Global aspects of radiation memory

TL;DR

This paper proves that physically realistic sources cannot produce magnetic (B mode) radiation memory in gravitational or electromagnetic fields, and that electric (E mode) memory is limited to certain conditions.

Contribution

It provides a global null cone analysis demonstrating the non-existence of B mode radiation memory and E mode memory from bound charges.

Findings

B mode radiation memory does not occur in realistic sources.

E mode electromagnetic memory is absent for bound charge distributions.

The analysis uses a global null cone approach.

Abstract

Gravitational radiation has a memory effect represented by a net change in the relative positions of test particles. Both the linear and nonlinear sources proposed for this radiation memory are of the "electric" type, or E mode, as characterized by the even parity of the polarization pattern. Although "magnetic" type, or B mode, radiation memory is mathematically possible, no physically realistic source has been identified. There is an electromagnetic counterpart to radiation memory in which the velocity of charged particles obtain a net "kick". Again, the physically realistic sources of electromagnetic radiation memory that have been identified are of the electric type. In this paper, a global null cone description of the electromagnetic field is applied to establish the non-existence of B mode radiation memory and the non-existence of E mode radiation memory due to a bound charge distribution.