arXiv subjects
Publications and source records attributed to Andreas Jaster.
Starting from the ordered state, we investigate the short-time behaviour of the hard-disk model. For the positional order, we determine the critical exponents eta and z from the dynamic relaxation of the order parameter and the cumulant with molecular dynamics simulations. The results are compared with previous Monte Carlo (MC) simulations. The bond orientational order is studied with MC dynamics.
We investigate the dynamic relaxation for SU(2) gauge theory at finite temperatures in (3+1) dimensions. Using the Hybrid Monte Carlo algorithm, we examine the time dependence of the system in the short-time regime. Starting from the ordered state, the critical exponents beta, nu and z are calculated from the power law behaviour of the Polyakov loop and the cumulant at or near the critical point. The results for the static exponents are in agreement with those obtained from simulations in equilibrium and those of the three-dimensional Ising model. The value for the dynamic critical exponent was determined with z=2.0(1).
We investigate the positional order of the two-dimensional hard disk model with short-time dynamics and equilibrium simulations. The melting density and the critical exponents z and eta are determined. Our results rule out a phase transition as predicted by the Kosterlitz-Thouless-Halperin-Nelson-Young theory as well as a first-order transition.
We investigate the short-time dynamic relaxation of the two-dimensional XY model in the high temperature phase. Starting from the ordered state, we measure the autocorrelation function and determine the autocorrelation time. It is shown that apart from a constant the equilibrium spatial correlation length can be calculated in this way.
We present detailed Monte Carlo results for the two-dimensional melting transition of various systems up to N=65536 hard disks. The simulations are performed in the NVT ensemble, using a new updating scheme. In the isotropic phase the bond orientational correlation length xi_6 and the susceptibility chi_6 are measured and compared with the predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory. From the scaling relation of xi_6 and chi_6 we calculate the critical exponent eta_6. In the phase transition region we use finite-size scaling methods to locate the disclination binding transition point and compare the results with the values obtained from the behaviour in the isotropic phase. Additionally, we measure the topological defect density, the pressure and the distribution of the second moment of the local bond orientational order parameter. All results are in good agreement with the KTHNY theory, while a first-order phase transition with small correlation length and a one-stage continuous transition can be ruled out.
We report Monte Carlo results for the two-dimensional hard disk system. Simulations were performed in the NVT ensemble with up to 65536 disks, using a new updating scheme. We analyze the bond orientational order parameter and correlation length in the isotropic phase and the scaling behaviour of the bond orientational order parameter in the transition region. The data are consistent with predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young theory, while a first-order phase transition is unlikely and a one-stage continuous transition can be ruled out.
We present an improved Metropolis algorithm for arbitrary hard core systems in any dimensions. In the new updating scheme the conventional Metropolis step of a single particle is replaced by a collective step of a chain of particles. For the two-dimensional hard sphere model we show that this algorithm essentially reduces autocorrelation times in vicinity of the transition point.
We study the phenomenon of lack of reversibility in molecular dynamics algorithms for the case of Wilson's lattice QCD. We demonstrate that the classical equations of motion that are employed in these algorithms are chaotic in nature. The leading Liapunov exponent is determined in a range of coupling parameters. We give a quantitative estimate of the consequences of the breakdown of reversibility due to round-off errors.
Some time ago Kaplan proposed a new model for the description of chiral fermions on the lattice by adding an extra dimension for the fermions. A variant of this proposal was introduced by Shamir and can be used to describe vector-like theories in even dimensions. We used this model for the simulation of the massive Schwinger model at different gauge couplings. The prediction that the fermion mass gets only multiplicative renormalization was tested and verified.