67 research outputs found
Semileptonic decays of heavy-light pseudoscalar mesons
I discuss the results of a recent quenched lattice calculation of the two
independent form factors parametrizing the semileptonic decays between
heavy-light pseudoscalar mesons. The differential decay rate of the process B
--> D l nu has been calculated at non vanishing momentum transfer both in the
case of the light leptons, l=e,mu, and in the case of a non vanishing lepton
mass, l=tau.Comment: Talk presented at Lattice2007, Regensburg, July 30 - August 4, 2007;
7 pages, 3 figure
Lattice calculation of isospin corrections to Kl2 and Kl3 decays
In this talk I discuss the theoretical issues associated with lattice
calculations of isospin breaking corrections to hadronic matrix elements. I
concentrate on the calculation of QCD isospin breaking effects for the Kl2 and
Kl3 decay rates and illustrate the recent lattice results obtained by the RM123
collaboration.Comment: Proceedings of CKM 2012, the 7th International Workshop on the CKM
Unitarity Triangle, University of Cincinnati, USA, 28 September - 2 October
201
Isospin Breaking Effects on the Lattice
Isospin symmetry is not exact and the corrections to the isosymmetric limit
are, in general, at the percent level. For gold plated quantities, such as
pseudoscalar meson masses or the kaon leptonic and semileptonic decay rates,
these effects are of the same order of magnitude of the errors quoted in
nowadays lattice calculations and cannot be neglected any longer. In this talk
I discuss the methods that have been developed in the last few years to
calculate isospin breaking corrections by starting from first principles
lattice simulations. In particular, I discuss how to perform a combined QCD+QED
lattice simulation and a renormalization prescription to be used in order to
separate QCD from QED isospin breaking effects. A brief review of recent
lattice results of isospin breaking effects on the hadron spectrum is also
included.Comment: 15 pages, plenary talk presented at the 31st International Symposium
on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz,
German
Non-perturbative improvement of quark mass renormalization in two-flavour lattice QCD
We non-perturbatively determine the renormalization constant and the
improvement coefficients relating the renormalized current and subtracted quark
mass in O(a) improved two-flavour lattice QCD. We employ the Schr\"odinger
functional scheme and fix the physical extent of the box by working at a
constant value of the renormalized coupling. Our calculation yields results
which cover two regions of bare parameter space. One is the weak-coupling
region suitable for volumes of about half a fermi. By making simulations in
this region, quarks as heavy as the bottom can be propagated with the full
relativistic QCD action and renormalization problems in HQET can be solved
non-perturbatively by a matching to QCD in finite volume. The other region
refers to the common parameter range in large-volume simulations of two-flavour
lattice QCD, where our results have particular relevance for charm physics
applications.Comment: 31 pages including figures and tables, latex2e, uses JHEP3.cls;
revised version published in JHEP, clarifying remarks and references added;
typo(s) corrected, especially in eq. (3.10
On the extraction of spectral densities from lattice correlators
Hadronic spectral densities are important quantities whose non-perturbative
knowledge allows for calculating phenomenologically relevant observables, such
as inclusive hadronic cross-sections and non-leptonic decay-rates. The
extraction of spectral densities from lattice correlators is a notoriously
difficult problem because lattice simulations are performed in Euclidean time
and lattice data are unavoidably affected by statistical and systematic
uncertainties. In this paper we present a new method for extracting hadronic
spectral densities from lattice correlators. The method allows for choosing a
smearing function at the beginning of the procedure and it provides results for
the spectral densities smeared with this function together with reliable
estimates of the associated uncertainties. The same smearing function can be
used in the analysis of correlators obtained on different volumes, such that
the infinite volume limit can be studied in a consistent way. While the method
is described by using the language of lattice simulations, in reality it is
completely general and can profitably be used to cope with inverse problems
arising in different fields of research.Comment: 15 pages, 14 figures. Updated to match published versio
physics from fine lattices
We present a preliminary analysis of the charm quark mass and the mass and
decay constant of the meson obtained from dynamical simulations
of Wilson QCD on the large and fine lattices simulated by the CLS
effort.Comment: 6 pages, 2 figures; talk presented at Lattice 2008, XXVI
International Symposium on Lattice Field Theory, July 14-19, 2008,
Williamsburg, Virginia, US
Remarks on the discretization of physical momenta in lattice QCD
The calculation on the lattice of cross--sections, form--factors and decay
rates associated to phenomenologically relevant physical processes is
complicated by the spatial momenta quantization rule arising from the
introduction of limited box sizes in numerical simulations. A method to
overcome this problem, based on the adoption of two distinct boundary
conditions for two fermions species on a finite lattice, is here discussed and
numerical results supporting the physical significance of this procedure are
shown.Comment: 3 pages, 2 figures, Talk presented at Lattice2004(spectrum
Radiative corrections to decay amplitudes in lattice QCD
The precision of lattice QCD computations of many quantities has reached such
a precision that isospin-breaking corrections, including electromagnetism, must
be included if further progress is to be made in extracting fundamental
information, such as the values of Cabibbo-Kobayashi-Maskawa matrix elements,
from experimental measurements. We discuss the framework for including
radiative corrections in leptonic and semileptonic decays of hadrons, including
the treatment of infrared divergences. We briefly review isospin breaking in
leptonic decays and present the first numerical results for the ratio
in which these corrections have been
included. We also discuss the additional theoretical issues which arise when
including electromagnetic corrections to semileptonic decays, such as
decays. The separate definition of strong isospin-breaking effects
and those due to electromagnetism requires a convention. We define and advocate
conventions based on hadronic schemes, in which a chosen set of hadronic
quantities, hadronic masses for example, are set equal in QCD and in QCD+QED.
This is in contrast with schemes which have been largely used to date, in which
the renormalised and quark masses are set equal in QCD and in
QCD+QED in some renormalisation scheme and at some scale .Comment: Presented at the 36th Annual International Symposium on Lattice Field
Theory (Lattice2018), Michigan State University, July 22nd - 28th 201
Quenched lattice calculation of semileptonic heavy-light meson form factors
We calculate, in the continuum limit of quenched lattice QCD, the matrix
elements of the heavy-heavy vector current between heavy-light pseudoscalar
meson states. We present the form factors for different values of the initial
and final meson masses at finite momentum transfer. In particular, we calculate
the non-perturbative correction to the differential decay rate of the process B
--> D l nu including the case of a non-vanishing lepton mass.Comment: 16 pages, 10 figures, version accepted for publication on JHE
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