Horizon Strings as 3d Black Hole Microstates

We propose that 3d black holes are an ensemble of tensionless null string states. These microstates typically have non-zero winding. We evaluate their partition function in the limit of large excitation numbers and show that their combinatorics reproduces the Bekenstein-Hawking entropy and its semiclassical logarithmic corrections.
Comment: 24pp; v2: considerably extended version with details and text added but otherwise same content, v3: converted to SciPost style