Thu·Oct 11, 2007Thursday·October 11, 2007

1. 01*

   Electric polarizability of the neutron in dynamical quark ensembles

   Michael Engelhardt (LHPC)🇺🇸

   The background field method for measuring the electric polarizability of the neutron is adapted to the dynamical quark case, resulting in the calculation of (certain space-time integrals over) three- and four-point functions. Particular care is taken to disentangle polarizability effects from the effects of subjecting the neutron to a constant background gauge field; such a field is not a pure gauge on a finite lattice and engenders a mass shift of its own. At a pion mass of m_pi = 759 MeV, a small, slightly negative electric polarizability is found for the neutron.

   hep-latPoS(2007)·2 citations
2. 02*

   Deriving confinement via RG decimations

   E. T. Tomboulis🇺🇸

   We present the general framework and building blocks of a recent derivation of the fact that the SU(2) LGT is in a confining phase for all values of the coupling $0<\beta <\infty$, for space-time dimension $d\le 4$. The method employs approximate but explicitly computable RG decimations that are shown to constrain the exact partition function and order parameters from above and below, and flow from the weak to the strong coupling regime without encountering a fixed point.

   hep-latPoS(2007)·6 citations
3. 03*

   Eradication of singularities in the next-to-leading order RG evolution for the \Delta S = 1 effective Hamiltonian with 3 quark flavours

   David H. Adams🇰🇷 · Weonjong Lee🇰🇷

   We consider the renormalization group evolution for the operators in the $\Delta S=1$ effective Hamiltonian with 3 active quark flavors, which is needed in the numerical analysis of data sets for ${ϵ}^{\prime }/ϵ$ calculated in lattice QCD. Singularities are present in the original solution of Buras et al. at next-to-leading order. We show how these can be eradicated through a method of analytic continuation to obtain the correct finite solution in this case. Furthermore, we trace the origin of the singularities to a breakdown of the approach of Buras et al. in the 3 flavour case, and show how it can be rectified so that singularitites are absent from the beginning.

   hep-latPoS(2007)·0 citations
4. 04*

   General properties of logarithmically divergent one-loop lattice Feynman integrals

   Jongjeong Kim🇰🇷 · David H. Adams🇰🇷 · Weonjong Lee🇰🇷

   We prove that logarithmically divergent one-loop lattice Feynman integrals have the general form I(p,a) = f(p)log(aM)+g(p,M) up to terms which vanish for lattice spacing a -> 0. Here p denotes collectively the external momenta and M is an arbitrary mass scale. The f(p) is shown to be universal and to coincide with the analogous quantity in the corresponding continuum integral (regularized, e.g., by momentum cut-off). This is essential for universality of the lattice QCD beta-function and anomalous dimensions of renormalized lattice operators at one loop. The result and argument presented here are simplified versions of ones given in arXiv:0709.0781. A noteworthy feature of the argument here is that it does not involve Taylor expansion in external momenta, hence infra-red divergences associated with that expansion do not arise.

   hep-latPoS(2007)·0 citations
5. 05*

   Hadron Spectrum in a Two-Colour Baryon-Rich Medium

   Simon Hands🇬🇧 · Peter Sitch🇬🇧 · Jon-Ivar Skullerud🇮🇪

   The hadron spectrum of SU(2) lattice gauge theory with two flavours of Wilson quark is studied on an 8^3x16 lattice using all-to-all propagators, with particular emphasis on the dependence on quark chemical potential mu. As mu is increased from zero the diquark states with non-zero baryon number B respond as expected, while states with B=0 remain unaffected until the onset of non-zero baryon density at mu=m_pi/2. Post onset the pi-meson mass increases in accordance with chiral perturbation theory while the rho becomes lighter. In the diquark sector a Goldstone state associated with a superfluid ground state can be identified. A further consequence of superfluidity is an approximate degeneracy between mesons and baryons with the same spacetime and isospin quantum numbers. Finally we find tentative evidence for the binding of states with kaon quantum numbers within the baryonic medium.

   hep-lathep-phnucl-thPLB(2008)·52 citations
6. 06*

   The Landau gauge gluon and ghost propagators in 4D SU(3) gluodynamics in large lattice volumes

   I.L. Bogolubsky (JINR Dubna)🇷🇺 · E.-M. Ilgenfritz🇩🇪 · M. Müller-Preussker (HU Berlin)🇩🇪 · A. Sternbeck (U Adelaide)🇦🇺

