Scalar memory from compact binary coalescences

TL;DR

This paper explores how scalar memory from binary black hole mergers in Ricci-coupled scalar-Gauss-Bonnet gravity can significantly alter gravitational wave signals, offering a new low-frequency signature of modified gravity theories.

Contribution

It demonstrates that scalar charge changes during mergers produce observable scalar-memory effects, enhancing deviations from general relativity in gravitational wave signals.

Findings

Scalar memory can modify GW signals on observable timescales.

The effect is comparable to pure scalar-Gauss-Bonnet corrections.

Memory effects can serve as signatures of new gravitational physics.

Abstract

Gravitational memory provides a distinctive low-frequency probe of gravity, but explicit merger studies beyond general relativity remain limited. In this work, we investigate memory from binary black hole mergers in Ricci-coupled scalar-Gauss-Bonnet gravity, a natural extension of scalar-Gauss-Bonnet theory that admits an additional scalar breathing polarization. Based on numerical-relativity waveforms of binary black hole coalescences, we show that the change in the scalar charge of the system across merger generates a significant scalar-memory contribution. For a GW150914-like system, this effect modifies the memory signal in a gravitational-wave detector on the same observable timescale and by an amount comparable to the pure scalar-Gauss-Bonnet correction to tensor memory. Thus, it can substantially enhance the total deviation from the general-relativity prediction over a broad range of source and detector configurations. We argue that this identifies a general mechanism: whenever a compact-binary merger changes the asymptotic charge of an additional gravitational field, and that field sources an observable extra polarization, the resulting memory can provide a leading low-frequency signature of new gravitational physics.