Simulating full QCD at nonzero density using the complex Langevin equation

The complex Langevin method is extended to full QCD at non-zero chemical potential. The use of gauge cooling stabilizes the simulations at small enough lattice spacings. At large fermion mass the results are compared to the HQCD approach, in which the spatial hoppings of fermionic variables are neglected, and good agreement is found. The method allows simulations also at high densities, all the way up to saturation.Comment: 5 pages, 5 figures, PLB version, minor change

Prethermalisation and the Build Up of the Higgs Effect

Real time field excitations in the broken symmetry phase of the classical abelian Gauge+Higgs model are studied numerically in the unitary gauge, for systems starting from the unstable maximum of the Higgs potential.Comment: 5 pages, 6 figures, to appear in proceedings of SEWM'0

Superfluid Turbulence: Nonthermal Fixed Point in an Ultracold Bose Gas

Nonthermal fixed points of far-from-equilibrium dynamics of a dilute degenerate Bose gas are analysed in two and three spatial dimensions. For such systems, universal power-law distributions, previously found within a nonperturbative quantum-field theoretic approach, are shown to be related to vortical dynamics and superfluid turbulence. The results imply an interpretation of the momentum scaling at the nonthermal fixed points in terms of independent vortex excitations of the superfluid. Long-wavelength acoustic excitations on the top of these are found to follow a non-thermal power law. The results shed light on fundamental aspects of superfluid turbulence and have strong potential implications for related phenomena studied, e.g., in early-universe inflation or quark-gluon plasma dynamics.Comment: 5 pages, 5 figure

Real-time gauge theory simulations from stochastic quantization using optimized updating

Stochastic quantisation is applied to the problem of calculating real-time evolution on a Minkowskian space-time lattice. We employ optimized updating using reweighting, or gauge fixing, respectively. These procedures do not affect the underlying theory, but strongly improve the stability properties of the stochastic dynamics.Comment: 4 pages, 3 figures, contributed talk to SEWM 2008, Amsterda

Turbulence in nonabelian gauge theory

Kolmogorov wave turbulence plays an important role for the thermalization process following plasma instabilities in nonabelian gauge theories. We show that classical-statistical simulations in SU(2) gauge theory indicate a Kolmogorov scaling exponent known from scalar models. In the range of validity of resummed perturbation theory this result is shown to agree with analytical estimates. We study the effect of classical-statistical versus quantum corrections and demonstrate that the latter lead to the absence of turbulence in the far ultraviolet.Comment: 13 pages, 4 figures. PLB version, improved statistics indicates Kolmogorov exponent 4/

Nonequilibrium Goldstone phenomenon in Hybrid Inflation

We study the onset of Goldstone phenomenon in a hybrid inflation scenario. The physically motivated range of parameters is analyzed in order to meet the cosmological constraints. Classical equations of motion are solved and the evolution through the spontaneous symmetry breaking is followed. We emphasize the role of topological defects that partially maintain the disordered phase well after the waterfall. We study the emergence of the Goldstone excitations and their role in the onset of the radiation dominated universe.Comment: 10 pages with 7 figures. Contribution to Strong and Electroweak Matter (Heidelberg, 2002

Dynamic critical phenomena from spectral functions on the lattice

We investigate spectral functions in the vicinity of the critical temperature of a second-order phase transition. Since critical phenomena in quantum field theories are governed by classical dynamics, universal properties can be computed using real-time lattice simulations. For the example of a relativistic single-component scalar field theory in 2+1 dimensions, we compute the spectral function described by universal scaling functions and extract the dynamic critical exponent z. Together with exactly known static properties of this theory, we obtain a verification from first principles that the relativistic theory is well described by the dynamic universality class of relaxational models with conserved density (Model C).Comment: 18 pages, 6 figures, NPB version, minor change