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Guido Martinelli

Publications and source records attributed to Guido Martinelli.

34 records · Page 2Linked to original sources
arXiv2018

HVP contribution of the light quarks to the muon $(g - 2)$ including isospin-breaking corrections with Twisted-Mass fermions

We 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-$QED$ approximation using the $QCD$ gauge configurations generated by the European Twisted Mass Collaboration (ETMC) with $N_f = 2 + 1 + 1$ dynamical quarks, at three values of the lattice spacing varying from $0.089$ to $0.062 ~ \mbox{fm}$, at several lattice volumes and with pion masses in the range $M_π\simeq 220 ÷490 ~ \mbox{MeV}$.

hep-lat↗
arXiv2018

Study of Anomalies in Exclusive Semileptonic B Decays

Our Vcb extraction is based on recent Belle results, with unfolded kinematical dependence. We use two different parameterizations of the form factors, the CLN and BGL parameterizations. We discuss how the known discrepancy between the inclusive and exclusive determinations of Vcb depends on an underestimate of the uncertainty with parameterizations that use heavy quark expansion. We investigate the results of the semileptonic B decay with heavy leptons (tau) compared to the decays into light leptons. Experimental ratio of the two branching ratios is systematically larger than the Standard Model(SM) prediction. Effects of new physics operators on the data about these decays are studied.

hep-ph↗
arXiv2017

Unitarity Triangle Analysis in the Standard Model and Beyond

Flavour physics represents a unique test bench for the Standard Model (SM). New analyses performed at the LHC experiments are now providing unprecedented insights into CKM metrology and new evidences for rare decays. The CKM picture can provide very precise SM predictions through global analyses. We present here the results of the latest global SM analysis performed by the UTfit collaboration including all the most updated inputs from experiments, lattice QCD and phenomenological calculations. In addition, the Unitarity Triangle (UT) analysis can be used to constrain the parameter space in possible new physics (NP) scenarios. We update here also the UT analysis beyond the SM by the UTfit collaboration. All of the available experimental and theoretical information on $ΔF=2$ processes is reinterpreted including a model-independent NP parametrisation. We determine the allowed NP contributions in the kaon, $D$, $B_d$, and $B_s$ sectors and, in various NP scenarios, we translate them into bounds for the NP scale as a function of NP couplings.

hep-ph↗
arXiv2017

Effects of finite volume on the $K_L$-$K_S$ mass difference

Phenomena that involve two or more on-shell particles are particularly sensitive to the effects of finite volume and require special treatment when computed using lattice QCD. In this paper we generalize the results of Lüscher, and Lellouch and Lüscher, which determine the leading order effects of finite volume on the two-particle spectrum and two-particle decay amplitudes to determine the finite-volume effects in the second order mixing of the $K^0$ and $\overline{K^0}$ states. We extend the methods of Kim, Sachrajda and Sharpe to provide a direct, uniform treatment of these three, related, finite-volume corrections. In particular, the leading, finite-volume corrections to the $K_L$-$K_S$ mass difference $ΔM_K$ and the CP violating parameter $ε_K$ are determined, including the potentially large effects which can arise from the near degeneracy of the kaon mass and the energy of a finite-volume, two-pion state.

hep-lat↗
arXiv2016

Recent progress on QCD inputs for axion phenomenology

The properties of the QCD axion are strictly related to the dependence of strong interactions on the topological parameter theta. We present a determination of the topological properties of QCD for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors and physical quark masses. Numerical results for the topological susceptibility, when compared to instanton gas computations, differ both in size and in the temperature dependence. We discuss the implications of such findings for axion phenomenology, also in comparison to similar studies in the literature, and the prospects for future investigations.

hep-lat↗
arXiv2016

Metadynamics Surfing on Topology Barriers: the $CP^{N-1}$ Case

As one approaches the continuum limit, $QCD$ systems, investigated via numerical simulations, remain trapped in sectors of field space with fixed topological charge. As a consequence the numerical studies of physical quantities may give biased results. The same is true in the case of two dimensional $CP^{N-1}$ models. In this paper we show that metadynamics, when used to simulate $CP^{N-1}$, allows to address efficiently this problem. By studying $CP^{20}$ we show that we are able to reconstruct the free energy of the topological charge $F(Q)$ and compute the topological susceptibility as a function of the coupling and of the volume. This is a very important physical quantity in studies of the dynamics of the $θ$ vacuum and of the axion. This method can in principle be extended to $QCD$ applications.

