Tue·Oct 30, 2001Tuesday·October 30, 2001

1. 01*

   A Lattice Calculation of Thermal Dilepton Rates

   F. Karsch🇩🇪 · E. Laermann🇩🇪 · P. Petreczky🇩🇪 · S. Stickan🇩🇪 · I. Wetzorke🇩🇪

   Using clover improved Wilson fermions we calculate thermal vector meson correlation functions above the deconfinement phase transition of quenched QCD. At temperatures 1.5 Tc and 3Tc they are found to differ by less than 15% from that of a freely propagating quark anti-quark pair. This puts severe constraints on the dilepton production rate and in particular rules out a strong divergence of the dilepton rate at low energies. The vector spectral function, which has been reconstructed using the Maximum Entropy Method, yields an enhancement of the dilepton rate over the Born rate of at most a factor two in the energy interval 4 < E/T < 8 and suggests that the spectrum is cut-off at low energies by a thermal mass threshold of about (2-3)T.

   hep-lathep-phnucl-thPLB(2002)·164 citations
2. 02*

   Continuum limit in abelian projected SU(2) lattice gauge theory

   V. Bornyakov🇩🇪 · M. Muller-Preussker🇩🇪

   We study the continuum limit of the abelian string tension and the density of abelian monopoles calculated after carefully fixing the maximal abelian gauge by employing the simulated annealing algorithm. We present the evidence that the abelian string tension converges to the nonabelian one in the continuum limit. For the monopole density we confirm earlier findings that the density of the properly defined infrared monopoles has correct scaling while the total density seems divergent in the continuum limit due to ultraviolate contributions. We also compare with results obtained with the usual iterative gauge fixing algorithm.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·30 citations
3. 03*

   Separating perturbative and non-perturbative contributions to the plaquette

   R. Horsley🇩🇪 · P.E.L. Rakow🇩🇪 · G. Schierholz🇩🇪

   We try to separate the perturbative and non-perturbative contributions to the plaquette of pure SU(3) gauge theory. To do this we look at the large-n asymptotic behaviour of the perturbation series in order to estimate the contribution of the as-yet uncalculated terms in the series. We find no evidence for the previously reported Lambda^2 contribution to the gluon condensate. Attempting to determine the conventional Lambda^4 condensate gives a value of approximately 0.03(2) GeV^4, in reasonable agreement with sum rule estimates, though with very large uncertainties.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·59 citations
4. 04*

   The three-loop beta-fuction of QCD with the clover action

   A. Bode (1)🇺🇸 · H. Panagopoulos (2) ((1) CSIT, Tallahassee, USA, (2) University of Cyprus, Nicosia, Cyprus)🇨🇾

   We calculate, to 3 loops in perturbation theory, the bare $\beta$-function of QCD, formulated on the lattice with the clover fermionic action. The dependence of our result on the number of colors $N$, the number of fermionic flavors $N_f$, as well as the clover parameter $c_{SW}$, is shown explicitly. A direct outcome of our calculation is the two-loop relation between the bare coupling constant $g_0$ and the one renormalized in the MS-bar scheme. Further, we can immediately derive the three-loop correction to the relation between the lattice $\Lambda$-parameter and $g_0$, which is important in checks of asymptotic scaling. For typical values of $c_{SW}$, this correction is found to be very pronounced.

   hep-latNPB(2002)·40 citations
5. 05*

   Classical solutions with nontrivial holonomy in SU(2) LGT at T \ne 0

   E.-M. Ilgenfritz🇯🇵 · B. V. Martemyanov🇷🇺 · M. Müller-Preussker🇩🇪 · A. I. Veselov🇷🇺

   We generate SU(2) lattice gauge fields at finite temperature and cool them in order to characterize the two phases by the occurrence of specific classical solutions.We apply two kinds of spatial boundary conditions: fixed holonomy and standard periodic b.c. For T < T_c our findings concerning classical configurations semi-quantitatively agree for both types of boundary conditions. We find in the confinement phase a mixture of undissociated calorons with lumps of positive or negative half-integer topological charges.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·4 citations
6. 06*

