Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite-volume effects

In Carrasco et al. we have recently proposed a method to calculate $O(e^2)$ electromagnetic corrections to leptonic decay widths of pseudoscalar mesons. The method is based on the observation that the infrared divergent contributions (that appear at intermediate stages of the calculation and that cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are universal, i.e. depend on the charge and the mass of the meson but not on its internal structure. In this talk we perform a detailed analysis of the finite-volume effects associated with our method. In particular we show that also the leading $1/L$ finite-volume effects are universal and perform an analytical calculation of the finite-volume leptonic decay rate for a point-like meson

Finite-Volume QED Corrections to Decay Amplitudes in Lattice QCD

We demonstrate that the leading and next-to-leading finite-volume effects in the evaluation of leptonic decay widths of pseudoscalar mesons at $O(\alpha)$ are universal, i.e. they are independent of the structure of the meson. This is analogous to a similar result for the spectrum but with some fundamental differences, most notably the presence of infrared divergences in decay amplitudes. The leading non-universal, structure-dependent terms are of $O(1/L^2)$ (compared to the $O(1/L^3)$ leading non-universal corrections in the spectrum). We calculate the universal finite-volume effects, which requires an extension of previously developed techniques to include a dependence on an external three-momentum (in our case, the momentum of the final state lepton). The result can be included in the strategy proposed in Ref.\,\cite{Carrasco:2015xwa} for using lattice simulations to compute the decay widths at $O(\alpha)$, with the remaining finite-volume effects starting at order $O(1/L^2)$. The methods developed in this paper can be generalised to other decay processes, most notably to semileptonic decays, and hence open the possibility of a new era in precision flavour physics

Leading isospin-breaking corrections to pion, kaon and charmed-meson masses with Twisted-Mass fermions

We present a lattice computation of the isospin-breaking corrections to pseudoscalar meson masses using the gauge configurations produced by the European Twisted Mass collaboration with $N_f = 2 + 1 + 1$ dynamical quarks at three values of the lattice spacing ($a \simeq 0.062, 0.082$ and $0.089$ fm) with pion masses in the range $M_\pi \simeq 210 - 450$ MeV. The strange and charm quark masses are tuned at their physical values. We adopt the RM123 method based on the combined expansion of the path integral in powers of the $d$- and $u$-quark mass difference ($\widehat{m}_d - \widehat{m}_u$) and of the electromagnetic coupling $\alpha_{em}$. Within the quenched QED approximation, which neglects the effects of the sea-quark charges, and after the extrapolations to the physical pion mass and to the continuum and infinite volume limits, we provide results for the pion, kaon and (for the first time) charmed-meson mass splittings, for the prescription-dependent parameters $\epsilon_{\pi^0}$, \epsilon_\gamma(\overline{MS}, 2~\mbox{GeV}), \epsilon_{K^0}(\overline{MS}, 2~\mbox{GeV}), related to the violations of the Dashen's theorem, and for the light quark mass difference (\widehat{m}_d - \widehat{m}_u)(\overline{MS}, 2~\mbox{GeV}).Comment: 47 pages, 20 figures, 4 tables; comments on QED and QCD splitting prescriptions added; version to appear in PR

Chiral behaviour of the lattice BKB_K-parameter with the Wilson and Clover Actions at β=6.0\beta = 6.0

We present results for the kaon $B$-parameter $B_K$ from a sample of $200$ configurations using the Wilson action and $460$ configurations using the SW-Clover action, on a $18^3 \times 64$ lattice at $\beta=6.0$. We compare results obtained by renormalizing the relevant operator with different ``boosted" values of the strong coupling constant $\alpha_s$. In the case of the SW-Clover action, we also use the operator renormalized non-perturbatively. In the Wilson case, we observe a strong dependence of $B_K$ on the prescription adopted for $\alpha_s$, contrary to the results of the Clover case which are almost unaffected by the choice of the coupling. We also find that the matrix element of the operator renormalized non-perturbatively has a better chiral behaviour. This gives us our best estimate of the renormalization group invariant $B$-parameter, $\hat B_K=0.86 \pm 0.15$.Comment: LaTeX, 17 pages, 3 postscript figures uuencode

First lattice calculation of the QED corrections to leptonic decay rates

The leading-order electromagnetic and strong isospin-breaking corrections to the ratio of $K_{\mu 2}$ and $\pi_{\mu 2}$ decay rates are evaluated for the first time on the lattice, following a method recently proposed. The lattice results are obtained using the gauge ensembles produced by the European Twisted Mass Collaboration with $N_f = 2 + 1 + 1$ dynamical quarks. Systematics effects are evaluated and the impact of the quenched QED approximation is estimated. Our result for the correction to the tree-level $K_{\mu 2} / \pi_{\mu 2}$ decay ratio is $-1.22\,(16) \%$ to be compared to the estimate $-1.12\,(21) \%$ based on Chiral Perturbation Theory and adopted by the Particle Data Group.Comment: 5 pages, 6 figures; extended supplemental material with 1 table and 1 figure, results unchange

Studi di dettaglio della pericolosità sismica in aree ad elevata esposizione: un esempio per la Sicilia Orientale

