Search

We present a determination of the gradient flow scales w0√t0 and t0/w0 in isosymmetric QCD, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with N f = 2 + 1 + 1 flavours of Wilson-clover twisted-mass quarks including configurations close to the physical point for all dynamical flavours. The simulations are carried out at three values of the lattice spacing and the scale is set through the PDG value of the pion decay constant, yielding w0 = 0.17383(63) fm, √t0 = 0.14436(61) fm and t0/w0 = 0.11969(62) fm. Finally, fixing the kaon mass to its isosymmetric value, we determine the ratio of the kaon and pion leptonic decay constants to be fK/fπ = 1.1995(44).

We present an application of the unitarity-based dispersion matrix (DM) approach to the extraction of the CKM matrix element $|V_{cb}|$ from the experimental data on the exclusive semileptonic $B_{(s)} \to D_{(s)}^{(*)} \ell ν_\ell$ decays. The DM method allows to achieve a non-perturbative, model-independent determination of the momentum dependence of the semileptonic form factors. Starting from lattice results available at large values of the 4-momentum transfer and implementing non-perturbative unitarity bound, the behaviour of the form factors in their whole kinematical range is obtained without introducing any explicit parameterization of their momentum dependence. We consider the four exclusive semileptonic $B_{(s)} \to D_{(s)}^{(*)} \ell ν_\ell$ decays and extract $|V_{cb}|$ from the experimental data for each transition. The average over the four channels is $|V_{cb}| = (41.2 \pm 0.8) \cdot 10^{-3} $, which is compatible with the latest inclusive determination at $1σ$ level. We address also the issue of Lepton Flavour Universality by computing pure theoretical estimates of the $τ/\ell$ ratios of the branching fractions for each channel, where $\ell$ is a light lepton. In the case of a light spectator quark we obtain $R(D^*) = 0.275(8)$ and $R(D) = 0.296(8)$, which are compatible with the corresponding experimental values within $1.3σ$. In the case of a strange spectator quark we obtain $\textit{R}(D_s^*) =0.2497(60)$ and $\textit{R}(D_s) = 0.298(5)$. The different values for $R(D_s^*)$ and $R(D^*)$ may reflect $SU(3)_F$ symmetry breaking effects, which seem to be present in some of the lattice form factors, especially at large values of the recoil., Contribution to ICHEP-2022

We discuss the general properties of the B-meson decay form factors F(q2,q′2), describing B-meson decays induced by two currents, e.g., B decays into four leptons in the final state. We study the analytic properties of these complicated objects and identify those regions of q2 and q′2, where perturbative QCD can be applied for obtaining predictions for the physical form factors.

The anomalous magnetic moment of the muon $a_\mu$ is one of the most accurate quantities in Particle Physics. The long-standing discrepancy of about $3.7$ standard deviations between the experimental value and the prediction of the Standard Model could represent an intriguing indication of New Physics. The experiments at Fermilab (E989) and at J-PARC (E34) aim at reducing significantly the experimental uncertainty, thus making the theoretical one due to hadronic corrections the main limitation of this stringent test of the Standard Model. In this contribution we present the results of a first-principles lattice calculation of the hadronic vacuum polarization (HVP) contribution to $a_\mu$, including electromagnetic and $SU(2)$-breaking corrections. Our determination, $a_\mu^{\rm HVP} = 682.0 ~ (18.7) \cdot 10^{-10}$, turns out to be in agreement with recent theoretical determinations based on the dispersive analyses of the experimental cross section data for the annihilation process $e^+e^- \to hadrons$. Furthermore, we provide for the first time a lattice estimate for the missing part of $a_\mu^{\rm HVP}$ not covered in the MUonE experiment, $\left[a_\mu^{\rm HVP}\right]_> = 91.6 ~ (2.0) \cdot 10^{-10}$., Comment: Invited plenary talk at IFAE 2019, Napoli (Italy), 08-10 April 2019. v2: extended version, 5 pages, 1 figure

We 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 $\lvert V_cd \rvert$ 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.

In 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., Comment: Corrected a typo affecting the 1/L^3 term. The typo has been discovered from the authors of arXiv:2109.05002

We 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.

QCD sum rules are analytic predictions of hadron observables from quantum chromodynamics. In the so-called local-duality limit of their Borel-transformed form, all nonperturbative contributions are encompassed by just a single quantity, an effective threshold beyond which, by assumption, all hadronic contributions are reliably described by perturbative QCD. Reconstructing its quark-mass dependence enables us to investigate the differences of the leptonic decay constants of heavy-light mesons effectuated by the tiny isospin-violating discrepancy of the masses of up and down quarks. By and large, our findings enjoy excellent agreement with the outcomes of earlier studies, the only exception being a lattice-QCD prediction for the $B$ mesons, where we find dramatic disagreement., 4 pages, 1 figure, contributed to "The European Physical Society Conference on High Energy Physics - EPS-HEP 2017" (5 - 12 July 2017, Venice, Italy)

We present unquenched lattice QCD results for the matrix elements of four-fermion operators relevant to the description of the neutral K and D mixing in the standard model and its extensions. We have employed simulations with Nf=2+1+1 dynamical sea quarks at three values of the lattice spacings in the interval 0.06-0.09 fm and pseudoscalar meson masses in the range 210-450 MeV. Our results are extrapolated to the continuum limit and to the physical pion mass. Renormalization constants have been determined nonperturbatively in the RI-MOM scheme. In particular, for the kaon bag parameter, which is relevant for the K¯0-K0 mixing in the standard model, we obtain BKRGI=0.717(24).