Nonrelativistic Expansion of Closed Bosonic Strings

We develop a novel approach to non-relativistic closed bosonic string theory that is based on a string 1/c2 expansion of the relativistic string, where c is the speed of light. This approach has the benefit that one does not need to take a limit of a string in a near-critical Kalb-Ramond background. The 1/c2-expanded Polyakov action at next-to-leading order reproduces the known action of non-relativistic string theory provided that the target space obeys an appropriate foliation constraint. We compute the spectrum in a flat target space, with one circle direction that is wound by the string, up to next-to-leading order and show that it reproduces the spectrum of the Gomis-Ooguri string.