1,315 research outputs found
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
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
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
Dynamic mechanical behavior analysis of flax/jute fiber-reinforced composites under salt-fog spray environment
Over the last decades, natural fiber-reinforced polymer composites (NFRPs) gained great attention in several engineering fields thanks to the reduction of the environmental impact and the end-of-life cost disposal. Unfortunately, the use of NFRPs is limited, mainly due to their weak resistance against humid environments. Since limited literature is available about the evolution of the dynamic mechanical response of NFRPs under aggressive environments, this paper aims to investigate the damping properties of flax, jute and flax/jute epoxy composites exposed to salt-fog up to 60 days. Furthermore, sodium bicarbonate fiber treatment was performed to improve the composites' durability. The effectiveness of treatment was evidenced for full flax-reinforced composites, whereas no beneficial effect was found for jute composites. Moreover, treated hybrid laminates having outer laminae reinforced with flax showed better damping behavior than their hybrid counterparts during the whole aging campaign
Quark masses with Nf=2 twisted mass lattice QCD
We present the results of the recent high precision lattice calculation of
the average up/down, strange and charm quark masses performed by ETMC with Nf=2
twisted mass Wilson fermions. The analysis includes data at four values of the
lattice spacing and pion masses as low as ~270 MeV, allowing for accurate
continuum limit and chiral extrapolation. The strange and charm masses are
extracted by using several methods, based on different observables: the kaon
and the eta_s meson for the strange quark and the D, D_s and eta_c mesons for
the charm. The quark mass renormalization is carried out non-perturbatively
using the RI-MOM method. The results for the quark masses in the MSbar scheme
read: m_ud(2 GeV)= 3.6(2) MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV.
We have also obtained the ratios m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).
Moreover, we provide the updated result for the bottom quark mass,
m_b(m_b)=4.3(2) GeV, obtained using the method presented in 0909.3187
[hep-lat].Comment: 7 pages, 7 figures, talk given at the XXVIII International Symposium
on Lattice Field Theory (Lattice 2010), June 14-19 2010, Villasimius, Ital
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
Modulation by internal protons of native cyclic nucleotide-gated channels from retinal rods
Ion channels directly activated by cyclic nucleotides are present in the plasma membrane of retinal rod outer segments. These channels can be modulated by several factors including internal pH (pH(i)). Native cyclic nucleotide-gated channels were studied in excised membrane patches from the outer segment of retinal rods of the salamander. Channels were activated by cGMP or cAMP and currents as a function of voltage and cyclic nucleotide concentrations were measured as pH(i) was varied between 7.6 and 5.0. Increasing internal proton concentrations reduced the current activated by cGMP without modifying the concentration (K(1/2)) of cGMP necessary for half-activation of the maximal current. This effect could be well described as a reduction of single-channel current by protonation of a single acidic residue with a pK(1) of 5.1. When channels were activated by cAMP a more complex phenomenon was observed. K(1/2) for cAMP decreased by increasing internal proton concentration whereas maximal currents activated by cAMP increased by lowering pH(i) from 7.6 to 5.7-5.5 and then decreased from pH(i) 5.5 to 5.0. This behavior was attributed both to a reduction in single-channel current as measured with cGMP and to an increase in channel open probability induced by the binding of three protons to sites with a pK(2) of 6
Average up/down, strange and charm quark masses with Nf=2 twisted mass lattice QCD
We present a high precision lattice calculation of the average up/down,
strange and charm quark masses performed with Nf=2 twisted mass Wilson
fermions. The analysis includes data at four values of the lattice spacing and
pion masses as low as ~270 MeV, allowing for accurate continuum limit and
chiral extrapolation. The strange and charm masses are extracted by using
several methods, based on different observables: the kaon and the eta_s meson
for the strange quark and the D, D_s and eta_c mesons for the charm. The quark
mass renormalization is carried out non-perturbatively using the RI-MOM method.
The results for the quark masses in the MSbar scheme read: m_ud(2 GeV)= 3.6(2)
MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV. We also obtain the ratios
m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).Comment: 20 pages, 5 figures. Typos corrected in eqs. (15)-(17). Version
published in Phys. Rev.
Left ventricular systolic function evaluated by strain echocardiography and relationship with mortality in patients with severe sepsis or septic shock. a systematic review and meta-analysis
Sepsis-induced myocardial dysfunction is associated with poor outcomes, but traditional measurements of systolic function such as left ventricular ejection fraction (LVEF) do not directly correlate with prognosis. Global longitudinal strain (GLS) utilizing speckle-tracking echocardiography (STE) could be a better marker of intrinsic left ventricular (LV) function, reflecting myocardial deformation rather than displacement and volume changes. We sought to investigate the prognostic value of GLS in patients with sepsis and/or septic shock
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