The holographic entropy increases in quadratic curvature gravity

Understand

Standard methods for calculating the black hole entropy beyond general relativity are ambiguous when the horizon is non stationary.

• We fix these ambiguities in all quadratic curvature gravity theories, by demanding that the entropy be increasing at every time, for linear perturbations to a stationary black hole.
• Our result matches with the entropy formula found previously in holographic entanglement entropy calculations.
• We explicitly calculate the entropy increase for Vaidya-like solutions in Ricci-tensor gravity to show that (unlike the Wald entropy) the holographic entropy obeys a Second Law.