arXiv subjects

Federico Mescia

Publications and source records attributed to Federico Mescia.

63 records · Page 4Linked to original sources

arXiv2007

Improved estimates of rare K decay matrix-elements from Kl3 decays

The estimation of rare K decay matrix-elements from Kl3 experimental data is extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative corrections are now accounted for. The analysis relies mainly on the cleanness of two specific ratios of form-factors, for which the theoretical control is excellent. As a result, the uncertainties on the K+ --> pi+ nu nubar and KL --> pi0 nu nubar matrix-elements are reduced by a factor of about 7 and 4, respectively, and similarly for the direct CP-violating contribution to KL --> pi0 l+ l-. They could be reduced even further with better experimental data for the Kl3 slopes and the K+l3 branching ratios. As a result, the non-parametric errors for B(K --> pi nu nubar) and for the direct CP-violating contributions to B(KL --> pi0 l+ l-) are now completely dominated by those on the short-distance physics.

hep-ph↗

arXiv2007

Flavour physics at large tan(beta) with a Bino-like LSP

The MSSM with large tan(beta) and heavy squarks is a theoretically well motivated and phenomenologically interesting extension of the SM. This scenario naturally accommodates the (g-2)_μanomaly and the upper bound on the Higgs boson mass. In a wide region of the parameter space, visible non-standard effects are expected in a few low-energy observables, such as BR(B->tau nu), BR(B->l+ l-), BR(B->Xs gamma), and BR(mu->e gamma). We analyse the correlations of these non-standard effects under the additional assumption that the relic density of a Bino-like LSP accommodates the observed dark matter distribution.

hep-ph↗

arXiv2006

An estimate of the B-->K*gamma form factor

We present the results of a lattice QCD calculation of the form factor relevant to B-->K*gamma decay. Our final value, T(0) = 0.24 +/- 0.03(+0.04/-0.01), is obtained in the quenched approximation, and by extrapolating T(q2=0;H--> K*)MH^(3/2) from the directly accessed H-heavy mesons to the meson B. We also show that the extrapolation from B-->K*gamma* to B-->K*gamma 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(q2=0;B--> K*)/T(q2=0;B-->rho)=1.2(1), as our best estimate.

hep-ph↗

arXiv2006

KL to pi0 e+ e- and KL to pi0 mu+ mu- : A binary star on the stage of flavor physics

A systematic analysis of New Physics impacts on the rare decays KL to pi0 l+ l- is performed. Thanks to their different sensitivities to flavor-changing local effective interactions, these two modes could provide valuable information on the nature of the possible New Physics at play. In particular, a combined measurement of both modes could disentangle scalar/pseudoscalar from vector or axial-vector contributions. For the latter, model-independent bounds are derived. Finally, the KL to pi0 mu+ mu- forward-backward CP-asymmetry is considered, and shown to give interesting complementary information.

hep-ph↗

arXiv2006

Exploring the flavour structure of the MSSM with rare K decays

We present an extensive analysis of rare K decays, in particular of the two neutrino modes K+->pi+ nu nu-bar and KL->pi0 nu nu-bar, in the Minimal Supersymmetric extension of the Standard Model. We analyse the expectations for the branching ratios of these modes, both within the restrictive framework of the minimal flavour violation hypothesis and within a more general framework with new sources of flavour-symmetry breaking. In both scenarios, the information that can be extracted from precise measurements of the two neutrino modes turn out to be very useful in restricting the parameter space of the model, even after taking into account the possible information on the mass spectrum derived from high-energy colliders, and the constraints from B-physics experiments. In the presence of new sources of flavour-symmetry breaking, additional significant constraints on the model can be derived also from the two KL->pi0 l+l- modes.

hep-ph↗

arXiv2005

Rare Kaon Decays K->pi n n and KL->pi l+l-

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.

hep-ph↗

arXiv2005

Light-quark Loops in K->pi nu nu

We present a comprehensive analysis of the contributions to K->pi nu nu 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(GF^2 p^2). Using this new chiral Lagrangian, we analyze the long-distance structure of K->pi nu nu 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(GF^2 LambdaQCD^2) corrections enhance the SM prediction of Br(K+->pi+ nu nu) by about 6%

hep-ph↗

arXiv2004

Vus from Kl3 Decays

Important progress made this year, both in theory and in experiment, helped solving the problem of 2 sigma-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 q^2-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.

hep-ph↗

arXiv2003

Coupling of the light vector meson to the vector and to the tensor current

We present results for the coupling of the light vector mesons to the tensor current, relative to the standard vector meson decay constants. From an O(a)-improved lattice study, performed at three values of the lattice spacing in the quenched approximation, our final values (in the continuum limit), in the MS-scheme at 2 GeV, are: (f^T/f)_rho =0.72(2)(+2/-0), (f^T/f)_K* =0.74(2), (f^T/f)_phi =0.76(1).

hep-lat↗