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Register a new userRelative scale setting for two-color QCD with Nf=2 Wilson fermions
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We determine the scale setting function and the pseudo-critical temperature on the lattice in $N_f=2$ two-color QCD using the Iwasaki gauge and Wilson fermion actions. Although two-color QCD does not correspond to the real world, it is very useful as a good testing ground for three-color QCD. The scale setting function gives the relative lattice spacings of simulations performed at different values of the bare coupling. It is a necessary tool for taking the continuum limit. Firstly, we measure the meson spectra for various combinations of ($beta,kappa$) and find a line of constant physics in $beta$--$kappa$ plane. Next, we determine the scale setting function via $w_0$ scale in the gradient flow method. Furthermore, we estimate the pseudo-critical temperature at zero chemical potential from the chiral susceptibility. Combining these results, we can discuss the QCD phase diagram in which both axes are given by dimensionless quantities, namely, the temperature normalized by the pseudo-critical temperature on the lattice and the chemical potential normalized by the pseudoscalar meson mass. It makes it easy to compare among several lattice studies and also makes it possible to compare theoretical analyses and lattice studies in the continuum limit.
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We give a determination of the phenomenological value of the Wilson (or gradient) flow scales t0 and w0 for 2+1 flavours of dynamical quarks. The simulations are performed keeping the average quark mass constant, which allows the approach to the physical point to be made in a controlled manner. O(a) improved clover fermions are used and together with four lattice spacings this allows the continuum extrapolation to be taken.
We investigate chemical-potential (mu) dependence of static-quark free energies in both the real and imaginary mu regions, performing lattice QCD simulations at imaginary mu and extrapolating the results to the real mu region with analytic continuation. Lattice QCD calculations are done on a 16^{3}times 4 lattice with the clover-improved two-flavor Wilson fermion action and the renormalization-group improved Iwasaki gauge action. Static-quark potential is evaluated from the Polyakov-loop correlation functions in the deconfinement phase. As the analytic continuation, the potential calculated at imaginary mu=imu_{rm I} is expanded into a Taylor-expansion series of imu_{rm I}/T up to 4th order and the pure imaginary variable imu_{rm I}/T is replaced by the real one mu_{rm R}/T. At real mu, the 4th-order term weakens mu dependence of the potential sizably. At long distance, all of the color singlet and non-singlet potentials tend to twice the single-quark free energy, indicating that the interactions between heavy quarks are fully color-screened for finite mu. For both real and imaginary mu, the color-singlet q{bar q} and the color-antitriplet qq interaction are attractive, whereas the color-octet q{bar q} and the color-sextet qq interaction are repulsive. The attractive interactions have stronger mu/T dependence than the repulsive interactions. The color-Debye screening mass is extracted from the color-singlet potential at imaginary mu, and the mass is extrapolated to real mu by analytic continuation. The screening mass thus obtained has stronger mu dependence than the prediction of the leading-order thermal perturbation theory at both real and imaginary mu.
QCD is investigated at finite temperature using Wilson fermions in the fixed scale approach. A 2+1 flavor stout and clover improved action is used at four lattice spacings allowing for control over discretization errors. The light quark masses in this first study are fixed to heavier than physical values. The renormalized chiral condensate, quark number susceptibility and the Polyakov loop is measured and the results are compared with the staggered formulation in the fixed N_t approach. The Wilson results at the finest lattice spacing agree with the staggered results at the highest N_t.
We present an update on our on-going project to compute hadronic observables for Nf=2 flavours of O(a) improved Wilson fermions at small lattice spacings. The procedure to determine the lattice scale via the mass of the Omega baryon is described. Furthermore we present preliminary results for the pion form factor computed using twisted boundary conditions, and report on the implementation of a novel approach to determine the contribution of the hadronic vacuum polarisation to the anomalous magnetic moment of the muon.
The twisted reduced model of large $N$ QCD with two adjoint Wilson fermions is studied numerically using the Hybrid Monte Carlo method. This is the one-site model, whose large $N$ limit (large volume limit) is expected to be conformal or nearly conformal. The symmetric twist boundary condition with flux $k$ is used. $k$=0 corresponds to periodic boundary conditions. It is shown that the quark mass and $N$ dependencies of the model with non-vanishing $k$ differ significantly from those of the $k$=0 model. A preliminary result for the string tension calculated at $N$=289 is presented. The string tension seems to vanish as the physical quark mass decreases to zero in a way consistent with the theory being governed by an infrared fixed point with $gamma_* = 0.8 sim 1.2$.
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