   Testing Asymptotic Scaling and Nonabelian Symmetry Enhancement

   Adrian Patrascioiu🇺🇸 · Erhard Seiler🇩🇪

   We determine some points on the finite size scaling curve for the correlation length in the two dimensional O(3) and icosahedron spin models. The Monte Carlo data are consistent with the two models possessing the same continuum limit. The data also suggest that the continuum scaling curve lies above the estimate of Kim and of Caracciolo et al and thus leads to larger thermodynamic values of of the correlation length than previously reported.

   hep-latPLB(2002)·3 citations
7. 07*

   Test of the Polyakov Loop Model

   Adrian Dumitru🇺🇸 · Robert D. Pisarski🇺🇸

   We discuss the two point functions for the real and imaginary parts of the Polyakov loop in a pure SU(3) gauge theory. The behavior of these correlation functions in the Polyakov Loop Model is markedly different from that in perturbation theory.

   hep-latNucl.Phys.B Proc.Suppl.(2002)·14 citations
8. 08*

   Quark number susceptibilities from HTL-resummed thermodynamics

   J.-P. Blaizot🇫🇷 · E. Iancu🇫🇷 · A. Rebhan🇦🇹

   We compute analytically the diagonal quark number susceptibilities for a quark-gluon plasma at finite temperature and zero chemical potential, and compare with recent lattice results. The calculation uses the approximately self-consistent resummation of hard thermal and dense loops that we have developed previously. For temperatures between 1.5 to 5 $T_c$, our results follow the same trend as the lattice data, but exceed them in magnitude by about 5-10%. We also compute the lowest order contribution, of order ${\alpha }_s^3\log (1/{\alpha }_s)$, to the off-diagonal susceptibility. This contribution, which is not a part of our self-consistent calculation, is numerically small, but not small enough to be compatible with a recent lattice simulation.

   ↳ hep-phhep-latPLB(2001)·172 citations
9. 09*

   Next-to-Leading Order QCD Corrections to Spectator Effects in Lifetimes of Beauty Hadrons

   M. Ciuchini🇮🇹 · E. Franco🇮🇹 · V. Lubicz🇮🇹 · F. Mescia🇮🇹

   Theoretical predictions of beauty hadron lifetimes, based on the heavy quark expansion up to and including order 1/mb^2, do not to reproduce the experimental measurements of the lifetime ratios tau(B+)/tau(Bd) and tau(Lambdab)/tau(Bd). Large corrections to these predictions come from phase-space enhanced 1/mb^3 contributions, i.e. hard spectator effects. In this paper we calculate the next-to-leading order QCD corrections to the Wilson coefficients of the local operators appearing at O(1/mb^3). We find that these corrections improve the agreement with the experimental data. The lifetime ratio of charged to neutral B mesons, tau(B+)/tau(Bd), turns out to be in very good agreement with the corresponding measurement, whereas for tau(Bs)/tau(Bd) and tau(Lambdab)/tau(Bd) there is a residual difference at the 1-sigma level. We discuss, however, why the theoretical predictions are less accurate in the latter cases.

   ↳ hep-phhep-latNPB(2002)·59 citations
10. 10*

    Generalized Lattice Gauge Theory, Spin Foams and State Sum Invariants

    Robert Oeckl (CPT)🇫🇷

    We construct a generalization of pure lattice gauge theory (LGT) where the role of the gauge group is played by a tensor category. The type of tensor category admissible (spherical, ribbon, symmetric) depends on the dimension of the underlying manifold (<=3, <=4, any). Ordinary LGT is recovered if the category is the (symmetric) category of representations of a compact Lie group. In the weak coupling limit we recover discretized BF-theory in terms of a coordinate free version of the spin foam formulation. We work on general cellular decompositions of the underlying manifold. In particular, we are able to formulate LGT as well as spin foam models of BF-type with quantum gauge group (in dimension <=4) and with supersymmetric gauge group (in any dimension). Technically, we express the partition function as a sum over diagrams denoting morphisms in the underlying category. On the LGT side this enables us to introduce a generalized notion of gauge fixing corresponding to a topological move between cellular decompositions of the underlying manifold. On the BF-theory side this allows a rather geometric understanding of the state sum invariants of Turaev/Viro, Barrett/Westbury and Crane/Yetter which we recover. The construction is extended to include Wilson loop and spin network type observables as well as manifolds with boundaries. In the topological (weak coupling) case this leads to TQFTs with or without embedded spin networks.

    ↳ hep-thgr-qchep-latmath.QAJ.Geom.Phys.(2003)·28 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.