Ph. de Forcrand

Renormalization group flow of SU(3) lattice gauge theory : Numerical studies in a two coupling space

We investigate the renormalization group (RG) flow of SU(3) lattice gauge theory in a two coupling space with couplings β11 and β12 corresponding to 1×1 and 1×2 loops, respectively. Extensive numerical calculations of the RG flow are made in the fourth quadrant of this coupling space, i.e., β11>0 and β12<0 . Swendsens factor two blocking and the Schwinger–Dyson method are used to find an effective action for the blocked gauge field. The resulting renormalization group flow runs quickly towards an attractive stream which has an approximate line shape. This is a numerical evidence of a renormalized trajectory which locates close to the two coupling space. A model flow equation which incorporates a marginal coupling (asymptotic scaling term), an irrelevant coupling and a non-perturbative attraction towards the strong coupling limit reproduces qualitatively the observed features. We further examine the scaling properties of an action which is closer to the attractive stream than the currently used improved actions. It is found that this action shows excellent restoration of rotational symmetry even for coarse lattices with a∼0.3 fm.

N-to-delta electromagnetic-transition form factors from lattice QCD.

The magnetic dipole (M1), the electric quadrupole (E2), and the Coulomb quadrupole (C2) amplitudes for gammaN-->Delta are calculated in quenched lattice QCD. Using a new method, which combines an optimal choice of interpolating fields for the Delta and an overconstrained analysis, we obtain statistically accurate results for the dipole form factor and for the ratios R(EM)=E2/M1 and R(SM)=C2/M1, up to momentum transfer squared 1.5 GeV2. We show for the first time, using lattice QCD, that both R(EM) and R(SM) are nonzero and negative, in qualitative agreement with experiment and indicating the presence of deformation in the N/Delta system.

The role of center vortices in QCD

Center vortices are unambiguously identified after Laplacian Center Gauge fixing and their influence on confinement and chiral symmetry breaking is investigated on a sample of SU(2) configurations at zero and finite temperature.

Monte Carlo simulations of regularized bosonic strings

Abstract The world sheet of the bosonic string is regularized by triangulation. The corresponding statistical theory of triangulated random surfaces is simulated by Monte Carlo methods and the critical exponent γ for the susceptibility determined. A careful analysis of the systematic and statistical errors reveals that we have to wait for the next generation of computers before a high-precision measurement of γ is possible.

Meson correlators in finite temperature lattice QCD

We analyze temporal and spatial meson correlators in quenched lattice QCD at T>0. Below Tc we observe little change in the meson properties as compared with T50. Above Tc we observe new features: chiral symmetry restoration and signals of plasma formation, but also an indication of persisting ‘‘mesonic’’ ~metastable! states and different temporal and spatial ‘‘masses’’ in the mesonic channels. This suggests a complex picture of QGP in the region (1 ‐1.5)Tc .

The relevance of center vortices

Abstract We show remnants of chiral symmetry breaking in the center-projected theory. We construct and study an unambiguous definition of center vortices.

Responses of hadrons to the chemical potential at finite temperature

We present a framework to compute the responses of hadron masses to the chemical potential in lattice QCD simulations. As a first trial, the screening mass of the pseudoscalar meson and its first and second responses are evaluated. We present results on a

Non-hermitian exact local bosonic algorithm for dynamical quarks

16\times 8^2\times 4

Probing hadron wave functions in lattice QCD

lattice with two flavors of staggered quarks below and above

UV-filtered fermionic Monte Carlo

T_c