Singularity resolution and unitarity in two-dimensional dilaton black holes with negative central charge

Abstract

We study a one-loop corrected extension of the classical Callan-Giddings-Harvey-Strominger (CGHS) model of two-dimensional dilaton gravity. The effective action combines the non-local Polyakov action for matter fluctuations, a Polyakov-type term built from an auxiliary flat metric that implements Strominger's mechanism for the Faddeev-Popov reparametrization ghosts, and a local counterterm that simultaneously preserves the flatness of the auxiliary metric, ensures exact solvability, and keeps two-dimensional Minkowski spacetime as an exact solution of the backreacted equations. In the regime of negative total central charge, the classical curvature singularity is resolved and gives way to asymptotically flat regions inside the horizon. The exterior Hawking flux is preserved and turns out to be correlated with an internal radiation flux supported on null surfaces that approach null infinity from beyond the horizon; this internal flux, in particular, presents a short interval of negative values. These correlations point to the preservation of unitarity, provided the relevant null surfaces remain at a finite affine distance from the collapsing matter trajectory. Within the present formulation, however, a fully consistent energy balance cannot yet be established. We discuss possible strategies to overcome this issue.