Fu, WenboHung, Ling-YanSachdev, Subir2015-06-122014Fu, Wenbo, Ling-Yan Hung, and Subir Sachdev. 2014. “Quantum Quenches and Competing Orders.” Phys. Rev. B 90 (2) (July). doi:10.1103/physrevb.90.024506.1098-0121http://nrs.harvard.edu/urn-3:HUL.InstRepos:16319730We study the nonequilibrium dynamics of an electronic model of competition between an unconventional charge density wave (a bond density wave) and d-wave superconductivity. In a time-dependent Hartree-Fock+BCS approximation, the dynamics reduces to the equations of motion of operators realizing the generators of SU(4) at each pair of momenta, (k,−k), in the Brillouin zone. We also study the nonequilibrium dynamics of a quantum generalization of a O(6) nonlinear σ model of competing orders in the underdoped cuprates [Hayward et al., Science 343, 1336 (2014)]. We obtain results, in the large N limit of a O(N) model, on the time dependence of correlation functions following a pulse disturbance. We compare our numerical studies with recent picosecond optical experiments. We find that, generically, the oscillatory responses in our models share various qualitative features with the experiments.en-USJournal Article2015-06-1210.1103/PhysRevB.90.024506