I am trying to understand the concept of anomalies and the global or gauge symmetry breaking, i.e. the Lepton and Baryon number symmetries. Could someone explain me, what we mean by saying that the Baryon or Lepton U(1) symmetries are broken? and how is that done? I've seen the loop diagram - eg a current of B or L coming in and annihilating into two U(1)_Y bosons- and how this leads into non trivial current divergence.... But I cannot or didn't see where the factor of energy comes in... (because in low energies, the B,L numbers are "good").