The CFT-interpolating Black Hole in Three Dimensions
K. Hotta, Y. Hyakutake, T. Kubota, T. Nishinaka, H. Tanida
TL;DR
The paper constructs a new exact extremal black hole in three-dimensional gravity coupled to a scalar field, yielding $AdS_3$ geometries at both spatial infinity and the horizon and thereby hosting two dual $CFT_2$s with different central charges. Using Brown-Henneaux techniques and near-horizon boundary conditions, it derives $c_{UV}=\frac{3L}{2G_N}$ and $c_{IR}=\frac{3\ell}{2G_N}$ with $c_{IR}<c_{UV}$, and shows the IR entropy from Cardy matches the Bekenstein-Hawking entropy while the UV entropy is larger. The holographic RG flow, analyzed via the Hamilton-Jacobi formalism, yields a superpotential $W(\phi)$, a monotone c-function $C(\phi)=\frac{3}{G_N W(\phi)}$, and a Callan-Symanzik framework for the dual $CFT_2$, confirming Zamolodchikov's $c$-theorem in this gravity setup. Altogether, the work provides a concrete AdS$_3$/CFT$_2$ realization of flow between two fixed points connected by a scalar-driven interpolating black hole and offers a platform for exploring holographic RG in lower dimensions.
Abstract
We present a new exact black hole solution in three dimensional Einstein gravity coupled to a single scalar field. This is one of the extended solutions of the BTZ black hole and has in fact $\textrm{AdS}_3$ geometries both at the spatial infinity and at the event horizon. An explicit derivation of Virasoro algebras for $\textrm{CFT}_2$ at the two boundaries is shown to be possible à la Brown and Henneaux's calculation. If we regard the scalar field as a running coupling in the dual two dimensional field theory, and its flow in the bulk as the "holographic" renormalization group flow, our black hole should interpolate the two $\textrm{CFT}_2$ living at the infinity and at the horizon. Following the Hamilton-Jacobi analysis by de Boer, Verlinde and Verlinde, we calculate the central charges $c_{\textrm{UV}}$ and $c_{\textrm{IR}}$ for the $\textrm{CFT}_2$ on the infinity and the horizon, respectively. We also confirm that the inequality $c_{\textrm{IR}} < c_{\textrm{UV}}$ is satisfied, which is consistent with the Zamolodchikov's c-theorem.
