Publications (251)641.49 Total impact

Article: Publisher’s Note: Strong threemeson couplings of J / ψ and η c [Phys. Rev. D 93 , 016004 (2016)]
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ABSTRACT: DOI:http://dx.doi.org/10.1103/PhysRevD.93.019902  [Show abstract] [Hide abstract]
ABSTRACT: We discuss the strong couplings gPPV and gVVP for vector (V) and pseudoscalar (P) mesons, at least one of which is a charmonium state J/ψ or ηc. The strong couplings are obtained as residues at the poles of suitable form factors, calculated in a broad range of momentum transfers using a dispersion formulation of the relativistic constituent quark model. The form factors obtained in this approach satisfy all constraints known for these quantities in the heavyquark limit. Our results suggest sizably higher values for the strong meson couplings than those reported in the literature from QCD sum rules.  [Show abstract] [Hide abstract]
ABSTRACT: We present a lattice QCD determination of the vector and scalar form factors of the semileptonic decays D>\pi l \nu and D > K l \nu 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 dynamical fermions. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Our preliminary estimates for the vector form factor at zero 4momentum transfer are f+(D > \pi)(0) = 0.610 (23) and f+(D > K)(0) = 0.747 (22), where the uncertainties are only statistical. By combining our results with the experimental values of f+(D > \pi)(0) Vcd and f+(D > K)(0) Vcs we obtain Vcd = 0.2336 (93) and Vcs = 0.975 (30), which together with the PDG determination of Vcb are in agreement with the unitarity constraint of the Standard Model.  [Show abstract] [Hide abstract]
ABSTRACT: We present a lattice QCD determination of the vector and scalar form factors of the kaon semileptonic decay $K \to \pi \ell \nu$, which is relevant for the determination of the CKM matrix element $V_{us}$ 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. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Our estimate for the vector form factor at zero 4momentum transfer is $f_+(0) = 0.9709 (46)$, where the uncertainty is both statistical and systematic. By combining our result with the latest experimental value of $f_+(0)V_{us}$ we obtain $V_{us} = 0.2230 (11)$, which satisfies the unitarity constraint of the Standard Model at the permille level using the updated determination of $V_{ud}$ coming from superallowed nuclear $\beta$ decays. We present also the momentum dependence of the vector and scalar form factors in the whole range of values of the squared 4momentum transfer measured in $K_{\ell 3}$ decays, obtaining a good agreement with the experimental data.  [Show abstract] [Hide abstract]
ABSTRACT: We present the implementation of twisted mass fermion operators for the QPhiX library. We analyze the performance on the Intel Xeon Phi (Knights Corner) coprocessor as well as on Intel Xeon Haswell CPUs. In particular, we demonstrate that on the Xeon Phi 7120P the Dslash kernel is able to reach 80\% of the theoretical peak bandwidth, while on a Xeon Haswell E52630 CPU our generated code for the Dslash operator with AVX2 instructions outperforms the corresponding implementation in the tmLQCD library by a factor of $\sim 5\times$ in single precision. We strong scale the code up to 6.8 (14.1) Tflops in single (half) precision on 64 Xeon Haswell CPUs.  [Show abstract] [Hide abstract]
ABSTRACT: We extract the strong coupling constants of three mesons, each of which is composed of either two charm quarks or one charm quark and one light (i.e., $u$, $d$, or $s$) quark, from the matrix elements for the transitions of two of these mesons induced by appropriate quark currents within the framework of a relativistic dispersion approach to the constituentquark picture of mesons. Among others, we also analyse the impact of the violation of the SU(3) flavour symmetry by the quark masses. In the case of mesons containing one light quark, we observe, in two respects, discrepancies between our findings and the predictions of QCD sum rules: our strong couplings exceed considerably the ones emerging from QCD sum rules, and, in our approach, the replacement of a light quark by a strange quark entails, in contrast to QCD sum rules, a reduction of the magnitudes of the strong couplings.  [Show abstract] [Hide abstract]
ABSTRACT: The relative magnitude of the decay constants of the pseudoscalar and vector beauty mesons poses (in contrast to the case of charmed mesons) a longstanding puzzle. We revisit this problem within the framework of our recent improvements of the QCD sumrule formalism for relating observable properties of mesons to quantum chromodynamics and are led to conclude that the decay constants of the beauty vector mesons are undoubtedly smaller than those of their pseudoscalar counterparts.  [Show abstract] [Hide abstract]
ABSTRACT: We correct Fig. 2 and its discussion in subsection II A. The remainder of the paper remains unaffected.  [Show abstract] [Hide abstract]
ABSTRACT: We discuss the strong couplings $g_{PPV}$ and $g_{VVP}$ for vector ($V$) and pseudoscalar ($P$) mesons, at least one of which is a charmonium state $J/\psi$ or $\eta_c$. The strong couplings are obtained as residues at the poles of suitable form factors, calculated in a broad range of momentum transfers by a relativistic dispersion approach relying on the constituent quark picture. The spectral representations for the couplings under discussion satisfy all constraints known for these quantities in the heavyquark limit. Our results suggest sizeably higher values than those reported in the literature from QCD sum rules. 
