Estimating spinning binary parameters and testing alternative theories of gravity with LISA

TL;DR

This paper analyzes how spin effects influence parameter estimation and tests of gravity theories with LISA, showing that spins degrade intrinsic parameter accuracy but have limited impact on extrinsic measurements.

Contribution

It provides a detailed assessment of spin effects on gravitational wave parameter estimation and bounds on alternative gravity theories using LISA data.

Findings

Spin effects degrade intrinsic parameter estimation by 10-100 times.

Spin couplings significantly weaken bounds on scalar-tensor gravity parameters.

Extrapolating LISA's low-frequency sensitivity improves parameter accuracy for massive binaries.

Abstract

We investigate the effect of spin-orbit and spin-spin couplings on the estimation of parameters for inspiralling compact binaries of massive black holes, and for neutron stars inspiralling into intermediate-mass black holes, using hypothetical data from the proposed Laser Interferometer Space Antenna (LISA). We work both in Einstein's theory and in alternative theories of gravity of the scalar-tensor and massive-graviton types. We restrict the analysis to non-precessing spinning binaries, i.e. to cases where the spins are aligned normal to the orbital plane. We find that the accuracy with which intrinsic binary parameters such as chirp mass and reduced mass can be estimated within general relativity is degraded by between one and two orders of magnitude. We find that the bound on the coupling parameter omega_BD of scalar-tensor gravity is significantly reduced by the presence of spin couplings, while the reduction in the graviton-mass bound is milder. Using fast Monte-Carlo simulations of 10^4 binaries, we show that inclusion of spin terms in massive black-hole binaries has little effect on the angular resolution or on distance determination accuracy. For stellar mass inspirals into intermediate-mass black holes, the angular resolution and the distance are determined only poorly, in all cases considered. We also show that, if LISA's low-frequency noise sensitivity can be extrapolated from 10^-4 Hz to as low as 10^-5 Hz, the accuracy of determining both extrinsic parameters (distance, sky location) and intrinsic parameters (chirp mass, reduced mass) of massive binaries may be greatly improved.