Searcharxiv⌕ Search

arXiv subjects

Denes Sexty

Publications and source records attributed to Denes Sexty.

23 records · Page 2Linked to original sources
arXiv2013

Stability of complex Langevin dynamics in effective models

The sign problem at nonzero chemical potential prohibits the use of importance sampling in lattice simulations. Since complex Langevin dynamics does not rely on importance sampling, it provides a potential solution. Recently it was shown that complex Langevin dynamics fails in the disordered phase in the case of the three-dimensional XY model, while it appears to work in the entire phase diagram in the case of the three-dimensional SU(3) spin model. Here we analyse this difference and argue that it is due to the presence of the nontrivial Haar measure in the SU(3) case, which has a stabilizing effect on the complexified dynamics. The freedom to modify and stabilize the complex Langevin process is discussed in some detail.

hep-lat↗
arXiv2012

Charge separation in Reheating after Cosmological Inflation

New aspects of parametrically resonant heating of a relativistic scalar O(2)-symmetric self-interacting field are presented. This process is a candidate for reheating at the end of the early-universe epoch of inflation. Although a model with a fully O(2)-symmetric ground state is used, transient, metastable spontaneous symmetry breaking can be observed. This manifests itself in the form of persistent regimes of opposite and, inside these, uniform charge overdensities separated by thin lines and walls similar to topological defects, in two and three spatial dimensions, respectively. The configuration is found to correspond to an attractive non-equilibrium fixed point of the underlying dynamic equations which prevents thermalisation over an extended period of time.

hep-ph↗
arXiv2010

Real-time effective-action approach to the Anderson quantum dot

The non-equilibrium time evolution of an Anderson quantum dot is investigated. The quantum dot is coupled between two leads forming a chemical-potential gradient. We use Kadanoff-Baym dynamic equations within a non-perturbative resummation of the s-channel bubble chains. The effect of the resummation leads to the introduction of a frequency-dependent 4-point vertex. The tunneling to the leads is taken into account exactly. The method allows the determination of the transient as well as stationary transport through the quantum dot, and results are compared with different schemes discussed in the literature (fRG, ISPI, tDMRG and QMC).

cond-mat.mes-hall↗
arXiv2005

Chern-Simons and Winding Number in a Tachyonic Electroweak Transition

We investigate the development of winding number and Chern-Simons number in a tachyonic transition in the SU(2) Higgs model, motivated by the scenario of cold electroweak baryogenesis. We find that localized configurations with approximately half-integer winding number, dubbed half-knots, play an important role in this process. When the Chern-Simons number adjusts locally to the winding number, the half-knots can stabilize and acquire half-integer Chern-Simons number as well. We present two examples from numerical simulations: one half-knot that stabilizes early and one that gives rise to a late sphaleron transition. We also study the winding number distribution after the transition and present new results on the development of the Chern-Simons susceptibility.

hep-ph↗