Spontaneous symmetry breaking, spectral statistics, and the ramp

Ensembles of quantum chaotic systems are expected to exhibit energy eigenvalues with random-matrix-like level repulsion between pairs of energies separated by less than the inverse Thouless time. Recent research has shown that exact and approximate global symmetries of a system have clear signatures in these spectral statistics, enhancing the spectral form factor or correspondingly weakening level repulsion. This paper extends those results to the case of spontaneous symmetry breaking and shows that, surprisingly, spontaneously breaking a symmetry further enhances the spectral form factor. For both random-matrix-theory-inspired toy models and models where the symmetry breaking has a description in terms of fluctuating hydrodynamics, we obtain formulas for this enhancement for arbitrary symmetry breaking patterns, including broken Abelian symmetries Z(n) and U(1) and partially or fully broken non-Abelian symmetries.