Decreasing entropy of dynamical black holes in critical gravity

Decreasing entropy of dynamical black holes in critical gravity

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Abstract Critical gravity Sunscreen is a quadratic curvature gravity in four dimensions which is ghost-free around the AdS background.Constructing a Vaidya-type exact solution, we show that the area of a black hole defined by a future outer trapping horizon can shrink by injecting a charged null fluid with positive energy density, so that a black hole is no more a one-way membrane even under the null energy condition.In addition, the solution shows that the Wald-Kodama dynamical entropy of a black hole is negative and Desk w/Bench can decrease.

These properties expose the pathological aspects of critical gravity at the non-perturbative level.