Browsing by Author "Yao, Louie Hong"
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- Critical dynamics of the antiferromagnetic O(3) nonlinear sigma model with conserved magnetizationYao, Louie Hong; Täuber, Uwe C. (American Physical Society, 2022-06-01)We study the near-equilibrium critical dynamics of the O(3) nonlinear sigma model describing isotropic antiferromagnets with a nonconserved order parameter reversibly coupled to the conserved total magnetization. To calculate response and correlation functions, we set up a description in terms of Langevin stochastic equations of motion, and their corresponding Janssen-De Dominicis response functional. We find that in equilibrium, the dynamics is well-separated from the statics, at least to one-loop order in a perturbative treatment with respect to the static and dynamical nonlinearities. Since the static nonlinear sigma model must be analyzed in a dimensional d=2+ɛ expansion about its lower critical dimension dlc=2, whereas the dynamical mode-coupling terms are governed by the upper critical dimension dc=4, a simultaneous perturbative dimensional expansion is not feasible, and the reversible critical dynamics for this model cannot be accessed at the static critical renormalization group fixed point. However, in the coexistence limit addressing the long-wavelength properties of the low-temperature ordered phase, we can perform an ϵ=4-d expansion near dc. This yields anomalous scaling features induced by the massless Goldstone modes, namely subdiffusive relaxation for the conserved magnetization density with asymptotic scaling exponent zΓ=d-2, which may be observable in neutron scattering experiments. Intriguingly, if initialized near the critical point, the renormalization group flow for the effective dynamical exponents recovers their universal critical values zc=d/2 in an intermediate crossover region.
- Perturbative field-theoretical analysis of three-species cyclic predator-prey modelsYao, Louie Hong; Swailem, Mohamed; Dobramysl, Ulrich; Tauber, Uwe C. (IOP Publishing, 2023-06)We apply a perturbative Doi-Peliti field-theoretical analysis to the stochastic spatially extended symmetric Rock-paper-Scissors (RPS) and May-Leonard (ML) models, in which three species compete cyclically. Compared to the two-species Lotka-Volterra predator-prey (LV) model, according to numerical simulations, these cyclical models appear to be less affected by intrinsic stochastic fluctuations. Indeed, we demonstrate that the qualitative features of the ML model are insensitive to intrinsic reaction noise. In contrast, and although not yet observed in numerical simulations, we find that the RPS model acquires significant fluctuation-induced renormalizations in the perturbative regime, similar to the LV model. We also study the formation of spatio-temporal structures in the framework of stability analysis and provide a clearcut explanation for the absence of spatial patterns in the RPS system, whereas the spontaneous emergence of spatio-temporal structures features prominently in the LV and the ML models.
- Social distancing and epidemic resurgence in agent-based susceptible-infectious-recovered modelsMukhamadiarov, Ruslan I.; Deng, Shengfeng; Serrao, Shannon R.; Priyanka; Nandi, Riya; Yao, Louie Hong; Täuber, Uwe C. (Nature Research, 2021-01-08)Once an epidemic outbreak has been effectively contained through non-pharmaceutical interventions, a safe protocol is required for the subsequent release of social distancing restrictions to prevent a disastrous resurgence of the infection. We report individual-based numerical simulations of stochastic susceptible-infectious-recovered model variants on four distinct spatially organized lattice and network architectures wherein contact and mobility constraints are implemented. We robustly find that the intensity and spatial spread of the epidemic recurrence wave can be limited to a manageable extent provided release of these restrictions is delayed sufficiently (for a duration of at least thrice the time until the peak of the unmitigated outbreak) and long-distance connections are maintained on a low level (limited to less than five percent of the overall connectivity).