternative theories of gravity. The information that a GW waveform carries not only will allow us to map the strong gravitational field of its source, but also determine the theory of gravity ruling its dynamics. In this work, we explore the extent to which we could distinguish between GR and other theories of gravity through the detection of low-frequency GWs from extreme-mass-ratio inspirals (EMRIs) and, in particular, we focus on dynamical Chern-Simons modified gravity (DCSMG). To that end, we develop a framework that enables us, for the first time, to perform a parameter estimation analysis for EMRIs in DCSMG. Our model is described by a 15-dimensional parameter space, that includes the Chern-Simons (CS) parameter which characterises the deviation between the two theories, and our analysis is based on Fisher information matrix techniques together with a (maximum-mismatch) criterion to assess the validity of our results. In our analysis, we study a 5-dimensional parameter space, finding that a GW detector like the Laser Interferometer Space Antenna (LISA) or eLISA (evolved LISA) should be able to discriminate between GR and DCSMG with fractional errors below 5%, and hence place bounds four orders of magnitude better than current Solar System bounds.