Strings in AdS₃: one-loop partition function and near-extremal BTZ thermodynamics

We revisit the computation of the string partition function in AdS₃ focussing on the appearance of spacetime (super) symmetries. We show how the asymptotic symmetries of the AdS₃ spacetime, which generate the boundary (super) Virasoro currents, are captured by the one-loop partition sum. We use this to argue that the recent understanding of near-extremal black hole thermodynamics based on the gravitational path integral continues to hold for finite string length. Along the way we clarify some aspects of the AdS₃/CFT₂ duality and, in particular, deduce which bulk gauge fields lead to boundary currents. We also explain how one can interpolate between supersymmetric and thermal (Atick-Witten) fermion boundary conditions in the target space by suitably tuning rotational chemical potentials in the string partition function.