Two-colour QCD at finite fundamental quark-number density and related theories

We are simulating SU(2) Yang-Mills theory with four flavours of dynamical q uarks in the fundamental representation of SU(2) 'colour' at finite chemica l potential, mu for quark number, as a model for QCD at finite baryon numbe r density. In particular we observe that for mu large enough this theory un dergoes a phase transition to a state with a diquark condensate which break s quark-number symmetry. In this phase we examine the spectrum of light sca lar and pseudoscalar bosons and see evidence for the Goldstone boson associ ated with this spontaneous symmetry breaking. This theory is closely relate d to QCD at finite chemical potential for isospin, a theory which we are no w studying for SU(3) colour.