Memory effect for generalized modes in pp-waves spacetime

TL;DR

This paper investigates the memory effect of test particles in pp-wave spacetimes with various polarization modes, revealing how energy variations depend on wave amplitude and multipolar structure.

Contribution

It extends the analysis of gravitational memory effects to higher polarization modes in pp-wave spacetimes using numerical solutions of geodesic equations.

Findings

Relative kinetic energy varies quartically with wave amplitude at low initial velocities.

The energy memory effect depends on the integrated tidal field and the wave's multipolar structure.

Higher polarization modes influence the spatial gradients and energy transfer in the wave.

Abstract

The memory effect of test particles interacting with pp-wave Gaussian pulses is investigated for polarization modes beyond the standard quadrupolar $+$ and $\times$ states. Massive geodesic equations are solved numerically for several values of the multipolar index $m$, allowing the analysis of velocity and energy memory effects. In order to eliminate possible coordinate artifacts, the study is formulated in terms of the relative motion between two test particles. The results show that the relative kinetic energy variation exhibits a quartic dependence on the wave amplitude in the regime of low initial velocities. The coefficient of this scaling is found to depend on the multipolar structure of the wave, reflecting the spatial gradients associated with higher polarization modes. It is further shown that the energy memory effect is determined by the integrated tidal field, linking the permanent change in the relative kinetic energy to the history of the spacetime curvature carried by the wave.13