Wed·Aug 31, 2005Wednesday·August 31, 2005

1. 01*

   Two Color QCD beyond the BEC regime

   Simon Hands🇬🇧 · Seyong Kim🇰🇷 · Jon-Ivar Skullerud🇮🇪

   We present results of simulations of Two Color QCD using two flavors of Wilson quark in the fundamental representation, at non-zero quark chemical potential mu, on an 8^3x16 lattice. Results for the quark number density, quark and gluon energy densities, and superfluid condensate are qualitatively distinct from the behaviour expected on the assumption that the dominant degrees of freedom are tightly bound scalar diquarks which Bose condense; rather the scaling with mu is more suggestive of a Fermi surface disrupted by a Cooper pair condensate. We also present evidence both for screening of the static potential, and color deconfinement, arising solely as a result of a non-zero quark density.

   hep-lathep-phnucl-thPoS(2006)·4 citations
2. 02*

   Ghost condensation on the lattice

   Attilio Cucchieri🇧🇷 · Tereza Mendes🇧🇷 · Antonio Mihara🇧🇷

   We perform a numerical study of ghost condensation -- in the so-called Overhauser channel -- for SU(2) lattice gauge theory in minimal Landau gauge. The off-diagonal components of the momentum-space ghost propagator G^{cd}(p) are evaluated for lattice volumes V = 8^4, 12^4, 16^4, 20^4, 24^4 and for three values of the lattice coupling: \beta = 2.2, 2.3, 2.4. Our data show that the quantity \phi^b(p) = \epsilon^{bcd} G^{cd}(p) / 2 is zero within error bars, being characterized by very large statistical fluctuations. On the contrary, |\phi^b(p)| has relatively small error bars and behaves at small momenta as L^{-2} p^{-z}, where L is the lattice side in physical units and z \approx 4. We argue that the large fluctuations for \phi^b(p) come from spontaneous breaking of a global symmetry and are associated with ghost condensation. It may thus be necessary (in numerical simulations at finite volume) to consider |\phi^b(p)| instead of \phi^b(p), to avoid a null average due to tunneling between different broken vacua. Also, we show that \phi^b(p) is proportional to the Fourier-transformed gluon field components {\widetilde A}_{\mu}^b(q). This explains the L^{-2} dependence of |\phi^b(p)|, as induced by the behavior of | {\widetilde A}_{\mu}^b(q) |. We fit our data for |\phi^b(p)| to the theoretical prediction (r / L^2 + v) / (p^4 + v^2), obtaining for the ghost condensate v an upper bound of about 0.058 GeV^2. In order to check if v is nonzero in the continuum limit, one probably needs numerical simulations at much larger physical volumes than the ones we consider. As a by-product of our analysis, we perform a careful study of the color structure of the inverse Faddeev-Popov matrix in momentum space.

   hep-lathep-thnucl-thPRD(2005)·23 citations
3. 03*

   A New Method for Determining $F_{\pi }$ on the Lattice

   P.H. Damgaard🇩🇰 · Urs M. Heller🇺🇸 · K. Splittorff🇸🇪 · B. Svetitsky🇮🇱

   We derive the two-point spectral correlation function of the Dirac operator with a specific external source in the $ϵ$-regime of QCD. This correlation function has a unique and strong dependence on $F_{\pi }$, and thus provides an novel way to extract $F_{\pi }$ from lattice simulations. We test the method in a quenched lattice simulation with staggered fermions.

   hep-lathep-thPRD(2005)·60 citations
4. 04*

   Simulating nonequilibrium quantum fields with stochastic quantization techniques

   J. Berges🇩🇪 · I.-O. Stamatescu🇩🇪

   We present lattice simulations of nonequilibrium quantum fields in Minkowskian space-time. Starting from a non-thermal initial state, the real-time quantum ensemble in 3+1 dimensions is constructed by a stochastic process in an additional (5th) ``Langevin-time''. For the example of a self-interacting scalar field we show how to resolve apparent unstable Langevin dynamics, and compare our quantum results with those obtained in classical field theory. Such a direct simulation method is crucial for our understanding of collision experiments of heavy nuclei or other nonequilibrium phenomena in strongly coupled quantum many-body systems.

   hep-latcond-mat.otherhep-phhep-th+1PRL(2005)·121 citations
5. 05*

   B-Meson Mixing and Lifetimes

   C. Tarantino🇮🇹

   $B_d$ and $B_s$ meson systems play a fundamental role to test and improve our understanding of Standard Model flavor dynamics. The mixing parameters $\Delta m_{d,s}$ represent important constraints in the unitarity triangle analysis. Their theoretical estimates require non-perturbative calculations of B-meson decay constants and B-parameters; accurate results, recently obtained from the lattice, are reviewed. Other phenomenologically interesting quantities are the beauty hadron lifetime ratios and, the width differences and CP-violation parameters in $B_d$ and $B_s$ systems. We discuss their theoretical predictions which, in the last four years, have been improved thanks to accurate lattice calculations and next-to-leading order perturbative computations.

   ↳ hep-phhep-latNucl.Phys.B Proc.Suppl.(2006)·17 citations
6. 06*

   Regular and chaotic interactions of two BPS dyons at low energy

   Ricardo Fariello🇧🇷 · Hilmar Forkel🇧🇷 · Gastao Krein🇧🇷

   We identify and analyze quasiperiodic and chaotic motion patterns in the time evolution of a classical, non-Abelian Bogomol'nyi-Prasad-Sommerfield (BPS) dyon pair at low energies. This system is amenable to the geodesic approximation which restricts the underlying SU(2) Yang-Mills-Higgs dynamics to an eight-dimensional phase space. We numerically calculate a representative set of long-time solutions to the corresponding Hamilton equations and analyze quasiperiodic and chaotic phase space regions by means of Poincare surfaces of section, high-resolution power spectra and Lyapunov exponents. Our results provide clear evidence for both quasiperiodic and chaotic behavior and characterize it quantitatively. Indications for intermittency are also discussed.

   ↳ hep-thhep-lathep-phnlin.CDPRD(2005)·3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.