An integrable spin chain for the SL(2,R)/U(1) black hole sigma model

TL;DR

This paper constructs a spin chain model that captures the low-energy behavior of the SL(2,R)/U(1) black hole conformal field theory, providing a new physical realization and detailed spectral analysis.

Contribution

It introduces a novel spin chain model with non-hermitian Hamiltonian that accurately describes the SL(2,R)/U(1) black hole CFT at low energies.

Findings

The spin chain's low-energy spectrum matches the black hole CFT.

The density of states agrees with established theoretical formulas.

The model provides a physical measurement of the reflection amplitude.

Abstract

We introduce a spin chain based on finite-dimensional spin-1/2 SU(2) representations but with a non-hermitian `Hamiltonian' and show, using mostly analytical techniques, that it is described at low energies by the SL(2,R)/U(1) Euclidian black hole Conformal Field Theory. This identification goes beyond the appearance of a non-compact spectrum: we are also able to determine the density of states, and show that it agrees with the formulas in [J. Math. Phys. 42, 2961 (2001)] and [JHEP 04, 014 (2002)], hence providing a direct `physical measurement' of the associated reflection amplitude.