479 research outputs found
First Lattice QCD Study of the Sigma -> n Axial and Vector Form Factors with SU(3) Breaking Corrections
We present the first quenched lattice QCD study of the form factors relevant
for the hyperon semileptonic decay Sigma -> n l nu. The momentum dependence of
both axial and vector form factors is investigated and the values of all the
form factors at zero-momentum transfer are presented. Following the same
strategy already applied to the decay K0 -> pi- l nu, the SU(3)-breaking
corrections to the vector form factor at zero-momentum transfer, f1(0), are
determined with great statistical accuracy in the regime of the simulated quark
masses, which correspond to pion masses above ~ 0.7 GeV. Besides f1(0) also the
axial to vector ratio g1(0) / f1(0), which is relevant for the extraction of
the CKM matrix element Vus, is determined with significant accuracy. Due to the
heavy masses involved, a polynomial extrapolation, which does not include the
effects of meson loops, is performed down to the physical quark masses,
obtaining f1(0) = -0.948 +/- 0.029 and g1(0) / f1(0) = -0.287 +/- 0.052, where
the uncertainties do not include the quenching effect. Adding a recent
next-to-leading order determination of chiral loops, calculated within the
Heavy Baryon Chiral Perturbation Theory in the approximation of neglecting the
decuplet contribution, we obtain f1(0) = -0.988 +/- 0.029(lattice) +/-
0.040(HBChPT). Our findings indicate that SU(3)-breaking corrections are
moderate on both f1(0) and g1(0). They also favor the experimental scenario in
which the weak electricity form factor, g2(0), is large and positive, and
correspondingly the value of |g1(0) / f1(0)| is reduced with respect to the one
obtained with the conventional assumption g2(q**2) = 0 based on exact SU(3)
symmetry.Comment: final version to appear in Nucl. Phys.
Lab-frame observables for probing the top-Higgs interaction
We investigate methods to explore the CP nature of the coupling
at the LHC, focusing on associated production of the Higgs with a
pair. We first discuss the constraints implied by low-energy observables and by
the Higgs-rate information from available LHC data, emphasizing that they
cannot provide conclusive evidence on the nature of this coupling. We then
investigate kinematic observables that could probe the coupling
directly, in particular quantities that can be constructed out of just
lab-frame kinematics. We define one such observable by exploiting the fact that
spin correlations do also carry information about the CP-nature of
the coupling. Finally, we introduce a CP-odd quantity and a
related asymmetry, able to probe CP violation in the coupling and
likewise constructed out of lab-frame momenta only.Comment: 32 pages, updated with latest data from ATLAS and references adde
Responsive Urban Models by Processing Sets of Heterogeneous Data
This paper presents some steps in experimentation aimed at describing urban spaces made following the series of earthquakes that affected a vast area of central Italy starting on 24 August 2016. More specifically, these spaces pertain to historical centres of limited size and case studies that can be called "problematic" (due to complex morphological and settlement conditions, because they are difficult to access, or because they have been affected by calamitous events, etc.). The main objectives were to verify the use of sets of heterogeneous data that are already largely available to define a workflow and develop procedures that would allow some of the steps to be automated as much as possible. The most general goal was to use the experimentation to define a methodology to approach the problem aimed at developing descriptive responsive models of the urban space, that is, morphological and computer-based models capable of being modified in relation to the constantly updated flow of input data
Semileptonic Hyperon Decays on the Lattice: an Exploratory Study
We present preliminary results of an exploratory lattice study of the vector
form factor relevant for the semileptonic hyperon decay
. This study is based on the same method used for the
extraction of for the decay . The main purpose
of this study is to test the method for hyperon form factors in order to
estimate the precision that can be reached and the importance of SU(3)-breaking
effects.Comment: 3 pages, 5 figures, talk presented at Lattice2004(weak), Fermilab,
Batavia, Illinois, 21-26 June 200
SU(3)-breaking effects in kaon and hyperon semileptonic decays from lattice QCD
We discuss the result of a recent quenched lattice calculation of the K -> pi
vector form factor at zero-momentum transfer, relevant for the determination of
|V_us| from K-> pi l nu decays. Using suitable double ratios of three-point
correlation functions, we show that it is possible to calculate this quantity
at the percent-level precision. The leading quenched effects are corrected for
by means of quenched chiral perturbation theory. The final result, f+(0) =
