1,721,029 research outputs found
First lattice calculation of the electromagnetic operator amplitude (Pi0|Q(+)gamma|K0)
No full textWe present the first lattice calculation of the matrix element of the electromagnetic operator [pi (0)|Q(+)(gamma)|K(0)], where = Q(+)(gamma) = (Q(d)e/16 pi (2))((s) over bar (L)sigma (mu nu) F(mu nu)d(R) + (s) over bar (R)sigma (mu nu) F(mu nu)d(L)) This matrix element plays an important roe, since it contributes to enhance the CP violating part of the K-L --> pi (0)e(+)e(-) amplitude in supersymmetric extensions of the Standard Model
Estimate of the chiral condensate in quenched lattice QCD
No full textWe determine the value of the quark condensate from quenched QCD simulations on the lattice in two ways: (i) by using the Gell-Mann-Oakes-Renner (GMOR) formula; (ii) by comparing the OPE prediction for the Goldstone pole contribution to the pseudoscalar vertex, at moderately large momenta. In the MS scheme at mu = 2 GeV, from the GMOR formula we obtain (qq) = - (273 +/- 19 MeV)(3). We show that the value extracted from the pseudoscalar vertex, (qq) (312 +/- 24 MeV)(3), although larger, is consistent with the result obtained from the first (standard) method. (C) 2004 Published by Elsevier B.V
Continuum determination of light quark masses from quenched lattice QCD
No full textWe compute the strange and the average up/down quark masses in the quenched approximation of lattice QCD, by using the O(a)-improved Wilson action and operators and implementing the non-perturbative renormalization. Our computation is performed at four values of the lattice spacing, from which we could extrapolate to the continuum limit. Our final result for the strange quark mass is m(s)((MS) over bar) (2 GeV) = (106 +/- 2 +/- 8) MeV. For the average up/down quark mass we obtain m(l)((MS) over bar) (2 GeV) = (4.4 +/- 0.1 +/- 0.4) MeV and the ratio m(s)/m(l) = (24.3 +/- 0.2 +/- 0.6)
The role of lattice QCD in flavor physics
Full text linkWe discuss the current status of the QCD simulations on the lattice and outline the perspectives for precision computation of hadronic quantities relevant to flavor physics phenomenology. High precision results, that have been recently obtained on the lattice for selected quantities, such as the kaon decay constant and the K-l3 form factor, demonstrated the feasibility of a precision comparison between theory and experiment in the kaon sector. A similar level of accuracy has not yet been reached in the D-(s)- and B-(s)-meson decays, but the existing methodology, as well as increased computing resources, allow for substantial improvement in the near future. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved
Coupling of the light vector meson to the vector and to the tensor current
No full textWe present results for the coupling of the light vector mesons to the tensor current, relative to the standard vector meson decay constants. From an O(a)-improved lattice study, performed at three values of the lattice spacing in the quenched approximation, our final values (in the continuum limit), in the (MS) over bar scheme at mu = 2 GeV, are: f(rho)(T)/f(rho) = 0.72(2)((+2)(-0)), f(K)(T)*/f(K)* = 0.74(2), f(phi)(T)/ f(phi) = 0.76(1)
Lepton flavor violating decays of vector quarkonia and of the Z boson
No full textWe address the impact of sterile fermions on the lepton flavor violating decays of quarkonia as well as of the Z boson. We compute the relevant Wilson coefficients and show that the B(V→αβ), where V=φ,ψ(n),(n),Z can be significantly enhanced in the case of large sterile fermion masses and a non-negligible active-sterile mixing. We illustrate that feature in a specific minimal realization of the inverse seesaw mechanism, known as (2, 3)-ISS, and in an effective model in which the presence of nonstandard sterile fermions is parametrized by means of one heavy sterile (Majorana) neutrino
Charm quark mass
No full textWe report on the result for the charm quark mass as obtained from our lattice QCD computation in the quenched approximation. Our result is m(c)((MS) over bar)(m(c)) = 1.26(4) (12) GeV
Heavy to light vector meson semileptonic decays
No full textNew (preliminary) results for the form factors relevant for the semileptonic decays of heavy pseudoscalar to a light vector meson are presented. In particular, we discuss the form factors for D → K* and B → π modes
Semileptonic D-decays with twisted mass QCD on the lattice
No full textWe study matrix elements of the "chromomagnetic" operator on the lattice. This operator is contained in the strangeness-changing 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 2-point (quark-antiquark) and 3-point (gluon-quark-antiquark) Green's functions at nonzero quark masses. We use the twisted mass lattice formulation, with Symanzik improved gluon action. For a comprehensive presentation of our results, along with detailed explanations and a more complete list of references, we refer to our forthcoming publication [1]
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