457 research outputs found
Isgur-Wise form factors of heavy baryons within a light-front constituent quark model
The space-like elastic form factors of baryons containing a heavy quark are
investigated within a light-front constituent quark model in the limit of
infinite heavy-quark mass, adopting a gaussian-like ansatz for the three-quark
wave function. The results obtained for the Isgur-Wise form factors
corresponding both to a spin-0 and a spin-1 light spectator pair are presented.
It is found that the Isgur-Wise functions depend strongly on the baryon
structure, being sharply different in case of diquark-like or collinear-type
configurations in the three-quark system. It is also shown that the
relativistic effects lead to a saturation property of the form factors as a
function of the baryon size. Our results are compared with those of different
models as well as with recent predictions from QCD sum rules and lattice QCD
simulations; the latter ones seem to suggest the dominance of collinear-type
configurations, in which the heavy-quark is sitting close to the center-of-mass
of the light quark pair.Comment: latex, 15 pp., 6 figures with epsfig.st
The light-quark contribution to the leading HVP term of the muon from twisted-mass fermions
We present a lattice calculation of the leading Hadronic Vacuum Polarization
(HVP) contribution of the light u- and d-quarks to the anomalous magnetic
moment of the muon, , adopting the gauge configurations
generated by the European Twisted Mass Collaboration with
dynamical quarks at three values of the lattice spacing with pion masses in the
range 210 - 450 MeV. Thanks to several lattices at fixed values of the
light-quark mass and scale but with different sizes we perform a careful
investigation of finite-volume effects (FVEs). In order to remove FVEs we
develop an analytic representation of the vector correlator, which describes
the lattice data for time distances larger than fm. The
representation is based on quark-hadron duality at small and intermediate time
distances and on the two-pion contributions in a finite box at larger time
distances. After extrapolation to the physical pion point and to the continuum
limit we obtain . Adding the
contribution of strange and charm quarks, obtained by ETMC, and an estimate of
the isospin-breaking corrections and quark-disconnected diagrams from the
literature we get , which is
consistent with recent results based on dispersive analyses of the experimental
cross section data for annihilation into hadrons. Using our analytic
representation of the vector correlator, taken at the physical pion mass in the
continuum and infinite volume limits, we provide the first eleven moments of
the polarization function and we compare them with recent results of the
dispersive analysis of the channels. We estimate also the
light-quark contribution to the missing part of not covered
in the MUonE experiment.Comment: 34 pages, 20 figures, 7 tables. Version to appear in PR
Electromagnetic and strong isospin-breaking corrections to the muon from Lattice QCD+QED
We present a lattice calculation of the leading-order electromagnetic and
strong isospin-breaking corrections to the hadronic vacuum polarization (HVP)
contribution to the anomalous magnetic moment of the muon. We employ the gauge
configurations generated by the European Twisted Mass Collaboration (ETMC) with
dynamical quarks at three values of the lattice spacing ( fm) with pion masses between and
MeV. The results are obtained adopting the RM123 approach in the
quenched-QED approximation, which neglects the charges of the sea quarks. Quark
disconnected diagrams are not included. After the extrapolations to the
physical pion mass and to the continuum and infinite-volume limits the
contributions of the light, strange and charm quarks are respectively equal to
, and . At leading order in and we obtain , which is currently the most accurate determination of the
isospin-breaking corrections to .Comment: 23 pages, 7 figures, 5 tables. Version to appear in PRD. A bug in the
update of the strange and charm contributions is removed and an extended
discussion on the identification of the ground-state is included. arXiv admin
note: text overlap with arXiv:1808.00887, arXiv:1707.0301
Lattice study of semileptonic form factors with twisted boundary conditions
We apply twisted boundary conditions to lattice QCD simulations of
three-point correlation functions in order to access spatial components of
hadronic momenta different from the integer multiples of 2 pi / L. We calculate
the vector and scalar form factors relevant to the K -> pi semileptonic decay
and consider all the possible ways of twisting one of the quark lines in the
three-point functions. We show that the momentum shift produced by the twisted
boundary conditions does not introduce any additional noise and easily allows
to determine within a few percent statistical accuracy the form factors at
quite small values of the four-momentum transfer, which are not accessible when
periodic boundary conditions are considered. The use of twisted boundary
conditions turns out to be crucial for a precise determination of the form
factor at zero-momentum transfer, when a precise lattice point sufficiently
close to zero-momentum transfer is not accessible with periodic boundary
conditions.Comment: latex 15 pages, 4 figures and 3 tables; modified intro and
discussions of the results; version to appear in PR
The nucleon Drell-Hearn-Gerasimov sum rule within a relativistic constituent quark model
The Drell-Hearn-Gerasimov sum rule for the nucleon is investigated within a relativistic constituent quark model formulated on the light-front. The contribution of the N - Delta(1232) transition is explicitly evaluated using different forms for the baryon wave functions and adopting a one-body relativistic current for the constituent quarks. It is shown that the N - Delta(1232) contribution to the sum rule is sharply sensitive to the introduction of anomalous magnetic moments for the constituent quarks, at variance with the findings of non-relativistic and relativized quark models. The experimental value of the isovector-isovector part of the sum rule is almost totally reproduced by the N - Delta(1232) contribution, when the values of the quark anomalous magnetic moments are fixed by fitting the experimental nucleon magnetic moments. Our results are almost independent of the adopted form of the baryon wave functions and only slightly sensitive to the violation of the angular condition caused by the use of a one-body current. The calculated average slope of the generalized sum rule around the photon point results to be only slightly negative at variance with recent predictions of relativized quark models
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