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Register a new userLattice study on two-color QCD with six flavors of dynamical quarks
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We study the dynamics of SU(2) gauge theory with NF=6 Dirac fermions by means of lattice simulation to investigate if they are appropriate to realization of electroweak symmetry breaking. The discrete analogue of beta function for the running coupling constant defined under the Schroedinger functional boundary condition are computed on the lattices up to linear size of L/a=24 and preclude the existence of infrared fixed point below 7.6. Gluonic observables such as heavy quark potential, string tension, Polyakov loop suggest that the target system is in the confining phase even in the massless quark limit.
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We investigate the chiral properties of SU(2) gauge theory with six flavors, i.e. six light Dirac fermions in the fundamental representations by lattice simulation, and point out that the spontaneous breakdown of chiral symmetry does not occur in this system. The quark mass dependence of the mesonic spectrum provides an evidence for such a possibility. The decay constant tends to be increased by the finite size effect, which is opposite to the behavior predicted by chiral perturbation theory and indicates that the long distance dynamics in the six-flavor theory could be different from the theory with chiral symmetry breaking. The subtracted chiral condensate, whose utility is demonstrated by the simulation of two-flavor theory, is shown to vanish in the chiral limit within the precision of available data.
We present a study of the topological susceptibility in lattice QCD with two degenerate flavors of dynamical quarks. The topological charge is measured on gauge configurations generated with a renormalization group improved gauge action and a mean field improved clover quark action at three values of $beta=6/g^2$, corresponding to lattice spacings of $a approx 0.22$, 0.16 and 0.11 fm, with four sea quark masses at each $beta$. The study is supplemented by simulations of pure SU(3) gauge theory with the same gauge action at 5 values of $beta$ with lattice spacings 0.09 fm$simlt a simlt$0.27 fm. We employ a field theoretic definition of the topological charge together with cooling. For the topological susceptibility in the continuum limit of pure SU(3) gauge theory we obtain $chi_t^{1/4} = 197^{+13}_{-16}$ MeV where the error shows statistical and systematic ones added in quadrature. In full QCD $chi_t$ at heavy sea quark masses is consistent with that of pure SU(3) gauge theory. A decrease of $chi_t$ toward light quark masses, as predicted by the anomalous Ward-Takahashi identity for U(1) chiral symmetry, becomes clearer for smaller lattice spacings. The cross-over in the behavior of $chi_t$ from heavy to light sea quark masses is discussed.
We present results obtained in QCD with two flavors of non-perturbatively improved Wilson fermions at finite temperature on $16^3 times 8$ and $24^3 times 10$ lattices. We determine the transition temperature in the range of quark masses $0.6<m_pi/m_rho<0.8$ at lattice spacing a$approx$0.1 fm and extrapolate the transition temperature to the continuum and to the chiral limits.
We present results for $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios in the presence of two flavors of light sea quarks ($N_f=2$). We use Wilson light valence quarks and Wilson and static heavy valence quarks; the sea quarks are simulated with staggered fermions. Additional quenched simulations with nonperturbatively improved clover fermions allow us to improve our control of the continuum extrapolation. For our central values the masses of the sea quarks are not extrapolated to the physical $u$, $d$ masses; that is, the central values are partially quenched. A calculation using fat-link clover valence fermions is also discussed but is not included in our final results. We find, for example, $f_B = 190 (7) (^{+24}_{-17}) (^{+11}_{-2}) (^{+8}_{-0})$ MeV, $f_{B_s}/f_B = 1.16 (1) (2) (2) (^{+4}_{-0})$, $f_{D_s} = 241 (5) (^{+27}_{-26}) (^{+9}_{-4}) (^{+5}_{-0})$ MeV, and $f_{B}/f_{D_s} = 0.79 (2) (^{+5}_{-4}) (3) (^{+5}_{-0})$, where in each case the first error is statistical and the remaining three are systematic: the error within the partially quenched $N_f=2$ approximation, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass. The last error, though quite significant in decay constant ratios, appears to be smaller than has been recently suggested by Kronfeld and Ryan, and Yamada. We emphasize, however, that as in other lattice computations to date, the lattice $u,d$ quark masses are not very light and chiral log effects may not be fully under control.
We present results obtained in QCD with two flavors of non-perturbatively improved Wilson fermions at finite temperature on $16^3 times 8$ and $24^3 times 10$ lattices. We determine the transition temperature in the range of quark masses $0.6<m_pi/m_rho<0.8$ at lattice spacing a$approx$0.1 fm and extrapolate the transition temperature to the continuum and to the chiral limits. We also discuss the order of phase transition.
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