Probability distribution function of the diquark condensate in two colours QCD

We consider diquark condensation in finite density lattice SU(2). We first present an extension of Vafa-Witten result, on spontaneous breaking of vector-like global symmetries, that allows us to formulate a no-go theorem for diquark condensation in a region of the chemical potential-mass parameter space. We then describe a new technique to calculate diquark condensate in unquenched lattice simulations with any number of flavours directly at zero external source, without using any potentially dangerous extrapolation procedure. We apply it to the strong coupling limit and find compelling evidences for a second order transition to a phase with nonzero diquark condensate. Our results are in quantitative agreement with low-energy effective Lagrangian calculations. (C) 2001 Elsevier Science B.V All rights reserved.