0.960 +- 0.005_stat +- 0.007_syst, turns out to be in good agreement with the
old quark model estimate made by Leutwyler and Roos. In this paper, we discuss
the phenomenological impact of the lattice result for the extraction of |V_us|,
by updating the analysis of K -> pi l nu decays with the most recent
experimental data. We also present a preliminary lattice study of hyperon Sigma
-> n l nu decays, based on a similar strategy.Comment: 17 pages, 8 figures. Based on talks given at: DAFNE 2004: Physics at
meson factories, Laboratori Nazionali di Frascati (Italy), June 7-11, 2004;
VIII International Conference on "Electron-Nucleus Scattering", Marciana
Marina (Italy), June 21-25, 2004; Lattice 2004, Fermi National Accelerator
Laboratory, Batavia, Illinois (USA), June 21-26, 2004; ICHEP 2004, Beijing
(China), August 16-22, 200
Bs to l+ l- gamma as a Test of Lepton Flavor Universality
We discuss a number of strategies to reduce the theoretical error, and make such a measurement a new
probe of the interactions that are interesting in the light of present-day
flavor discrepancies. In particular, for low di-lepton invariant mass we
propose to exploit the close parenthood between and the measured . For high , conversely, we exploit the fact that the decay is
dominated by two form-factor combinations, plus contributions from broad
charmonium that we model accordingly. We construct the ratio , akin
to and likewise sensitive to lepton-universality violation. Provided the
two rates in this ratio are integrated in a suitable region that minimises
bremsstrahlung contributions while maximising statistics, the ratio is very
close to unity and the form-factor dependence cancels to an extent that makes
it a new valuable probe of lepton-universality violating contributions in the
effective Hamiltonian. We finally speculate on additional ideas to extract
short-distance information from resonance regions, which are theoretically
interesting but statistically limited at present.Comment: 21 pages, 4 figures. v4: in appendix removed equation already present
in main tex
Per una ridefinizione del modello turistico nazionale. Spunti di riflessioni a partire dalle criticità emerse durante il Covid-19
The new emergency we are facing with current spread of coronavirus impos-es restrictions in everyday life and mobility across different territories and countries; we are globally compelled to face mutual problems, re-gardless of unilateral positions and this is giving strength to globalization just when a crisis of the globalized world model seemed to be consolidat-ing. Even modern tourism in the pre-pandemic economic and political situation was building a path of progressive quantitative growth and showing positive signs even in the most difficult moments of the recent international economic crisis. However, global tourism is now displaying an overall weakness as never happened in the pasts and it is starting fea-turing negative data and forecasts showing how this emergency is affect-ing a substantial portion of the Italian economy, which has reached 13,2% of GDP in 2018 with subsequent significant meaning also in terms of employment. Although it is difficult to foresee future tourism developments, this paper wants to suggest a reflection on the possible scenarios that could be configured out in the medium term, starting from considerations on the role that the national corporate system in tourism has played within the Italian supply chain
Extracting excited states from lattice QCD: the Roper resonance
We present a new method for extracting excited states from a single two-point
correlation function calculated on the lattice. Our method simply combines the
correlation function evaluated at different time slices so as to ``subtract''
the leading exponential decay (ground state) and to give access to the first
excited state. The method is applied to a quenched lattice study (volume = 24^3
x 64, beta = 6.2, 1/a = 2.55 GeV) of the first excited state of the nucleon
using the local interpolating operator O = [uT C gamma5 d] u. The results are
consistent with the identification of our extracted excited state with the
Roper resonance N'(1440). The switching of the level ordering with respect to
the negative-parity partner of the nucleon, N*(1535), is not seen at the
simulated quark masses and, basing on crude extrapolations, is tentatively
expected to occur close to the physical point.Comment: version to apper in Phys. Lett. B; additions in the presentation of
the method; 3 references added; no change in the results and in the figure
D0 - D0bar mixing: theory basics
I discuss how the novel experimental data on D0 - D0bar mixing can be
combined to provide information on the fundamental theoretical quantities
describing the mixing itself. I then discuss the theoretical impact of the new
data, focusing in particular on the MSSM.Comment: Proceedings of the EPS-HEP 2007 Conference, Manchester (UK). 3 pages,
1 table, 1 figur
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