Asymptotically nonrelativistic string backgrounds

In recent years, interesting curved-space extensions of nonrelativistic (NR) string theory have been very actively pursued, where the background has a structure that is a stringy generalization of Newton-Cartan geometry. Here we show that the natural black branes of the NR theory, sourced by the familiar repertoire of stringy objects, generally have a different structure. The black string is our main example. We find that the source distorts the background significantly, generating a large throat within which physics is in fact relativistic. It is only far away from the throat that the background approaches the string Newton-Cartan form. We show that exactly the same is true for the longitudinal RR-charged black brane. On the other hand, the transverse RR-charged black brane turns out to have a proper string Newton-Cartan structure everywhere, not just asymptotically.