A holographic proof of the universality of corner entanglement for CFTs

There appears a universal logarithmic term of entanglement entropy, i.e., -a(Q) log(H/delta), for 3d CFTs when the entangling surface has a sharp corner. a(Omega) is a function of the corner opening angle and behaves as a(Omega -> pi) similar or equal to sigma(pi - Omega)(2) and a(Omega -> 0) similar or equal to kappa/Omega, respectively. Recently, it is conjectured that sigma/C-T = pi(2)/24, where C-T is central charge in the stress tensor correlator, is universal for general CFTs in three dimensions. In this paper, by applying the general higher curvature gravity, we give a holographic proof of this conjecture. We also clarify some interesting problems. Firstly, we find that, in contrast to a/C-T, kappa/C-T is not universal. Secondly, the lower bound a(E)(Omega)/C-T associated to Einstein gravity can be violated by higher curvature gravity. Last but not least, we find that there are similar universal laws for CFTs in higher dimensions. We give some holographic tests of these new conjectures.