A Gravitational non-Radiative Memory Effect

TL;DR

This paper explores a non-radiative gravitational memory effect caused by scalar curvature changes, revealing a velocity memory phenomenon that is difficult to observe with current detectors.

Contribution

It demonstrates the existence of a non-radiative, scalar-based memory effect in gravitational fields, expanding understanding beyond radiative gravitational wave effects.

Findings

Identifies a velocity memory effect linked to scalar curvature changes.

Shows the effect's amplitude diminishes with the inverse square of distance.

Highlights observational challenges due to detector noise limitations.

Abstract

We revisit the issue of memory effects, i.e. effects giving rise to a net cumulative change of the configuration of test particles, using a toy model describing the emission of radiation by a compact source and focusing on the scalar, hence non-radiative, part of the Riemann curvature. Motivated by the well known fact that gravitational radiation is accompanied by a memory effect, i.e. a permanent displacement of the relative separation of test particles, present after radiation has passed, we investigate the existence of an analog effect in the non-radiative part of the gravitational field. While quadrupole and higher multipoles undergo oscillations responsible for gravitational radiation, energy, momentum and angular momentum are conserved charges undergoing non-oscillatory change due to radiation emission. We show how the source re-arrangement due to radiation emission produce time-dependent scalar potentials which induce a time variation in the scalar part of the Riemann curvature tensor. As a result, on general grounds a velocity memory effect appears, depending on the inverse of the square of the distance of the observer from the source, thus making it almost impossible to observe, as shown by comparison to the planned gravitational detector noise spectral densities.