A toy model of (grand) unified monopoles

We explore the old idea that, in a theory containing several gauge groups, the topological defects of one gauge group coincide with those of another gauge group. This simple 'unification' constraint has deep consequences, the best known of which is a natural explanation of the fractional electric charge of quarks. Here we explore the consequences of this idea for the phase diagram, in a toy model U(1)x U(1).