Description
Title: BPS states in AdS_3 x S^3 x S^3 x S^1
The BPS spectrum of string theory on AdS_3 x S^3 x S^3 x S^1 is determined using a world-sheet description in terms of WZW models. It is found that the theory only has BPS states with j^+ = j^- where j^{\pm} refer to the spins of the two su(2) algebras of the large N=4 superconformal algebra. We then re-examine the BPS spectrum of the corresponding supergravity and find that, in contradistinction to previous claims in the literature, also in supergravity only the states with j^+=j^- are BPS. This resolves a number of long-standing puzzles regarding the BPS spectrum of string theory and supergravity in this background. [This is based on joint work with Lorenz Eberhardt, Rajesh Gopakumar and Wei Li.]
