New electromagnetic memories and soft photon theorems

TL;DR

This work introduces a new electromagnetic memory effect: a B-mode, displacement-type memory that induces a position shift of a charged particle. It builds a Maxwell-at-null-infinity framework to derive ordinary (kick) and null displacement memories, with antipodal matching connecting data at future and past null infinity. The authors establish a precise equivalence between the memory formulas and soft-photon theorems, showing that the leading memory corresponds to the leading soft factor and the displacement memory to the sub-leading soft factor, via Fourier transforms. These results extend the EM-memory–soft-theorem correspondence beyond velocity kicks to a magnetic-type memory with potential experimental relevance and deeper links to foundational aspects like the Aharonov-Bohm effect and gravitational memory structures.

Abstract

In this paper, we present a new type of electromagnetic memory. It is a `magnetic' type, or B mode, radiation memory effect. Rather than a residual velocity, we find a position displacement of a charged particle induced by the B mode radiation with memory. We find two types of electromagnetic displacement (ordinary and null). We also show that the null electromagnetic memory formulas are nothing but a Fourier transformation of soft photon theorems.