308 research outputs found
Hypercubic effects in semileptonic decays of heavy mesons, toward B -> pi l nu with Nf=2+1+1 Twisted fermions
No full textWe present a preliminary study toward a lattice determination of the vector and scalar form factors of the B -> pi l nu semileptonic decays. We compute the form factors relative to the transition between heavy-light pseudoscalar mesons, with masses above the physical D-mass, and the pion. We simulate heavy-quark masses in the range mc^phys < mh < 2 mc^phys. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data, and included in the decomposition of the current matrix elements in terms of additional form factors. We discuss the size of this breaking as the parent-meson mass increases. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2+1+1 flavors of dynamical quarks at three different values of the lattice spacing and with pion masses as small as 210 MeV
Hypercubic Effects in semileptonic decays on the lattice
No full textWe present a lattice determination of the vector and scalar form factors of the semileptonic D -> pi l nu decays, which are relevant for the extraction of the CKM matrix element from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with N_f = 2 + 1 + 1 flavors of dynamical
quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Quark momenta are injected on the lattice using non-periodic boundary conditions. The matrix elements of both vector and
scalar currents are determined for a plenty of kinematical conditions in which parent and child mesons are either moving or at rest. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data and included in the
decomposition of the current matrix elements in terms of additional form factors. Our preliminary estimate for the vector form factor at zero 4-momentum transfer is f_+(D -> pi)(0) = 0.631(40), which can be compared with the latest FLAG average f_+(D -> pi)(0) = 0.666 (29) available only at N_f = 2 + 1
Tensor form factor for the <i>D</i> → <i>π(K)</i> transitions with Twisted Mass fermions.
No full textWe present a preliminary lattice calculation of the D → π and D → K tensor form factors fT (q2) as a function of the squared 4-momentum transfer q2. ETMC recently computed the vector and scalar form factors f+(q2) and f0(q2) describing D → π(K)lv semileptonic decays analyzing the vector current and the scalar density. The study of the weak tensor current, which is directly related to the tensor form factor, completes the set of hadronic matrix element regulating the transition between these two pseudoscalar mesons within and beyond the Standard Model where a non-zero tensor coupling is possible. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 flavors of dynamical quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV and with the valence heavy quark in the mass range from ≃ 0.7 mc to ≃ 1.2mc. The matrix element of the tensor current are determined for a plethora of kinematical conditions in which parent and child mesons are either moving or at rest. As for the vector and scalar form factors, Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data. We will present preliminary results on the removal of such hypercubic lattice effects.</jats:p
<i>D</i> → <i>π</i> and <i>D</i> → <i>K</i> semileptonic form factors with <i>N</i><sub><i>f</i></sub> = 2 + 1 + 1 twisted mass fermions
No full textWe present a lattice determination of the vector and scalar form factors of the D → π(K)lv semileptonic decays, which are relevant for the extraction of the CKM matrix elements |Vcd| and |Vcs| from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 +1 flavors of dynamical quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. The matrix elements of both vector and scalar currents are determined for a plenty of kinematical conditions in which parent and child mesons are either moving or at rest. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data and included in the decomposition of the current matrix elements in terms of additional form factors. After the extrapolations to the physical pion mass and to the continuum limit the vector and scalar form factors are determined in the whole kinematical region from q2 = 0 up to [see formula in PDF] accessible in the experiments, obtaining a good overall agreement with experiments, except in the region at high values of q2 where some deviations are visible.</jats:p
Electromagnetic Form Factor of the Pion from Twisted-mass Lattice QCD at Nf=2
No full textWe present a lattice calculation of the electromagnetic form factor of the pion obtained using the tree-level Symanzik improved gauge action with two flavors of dynamical twisted Wilson quarks. The simulated pion masses range approximately from 260 to 580 MeV, and the lattice box sizes are chosen in order to guarantee that Mpi*L>~4. Accurate results for the form factor are obtained using all-to-all quark propagators evaluated by a stochastic procedure. The momentum dependence of the pion form factor is investigated up to values of the squared four-momentum transfer Q^2~=0.8 GeV^2 and, thanks to the use of twisted boundary conditions, down to Q^2~=0.05 GeV^2. Volume and discretization effects on the form factor appear to be within the statistical errors. Our results for the pion mass, decay constant and form factor are analyzed using (continuum) chiral perturbation theory at next-to-next-to-leading order. The extrapolated value of the pion charge radius is <r2>_phys=0.456±0.030(stat)±0.024(syst) in nice agreement with the experimental result. The extrapolated values of the pion form factor agree very well with the experimental data up to Q^2~=0.8 GeV^2 within uncertainties which become competitive with the experimental errors for Q^2>~0.3 GeV^2. The relevant low-energy constants appearing in the chiral expansion of the pion form factor are extracted from our lattice data, which come essentially from a single lattice spacing, adding the experimental value of the pion scalar radius in the fitting procedure. Our findings are in nice agreement with the available results of chiral perturbation theory analyses of pi-pi scattering data as well as with other analyses of our collaboration
Radiative corrections to decay amplitudes in lattice QCD
No full textThe 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 Gamma(Kmu2)=Gamma(pimu2) 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 Kl3 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 alphas(mu) and quark masses are set equal in QCD and in QCD+QED in some renormalisation scheme and at some scale mu
HVP contribution of the light quarks to the muon including isospin-breaking corrections with Twisted-Mass fermions
No full textWe present a preliminary lattice calculation of the leading-order electromagnetic and strong isospin-breaking corrections to the Hadronic Vacuum Polarization (HVP) contribution of the light quarks to the anomalous magnetic moment of the muon. The results are obtained in the quenched- approximation using the gauge configurations generated by the European Twisted Mass Collaboration (ETMC) with dynamical quarks, at three values of the lattice spacing varying from to 0.062 ~ \mbox{fm}, at several lattice volumes and with pion masses in the range M_\pi \simeq 220 \div 490 ~ \mbox{MeV}
Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite-volume effects
No full textIn 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
K →π semileptonic form factors with Nf=2+1+1 twisted mass fermions
No full textWe present a lattice QCD determination of the vector and scalar form factors of the semileptonic K→ decay which are relevant for the extraction of the Cabibbo-Kobayashi-Maskawa matrix element |Vus| from experimental data. Our results are based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 dynamical fermions, which include in the sea, besides two light mass degenerate quarks, also the strange and the charm quarks. We use data simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Our final result for the vector form factor at zero momentum transfer is f+(0)=0.9709(46), where the uncertainty is both statistical and systematic combined in quadrature. Using the latest experimental value of f+(0)|Vus| from K 3 decays, we obtain |Vus|=0.2230(11), which allows us to test the unitarity constraint of the Standard Model below the permille level once the determination of |Vud| from superallowed nuclear β decays is adopted. A slight tension with unitarity at the level of ∼2 standard deviations is observed. Moreover, we present our results for the semileptonic scalar f0(q2) and vector f+(q2) form factors in the whole range of values of the squared four-momentum transfer q2 measured in K 3 decays, obtaining a very good agreement with the momentum dependence of the experimental data. We provide a set of synthetic data points representing our results for the vector and scalar form factors at the physical point for several selected values of q2
Silvano Arieti: remembering his message
No full textThis paper reviews the contributions of Silvano Arieti to the psychodynamic treatment of schizophrenia and places them in the context of the current era and its intellectual tensions regarding this disorder and its treatment. The author includes personal anecdotes to illustrate her thesis that psychodynamic approaches remain vitally important and are tragically underutilized currently . The International Society for the Psychological treatments of the Schizophrenias and other psychoses, ISPS, aims at redressing this proble
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