Black hole thermodynamics from Iyer-Wald formalism with variable Newton's constant

TL;DR

This paper develops a geometric framework for black hole thermodynamics using the Iyer-Wald formalism with a variable Newton's constant, establishing a consistent thermodynamic structure beyond the extended phase space approach.

Contribution

It applies the Iyer-Wald formalism to restricted phase space thermodynamics, providing a geometric foundation for black hole thermodynamics with variable Newton's constant.

Findings

Constructs a self-consistent thermodynamic structure for black holes.

Shows the applicability of Iyer-Wald formalism to restricted phase space.

Establishes a geometric foundation for this thermodynamic approach.

Abstract

Recent advances in black hole thermodynamics have intensified efforts to investigate its thermodynamic framework analogues to that of classical thermal systems. Departing from the extended phase space approach which involves a variable cosmological constant, the restricted phase space formalism focusing on the variations of Newton's gravitational constant in black hole thermodynamics is proposed. This approach enables the construction of a self-consistent thermodynamic structure that features both the first law and the Euler relation. In this paper, we demonstrate that for any diffeomorphism-invariant gravitational theory, the Iyer-Wald formalism is applicable to restricted phase space thermodynamics and construct a self-consistent extensive black hole thermodynamic system. Our work thereby establishes the Iyer-Wald approach as the geometric foundation for restricted phase space black hole thermodynamics.