We present a lattice QCD calculation of the up, down, strange and charm quark masses performed using the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 ...dynamical quarks, which include in the sea, besides two light mass degenerate quarks, also the strange and charm quarks with masses close to their physical values. The simulations are based on a unitary setup for the two light quarks and on a mixed action approach for the strange and charm quarks. The analysis uses data at three values of the lattice spacing and pion masses in the range 210–450 MeV, allowing for accurate continuum limit and controlled chiral extrapolation. The quark mass renormalization is carried out non-perturbatively using the RI′-MOM method. The results for the quark masses converted to the MS¯ scheme are: mud(2 GeV)=3.70(17) MeV, ms(2 GeV)=99.6(4.3) MeV and mc(mc)=1.348(46) GeV. We obtain also the quark mass ratios ms/mud=26.66(32) and mc/ms=11.62(16). By studying the mass splitting between the neutral and charged kaons and using available lattice results for the electromagnetic contributions, we evaluate mu/md=0.470(56), leading to mu=2.36(24) MeV and md=5.03(26) MeV.
In the framework of Wilson chiral perturbation theory 1, we study the effect induced by a twisted Wilson term, as it appears in twisted mass QCD 2 (with two degenerate quarks). In particular we ...consider the vacuum orientation and the pion masses. The computations are done to NLO both in the mass and in the lattice spacing (i.e. to O(a2)). There are no restrictions on the relative size of lattice artifacts with respect to the physical mass, thus allowing, in principle, to bridge between the physical regime and the unphysical one, where lattice artifacts tend to dominate. The inclusion of O(a2) lattice artifacts can account for the splitting of degeneracy of the three pion masses. Moreover O(a2) terms are necessary to model non-trivial behaviors of the vacuum orientation such as possible Aoki phases. It turns out that these last two phenomena are determined by the same constant.
We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for
N
f
= 2 mass-degenerate quark flavours. By employing four values of the lattice spacing, ...spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 ≲
m
PS
≲ 650MeV we control the major systematic effects of our calculation. This enables us to confront our
N
f
= 2 data with SU(2) chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass.
We present results of dynamical simulations of Nf=2 degenerate Wilson twisted mass quarks at maximal twist in the range of pseudo scalar masses 300 MeV≲mPS≲550 MeV. Reaching such small masses was ...made possible owing to a recently developed variant of the HMC algorithm. The simulations are performed at one value of the lattice spacing a≲0.1 fm. In order to have O(a) improvement and aiming at small residual O(a2) cutoff effects, the theory is tuned to maximal twist by requiring the vanishing of the untwisted quark mass. Precise results for the pseudo scalar decay constant and the pseudo scalar mass are confronted with chiral perturbation theory predictions and the low energy constants F, l¯3 and l¯4 are evaluated with small statistical errors.
A first study of numerical Monte Carlo simulations with two quark doublets, a mass-degenerate one and a mass-split one, interpreted as u, d, s and c quarks, is carried out in the framework of the ...twisted mass Wilson lattice formulation. Tuning the bare parameters of this theory is explored on 123·24 and 163·32 lattices at lattice spacings a≃0.20 fm and a≃0.15 fm, respectively.
The effect of changing the lattice action for the gluon field on the recently observed F. Farchioni, R. Frezzotti, K. Jansen, I. Montvay, G.C. Rossi, E. Scholz, A. Shindler, N. Ukita, C. Urbach, I. ...Wetzorke, Eur. Phys. J. C 39, 421 (2005); hep-lat/0406039 first order phase transition near zero quark mass is investigated by replacing the Wilson plaquette action by the DBW2 action. The lattice action for quarks is unchanged: it is in both cases the original Wilson action. It turns out that Wilson fermions with the DBW2 gauge action have a phase structure where the minimal pion mass and the jump of the average plaquette are decreased, when compared to Wilson fermions with Wilson plaquette action at similar values of the lattice spacing. Taking the DBW2 gauge action is advantageous also from the point of view of the computational costs of numerical simulations.
We identify the global symmetries of SU(2) lattice gauge theory with N flavors of staggered fermion in the presence of a quark chemical potential \(\mu\), for fermions in both fundamental and adjoint ...representations, and anticipate likely patterns of symmetry breaking at both low and high densities. Results from numerical simulations of the model with N = 1 adjoint flavor on a \(4^3\times8\) lattice are presented, using both hybrid Monte Carlo and Two-Step Multi-Boson algorithms. It is shown that the sign of the fermion determinant starts to fluctuate once the model enters a phase with non-zero baryon charge density. HMC simulations are not ergodic in this regime, but TSMB simulations retain ergodicity even in the dense phase, and in addition appear to show superior decorrelation. The HMC results for the equation of state and the pion mass show good quantitative agreement with the predictions of chiral perturbation theory, which should hold only for \(N\ge2\). The TSMB results incorporating the sign of the determinant support a delayed onset transition, consistent with the pattern of symmetry breaking expected for N = 1.
We present a high order perturbative computation of the renormalization constants ZV, ZA and of the ratio ZP/ZS for Wilson fermions. The computational setup is the one provided by the RI’-MOM scheme. ...Three- and four-loop expansions are made possible by numerical stochastic perturbation theory. Results are given for various numbers of flavors and/or (within a finite accuracy) for generic nf up to three loops. For the case nf=2 we also present four-loop results. Finite-size effects are well under control, and the continuum limit is taken by means of hypercubic symmetric Taylor expansions. The main indetermination comes from truncation errors, which should be assessed in connection with the convergence properties of the series. The latter is best discussed in the framework of boosted perturbation theory, whose impact we try to assess carefully. Final results and their uncertainties show that high-loop perturbative computations of lattice QCD renormalization constants (RCs) are feasible and should not be viewed as a second choice. As a by-product, we discuss the perturbative expansion for the critical mass, for which results are also for generic nf up to three loops, while a four-loop result is obtained for nf=2.
Diquark condensation in dense adjoint matter Hands, S.; Montvay, I.; Scorzato, L. ...
The European physical journal. C, Particles and fields,
12/2001, Letnik:
22, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We study SU(2) lattice gauge theory at non-zero chemical potential with one staggered quark flavor in the adjoint representation. In this model the fermion determinant, although real, can be both ...positive and negative. We have performed numerical simulations using both hybrid Monte Carlo and two-step multibosonic algorithms, the latter being capable of exploring sectors with either determinant sign. We find that the positive determinant sector behaves like a two-flavor theory, with the chiral condensate rotating into a two-flavor diquark condensate for \(\mu>m_\pi/2\), implying a superfluid ground state. Good agreement is found with analytical predictions made using chiral perturbation theory. In the ‘full’ model there is no sign of either onset of baryon density or diquark condensation for the range of chemical potentials we have considered. The impact of the sign problem has prevented us from exploring the true onset transition and the mode of diquark condensation, if any, for this model.
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