Electromagnetic memory in arbitrary curved space-times

Abstract: The gravitational memory effect and its electromagnetic (EM) analog are potential probes in the strong gravity regime. In the literature, this effect is derived for static observers at asymptotic infinity. While this is a physically consistent approach, it restricts the space-time geometries for which one can obtain the EM memory effect. To circumvent this, we evaluate the EM memory effect for comoving observers (defined by the 4-velocity $u_{\mu}$) in arbitrary curved space-times. Using the covariant approach, we split Maxwell's equations into two parts -- projected parallel to the 4-velocity $u_{\mu}$ and into the 3-space orthogonal to $u_{\mu}$. Further splitting the equations into $1+1+2$-form, we obtain \emph{master equation} for the EM memory in an arbitrary curved space-time. We provide a geometrical understanding of the contributions to the memory effect. We then obtain EM memory for specific space-time geometries and discuss the salient features.