Minimal Massive Gravity (MMG) is an extension of three-dimensional
Topologically Massive Gravity that, when formulated about Anti-de Sitter space,
accomplishes to solve the tension between bulk and boundary unitarity that
other models in three dimensions suffer from. We study this theory at the
chiral point, i.e. at the point of the parameter space where one of the central
charges of the dual conformal field theory vanishes. We investigate the
non-linear regime of the theory, meaning that we study exact solutions to the
MMG field equations that are not Einstein manifolds. We exhibit a large class
of solutions of this type, which behave asymptotically in different manners. In
particular, we find analytic solutions that represent two-parameter
deformations of extremal Banados-Teitelboim-Zanelli (BTZ) black holes. These
geometries behave asymptotically as solutions of the so-called Log Gravity,
and, despite the weakened falling-off close to the boundary, they have finite
mass and finite angular momentum, which we compute. We also find time-dependent
deformations of BTZ that obey Brown-Henneaux asymptotic boundary conditions.
The existence of such solutions show that Birkhoff theorem does not hold in MMG
at the chiral point. Other peculiar features of the theory at the chiral point,
such as the degeneracy it exhibits in the decoupling limit of the Cotton
tensor, are discussed.Comment: 13 pages. v2 minor typos corrected. Accepted for publication in Phys.
Rev.