Soft hairy horizons in three spacetime dimensions

We discuss some aspects of soft hairy black holes and a new kind of ``soft hairy cosmologies,'' including a detailed derivation of the metric formulation, results on flat space, and novel observations concerning the entropy. Remarkably, like in the case with negative cosmological constant, we find that the asymptotic symmetries for locally flat spacetimes with a horizon are governed by infinite copies of the Heisenberg algebra that generate soft hair descendants. It is also shown that the generators of the three-dimensional Bondi-Metzner-Sachs algebra arise from composite operators of the affine ^u(1) currents through a twisted Sugawara-like construction. We then discuss entropy macroscopically and microscopically and discover that a microscopic formula derived recently for boundary conditions associated with the Korteweg--de Vries hierarchy fits perfectly our results for entropy and ground state energy. We conclude with a comparison to related approaches.