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We present first results for light hadron masses, quark masses and decay constants in the continuum limit using O(a) improved fermions at three different values of the gauge coupling beta.
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We improve a previous quenched result for heavy-light pseudoscalar meson decay constants with the light quark taken to be the strange quark. A finer lattice resolution (a ~ 0.05 fm) in the continuum limit extrapolation of the data computed in the static approximation is included. We also give further details concerning the techniques used in order to keep the statistical and systematic errors at large lattice sizes L/a under control. Our final result, obtained by combining these data with determinations of the decay constant for pseudoscalar mesons around the D_s, follows nicely the qualitative expectation of the 1/m-expansion with a (relative) 1/m-term of about -0.5 GeV/m_PS. At the physical b-quark mass we obtain F_{B_s} = 193(7) MeV, where all errors apart from the quenched approximation are included.
We compute the decay constants for the heavy--light pseudoscalar mesons in the quenched approximation and continuum limit of lattice QCD. Within the Schrodinger Functional framework, we make use of the step scaling method, which has been previously introduced in order to deal with the two scale problem represented by the coexistence of a light and a heavy quark. The continuum extrapolation gives us a value $f_{B_s} = 192(6)(4)$ MeV for the $B_s$ meson decay constant and $f_{D_s} = 240(5)(5)$ MeV for the $D_s$ meson.
We present results for the decay constants of the $D$ and $D_s$ mesons computed in lattice QCD with $N_f=2+1$ dynamical flavours. The simulations are based on RBC/UKQCDs domain wall ensembles with both physical and unphysical light-quark masses and lattice spacings in the range 0.11--0.07$,$fm. We employ the domain wall discretisation for all valence quarks. The results in the continuum limit are $f_D=208.7(2.8)_mathrm{stat}left(^{+2.1}_{-1.8}right)_mathrm{sys},mathrm{MeV}$ and $f_{D_{s}}=246.4(1.3)_mathrm{stat}left(^{+1.3}_{-1.9}right)_mathrm{sys},mathrm{MeV}$ and $f_{D_s}/f_D=1.1667(77)_mathrm{stat}left(^{+57}_{-43}right)_mathrm{sys}$. Using these results in a Standard Model analysis we compute the predictions $|V_{cd}|=0.2185(50)_mathrm{exp}left(^{+35}_{-37}right)_mathrm{lat}$ and $|V_{cs}|=1.011(16)_mathrm{exp}left(^{+4}_{-9}right)_mathrm{lat}$ for the CKM matrix elements.
We calculate the masses and weak decay constants of flavorless ground and radially excited $J^P=1^-$ mesons and the corresponding quantities for the K^*, within a Poincare covariant continuum framework based on the Bethe-Salpeter equation. We use in both, the quarks gap equation and the meson bound-state equation, an infrared massive and finite interaction in the leading symmetry-preserving truncation. While our numerical results are in rather good agreement with experimental values where they are available, no single parametrization of the QCD inspired interaction reproduces simultaneously the ground and excited mass spectrum, which confirms earlier work on pseudoscalar mesons. This feature being a consequence of the lowest truncation, we pin down the range and strength of the interaction in both cases to identify common qualitative features that may help to tune future interaction models beyond the rainbow-ladder approximation.
We present a quenched lattice QCD calculation of the alpha and beta parameters of the proton decay matrix element. The simulation is carried out using the Wilson quark action at three values of the lattice spacing in the range aapprox 0.1-0.064 fm to study the scaling violation effect. We find only mild scaling violation when the lattice scale is determined by the nucleon mass. We obtain in the continuum limit, |alpha(NDR,2GeV)|=0.0090(09)(^{+5}_{-19})GeV^3 and |beta(NDR,2GeV)|=0.0096(09)(^{+6}_{-20})GeV^3 with alpha and beta in a relatively opposite sign, where the first error is statistical and the second is due to the uncertainty in the determination of the physical scale.
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