New scenario for high-T_c cuprates: electronic topological transition as   a motor for anomalies in the underdoped regime
  We have discovered a new nontrivial aspect of electronic topological transition (ETT) in a 2D free fermion system on a square lattice. The corresponding exotic quantum critical point, \delta=\delta_c, T=0, (n=1-\delta is an electron concentration) is at the origin of anomalous behaviour in the interacting system on one side of ETT, \delta<\delta_c. The most important is an appearance of the line of characteristic temperatures, T^*(\delta) \propto \delta_c-\delta. Application of the theory to high-T_c cuprates reveals a striking similarity to the observed experimentally behaviour in the underdoped regime (NMR and ARPES). 
F. Onufrieva, P. Pfeuty and M. Kiselev (Laboratoire Leon Brillouin,   CE-Saclay, France)