No logarithmic corrections to entropy in shift-symmetric Gauss-Bonnet gravity

TL;DR

This paper demonstrates that in shift-symmetric Gauss-Bonnet gravity, black hole entropy remains uncorrected by logarithmic terms, and the Hawking temperature requires modification, highlighting the impact of boundary terms on black hole thermodynamics.

Contribution

It shows that logarithmic entropy corrections do not appear in shift-symmetric Gauss-Bonnet gravity and explores how boundary terms influence black hole temperature and entropy.

Findings

Logarithmic corrections to entropy are absent in this theory.

Temperature modifications are necessary to satisfy the first law.

Boundary terms significantly affect black hole thermodynamics.

Abstract

Employing the covariant phase space formalism, we discuss black hole thermodynamics in four-dimensional scalar-tensor Einstein-Gauss-Bonnet gravity. We argue that logarithmic corrections to Wald entropy previously reported in this theory do not appear, due to the symmetry of the theory under constant shifts of the scalar field. Instead, we obtain the standard Bekenstein entropy of general relativity. Then, to satisfy the first law of black hole mechanics, the Hawking temperature must be modified. It has been proposed that such temperature modifications occur generically in scalar-tensor theories, due to different propagation speeds of gravitons and photons. We show that the temperature modifications also emerge in the Euclidean canonical ensemble approach to black hole thermodynamics. Notably, the boundary terms of the type we consider here can be considered in any scalar-tensor gravitational theories. Hence, we illustrate that adding a suitable boundary term to action may drastically affect black hole thermodynamics, changing both the entropy and the temperature.