New scenario for high-T-c cuprates: Electronic topological transition as amotor for anomalies in the underdoped regime

We have discovered a new nontrivial aspect of electronic topological transi tion (ETT) in a 2D free fermion system on a square lattice. The correspondi ng exotic quantum critical point, delta = delta(c), T = 0 (n = 1 - delta is the electron concentration), is at the origin of anomalous behavior in the interacting system on one side of ETT, delta < delta(c). Most important is the appearance of the line of characteristic temperatures, T*(delta) propo rtional to delta(c) - delta. Application of the theory to high-T-c cuprates reveals a striking similarity to the behavior observed experimentally in t he underdoped regime.