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We analyse available data on the quark pseudoscalar vertex and extract the contribution og the Goldstone boson pole. The strength of the pole is found to be quite large at presently accessible scales. We draw the important consequences of this finding for the various definitions of quark masses.
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We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non-perturbative RI-MOM renormalization procedure. Our results for the light quark masses are m_ud^{msbar}(2 GeV)= 3.85 +- 0.12 +- 0.40 MeV, m_s^{msbar}(2 GeV) = 105 +- 3 +- 9 MeV and m_s/m_ud = 27.3 +- 0.3 +- 1.2. We also obtain fK = 161.7 +- 1.2 +- 3.1 MeV and the ratio fK/fpi=1.227 +- 0.009 +- 0.024. From this ratio, by using the experimental determination of Gamma(K-> mu nu (gamma))/Gamma(pi -> mu nu (gamma)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus|=0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint.
We perform a lattice mass analysis in the flavour singlet pseudoscalar channel on the SESAM and TXL full QCD vacuum configurations, with 2 active flavours of dynamical Wilson fermions at beta = 5.6. At our inverse lattice spacing, a^-1 = 2.3 GeV, we retrieve by a chiral extrapolation to the physical light quark masses the value m_eta = 3.7(+8)(-4) m_pi. A crude extrapolation from (N_f = 3) phenomenology would suggest m_eta approx 5.1 m_pi for N_f = 2 QCD. we verify that the mass gap between the singlet state eta and the pi flavour triplt state is due to gauge configurations with non-trivial topology.
Using a simple model in the context of the Dyson-Schwinger-Bethe-Salpeter approach, we investigate the effects of a dressed-quark-gluon vertex on pseudoscalar meson masses. In particular, we focus on the unequal-mass case and investigate heavy-light meson masses; in addition, we study the premise of the effective treatment of heavy quarks in our approach.
Lattice determinations of quark mass have made significant progress in the last few years. I will review recent advances in calculations of charm and bottom mass, which are near to achieving percent-level precision and with fully controlled systematics. Precise knowledge of these parameters is of particular interest for precision Higgs studies at future accelerators.
We calculate pseudoscalar masses on gauge configurations containing the effects of 2+1 flavors of dynamical asqtad quarks and quenched electromagnetism. The lattice spacings vary from 0.12 to 0.06 fm. The masses are fit with staggered chiral perturbation theory including NLO electromagnetic terms. We attempt to extract the fit parameters for the electromagnetic contributions, while taking into account the finite volume effects, and extrapolate them to the physical limit.
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