La Sicilia Orientale è una delle aree che presenta i valori di pericolosità sismica tra i più elevati in Italia nella mappa di riferimento MPS04 (Gruppo di Lavoro MPS 2004). Considerando che questa è una zona con una elevata esposizione, sia in termini di Beni Culturali che di attività industriali, è stato compiuto uno studio particolareggiato che prendesse in considerazione i molti elementi conoscitivi resisi disponibili negli ultimi anni. E’ stato anche possibile utilizzare i notevoli progressi metodologici, resi possibili grazie allo sviluppo di codici di calcolo sempre più raffinati, che, insieme alle moltiplicate capacità di calcolo dei processori oggi disponibili, rendono queste valutazioni realizzabili in tempi molto brevi e quindi consentono anche di sviluppare modelli con un grado di complessità elevato. I calcoli sono stati realizzati utilizzando la versione 2007 del software CRISIS, un codice Open Source e liberamente distribuito, messo a punto presso l’Università Autonoma del Messico (Ordaz et al., 1999), in particolare usando l’applicazione web sviluppata nell’ambito del progetto INGV-DPC S2 (http://nuovoprogettoesse2.stru.polimi.it) che aggiunge alla versione desktop alcune importanti funzionalità, quali la possibilità di condividere dati tra diversi utenti, l’indipendenza dal sistema operativo utilizzato per lo sviluppo dell’applicazione, l’esecuzione dei calcoli da parte del server liberando le risorse locali dell’utente. CRISIS si basa essenzialmente sull’approccio standard di Cornell (1968) alla stima probabilistica della pericolosità sismica e consente di utilizzare due diversi modelli di sismicità: quello “poissoniano” (vale a dire di eventi indipendenti tra loro e con modalità di rilascio “costanti” nel tempo) e il modello “caratteristico” (che si applica a faglie sismogenetiche per le quali si ipotizza il rilascio di energia attraverso terremoti di magnitudo prefissata e con periodo di ritorno noto). Secondo la prassi standard e consolidata a livello internazionale per la stima della pericolosità sismica (SSHAC, 1997), è stato seguito un approccio cosiddetto ad albero logico per considerare tutte le possibili alternative nella scelta dei modelli utilizzati nel calcolo e valutare l’incertezza epistemica delle stime prodotte derivante dall’uso di queste opzioni

Probabilistic seismic hazard assessment in the high-risk area of south-eastern Sicily (Italy)

A probabilistic seismic hazard analysis (PSHA) was carried out for the SE sector of Sicily, an area characterized by highest levels of seismic hazard in Italy and high exposure, both in terms of cultural heritage and of critical industrial facilities. Compared to the Italian reference PSH map (MPS04), this study is based on most updated information about regional seismic sources and ground-motion attenuation. Epistemic uncertainties associated with the input elements of the computational model were taken into account following a logic-tree approach. Special care was devoted to define the regional source zones model by considering four alternative models, which share the zones defining the boundary conditions of the study area but differ in the seismotectonic characterization of SE Sicily. Seismic hazard was assessed in terms of PGA, PGV, acceleration and displacement elastic response spectra on rock for four return periods (30, 50, 475, 975 years). A disaggregation analysis was then performed for some sites of interest. Results confirm the very high hazard of the area, with expected values of PGA (at 10% probability of exceedance in 50 years) slightly higher than the reference MPS04 map. Strong differences emerge instead between the acceleration response spectra of this study and the reference ones, for the longest return periods

Homogeneous determination of maximum magnitude

This deliverable represents the result of the activities performed by a working group at INGV. The main object of the Task 3.5 is defined in the Description of Work. This task will produce a homogeneous assessment (possibly multiple models) of the distribution of the expected Maximum Magnitude for earthquakes expected in various tectonic provinces of Europe, to serve as input for the computation and validation of seismic hazard. This goal will be achieved by combining input from earthquake catalogues, regional strain rates, knowledge of active faults and seismogenic zones, as well as the definition of the seismic source zones. As stated above, the maximum magnitude (Mmax) has to be derived by the combination of several products of the Work Package 3. The deadline of the other deliverables is contemporary or subsequent to the scheduled release of the Mmax map; this means that at the moment it is not possible to provide a final map, but only to describe the preliminary work and the delineated approach for getting the final version of the deliverable. In fact the determination of Mmax has to be based on an earthquake catalog and on a seismic source zones (SSZs) model. At the 18-months deadline (the deadline for Deliverable 3.3) the catalog is not yet released in a proper way for the aim of this task and the seismic source zones model is available in a preliminary release. According to the temporal alignment of the deliverables, the SHARE Management Committee decided in the 4th teleconference meeting that an outline of the methods to be used in the PSHA including a review of state-of-the-art Mmax determination practices shall be presented including preliminary examples. This first version is presented here. With both, the final earthquake catalog and source zones models available (D3.1, D3.2 and D3.4), a final version will be released

K^0-\bar{K}^0 Mixing Beyond the SM from Nf=2 tmQCD

We present preliminary results on the of neutral kaon oscillations in extensions of the Standard Model. Using Nf=2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks, we achieve both O(a)-improvement and continuum-like renormalization pattern for the relevant four-fermion operators. We perform simulations at three values of the lattice spacing and extrapolate/interpolate our results to the continuum limit and physical light/strange quark mass. The calculation of the renormalization constants of the complete operator basis is performed non- perturbatively in the RI-MOM scheme.Comment: 7 pages, 2 figures; presented at the XXVIII International Symposium on Lattice Field Theory Villasimius, Sardinia, Ital

B-physics from lattice QCD...with a twist

We present a precise lattice QCD determination of the b-quark mass, of the B and Bs decay constants and first results for the B-meson bag parameters. For our computation we employ the so-called ratio method and our results benefit from the use of improved interpolating operators for the B-mesons. QCD calculations are performed with Nf = 2 dynamical light-quarks at four values of the lattice spacing and the results are extrapolated to the continuum limit. The preliminary results are mb(mb) = 4.35(12) GeV for the MSbar b-quark mass, fBs = 234(6) MeV and fB = 197(10) MeV for the B-meson decay constants, BBs(mb) = 0.90(5) and BB(mb) = 0.87(5) for the B-meson bag parameters.Comment: 6 pages, 3 figures. Proceedings of the 36th International Conference on High Energy Physics - ICHEP 2012; July 4-11 2012; Melbourne, Australi