The Ademollo-Gatto theorem for lattice semileptonic decays

We present the results of the calculation of the Kl3 semileptonic form factor at zero momentum transfer, f(0), obtained at one-loop in partially quenched Chiral Perturbation Theory (with either Nf=2, or Nf=3, and with generic valence and sea quark masses). We show that for Nf=2, when the masses of the valence and sea light quarks are equal, the correction is of the order (MK^2-Mpi^2)^3. The formulae presented here can be useful for the mass extrapolation of the results obtained in lattice simulations to the physical point.Comment: 7 page

Chiral loop corrections to weak decays of B mesons to positive and negative parity charmed mesons

We determine chiral loop corrections to the B meson decay amplitudes to positive and negative parity charmed mesons within a framework which combines heavy quark and chiral symmetries. Then we investigate the impact of the lowest-lying positive parity heavy mesons on the determination of the Isgur-Wise functions. The corrections due to these states are competitive with the contributions arising from K and eta meson loops. Since lattice studies rely on the chiral behavior of the amplitudes we discuss the chiral limit of our results. We find that the determination of the slope at zero recoil of the Isgur-Wise function xi for the B transition to negative parity charm mesons is moderately affected by the inclusion of new states, while the slope of tau_{1/2} is affected significantly more.Comment: 10 pages, 4 figure

Continuum Determination of Light Quark Masses from Quenched Lattice QCD

We compute the strange and the average up/down quark masses in the quenched approximation of lattice QCD, by using the O(a)-improved Wilson action and operators and by implementing the non-perturbative renormalization. Our computation is performed at four values of the lattice spacing, from which we could extrapolate to the continuum limit. Our final result for the strange quark mass (in the MSbar scheme) is ms(2 GeV) = (106 +/- 2 +/- 8) MeV. For the average up/down quark mass we have ml(2 GeV) = (4.4 +/- 0.1 +/- 0.4) MeV. The ratio ms/ml = (24.3 +/- 0.2 +/- 0.6).Comment: 14 pages, 3 PostScript figure

Status of Lattice Flavor Physics

This talk reviews recent lattice QCD calculations relevant for quark flavor physics. Since lattice results must be accurate and precise to play a definitive role in phenomenology, the focus is on unquenched results of quantities which can be calculated most reliably.Comment: Invited talk delivered at Lattice2004(plenary), Fermilab, June 21-26, 2004. 10 pages. v2: Corrected caption to Figure 4, updated reference

Lattice renormalisation of O(a) improved heavy-light operators

The analytical expressions and the numerical values of the renormalisation constants of ${\cal O}(a)$ improved static-light currents are given at one-loop order of perturbation theory in the framework of Heavy Quark Effective Theory: the static quark is described by the HYP action and the light quark is described either with the Clover or the Neuberger action. These factors are relevant to extract from a lattice computation the decay constants $f_B$, $f_{B_S}$ and the set of bag parameters $B_i$ associated with $B-\bar{B}$ mixing phenomenology in the Standard Model and beyond.Comment: 16 pages, 2 figures, 4 tables; few comments and references added; version to be published in Phys Rev

Semileptonic Hyperon Decays on the Lattice: an Exploratory Study

We present preliminary results of an exploratory lattice study of the vector form factor $f_1(q^2 = 0)$ relevant for the semileptonic hyperon decay $\Sigma^{-} --> n l \nu$. This study is based on the same method used for the extraction of $f^+(0)$ for the decay $K^0 --> \pi^{-} l \nu$. The main purpose of this study is to test the method for hyperon form factors in order to estimate the precision that can be reached and the importance of SU(3)-breaking effects.Comment: 3 pages, 5 figures, talk presented at Lattice2004(weak), Fermilab, Batavia, Illinois, 21-26 June 200

Remarks on the hadronic matrix elements relevant to the SUSY K-Kbar mixing amplitude

We compute the 1-loop chiral corrections to the bag parameters which are needed for the discussion of the SUSY K-Kbar mixing problem in both finite and infinite volume. We then show how the bag parameters can be combined among themselves and with some auxiliary quantities and thus sensibly reduce the systematic errors due to chiral extrapolations as well as those due to finite volume artefacts present in the results obtained from lattice QCD. We also show that in some cases these advantages remain as such even after including the 2-loop chiral corrections. Similar discussion is also made for the K --> pi electro-weak penguin operators.Comment: 13 pages, 3 figures [added 1 reference and a discussion about the impact of the NNLO chiral corrections to the "golden ratios" (c.f. Sec.6)