Black-hole dynamics in BHT massive gravity

TL;DR

This paper investigates the behavior of black holes in (2+1)-dimensional BHT massive gravity, demonstrating that while their area can decrease under null dust infall, their entropy consistently increases, supporting the validity of the entropy law.

Contribution

It provides an exact analysis of black hole dynamics in BHT massive gravity, focusing on area and entropy laws using a Vaidya-type solution.

Findings

Black hole area can decrease with positive energy null dust.

Dynamical entropy always increases during evolution.

Supports the entropy law in BHT massive gravity.

Abstract

Using an exact Vaidya-type null-dust solution, we study the area and entropy laws for dynamical black holes defined by a future outer trapping horizon in (2+1)-dimensional Bergshoeff-Hohm-Townsend (BHT) massive gravity. We consider the theory admitting a degenerate (anti-)de Sitter vacuum and pure BHT gravity. It is shown that, while the area of a black hole decreases by the injection of a null dust with positive energy density in several cases, the Wald-Kodama dynamical entropy always increases.