Second-order Lovelock gravity from entanglement in conformal field theories

Holographic entanglement entropy and the first law of thermodynamics are believed to decode the gravity theory in the bulk. In particular, assuming the Ryu-Takayanagi (RT) [Phys. Rev. Lett. 96, 181602 (2006)PRLTAO0031-900710.1103/PhysRevLett.96.181602] formula holds for ball-shaped regions on the boundary around conformal field theory vacuum states implies [J. High Energy Phys. 08 (2017) 057JHEPFG1029-847910.1007/JHEP08(2017)057] a bulk gravity theory equivalent to Einstein gravity through second-order perturbations. In this paper, we show that the same assumptions can also give rise to second-order Lovelock gravity. Specifically, we generalize the procedure in [J. High Energy Phys. 08 (2017) 057JHEPFG1029-847910.1007/JHEP08(2017)057] to show that the arguments there also hold for Lovelock gravity by proving through second-order perturbation theory, the entropy calculated using the Wald formula [Phys. Rev. D 48, R3427 (1993)PRVDAQ0556-282110.1103/PhysRevD.48.R3427] in Lovelock also obeys an area law (at least up to second order). Since the equations for second-order perturbations of Lovelock gravity are different in general from the second-order perturbation of the Einstein-Hilbert action, our work shows that the holographic area law cannot determine a unique bulk theory even for second-order perturbations assuming only RT on ball-shaped regions. It is anticipated that RT on all subregions is expected to encode the full nonlinear Einstein equations on asymptotically anti-de Sitter spacetimes.