   We present recent results of the Landau gauge gluon and ghost propagators in SU(3) pure gauge theory at Wilson \beta=5.7 for lattice sizes up to 80^4 corresponding to physical volumes up to (13.2 fm)^4. In particular, we focus on finite-volume and Gribov copy effects. We employ a gauge fixing method that combines a simulated annealing algorithm with finalizing overrelaxation. We find the gluon propagator for the largest volumes and at q^2 ~ 0.01 GeV^2 to become flat. Although not excluded by our data, there is still no clear indication of a gluon propagator tending towards zero in the zero-momentum limit. New data for the ghost propagator are reported, too.

   hep-latPoS(2007)·268 citations
7. 07*

   Comparing SU(2) to SU(3) gluodynamics on large lattices

   A. Sternbeck🇦🇺 · L. von Smekal🇦🇺 · D. B. Leinweber🇦🇺 · A. G. Williams🇦🇺

   We study the SU(2) gluon and ghost propagators in Landau gauge on lattices up to a size of 112^4. A comparison with the SU(3) case is made and finite-volume effects are then investigated. We find that for a large range of momenta the SU(2) and SU(3) propagators are remarkably alike. In the low-momentum region we compare with recent results obtained in DSE studies on a 4-torus.

   hep-latPoS(2007)·155 citations
8. 08*

   The spatial string tension and dimensional reduction in QCD

   RBC-Bielefeld Collaboration: Jack Liddle🇩🇪

   The spatial string tension for 3+1 dimensional QCD at finite temperature is measured. The gauge configurations we re generated with two light and one heavier strange quark on lattices of size $16^{3}4$ and $24^{3}6$. This spatial string tension is compared with the string tension of the 3 dimensional pure gauge theory together with the temperature dependent 2-loop running coupling. Further comparison is made with predictions from dimensionally reduced effective theories.

   hep-latPoS(2007)·5 citations
9. 09*

   Cutoff effects for Wilson twisted mass fermions at tree-level of perturbation theory

   K. Cichy🇵🇱 · J. Gonzalez Lopez🇩🇪 · K. Jansen🇩🇪 · A. Kujawa🇵🇱 · A. Shindler🇩🇪

   We study cutoff effects at tree-level of perturbation theory for standard Wilson and Wilson twisted mass fermionic lattice actions with Nf=2 flavour degenerate quarks. The discretization effects are investigated by computing the mass spectrum and decay amplitudes for different hadron interpolating fields and the scaling behaviour towards the continuum limit is analyzed. It is shown that the Wilson and the mass average methods are equivalent and lead to O(a) improved R5-parity even lattice observables. We also demonstrate that automatic O(a) improvement works in case of Wilson twisted mass fermions at maximal twist and that this improvement is realized even if the condition of maximal twist is achieved only up to O(a) cutoff effects. We demonstrate that in the chiral limit standard Wilson fermions show scaling violations of O(a^2) while for maximally twisted mass fermions these violations are only of O(a^4). For our analytical calculations, lattices with sizes L=aN and periodic boundary conditions in the spatial directions have been chosen while infinite extension in the time direction is considered.

   hep-latPoS(2007)·2 citations
10. 10*

    Analytic continuation of the critical line in 2-color QCD at nonzero temperature and density

    Paolo Cea🇮🇹 · Leonardo Cosmai🇮🇹 · Massimo D'Elia🇮🇹 · Alessandro Papa🇮🇹

    We determine the pseudo-critical line in the temperature - chemical potential plane of 2-color QCD by direct Monte Carlo simulations and by analytic continuation from imaginary chemical potential.

    hep-latPoS(2007)·7 citations
11. 11*

    Covariance, Dynamics and Symmetries, and Hadron Form Factors

    M.S. Bhagwat🇺🇸 · I.C. Cloet🇺🇸 · C.D. Roberts🇺🇸

    We summarise applications of Dyson-Schwinger equations to the theory and phenomenology of hadrons. Some exact results for pseudoscalar mesons are highlighted with details relating to the U_A(1) problem. We describe inferences from the gap equation relating to the radius of convergence for expansions of observables in the current-quark mass. We recapitulate upon studies of nucleon electromagnetic form factors, providing a comparison of the ln-weighted ratios of Pauli and Dirac form factors for the neutron and proton.

    ↳ nucl-thhep-lathep-phnucl-ex29 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.