201 research outputs found
Decreasing entropy of dynamical black holes in critical gravity
Critical gravity 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 can decrease. These
properties expose the pathological aspects of critical gravity at the
non-perturbative level.Comment: 11 pages, no figure, 2 tables; v2, revised version with more
references; v3, final version to appear in JHE
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