344 research outputs found
Vector and scalar form factors for K- and D-meson semileptonic decays from twisted mass fermions with Nf = 2
We present lattice results for the form factors relevant in the K -> pion and
D -> pion semileptonic decays, obtained from simulations with two flavors of
dynamical twisted-mass fermions and pion masses as light as 260 MeV. For K ->
pion decays we discuss the estimates of the main sources of systematic
uncertainties, including the quenching of the strange quark, leading to our
final result f+(0) = 0.9560 (57) (62). Combined with the latest experimental
data, our value of f+(0) implies for the CKM matrix element |Vus| the value
0.2267 (5) (20) consistent with the first-row CKM unitarity. For D -> pion
decays the application of Heavy Meson Chiral Perturbation Theory allows to
extrapolate our results for both the scalar and the vector form factors at the
physical point with quite good accuracy, obtaining a nice agreement with the
experimental data. In particular at zero-momentum transfer we obtain f+(0) =
0.64 (5).Comment: 8 pages, 4 figures, 1 table, proceedings of the XXVII Int'l Symposium
on Lattice Field Theory (LAT2009), July 26-31 2009, Peking University,
Beijing (China
Average up/down, strange and charm quark masses with Nf=2 twisted mass lattice QCD
We present a high precision lattice calculation of the average up/down,
strange and charm quark masses performed with Nf=2 twisted mass Wilson
fermions. The analysis includes data at four values of the lattice spacing and
pion masses as low as ~270 MeV, allowing for accurate continuum limit and
chiral extrapolation. The strange and charm masses are extracted by using
several methods, based on different observables: the kaon and the eta_s meson
for the strange quark and the D, D_s and eta_c mesons for the charm. The quark
mass renormalization is carried out non-perturbatively using the RI-MOM method.
The results for the quark masses in the MSbar scheme read: m_ud(2 GeV)= 3.6(2)
MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV. We also obtain the ratios
m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).Comment: 20 pages, 5 figures. Typos corrected in eqs. (15)-(17). Version
published in Phys. Rev.
Quark masses with Nf=2 twisted mass lattice QCD
We present the results of the recent high precision lattice calculation of
the average up/down, strange and charm quark masses performed by ETMC with Nf=2
twisted mass Wilson fermions. The analysis includes data at four values of the
lattice spacing and pion masses as low as ~270 MeV, allowing for accurate
continuum limit and chiral extrapolation. The strange and charm masses are
extracted by using several methods, based on different observables: the kaon
and the eta_s meson for the strange quark and the D, D_s and eta_c mesons for
the charm. The quark mass renormalization is carried out non-perturbatively
using the RI-MOM method. The results for the quark masses in the MSbar scheme
read: m_ud(2 GeV)= 3.6(2) MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV.
We have also obtained the ratios m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).
Moreover, we provide the updated result for the bottom quark mass,
m_b(m_b)=4.3(2) GeV, obtained using the method presented in 0909.3187
[hep-lat].Comment: 7 pages, 7 figures, talk given at the XXVIII International Symposium
on Lattice Field Theory (Lattice 2010), June 14-19 2010, Villasimius, Ital
Matrix elements of the electromagnetic operator between kaon and pion states
We compute the matrix elements of the electromagnetic (EM) operator between
kaon and pion states, using lattice QCD with maximally twisted-mass fermions
and two flavors of dynamical quarks (Nf = 2). The EM operator is renormalized
non-perturbatively in the RI'/MOM scheme and our simulations cover pion masses
as light as 260 MeV and three values of the lattice spacing, ranging from ~
0.07 up to ~ 0.1 fm. At the physical point our preliminary result for the K ->
pion tensor form factor at zero-momentum transfer is fT[K\pi](0) =
0.42(2_stat), which differs significantly from the old quenched result
fT[K\pi](0) = 0.78(6) obtained by the SPQcdR Collaboration with pion masses
above 500 MeV. We investigate the source of this difference and conclude that
it is mainly related to the chiral extrapolation of the quenched data. For the
case of the tensor charge of the pion we obtain the preliminary value
fT[\pi\pi](0) = 0.200(14_stat), which can be compared with the result
fT[\pi\pi](0) = 0.216(34) obtained at Nf = 2 by the QCDSF Collaboration using
higher pion masses.Comment: 7 pages, 5 figures, contribution to the XXVIII International
