Dirac operator as a random matrix and the quenched limit of QCD with chemical potential

The behavior of quenched QCD at nonzero chemical potential μ has been a long-standing puzzle. An explicit solution is found using the random matrix approach to chiral symmetry breaking. At nonzero μ the quenched QCD is not a simple n→0 limit of a theory with n quarks: a naive 'replica trick' fails. A limit that leads to the quenched QCD is that of a theory with 2n quarks: n quarks with original action and n quarks with conjugate action. (orig.)