7,693 research outputs found
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
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 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
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
(compared to the 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 , with the remaining finite-volume effects starting
at order . 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 dynamical quarks at
three values of the lattice spacing ( and fm)
with pion masses in the range 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
- and -quark mass difference () and of the
electromagnetic coupling . 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_\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 -parameter with the Wilson and Clover Actions at
We present results for the kaon -parameter from a sample of
configurations using the Wilson action and configurations using the
SW-Clover action, on a lattice at . We compare
results obtained by renormalizing the relevant operator with different
``boosted" values of the strong coupling constant . 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 on the prescription
adopted for , 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 -parameter, .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 and 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 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 decay
ratio is to be compared to the estimate 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
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
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
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