Symposium on Lattice Field Theory, Lattice2010, June 14-19, 2010,
Villasimius, Ital
Non perturbative renormalization in coordinate space
We present an exploratory study of a gauge-invariant non-perturbative
renormalization technique. The renormalization conditions are imposed on
correlation functions of composite operators in coordinate space on the
lattice. Numerical results for bilinears obtained with overlap and
O(a)-improved Wilson fermions are presented. The measurement of the quark
condensate is also discussed.Comment: Lattice2003(improve), 3 page
Two-loop neutrino masses with large R-parity violating interactions in supersymmetry
We attempt to reconcile large trilinear R-parity violating interactions in a
supersymmetric (SUSY) theory with the observed pattern of neutrino masses and
mixing. We show that, with a restricted number of such interaction terms with
the -type couplings in the range (0.1-1.0), it is possible to forbid
one-loop contributions to the neutrino mass matrix. This is illustrated with
the help of a `working example' where an econnomic choice of SUSY parameters is
made, with three non-vanishing and `large' R-parity violating terms in the
superpotential. The two-loop contributions in such a case can not only generate
the masses in the requisite order but can also lead us to specific allowed
regions of the parameter space.Comment: Revised version, 25 pages, 16 figure
Non-perturbatively Renormalized Light Quark Masses with Two Dynamical Fermions
We present the results of a partially quenched lattice QCD calculation of
light quark masses with degenerate dynamical flavors. Numerical
simulations are carried out using the plaquette gauge action and the Wilson
quark action at (a^{-1} \simeq 3.2\gev). The spatial extension
of the lattice is about 1.5 fm. Configurations have been
generated at four values of the sea quark masses, for which the ratio of
pseudoscalar over vector meson masses is in the range . An important feature of the present study is the use of non-perturbative
renormalization, performed with the \ri method. The effects of dynamical sea
quarks in the determination of light quark masses have been investigated by
performing a quenched calculation on a similar lattice. Our results for the
average up-down and strange quark masses are m_{ud}^{MS} (2\gev) = 4.3(4)
(^{+1.1}_{-0.4})\mev and m_s^{MS}(2\gev)=101(8)(^{+25}_{-9}) \mev. These
values are larger than those obtained by evaluating the quark mass
renormalization constants with one-loop (boosted) perturbation theory. Our
results for the light quark masses are compatible with those obtained in the
quenched simulation. No significant sea quark effects are seen, at the values
of sea quark masses used in the present study.Comment: 6 pages, 1 figure, Proceedings of "Lattice 2005" (Dublin, 25-30 July
2005), updated systematic errors, updated references and clarified
comparisons with previous result
f_B and f_Bs with maximally twisted Wilson fermions
We present a lattice QCD calculation of the heavy-light decay constants f_B
and f_Bs performed with Nf=2 maximally twisted Wilson fermions, at four values
of the lattice spacing. The decay constants have been also computed in the
static limit and the results are used to interpolate the observables between
the charm and the infinite-mass sectors, thus obtaining the value of the decay
constants at the physical b quark mass. Our preliminary results are f_B=191(14)
MeV, f_Bs=243(14) MeV, f_Bs/f_B=1.27(5). They are in good agreement with those
obtained with a novel approach, recently proposed by our Collaboration (ETMC),
based on the use of suitable ratios having an exactly known static limit.Comment: Proceedings of the 27th International Symposium on Lattice Field
Theory (Lattice 2009), Beijing, China, 2009 July 26-31. 8 pages, 3 figure
Non-perturbative renormalization of lattice operators in coordinate space
We present the first numerical implementation of a non-perturbative
renormalization method for lattice operators, based on the study of correlation
functions in coordinate space at short Euclidean distance. The method is
applied to compute the renormalization constants of bilinear quark operators
for the non-perturbative O(a)-improved Wilson action in the quenched
approximation. The matching with perturbative schemes, such as MS-bar, is
computed at the next-to-leading order in continuum perturbation theory. A
feasibility study of this technique with Neuberger fermions is also presented.Comment: 11 pages and 9 figures, LaTeX2
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