Papers by Federico Mescia
Nucl Phys B, 2005
We present a comprehensive analysis of the contributions to K→πνν¯ decays not described by the le... more We present a comprehensive analysis of the contributions to K→πνν¯ decays not described by the leading dimension-six effective Hamiltonian. These include both dimension-eight four-fermion operators generated at the charm scale, and genuine long-distance contributions which can be described within the framework of chiral perturbation theory. We show that a consistent treatment of the latter contributions, which turn out to be the dominant effect, requires the introduction of new chiral operators already at O(GF2p). Using this new chiral Lagrangian, we analyze the long-distance structure of K→πνν¯ amplitudes at the one-loop level, and discuss the role of the dimension-eight operators in the matching between short- and long-distance components. From the numerical point of view, we find that these O(GF2ΛQCD2) corrections enhance the SM prediction of B(K→πνν¯) by about ≈6%.
Phys Rev D, 2009
We present new lattice results of the K→πℓν semileptonic form factors obtained from simulations w... more We present new lattice results of the K→πℓν semileptonic form factors obtained from simulations with two flavors of dynamical twisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f+(0)=0.9560(84), which, combined with the latest experimental data for Kℓ3 decays, leads to |Vus|=0.2267(5)exp(20)f+(0). Using the PDG(2008) determinations of |Vud| and |Vub| our result implies for the unitarity relation |Vud|2+|Vus|2+|Vub|2=1.0004(15). For the O(p6) term of the chiral expansion of f+(0) we get Δf≡f+(0)-1-f2=-0.0214(84).
Nucl Phys B Proc Suppl, 2005
The results of a preliminary partially quenched (N f = 2) study of the light hadron spectrum, ren... more The results of a preliminary partially quenched (N f = 2) study of the light hadron spectrum, renormalization constants and light quark masses are presented. Numerical simulations are carried out with the LL-SSOR preconditioned Hybrid Monte Carlo with two degenerate dynamical fermions, using the plaquette gauge action and the Wilson quark action at β = 5.8. Finite volume effects have been investigated employing two lattice volumes: 16 3 × 48 and 24 3 × 48. Configurations have been generated at four values of the sea quark mass corresponding to MP S /MV ≃ 0.6 ÷ 0.8.
Nucl Phys B, 2007
We present the results of a lattice QCD calculation of the form factor relevant to B-->Kgamma dec... more We present the results of a lattice QCD calculation of the form factor relevant to B-->Kgamma decay. Our final value, T(0)=0.24±0.03-0.01+0.04, is obtained in the quenched approximation, and by extrapolating MH3/2×T(q=0) from the directly accessed H-heavy mesons to the meson B. We also show that the extrapolation from B-->Kgamma ( q!=0) to B-->Kgamma ( q=0), leads to a result consistent with the one quoted above. On the other hand, our results are not accurate enough to solve the SU(3) flavor breaking effects in the form factor and we quote T(0)/T(0)=1.2(1), as our best estimate.
Important progress made this year, both in theory and in experiment, helped solving the problem o... more Important progress made this year, both in theory and in experiment, helped solving the problem of 2σ-deviation from the unitarity of the first row elements in the CKM matrix. Today we have, |Vus|2 + |Vud|2 + |Vub|2 - 1 = -0.0008(13), -0.0010(13), or -0.0005(13), depending on whether the q2-dependence of the relevant Kℓ3 form factor is considered as pole-like, linear or quadratic function, and on the Leutwyler-Roos value of f+(0) = 0.961(8), whose validity has recently been reinforced by lattice studies. In this talk we summarize the recent developments.
In the last few years, the European Twisted Mass Collaboration (ETMC) has been investigating (max... more In the last few years, the European Twisted Mass Collaboration (ETMC) has been investigating (maximally) twisted-mass fermions for dynamical QCD simulations and reliable simulations has been carried out for very fine lattice spacings (a = 0.07fm) and for pion masses as light as 260 MeV. Maximally twisted-mass fermions, like Ginsparg-Wilson ones, are based from first principle QCD action, and have the necessary features to guarantee both O(a 2 ) improvement and simple renormalisation patterns. Moreover, with respect to Ginsparg-Wilson fermions, they have the advantage to be computationally cheap.
We present the first lattice calculation of the matrix element of the electromagnetic operator <p... more We present the first lattice calculation of the matrix element of the electromagnetic operator <pi0|Q+|K0>, where Q+ = (Q_d e/16 pi^2)* (\bar s_L sigma{mu,nu} F{mu,nu} d_R + \bar s_R sigma{mu,nu} F{mu,nu} d_L). This matrix element plays an important role, since it contributes to enhance the CP violating part of the K_L -> pi0 e+ e- amplitude in supersymmetric extensions of the Standard Model.
Over the next years, the Flavour Physics community will be looking for inconsistencies of the Sta... more Over the next years, the Flavour Physics community will be looking for inconsistencies of the Standard Model (SM) by exploiting new and precise measurements. In these ``indirect new physics'' searches, the key strategy is to concentrate on observables, which are theoretically clean and preferably suppressed in the SM. In this respect, the four golden modes K+->pi+ n n, KL->pi n n and KL->pi0 l+l- are very promising. The pollution from hadronic uncertainties in these decays is at present under control with good accuracy, thanks to the interplay between theory information (Chiral Perturbation Theory and OPE) and experimental inputs (KTeV, NA48). Their measurements might thus give rise to some unexpected scenario. Here, we briefly review the present situation for these four exclusive rare decays.
