Multicanonical Cluster Algorithm and the 2-D 7-State Potts Model

I present a hybrid-like two-step algorithm, which combines a microcanonical update of a spin system using demons, with a multicanonical demon refresh. The algorithm is free from the supercritical slowing down that burdens the canonical methods: the exponential increase of the tunnelling time between the metastable states in the first-order phase transitions, when the volume of the system is increased. The demons act as a buffer between the multicanonical heat bath and the spin system, allowing the spin system to be updated with any microcanonical demon procedure, including cluster methods. The cluster algorithm is demonstrated with the 2-dimensional 7-state Potts model, using volumes up to $128^2$. The tunnelling time is found to increase as $L^{1.82}$, where $L$ is the linear dimension of the system.Comment: 14 pages, 8 ps-figures, the flashy one missing to save space+troubles, sorry, the whole thing available from the author. Preprint CERN-TH.6654/9

QCD-like technicolor on the lattice

This talk gives an overview, aimed at non-experts, of the recent progress on the studies of technicolor models on the lattice. Phenomenologically successful technicolor models require walking coupling; thus, an emphasis is put on the determination of the beta-function of various models. As a case study we consider SU(2) gauge field theory with two adjoint representation fermions, so-called minimal walking technicolor theory.Comment: 6 pages; talk presented at "Quark Confinement and the Hadron Spectrum IX", Universidad Complutense de Madrid, 30 August--3 September 201

What's new with the electroweak phase transition?

We review the status of non-perturbative lattice studies of the electroweak phase transition. In the Standard Model, the complete phase diagram has been reliably determined, and the conclusion is that there is no phase transition at all for the experimentally allowed Higgs masses. In the Minimal Supersymmetric Standard Model (MSSM), in contrast, there can be a strong first order transition allowing for baryogenesis. Finally, we point out possibilities for future simulations, such as the problem of CP-violation at the MSSM electroweak phase boundary.Comment: LATTICE98(electroweak), 6 pages. List of references update

Quark number susceptibility of high temperature and finite density QCD

We utilize lattice simulations of the dimensionally reduced effective field theory (EQCD) to determine the quark number susceptibility of QCD at high temperature ($T>2T_c$). We also use analytic continuation to obtain results at finite density. The results extrapolate well from known perturbative expansion (accurate in extremely high temperatures) to 4d lower temperature lattice dataComment: 7 pages, 5 figures, Presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German

Universal features of JIMWLK and BK evolution at small x

In this paper we present the results of numerical studies of the JIMWLK and BK equations with a particular emphasis on the universal scaling properties and phase space structure involved. The results are valid for near zero impact parameter in DIS. We demonstrate IR safety due to the occurrence of a rapidity dependent saturation scale Q_s(\tau). Within the set of initial conditions chosen both JIMWLK and BK equations show remarkable agreement. We point out the crucial importance of running coupling corrections to obtain consistency in the UV. Despite the scale breaking induced by the running coupling we find that evolution drives correlators towards an asymptotic form with near scaling properties. We discuss asymptotic features of the evolution, such as the \tau- and A-dependence of Q_s away from the initial condition.Comment: 30 page

A Strong Electroweak Phase Transition up to m_H ~ 105 GeV

Non-perturbative lattice simulations have shown that there is no electroweak phase transition in the Standard Model for the allowed Higgs masses, m_H \gsim 75 GeV. In the Minimal Supersymmetric Standard Model, in contrast, it has been proposed that the transition should exist and even be strong enough for baryogenesis up to m_H ~ 105 GeV, provided that the lightest stop mass is in the range 100...160 GeV. However, this prediction is based on perturbation theory, and suffers from a noticeable gauge parameter and renormalization scale dependence. We have performed large-scale lattice Monte Carlo simulations of the MSSM electroweak phase transition. Extrapolating the results to the infinite volume and continuum limits, we find that the transition is in fact stronger than indicated by 2-loop perturbation theory. This guarantees that the perturbative Higgs mass bound m_H ~ 105 GeV is a conservative one, allows slightly larger stop masses (up to ~ 165 GeV), and provides a strong motivation for further studies of MSSM electroweak baryogenesis.Comment: 4 pages, 3 figure