Three-Dimensional Tricritical Gravity
  We consider a class of parity even, six-derivative gravity theories in three dimensions. After linearizing around anti-de Sitter space, the theories have one massless and two massive graviton solutions for generic values of the parameters. At a special, so-called tricritical, point in parameter space the two massive graviton solutions become massless and they are replaced by two solutions with logarithmic and logarithmic-squared boundary behavior. The theory at this point is conjectured to be dual to a rank-3 Logarithmic Conformal Field Theory (LCFT) whose boundary stress tensor, central charges and new anomaly we calculate. We also calculate the conserved Abbott-Deser-Tekin charges. At the tricritical point, these vanish for excitations that obey Brown-Henneaux and logarithmic boundary conditions, while they are generically non-zero for excitations that show logarithmic-squared boundary behavior. This suggests that a truncation of the tricritical gravity theory and its corresponding dual LCFT can be realized either via boundary conditions on the allowed gravitational excitations, or via restriction to a zero charge sub-sector. We comment on the structure of the truncated theory. 
Eric A. Bergshoeff, Sjoerd de Haan, Wout Merbis, Jan Rosseel and   Thomas Zojer
hep-th