Physics

Dr. Wout Merbis
Vienna University of Technology, Vienna

Lower dimensional theories of gravity have been a fruitful arena to address conceptual questions in quantum gravity. Especially the presence of black holes in 2+1 dimensional gravity provides an interesting window into the nature of black hole statistical mechanics and thermodynamics. The topological nature of three dimensional gravity ensures that dynamical degrees of freedom arise only on the boundary of the manifold, after choosing suitable boundary conditions. We will propose a new set of boundary conditions which solely accommodates spacetimes with horizons and show that the relevant degrees of freedom for these spacetimes are governed by simple u(1) current algebras, or equivalently: the Heisenberg algebra. The associated conserved charges can then be interpreted as "soft hair" on the horizon, in the sense that they are strictly zero-energy excitations. Finally, we address the relation between these soft horizon charges and the conformal generators at asymptotic infinity, black hole microstates and generalizations to cosmological horizons.