Scalar Hair from a Derivative Coupling of a Scalar Field to the Einstein   Tensor
  We consider a gravitating system of vanishing cosmological constant consisting of an electromagnetic field and a scalar field coupled to the Einstein tensor. A Reissner-Nordstr\"om black hole undergoes a second-order phase transition to a hairy black hole of generally anisotropic hair at a certain critical temperature which we compute. The no-hair theorem is evaded due to the coupling between the scalar field and the Einstein tensor. Within a first order perturbative approach we calculate explicitly the properties of a hairy black hole configuration near the critical temperature and show that it is energetically favorable over the corresponding Reissner-Nordstr\"om black hole. 
Theodoros Kolyvaris, George Koutsoumbas, Eleftherios Papantonopoulos   and George Siopsis
gr-qc hep-th