Consistency between black hole and mimetic gravity -- Case of $(2+1)$-dimensional gravity

Abstract

We show that the mimetic theory with the constraint g ρσ ∂ρφ∂σφ = 1 cannot realize the black hole geometry with the horizon(s). To overcome such issue, we may change the mimetic constraint a little bit by ω(φ)g ρσ ∂ρφ∂σφ = −1, where ω(φ) is a function of the scalar field φ. As an example, we consider (2 + 1)-dimensional mimetic gravity with the mimetic potential and construct black hole (BH) solutions by using this modified constraint. We study three different classes: In the first class, we assume the Lagrange multiplier and mimetic potential are vanishing and obtain a BH solution that fully matches the BH of GR despite the non-triviality of the mimetic field which ensures the study presented in JCAP 01 (2019) 058. In the second class, we obtain a BH having constant mimetic potential and a non-trivial form of the Lagrange multiplier. In the third class, we obtain a new BH solution with non-vanishing values of the mimetic field, the Lagrange multiplier, and the mimetic potential. In any case, the solutions correspond to the space-time with only one horizon but we show that the formalism for the constraint works.