SO(5) invariance and effective field theory for high-Tc superconductors

We set up the effective field theories which describe the SO(5)-invariant picture of the high-Tc cuprates in various regimes. We use these to get quantitative conclusions concerning the size of SO(5) breaking effects. We consider two applications in detail: (i) the thermodynamic free energy, which describes the phase diagram and critical behavior, and (ii) the Lagrangian governing the interactions of the pseudo-Goldstone bosons with each other …