First Law for Nonsingular Black Holes in 2D Dilaton Gravity

TL;DR

This paper uses 2D dilaton gravity to construct nonsingular black hole solutions, derive a consistent energy and first law, clarifying previous misunderstandings and offering insights potentially applicable to higher-dimensional black holes.

Contribution

It introduces a simplified method to construct nonsingular black holes in 2D dilaton gravity and establishes a correct energy formula and first law for these solutions.

Findings

Derived a correct energy formula matching the Casimir function.

Established a consistent first law for nonsingular black holes.

Clarified the cause of apparent first-law violations in previous work.

Abstract

A central issue in the thermodynamics of nonsingular black holes is the apparent violation of the first law. In this work, we use 2D dilaton gravity as a simple theoretical setting to study this issue. We systematically construct a broad class of nonsingular black hole solutions with metric function $A(x)=f(x)+c$, through a procedure that is considerably simpler than in higher-dimensional theories. Using the Iyer-Wald covariant phase space formalism, we derive the correct energy formula and establish a consistent first law for this entire class of solutions. The apparent first-law violation in a previous work is caused by an incorrect choice of energy. Our energy formula agrees, up to a normalization factor for the asymptotic Killing vector, with the Casimir function in 2D dilaton gravity, confirming its interpretation as the physical black hole energy. Our results clarify the correct first law for 2D nonsingular black holes and may provide insights into the first law of nonsingular black holes in higher dimensions.