Effective action approach to higher-order relativistic tidal interactions in binary systems and their effective one body description

TL;DR

This paper enhances the analytical modeling of tidal interactions in inspiralling neutron-star binaries by calculating higher-order relativistic corrections, significantly impacting the effective tidal polarizability crucial for gravitational-wave data analysis.

Contribution

It introduces the next-to-next-to-leading order relativistic correction to tidal interaction energy within an effective-action and EOB framework, improving the accuracy of late inspiral dynamics modeling.

Findings

Second-order relativistic effects increase tidal polarizability.

Derived new amplification coefficients for relativistic corrections.

Proposed a resummation method for higher-order effects.

Abstract

The gravitational-wave signal from inspiralling neutron-star--neutron-star (or black-hole--neutron-star) binaries will be influenced by tidal coupling in the system. An important science goal in the gravitational-wave detection of these systems is to obtain information about the equation of state of neutron star matter via the measurement of the tidal polarizability parameters of neutron stars. To extract this piece of information will require to have accurate analytical descriptions of both the motion and the radiation of tidally interacting binaries. We improve the analytical description of the late inspiral dynamics by computing the next-to-next-to-leading order relativistic correction to the tidal interaction energy. Our calculation is based on an effective-action approach to tidal interactions, and on its transcription within the effective-one-body formalism. We find that second-order relativistic effects (quadratic in the relativistic gravitational potential $u=G(m_1 +m_2)/(c^2 r)$) significantly increase the effective tidal polarizability of neutron stars by a distance-dependent amplification factor of the form $1 + \alpha_1 \, u + \alpha_2 \, u^2 +...$ where, say for an equal-mass binary, $\alpha_1=5/4=1.25$ (as previously known) and $\alpha_2=85/14\simeq6.07143$ (as determined here for the first time). We argue that higher-order relativistic effects will lead to further amplification, and we suggest a Pad\'e-type way of resumming them. We recommend to test our results by comparing resolution-extrapolated numerical simulations of inspiralling-binary neutron stars to their effective one body description.