# Effective-one-body multipolar waveform for tidally interacting binary neutron stars up to merger

## TL;DR

This paper introduces an improved effective-one-body waveform model for binary neutron star mergers that incorporates advanced tidal effects, validated against numerical relativity simulations, to enhance gravitational wave predictions up to merger.

## Contribution

It develops a new EOB waveform model with resummed tidal effects, including gravitoelectric and gravitomagnetic terms, improving accuracy near merger compared to previous models.

## Key findings

- Resummed gravitoelectric octupolar term causes up to 1 rad dephasing.
- Model validated with numerical relativity simulations across different EOS and mass ratios.
- Enhanced tidal effects lead to more accurate gravitational wave phasing.

## Abstract

Gravitational-wave astronomy with coalescing binary neutron star sources requires the availability of gravitational waveforms with tidal effects accurate up to merger. This article presents an improved version of \TEOBResum, a nonspinning effective-one-body (EOB) waveform model with enhanced analytical information in its tidal sector. The tidal potential governing the conservative dynamics employs resummed expressions based on post-Newtonian (PN) and gravitational self-force (GSF) information. In particular, we compute a GSF-resummed expression for the leading-order octupolar gravitoelectric term and incorporate the leading-order gravitomagnetic term (either in PN-expanded or GSF-resummed form). The multipolar waveform and fluxes are augmented with gravitoelectric and magnetic terms recently obtained in PN. The new analytical information enhances tidal effects toward merger accelerating the coalescence. We quantify the impact on the gravitational-wave phasing of each physical effect. The most important contribution is given by the resummed gravitoelectric octupolar term entering the EOB interaction potential, that can yield up to 1~rad of dephasing (depending on the NS model) with respect to its nonresummed version. The model's energetics and the gravitational wave phasing are validated with eccentricity-reduced and multi-resolution numerical relativity simulations with different equations of state and mass ratios. We also present EOB-NR waveform comparisons for higher multipolar modes beyond the dominant quadrupole one.