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Linearized Einstein's Equation around pure BTZ from Entanglement Thermodynamics

It is known that the linearized Einstein&#39;s equation around the pure $AdS$ can be obtained from the constraint $ ΔS = Δ\left< H \right> $, known as the first law of entanglement, on the boundary $CFT$. The corresponding dual state in the boundary $CFT$ is the vacuum state around which the linear perturbation is taken. In this paper we revisit this question, in the context of $ {AdS}_3/{CFT}_2 $, with the state of the boundary ${CFT}_2$ as a thermal state. The corresponding dual geometry is a planar BTZ black hole. By considering the linearized perturbation around this black brane we show that Einstein&#39;s equation follows from the first law of entanglement. The modular Hamiltonian in a thermal state of the ${CFT}_2$ that we have used has been recently found in arXiv:1608.01283 [cond-mat.stat-mech].