Article: \Delta S=2 and \Delta C=2 bag parameters in the SM and beyond from Nf=2+1+1 twistedmass LQCD
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ABSTRACT: We present unquenched lattice QCD results for the matrix elements of fourfermion 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 RIMOM scheme. In particular, for the Kaon bagparameter, which is relevant for the \overline{K}^0K^0 mixing in the Standard Model, we obtain B_K^{RGI} = 0.717(24). 
Article: Accurate decayconstant ratios $f_{B^*}/f_B$ and $f_{B_s^*}/f_{B_s}$ from Borel QCD sum rules
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ABSTRACT: We present our analysis of the decay constants of the beauty vector mesons $B^*$ and $B^*_s$ within the framework of dispersive sum rules for the twopoint correlator of vector currents in QCD. While the decay constants of the vector mesons $f_{B^*}$ and $f_{B_s^*}$ $$ similar to the decay constants of the pseudoscalar mesons $f_B$ and $f_{B_s}$ $$ individually have large uncertainties induced by theory parameters not known with a satisfactory precision, these uncertainties almost entirely cancel out in the ratios of vector over pseudoscalar decay constants. These ratios may be thus predicted with very high accuracy due to the good control over the systematic uncertainties of the decay constants gained upon application of our hadronparameter extraction algorithm. Our final results read $f_{B^*}/f_B=0.944\pm0.011_{\rm OPE}\pm0.018_{\rm syst}$ and $f_{B_s^*}/f_{B_s}=0.947\pm0.023_{\rm OPE}\pm0.020_{\rm syst}$. Thus, both $f_{B^*}/f_B$ and $f_{B_s^*}/f_{B_s}$ are less than unity at 2.5$\sigma$ and 2$\sigma$ level, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: We study matrix elements of the "chromomagnetic" operator on the lattice. This operator is contained in the strangenesschanging effective Hamiltonian which describes electroweak effects in the Standard Model and beyond. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with other operators of equal and lower dimensionality, including also non gauge invariant quantities; it is thus quite a challenge to extract from lattice simulations a clear signal for the hadronic matrix elements of this operator. We compute all relevant mixing coefficients to one loop in lattice perturbation theory; this necessitates calculating both 2point (quarkantiquark) and 3point (gluonquarkantiquark) Green's functions at nonzero quark masses. We use the twisted mass lattice formulation, with Symanzik improved gluon action. We also provide a nonperturbative method to compute mixing with lower dimensional operators; we use this method in numerical simulations, and extract the mixing with the 3dimensional scalar density, finding good agreement with oneloop results.  [Show abstract] [Hide abstract]
ABSTRACT: The Chromomagnetic operator (CMO) mixes with a large number of operators under renormalization. We identify which operators can mix with the CMO, at the quantum level. Even in dimensional regularization (DR), which has the simplest mixing pattern, the CMO mixes with a total of 9 other operators, forming a basis of dimensionfive, Lorentz scalar operators with the same flavor content as the CMO. Among them, there are also gauge noninvariant operators; these are BRST invariant and vanish by the equations of motion, as required by renormalization theory. On the other hand using a lattice regularization further operators with $d \leq 5$ will mix; choosing the lattice action in a manner as to preserve certain discrete symmetries, a minimul set of 3 additional operators (all with $d<5$) will appear. In order to compute all relevant mixing coefficients, we calculate the quarkantiquark (2pt) and the quarkantiquarkgluon (3pt) Green's functions of the CMO at nonzero quark masses. These calculations were performed in the continuum (dimensional regularization) and on the lattice using the maximally twisted mass fermion action and the Symanzik improved gluon action. In parallel, nonperturbative measurements of the $K\pi$ matrix element are being performed in simulations with 4 dynamical ($N_f = 2+1+1$) twisted mass fermions and the Iwasaki improved gluon action.  [Show abstract] [Hide abstract]
ABSTRACT: We present preliminary results of the first lattice QCD calculation of the K > pi matrix elements of the chromomagnetic operator O_{CM}=g sbar sigma_{munu} G_{munu} d, which appears in the effective Hamiltonian describing Delta S=1 transitions in and beyond the Standard Model. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with operators of equal and lower dimensionality. The multiplicative renormalization factor as well as the mixing coefficients with the operators of equal dimension have been computed at oneloop in perturbation theory. The power divergent coefficients controlling the mixing with operators of lower dimension have been computed nonperturbatively, by imposing suitable subtraction conditions. The numerical simulations have been carried out using the gauge field configurations produced by the European Twisted Mass Collaboration with N_f=2+1+1 dynamical quarks at three values of the lattice spacing. Our preliminary result for the Bparameter of the chromomagnetic operator is B_{CMO}=0.29(11), which can be compared with the estimate B_{CMO}~14 currently used in phenomenological analyses.  [Show abstract] [Hide abstract]
