arXiv subjects
Publications and source records attributed to Ph. de Forcrand.
We extend our study of the gluon propagator in quenched lattice QCD using the Laplacian gauge to a finer lattice. We verify the existence of a pole mass as we take the continuum limit and deduce a value of $\sim 600^{+150}_{-30}$ MeV for this pole mass. We find a finite value of $(454(5){\rm MeV})^{-2}$ for the renormalized zero-momentum propagator, in agreement with results on coarser lattices.
Responses to chemical potential of the pseudoscalar meson screening mass and the chiral condensate in lattice QCD are investigated. On a $16 \times 8^2 \times \4$ lattice with two flavors of staggered quarks the first and second responses below and above $T_c$ are evaluated. Different behavior in the low and the high temperature phases are observed, which may be explained as a consequence of the chiral symmetry breaking and restoration.
Using state of the art lattice techniques we investigate the static baryon potential. We employ the multi-hit procedure for the time links and a variational approach to determine the ground state with sufficient accuracy that, for distances up to $\sim 1.2$ fm, we can distinguish the $Y$- and $Δ$- Ansätze for the baryonic Wilson area law. Our analysis shows that the $Δ$-Ansatz is favoured. This result is also supported by the gauge-invariant nucleon wave function which we measure for the first time.
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 $16\times 8^2\times 4$ lattice with two flavors of staggered quarks below and above $T_c$. The responses to both the isoscalar and isovector chemical potentials are obtained. They show different behavior in the low and the high temperature phases, which may be explained as a consequence of chiral symmetry breaking and restoration, respectively.
We perform a study of the universality of the finite size scaling functions of interface free energies in the 3d Ising model. Close to the hot/cold phase transition, we observe very good agreement with the same scaling functions of the 4d SU(2) Yang--Mills theory at the deconfinement phase transition.
We study relativistic charmonium on very fine quenched lattices (beta=6.4 and 6.6). We concentrate on the calculation of the hyperfine splitting between eta_c and J/psi, aiming for a controlled continuum extrapolation of this quantity. Results for the eta_c and J/psi wave functions are also presented.
We present results for the static three- and four-quark potentials in SU(3) and SU(4) respectively. Using a variational approach, combined with multi-hit for the time-like links, we determine the ground state of the baryonic string with sufficient accuracy to test the $Y-$ and $Δ-$ ansätze for the baryonic Wilson area law. Our results favor the $Δ$ ansatz, where the potential is the sum of two-body terms.
As part of a systematic algorithm study, we present first results on a performance comparison between a multibosonic algorithm and the hybrid Monte Carlo algorithm as employed by the SESAM collaboration. The standard Wilson fermion action is used on 32*16^3 lattices at beta=5.5.
We present results on the static three- and four-quark potentials in SU(3) and SU(4) respectively within quenched lattice QCD. We use an analytic multi-hit procedure for the time links and a variational approach to determine the ground state. The three- and four-quark potentials extracted are consistent with a sum of two-body potentials, possibly with a weak many-body component. The results give support to the $Δ$ ansatz for the baryonic area law.
We study the behaviour of the spatial and temporal 't Hooft loop at zero and finite temperature in the 4D SU(2) Yang-Mills theory, using a new numerical method. In the deconfined phase $T>T_c$, the spatial 't Hooft loop exhibits a dual string tension, which vanishes at $T_c$ with 3D Ising-like critical exponent.
We study the gluon propagator in quenched lattice QCD using the Laplacian gauge which is free of lattice Gribov copies. We compare our results with those obtained in the Landau gauge on the lattice, as well as with various approximate solutions of the Dyson Schwinger equations. We find a finite value $\sim (445 \rm{MeV})^{-2}$ for the renormalized zero-momentum propagator (taking our renormalization point at 1.943 GeV), and a pole mass $\sim 640 \pm 140$ MeV.
We construct a smooth gauge for the adjoint field which is free of ambiguities on the lattice. In this Laplacian Center Gauge, center vortices and monopoles appear together as local gauge defects. A numerical study of center vortices in SU(2) and SU(3) supports equality of the $Z_N$ and SU(N) string tensions in the continuum limit, and only then.
We exhibit the connection between local gauge singularities in the Laplacian gauge and topological charge, which opens the possibility of studying instanton excitations without cooling. We describe our version of Laplacian gauge-fixing for SU(N).
Simulations of odd flavors QCD can be performed in the framework of the hybrid Monte Carlo algorithm where the inverse of the fermion matrix is approximated by a polynomial. In this exploratory study we perform three flavors QCD simulations. We make a comparison of the hybrid Monte Carlo algorithm and the R-algorithm which also simulates odd flavors systems but has step-size errors. We find that results from our hybrid Monte Carlo algorithm are in agreement with those from the R-algorithm obtained at very small step-size.
We study the potential between a static center monopole and antimonopole in 4d SU(2) Yang-Mills theory. Using a new numerical method, we show that the 't Hooft loop is a dual order parameter with respect to the Wilson loop, for the deconfinement phase transition. We observe a 3d Ising-like critical behaviour for the dual string tension related to the spatial 't Hooft loop as a function of the temperature.
We present an exact Monte Carlo algorithm designed to sample theories where the energy is a sum of many couplings of decreasing strength. The algorithm avoids the computation of almost all non-leading terms. Its use is illustrated by simulating SU(2) lattice gauge theory with a 5-loop improved action. A new approach for dynamical fermion simulations is proposed.
We present lattice results for the gluon propagator for SU(2) and SU(3) in the Laplacian gauge which avoids lattice Gribov copies. In SU(3) we compare with the most recent lattice calculation in Landau gauge and with various approximate solutions of the Dyson Schwinger equations (DSE).
I present a unified picture of center vortices and Abelian monopoles. Both appear as local gauge ambiguities in the Laplacian Center Gauge. This gauge is constructed for a general SU(N) theory. Numerical evidence is presented, for SU(2) and SU(3), that the projected $Z_N$ theory confines with a string tension similar to the non-Abelian one.