Complex Landau-Ginzburg theory of the hidden order in URu 2 Si 2

We develop a Landau-Ginzburg theory of the hidden-order phase and the local moment antiferromagnetic phase of URu 2 Si 2 . We unify the two broken symmetries in a common complex-order parameter and derive many experimentally relevant consequences such as the topology of the phase diagram in magnetic field and pressure. The theory accounts for the appearance of a moment under application of stress and the thermal expansion anomaly across the phase transitions. It identifies the low-energy mode which is seen in the hidden-order phase near the commensurate wave vector (0, 0, 1) as the pseudo-Goldstone mode of the approximate U (1) symmetry.