Guido Martinelli

Chiral symmetry on the lattice with Wilson fermions

Abstract The chiral properties of the continuum limit of lattice QCD with Wilson fermions are studied. We show that a partially conserved axial current can be defined, satisfying the usual current algebra requirements. A proper definition of the chiral symmetry order parameter, 〈0| ψ ψ|0〉 , is given, and the chiral properties of composite operators are investigated. The implications of our analysis to the lattice determination of non-leptonic weak amplitudes are also discussed.

2000 CKM-triangle analysis a critical review with updated experimental inputs and theoretical parameters

Within the Standard Model, a review of the current determination of the sides and angles of the CKM unitarity triangle is presented, using experimental constraints from the measurements of |?k|, |Vub/Vcb|, ?md and from the limit on ?ms, available in September 2000. Results from the experimental search for B0s?0s oscillations are introduced in the present analysis using the likelihood. Special attention is devoted to the determination of the theoretical uncertainties. The purpose of the analysis is to infer regions where the parameters of interest lie with given probabilities. The BaBar ``95% C.L. scanning method is also commented.

The 2004 UTfit collaboration report on the status of the unitarity triangle in the standard model

Using the latest determinations of several theoretical and experimental parameters, we update the Unitarity Triangle analysis in the Standard Model. The basic experimental constraints come from the measurements of |Vub/Vcb|, Δmd, the lower limit on Δms, K, and the measurement of the phase of the Bd–d mixing amplitude through the time-dependent CP asymmetry in B0→J/ψK0 decays. In addition, we consider the direct determination of α, γ, 2β+γ and cos 2β from the measurements of new CP-violating quantities, recently performed at the B factories. We also discuss the opportunities offered by improving the precision of the various physical quantities entering in the determination of the Unitarity Triangle parameters. The results and the plots presented in this paper can also be found at the URL http://www.utfit.org , where they are continuously updated with the newest experimental and theoretical results.

B-parameters of the complete set of matrix elements of (ΔB = 2) operators from the lattice

We compute on the lattice the “bag” parameters of the five ∆B = 2 operators of the supersymmetric basis, by combining their values determined in full QCD and in the static limit of HQET. The extrapolation of the QCD results from the accessible heavy-light meson masses to the B-meson mass is constrained by the static result. The matching of the corresponding results in HQET and in QCD is for the first time made at NLO accuracy in the MS(NDR) renormalization scheme. All results are obtained in the quenched approximation. PACS: 11.15.Ha (Lattice gauge theory), 12.38.Gc (Lattice QCD calculations), 13.75Lb (Meson-meson interactions), 14.40.Nd (Bottom mesons), 12.39.Hg (Heavy quark effective theory)

First evidence of new physics in b ↔ s transitions

We combine all the available experimental information on Bsmixing, including the very recent tagged analyses of Bs→ J/Ψϕ by the CDF and DØ collaborations. We find that the phase of the Bsmixing amplitude deviates more than 3σ from the Standard Model prediction. While no single measurement has a 3σ significance yet, all the constraints show a remarkable agreement with the combined result. This is a first evidence of physics beyond the Standard Model. This result disfavours New Physics models with Minimal Flavour Violation with the same significance.PACS Codes: 12.15.Ff, 12.15.Hh, 14.40.Nb

B(d) - anti-B(d) mixing and the B(d) ---> J / psi K(s) asymmetry in general SUSY models

Abstract We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B d – B d mixing and to the CP asymmetry a J / ψK s in the framework of the mass-insertion approximation. Using hadronic matrix elements recently computed on the lattice, we obtain improved constraints on the squark-mass splittings.

Renormalization constants of quark operators for the non-perturbatively improved Wilson action

We present the results of an extensive lattice calculation of the renormalization constants of bilinear and four-quark operators for the non-perturbatively O(a)-improved Wilson action. The results are obtained in the quenched approximation at four values of the lattice coupling by using the non-perturbative RI/MOM renormalization method. Several sources of systematic uncertainties, including discretization errors and final volume effects, are examined. The contribution of the Goldstone pole, which in some cases may affect the extrapolation of the renormalization constants to the chiral limit, is non-perturbatively subtracted. The scale independent renormalization constants of bilinear quark operators have been also computed by using the lattice chiral Ward identities approach and compared with those obtained with the RI-MOM method. For those renormalization constants the non-perturbative estimates of which have been already presented in the literature we find an agreement which is typically at the level of 1%.We present the results of an extensive lattice calculation of the renormalization constants of bilinear and four-quark operators for the non-perturbatively (a)-improved Wilson action. The results are obtained in the quenched approximation at four values of the lattice coupling by using the non-perturbative RI/MOM renormalization method. Several sources of systematic uncertainties, including discretization errors and final volume effects, are examined. The contribution of the Goldstone pole, which in some cases may affect the extrapolation of the renormalization constants to the chiral limit, is non-perturbatively subtracted. The scale independent renormalization constants of bilinear quark operators have been also computed by using the lattice chiral Ward identities approach and compared with those obtained with the RI-MOM method. For those renormalization constants the non-perturbative estimates of which have been already presented in the literature we find an agreement which is typically at the level of 1%.

Axion phenomenology and θ-dependence from N f = 2 + 1 lattice QCD

A bstractWe investigate the topological properties of Nf = 2 + 1 QCD with physical quark masses, both at zero and finite temperature. We adopt stout improved staggered fermions and explore a range of lattice spacings a ∼ 0.05 − 0.12 fm. At zero temperature we estimate both finite size and finite cut-off effects, comparing our continuum extrapolated results for the topological susceptibility χ with predictions from chiral perturbation theory. At finite temperature, we explore a region going from Tc up to around 4 Tc, where we provide continuum extrapolated results for the topological susceptibility and for the fourth moment of the topological charge distribution. While the latter converges to the dilute instanton gas prediction the former differs strongly both in the size and in the temperature dependence. This results in a shift of the axion dark matter window of almost one order of magnitude with respect to the instanton computation.

Light quark masses from lattice quark propagators at large momenta

We compute nonperturbatively the average up-down and strange quark masses from the large momentum (short-distance) behavior of the quark propagator in the Landau gauge. This method, which has never been applied so far, does not require the explicit calculation of the quark mass renormalization constant. Calculations were performed in the quenched approximation, by using

Rare kaon decays on the lattice

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