String memories ... lost and regained

We discuss stringy alpha' corrections to the gravitational wave signal generated in the merging of two black holes. We model the merging with two BPS compact massive objects in the heterotic string, described by standard vertex operators or coherent states. Despite the expected cubic suppression in alpha' w.r.t. the General Relativity result in the low-energy expansion, at tree level the infinite tower of string resonances leaves a clear footprint on the gravitational wave signals within the sensitivity region of aLIGO/VIRGO and future interferometers. Including loop effects that broaden and destabilise the string resonances suggests a sort of lost stringy memory effect that can be regained through the analysis of the quasi normal modes in the ring-down phase. (C) 2021 The Author(s). Published by Elsevier B.V.