Phase transitions of the BTZ black hole in new massive gravity

Abstract: We investigate thermodynamics of the BTZ black hole in new massive gravity explicitly. For $m^2\ell^2>1/2$ with $m^2$ the mass parameter of fourth-order terms and $\ell^2$ AdS$_3$ curvature radius, the Hawking-Page phase transition occurs between the BTZ black hole and AdS (thermal) soliton. For $m^2\ell^2<1/2$, however, this transition unlikely occurs but a phase transition between the BTZ black hole and the massless BTZ black hole is possible to occur. We may call the latter as the inverse Hawking-Page phase transition and this transition is favored in the new massive gravity.