A study of center vortices in SU(2) and SU(3) gauge theories

We show how center vortices and Abelian monopoles both appear as local gauge ambiguities in the Laplacian Center gauge. Numerical results, for SU(2) and SU(3), support the view that the string tension obtained in the center-projected theory matches the full string tension when the continuum limit is taken.Comment: 9 pages, 4 figures; talk presented at the International Workshop on Non-Perturbative Methods and Lattice QCD, Guangzhou, May 200

Laplacian Center Vortices

I present a unified picture of center vortices and Abelian monopoles. Both appear as local gauge ambiguities in the Laplacian Center Gauge. This gauge is constructed for a general SU(N) theory. Numerical evidence is presented, for SU(2) and SU(3), that the projected $Z_N$ theory confines with a string tension similar to the non-Abelian one.Comment: 9 pages, 5 figures; talk presented at "Confinement 2000", Osaka, March 200

Effective string picture for confinement at finite temperature: theoretical predictions and high precision numerical results

The effective string picture of confinement is used to derive theoretical predictions for the interquark potential at finite temperature. At short distances, the leading string correction to the linear confining potential between a heavy quark-antiquark pair is the "L\"uscher term''. We assume a Nambu--Goto effective string action, and work out subleading contributions in an analytical way. We discuss the contribution given by a possible ``boundary term'' in the effective action, comparing these predictions with results from simulations of lattice $Z_2$ gauge theory in three dimensions, obtained with an algorithm which exploits the duality of the $Z_2$ gauge model with the Ising spin model.Comment: Lattice2003(nonzero), 3 pages, 2 figure

The Quest for Light Sea Quarks: Algorithms for the Future

As part of a systematic algorithm study, we present first results on a performance comparison between a multibosonic algorithm and the hybrid Monte Carlo algorithm as employed by the SESAM collaboration. The standard Wilson fermion action is used on 32*16^3 lattices at beta=5.5.Comment: LaTeX, 3 pages, Lattice2001(algorithms

Dimensional reduction and the phase diagram of 5d Yang-Mills theory

We present a non-perturbative study of the phase diagram of 5d SU(2) Yang-Mills theory with one compact extra dimension on the lattice. Assuming at least a modest scale separation between the cutoff and the compactification scales leads to an exponential separation between the compactification scale and the four-dimensional correlation length. While we demonstrate that it is not possible to take a full five-dimensional continuum limit, this dynamical generation of scale hierarchy opens up the possibility for us to make limited, but non-perturbative, predictions about continuum theories whose low-energy sector is described by an effective 5d Yang-Mills theory.Comment: 7 pages. Presented at the XXVII International Symposium on Lattice Field Theory, July 26-31, 2009, Peking University, Beijing, Chin

The relevance of center vortices

We show remnants of chiral symmetry breaking in the center-projected theory. We construct and study an unambiguous definition of center vortices.Comment: LATTICE99(confine), 3 pages, 3 figure

Strange mass dependence of the tricritical point in the U(3)_L x U(3)_R chiral sigma model

We study the strange quark mass dependence of the tricritical point of the U(3)_L x U(3)_R linear sigma model in the chiral limit. Assuming that the tricritical point is at a large strange mass value, the strange sector as well as the \eta-a_0 sector decouples from the light degrees of freedom which determines the thermodynamics. By tracing this decoupling we arrive from the original U(3)_L x U(3)_R symmetric model, going through the U(2)_L x U(2)_R symmetric one, at the SU(2)_L x SU(2)_R linear sigma model. One-loop level beta functions for the running of the parameters in each of these models and tree-level matching of the coupling of these models performed at intermediate scales are used to determine the influence of the heavy sector on the parameters of the SU(2)_L x SU(2)_R linear sigma model. By investigating the thermodynamics of this latter model we identified the tricritical surface of the U(3)_L x U(3)_R linear sigma model in the chiral limit. To apply the results for QCD we used different scenarios for the m_s and \mu_q dependence of the effective model parameters, then the \mu_q^TCP(m_s) function can be determined. Depending on the details, a curve bending upwards or downwards near \mu_q=0 can be obtained, while with explicit chemical potential dependence of the parameters the direction of the curve can change with m_s, too.Comment: 17 pages, 6 figures, uses revtex4-

Noisy Monte Carlo revisited

We present an exact Monte Carlo algorithm designed to sample theories where the energy is a sum of many couplings of decreasing strength. Our algorithm, simplified from that of L. Lin et al. hep-lat/9905033, avoids the computation of almost all non-leading terms. We illustrate its use by simulating SU(2) lattice gauge theory with a 5-loop action, and discuss further applications to full QCD.Comment: latex, 8 page

Improved AdS/QCD Model with Matter

We study an improved AdS/QCD model at finite temperature and chemical potential. An Ansatz for the beta-function for the boundary theory allows for the derivation of a charged dilatonic black hole in bulk. The solution is asymptotically RN-AdS in the UV and AdS2 * R3 in the IR. We discuss the thermodynamical aspects of the solution. The fermionic susceptibilities are shown to deviate from the free fermionic limits at asymptotic temperatures despite the asymptotically free nature of the gauge coupling at the boundary. The Polyakov line, the temporal and spatial string tensions dependence on both temperature and chemical potential are also discussed

Center vortex model for the infrared sector of SU(3) Yang-Mills theory: Topological susceptibility

The topological susceptibility of the SU(3) random vortex world-surface ensemble, an effective model of infrared Yang-Mills dynamics, is investigated. The model is implemented by composing vortex world-surfaces of elementary squares on a hypercubic lattice, supplemented by an appropriate specification of vortex color structure on the world-surfaces. Topological charge is generated in this picture by writhe and self-intersection of the vortex world-surfaces. Systematic uncertainties in the evaluation of the topological charge, engendered by the hypercubic construction, are discussed. Results for the topological susceptibility are reported as a function of temperature and compared to corresponding measurements in SU(3) lattice Yang-Mills theory. In the confined phase, the topological susceptibility of the random vortex world-surface ensemble appears quantitatively consistent with Yang-Mills theory. As the temperature is raised into the deconfined regime, the topological susceptibility falls off rapidly, but significantly less so than in SU(3) lattice Yang-Mills theory. Possible causes of this deviation, ranging from artefacts of the hypercubic description to more physical sources, such as the adopted vortex dynamics, are discussed.Comment: 30 pages, 6 figure