ABSTRACT: We present a lattice QCD calculation of the pseudoscalar decay constants fK, fD and fDs performed using the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks, which include in the sea, besides two light mass degenerate quarks, also the strange and charm quarks with masses close to their values in the real world. The simulations are based on a unitary setup for the two light massdegenerate quarks and on a mixed action approach for the strange and charm quarks. We use data simulated at three different values of the lattice spacing in the range 0.06  0.09 fm and at pion masses in the range 210  450 MeV. Our main results are: fK+ / fpi+ = 1.183 (16), fK+ = 154.3 (2.0) MeV, which incorporate the leading strong isospin breaking correction due to the up and downquark mass difference, and fK = 155.0 (1.9) MeV, fD = 207.4 (3.8) MeV, fDs = 247.2 (4.1) MeV, fDs / fD = 1.192 (22) and (fD_s / fD) / (fK / fpi) = 1.003 (14) obtained in the isospin symmetric limit of QCD. Combined with the experimental measurements of the leptonic decay rates of kaon, pion, D and Dsmesons our results lead to the following determination of the CKM matrix elements: Vus = 0.2271 (29), Vcd = 0.2221 (67) and Vcs = 1.014 (24). Using the latest value of Vud from superallowed nuclear beta decays the unitarity of the first row of the CKM matrix is fulfilled at the permille level.  [Show abstract] [Hide abstract]
ABSTRACT: We present the outcomes of a very recent investigation of the decay constants of nonstrange and strange heavylight beauty vector mesons, with special emphasis on the ratio of any such decay constant to the decay constant of the corresponding pseudoscalar meson, by means of Boreltransformed QCD sum rules. Our results suggest that both these ratios are below unity.  [Show abstract] [Hide abstract]
ABSTRACT: We discuss a lattice QCD computation of the $B$meson decay constants by the ETM collaboration where suitable ratios allow to reach the bottom quark sector by combining simulations around the charmquark mass with an exactly known static limit. The different steps involved in this ratio method are discussed together with an account of the assessment of various systematic effects. A comparison of results from simulations with two and four flavour dynamical quarks is presented.  [Show abstract] [Hide abstract]
ABSTRACT: Updated predictions for the decay constants of the D, Ds, B and Bs mesons obtained from Borel QCD sum rules for heavylight currents are presented and compared with the recent lattice averages performed by the Flavor Lattice Averaging Group. An excellent agreement is obtained in the charm sector, while some tension is observed in the bottom sector. Moreover, available lattice and QCD sumrule calculations of the decay constants of the vector D*, Ds*, B* and Bs* mesons are compared. Again some tension in the bottom sector is observed.  [Show abstract] [Hide abstract]
ABSTRACT: We present a lattice QCD determination of the vector form factor of the kaon semileptonic decay K > pi l nu which is relevant for the extraction of the CKM matrix element V_{us} from experimental data. Our result is based on the gauge configurations produced by the European Twisted Mass Collaboration with N_f=2+1+1 dynamical fermions. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Our preliminary estimate for the vector form factor at zero momentum transfer is f_+(0)=0.9683(65), where the uncertainty is both statistical and systematic. By combining our result with the experimental value of f_+(0)V_{us} we obtain V_{us}=0.2234(16), which satisfies the unitarity constraint of the Standard Model at the permille level.  [Show abstract] [Hide abstract]
ABSTRACT: Within the realm of QCD sum rules, one of the most important areas of application of this nonperturbative approach is the prediction of the decay constants of heavy mesons. However, in spite of the fact that, indisputably, the adopted techniques are, of course, very similar, we encounter rather dissimilar challenges, or obstacles, when extracting from twopoint correlators of appropriate heavylight currents interpolating the mesons, the characteristics of charmed mesons with different spin. In view of this, it seems worthwhile to us to revisit this issue for the case of charmed pseudoscalar mesons $D_{(s)}$ and vector mesons $D^*_{(s)}.$
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5k  Citations  
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Institutions

20072014

Università Degli Studi Roma Tre
 Department of Mathematics and Physics
Roma, Latium, Italy


19842014

INFN  Istituto Nazionale di Fisica Nucleare
 Laboratori Nazionali del Sud LNS
Frascati, Latium, Italy


2010

Moscow State Forest University
Mytishi, Moskovskaya, Russia 
University of Vienna
 Fakultät für Physik
Wien, Vienna, Austria


20032010

University of Rome Tor Vergata
 Dipartimento di Fisica
Roma, Latium, Italy


2009

University of Liverpool
Liverpool, England, United Kingdom


19962004

Università degli Studi di Roma "La Sapienza"
 Department of Physics
Roma, Latium, Italy


2002

Florida International University
 Department of Physics
Miami, Florida, United States


1998

Università degli Studi di Genova
 Department of Physics
Genova, Liguria, Italy


19901991

Università degli Studi di Perugia
 Department of Physics
Perugia, Umbria, Italy


1985

Istituto Superiore di Sanità
Roma, Latium, Italy