hep-lat↗
arXiv2016

Axion phenomenology and $θ$-dependence from $N_f = 2+1$ lattice QCD

We investigate the topological properties of $N_f = 2+1$ QCD with physical quark masses, both at zero and finite temperature. We adopt stout improved staggered fermions and explore a range of lattice spacings $a \sim 0.05 - 0.12$ fm. At zero temperature we estimate both finite size and finite cut-off effects, comparing our continuum extrapolated results for the topological susceptibility $χ$ with predictions from chiral perturbation theory. At finite temperature, we explore a region going from $T_c$ up to around $4\, T_c$, where we provide continuum extrapolated results for the topological susceptibility and for the fourth moment of the topological charge distribution. While the latter converges to the dilute instanton gas prediction the former differs strongly both in the size and in the temperature dependence. This results in a shift of the axion dark matter window of almost one order of magnitude with respect to the instanton computation.

hep-lat↗
arXiv2014

Standard Model updates and new physics analysis with the Unitarity Triangle fit

We present here the update of the Unitarity Triangle (UT) analysis performed by the UTfit Collaboration within the Standard Model (SM) and beyond. Continuously updated flavour results contribute to improving the precision of several constraints and through the global fit of the CKM parameters and the SM predictions. We also extend the UT analysis to investigate new physics (NP) effects on $ΔF=2$ processes. Finally, based on the NP constraints, we derive upper bounds on the coefficients of the most general $ΔF=2$ effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of NP that contributes to these low-energy effective interactions.

hep-ph↗
arXiv2005

Cutoff effects in maximally twisted LQCD

The Symanzik analysis of correlators in lattice QCD with maximally twisted Wilson fermions reveals that there exist cutoff artifacts which tend to become large as the quark mass gets small. We show that these effects can be reduced to a negligible level by either introducing the clover term in the action or, as already suggested in the literature, by a suitable choice of the critical mass. Recent simulation data support these conclusions.

hep-lat↗
arXiv2005

The Ademollo-Gatto theorem for lattice semileptonic decays

We present the results of the calculation of the Kl3 semileptonic form factor at zero momentum transfer, f(0), obtained at one-loop in partially quenched Chiral Perturbation Theory (with either Nf=2, or Nf=3, and with generic valence and sea quark masses). We show that for Nf=2, when the masses of the valence and sea light quarks are equal, the correction is of the order (MK^2-Mpi^2)^3. The formulae presented here can be useful for the mass extrapolation of the results obtained in lattice simulations to the physical point.

hep-lat↗
arXiv2005

Rare Kaon Decays on the Lattice

We show that long distance contributions to the rare decays K -> pi nu nu-bar and K -> pi l+ l- can be computed using lattice QCD. The proposed approach requires well established methods, successfully applied in the calculations of electromagnetic and semileptonic form factors. The extra power divergences, related to the use of weak four-fermion operators, can be eliminated using only the symmetries of the lattice action without ambiguities or complicated non-perturbative subtractions. We demonstrate that this is true even when a lattice action with explicit chiral symmetry breaking is employed. Our study opens the possibility of reducing the present uncertainty in the theoretical predictions for these decays.

hep-lat↗
arXiv2001

Charm Quark Mass

We report on the result for the charm quark mass as obtained from our lattice QCD computation in the quenched approximation. Our result in the MSbar scheme is m_c(m_c)=1.26(4)(12) GeV.

hep-ph↗
arXiv2001

Kaon Physics from Lattice QCD

The latest lattice results on kaon decays and mixing are reviewed. The discussion is focused on recent theoretical progress and new numerical calculations which appeared after Kaon 1999.

hep-ph↗
arXiv1999

Light Quark Masses from Lattice Quark Propagators at Large Momenta

We compute non-perturbatively the average up-down and strange quark masses from the large momentum (short-distance) behaviour of the quark propagator in the Landau gauge. This method, which has never been applied so far, does not require the explicit calculation of the quark mass renormalization constant. Calculations were performed in the quenched approximation, by using O(a)-improved Wilson fermions. The main results of this study are ml^RI(2GeV)=5.8(6)MeV and ms^RI(2GeV)=136(11)MeV. Using the relations between different schemes, obtained from the available four-loop anomalous dimensions, we also find ml^RGI=7.6(8)MeV and ms^RGI=177(14)MeV, and the MSbar-masses, ml^MS(2GeV)=4.8(5)MeV and ms^MS(2GeV)=111(9)MeV.

hep-lat↗
arXiv1998

Hadronic Weak Interactions of Light Quarks

In this review, three subjects are discussed: a phenomenological application of lattice predictions to $K^0$--$\bar K^0$ mixing in Super Symmetry; a discussion of the non-perturbative renormalization methods for four-fermion operators and a new approach to extract weak matrix elements in effective theories denoted as OPE without OPE (operator product expansion without operator product expansion)

hep-lat↗