Nucl Phys B, 2007
We present the results of a lattice QCD calculation of the form factor relevant to B→K*γB→K*γ dec... more We present the results of a lattice QCD calculation of the form factor relevant to B→K*γB→K*γ decay. Our final value, T(0)=0.24±0.03−0.01+0.04, is obtained in the quenched approximation, and by extrapolating MH3/2×TH→K*(q2=0)(q2=0) from the directly accessed H-heavy mesons to the meson B . We also show that the extrapolation from B→K*γ*B→K*γ* (q2≠0q2≠0) to B→K*γB→K*γ (q2=0q2=0), leads to a result consistent with the one quoted above. On the other hand, our results are not accurate enough to solve the SU(3)SU(3) flavor breaking effects in the form factor and we quote TB→K*(0)/TB→ρ(0)=1.2(1)TB→K*(0)/TB→ρ(0)=1.2(1), as our best estimate.
European Physical Journal C Particles and Fields, 2010
Top-quark physics is one of the main fields of investigation at the Tevatron accelerator and, ult... more Top-quark physics is one of the main fields of investigation at the Tevatron accelerator and, ultimately, at the LHC. We perform a phenomenological analysis of tbar{t} events at hadron colliders, with a focus on observables relying on bottom-quark fragmentation in top-quark decay. In particular, we investigate the B-lepton invariant-mass distribution in the dilepton channel and give an estimate of the contribution of bottom fragmentation to the Monte Carlo uncertainty on the top-quark mass reconstruction.
We present the results of a lattice QCD calculation of the form factor relevant to B → K * γ deca... more We present the results of a lattice QCD calculation of the form factor relevant to B → K * γ decay. Our final value, T (0) = 0.24 ± 0.03 +0.04 −0.01 , is obtained in the quenched approximation, and by extrapolating M 3/2 H × T H→K * (q 2 = 0) from the directly accessed H-heavy mesons to the meson B. We also show that the extrapolation from B → K * γ * (q 2 = 0) to B → K * γ (q 2 = 0), leads to a result consistent with the one quoted above. On the other hand, our results are not accurate enough to solve the SU (3) flavor breaking effects in the form factor and we quote T B→K * (0)/T B→ρ (0) = 1.2(1), as our best estimate.
High Energy Physics, ICHEP 2004 - Proceedings of the 32nd International Conference, 2005
Important progress made this year, both in theory and in experiment, helped solving the problem o... more Important progress made this year, both in theory and in experiment, helped solving the problem of 2σ-deviation from the unitarity of the first row elements in the CKM matrix. Today we have, |V us | 2 + |V ud | 2 + |V ub | 2 − 1 = −0.0008(13), −0.0010(13), or −0.0005(13), depending on whether the q 2 -dependence of the relevant K ℓ3 form factor is considered as pole-like, linear or quadratic function, and on the Leutwyler-Roos value of f + (0) = 0.961(8), whose validity has recently been reinforced by lattice studies. In this talk we summarize the recent developments.
Physics Letters B, 1998
We have computed the light quark masses using the O(a 2 ) improved Alpha action, in the quenched ... more We have computed the light quark masses using the O(a 2 ) improved Alpha action, in the quenched approximation. The renormalized masses have been obtained non-perturbatively. By eliminating the systematic error coming from the truncation of the perturbative series, our procedure removes the discrepancies, observed in previous calculations, between the results obtained using the vector and the axial-vector Ward identities. It also gives values of the quark masses larger than those obtained by computing the renormalization constants using boosted) perturbation theory. Our main results, in the RI (MOM) scheme and at a renormalization scale µ = 2 GeV, are m RI s = 138(15) MeV and m RI l = 5.6(5) MeV, where m RI s is the mass of the strange quark and m RI l = (m RI u + m RI d )/2 the average mass of the up-down quarks. From these results, which have been obtained non-perturbatively, by using continuum perturbation theory we derive the MS masses, at the same scale, and the renormalization group invariant (m RGI ) masses. We find m N LO M S s = 121(13) MeV and m N LO M S l = 4.9(4) MeV at the next-to-leading order; m N 2 LO M S s = 111(12) MeV, m N 2 LO M S l = 4.5(4) MeV, m RGI s = 177(19) MeV and m RGI l = 7.2(6) MeV at the next-tonext-to-leading order.
Physics Letters B, 2001
We present the first lattice calculation of the matrix element of the electromagnetic operator
ABSTRACT Recent progress and future prospects in Kaon physics are summarized. I will mainly conce... more ABSTRACT Recent progress and future prospects in Kaon physics are summarized. I will mainly concentrate on the developments concerning the following four observables: ε&#39;/V, VK, the Cabibbo angle and the rare Kaon decays.
Nuclear Physics B, 2005
We present a comprehensive analysis of the contributions to K → πνν decays not described by the l... more We present a comprehensive analysis of the contributions to K → πνν decays not described by the leading dimension-six effective Hamiltonian. These include both dimensioneight four-fermion operators generated at the charm scale, and genuine long-distance contributions which can be described within the framework of chiral perturbation theory. We show that a consistent treatment of the latter contributions, which turn out to be the dominant effect, requires the introduction of new chiral operators already at O(G 2 F p 2 ). Using this new chiral Lagrangian, we analyze the long-distance structure of K → πνν amplitudes at the one-loop level, and discuss the role of the dimension-eight operators in the matching between short-and long-distance components. From the numerical point of view, we find that these O(G 2 F Λ 2 QCD ) corrections enhance the SM prediction of B(K + → π + νν) by about ≈ 6%.
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Papers by Federico Mescia