C. B. Lang

The triviality bound of the four-component Φ4 model☆

Abstract The four-dimensional O(4) Φ4 scalar theory is investigated in the broken phase at different values of the quartic coupling λ. The scalar mass, the field expectation value and the wave function renormalization constant are calculated. We demonstrate the λ dependence of the ratio R s = m s 〈ϕ s ren 〉 and estimate its upper bound to be around 2.7(1).

Quenched spectroscopy with fixed-point and chirally improved fermions

Abstract We present results from quenched spectroscopy calculations with the parametrized fixed-point and the chirally improved Dirac operators. Both these operators are approximate solutions of the Ginsparg–Wilson equation and have good chiral properties. This allows us to work at small quark masses and we explore pseudoscalar-mass to vector-mass ratios down to 0.28. We discuss meson and baryon masses, their scaling properties, finite volume effects and compare our results with recent large scale simulations. We find that the size of quenching artifacts of the masses is strongly correlated with their experimentally observed widths and that the gauge and hadronic scales are consistent.

D_{s0}^{*}(2317) Meson and D-Meson-Kaon Scattering from Lattice QCD

The scalar meson D*(s0)(2317) is found 37(17) MeV below the DK threshold in a lattice simulation of the J(P)=0(+) channel using, for the first time, both DK as well as s¯c interpolating fields. The simulation is done on N(f)=2+1 gauge configurations with m(π) is approximately equal to 156 MeV, and the resulting M(D*(s0))-1/4(M(D(s))+3M(D*(s)))=266(16) MeV is close to the experimental value 241.5(0.8) MeV. The energy level related to the scalar meson is accompanied by additional discrete levels due to DK scattering states. The levels near threshold lead to the negative DK scattering length a(0)=-1.33(20) fm that indicates the presence of a state below threshold.

Hopping parameter expansion for the meson spectrum in SU(3) lattice QCD

The low-lying pseudoscalar and vector mesons containing u, d, s and c quarks are studied by the method of the hopping parameter expansion combined with a Monte Carlo simulation at 1g2 = 0.0, 0.7, 0.9, 0.925, 0.95 and 1.0. The effect of virtual quark loops is taken into account. Meson masses, quark masses, the lattice scale and Ku, Ks and Kc as functions of g2 are determined.

The phase structure of a non-abelian gauge Higgs field system

Abstract The phase structure of a non-abelian gauge Higgs field system is studied by Monte Carlo (MC) simulations. The analysis is done on a 4 4 lattice and approximating both the gauge group and the Higgs manifold by the icosahedral subgroup of SU(2). Results are presented for a Higgs field in the fundamental representation, in which case the symmetry is completely broken for sufficiently strong coupling, and for a Higgs field in the adjoint representation, in which case a U(1) symmetry (approximated by Z 10 ) survives. No evidence for a “Coulomb pocket” is found.

Hadron spectroscopy with dynamical chirally improved fermions

We simulate two dynamical, mass-degenerate light quarks on

Potential and restoration of rotational symmetry in SU(2) lattice gauge theory

{16}^{3}\ifmmode\times\else\texttimes\fi{}32

Meson and baryon spectrum for QCD with two light dynamical quarks

lattices with a spatial extent of 2.4 fm using the chirally improved Dirac operator. The simulation method, the implementation of the action, and signals of equilibration are discussed in detail. Based on the eigenvalues of the Dirac operator we discuss some qualitative features of our approach. Results for ground-state masses of pseudoscalar and vector mesons as well as for the nucleon and delta baryons are presented.

SU(2) gauge-Higgs theory with radial degree of freedom

Abstract We study by numerical techniques the restoration of rotational invariance in SU(2) lattice gauge theory. Results on the potential between two static sources in the fundamental representation are also represented.

QCD with two light dynamical chirally improved quarks: Mesons

We present results of meson and baryon spectroscopy using the Chirally Improved Dirac operator on lattices of size 16{sup 3}x32 with two mass-degenerate light sea quarks. Three ensembles with pion masses of 322(5), 470(4), and 525(7) MeV and lattice spacings close to 0.15 fm are investigated. Results for ground and excited states for several channels are given, including spin two mesons and hadrons with strange valence quarks. The analysis of the states is done with the variational method, including two kinds of Gaussian sources and derivative sources. We obtain several ground states fairly precisely and find radial excitations in various channels. Excited baryon results seem to suffer from finite size effects, in particular, at small pion masses. We discuss the possible appearance of scattering states, considering masses and eigenvectors. Partially quenched results in the scalar channel suggest the presence of a 2-particle state, however, in most channels we cannot identify them. Where available, we compare our results to results of quenched simulations using the same action.