Gravity Seminars

Gravitational-wave (GW) memory effects are the permanent changes in asymptotically flat spacetime that persist after the passage of a wave. Three types of memory effects have been well studied: displacement memory (permanent change in the relative positions of comoving test masses), spin memory, and center-of-mass memory (both related to permanent change in separation for test masses with initial relative velocities). The evolution equations in the asymptotic region of spacetime predict a hierarchy of persistent effects that have recently been called “higher memory effects”, with the well-known memory effects being the leading and subleading contributions. The higher memory effects provide new GW observables that are determined by a set of temporal moments of the gravitational radiation from an isolated source. These effects can deepen our understanding of asymptotically flat spacetimes and how information about source dynamics is encoded in gravitational waves. This talk explores three key aspects of higher memory effects in the context of gravity. First, we present the contribution from the moments of the News to the GW strain in terms of the source multipole moments. Second, within the post-Newtonian framework, we demonstrate how these moments contribute to the terms in the radiative multipole moments of the strain. Third, we discuss the prospects for detecting these effects up to the second order. Lastly, the talk will also explore analogous hierarchies of persistent effects in other gauge theories, including electromagnetism and classical Yang-Mills theory.