147 research outputs found
Twisted mass QCD and the rule
We show that the application of twisted mass QCD (tmQCD) with four (Wilson)
quark flavours to the computation of lattice weak matrix elements relevant to
transitions has important advantages: the renormalisation of matrix elements does not require the subtraction of other dimension
six operators, the divergence arising from the subtraction of lower dimensional
operators is softened by one power of the lattice spacing and quenched
simulations do not suffer from exceptional configurations at small pion mass.
This last feature is also retained in the tmQCD computation of
matrix elements, which, as far as renormalisation and power subtractions are
concerned, has properties analogous to the standard Wilson case.Comment: Lattice2002(matrixel). Eq.(11) correcte
K* vector and tensor couplings from Nf = 2 tmQCD
The mass m_K* and vector coupling f_K* of the K*-meson, as well as the ratio
of the tensor to vector couplings fT/fV|_K*, are computed in lattice QCD. Our
simulations are performed in a partially quenched setup, with two dynamical
(sea) Wilson quark flavours, having a maximally twisted mass term. Valence
quarks are either of the standard or the Osterwalder-Seiler maximally twisted
variety. Results obtained at three values of the lattice spacing are
extrapolated to the continuum, giving m_K* = 981(33) MeV, f_K* = 240(18) MeV
and fT(2 GeV)/fV|_K* = 0.704(41).Comment: 1+11 page
Quenched Spectroscopy for the N=1 Super-Yang-Mills Theory
We present results for the Quenched SU(2) N=1 Super-Yang-Mills spectrum at
, on a lattice, in the OZI approximation. This is
a first step towards the understanding of the chiral limit of lattice N=1 SUSY.Comment: 3 pages, Latex, 2 ps figures, contribution to Lattice 97, Edinburgh
22-26 July 1997; to appear on Nucl. Phys. B. (Proc. Suppl.
Improved Renormalization of Lattice Operators: A Critical Reappraisal
We systematically examine various proposals which aim at increasing the
accuracy in the determination of the renormalization of two-fermion lattice
operators. We concentrate on three finite quantities which are particularly
suitable for our study: the renormalization constants of the vector and axial
currents and the ratio of the renormalization constants of the scalar and
pseudoscalar densities. We calculate these quantities in boosted perturbation
theory, with several running boosted couplings, at the "optimal" scale q*. We
find that the results of boosted perturbation theory are usually (but not
always) in better agreement with non-perturbative determinations of the
renormalization constants than those obtained with standard perturbation
theory. The finite renormalization constants of two-fermion lattice operators
are also obtained non-perturbatively, using Ward Identities, both with the
Wilson and the tree-level Clover improved actions, at fixed cutoff (=6.4
and 6.0 respectively). In order to amplify finite cutoff effects, the quark
masses (in lattice units) are varied in a large interval 0<am<1. We find that
discretization effects are always large with the Wilson action, despite our
relatively small value of the lattice spacing ( GeV). With
the Clover action discretization errors are significantly reduced at small
quark mass, even though our lattice spacing is larger ( GeV).
However, these errors remain substantial in the heavy quark region. We have
implemented a proposal for reducing O(am) effects, which consists in matching
the lattice quantities to their continuum counterparts in the free theory. We
find that this approach still leaves appreciable, mass dependent,
discretization effects.Comment: 54 pages, Latex, 5 figures. Minor changes in text between eqs.(86)
and (88
Renormalization of HQET operators: O() improvement and matching with QCD
We determine a basis of dimension-7 operators which arise at O() in the
Symanzik expansion of the operators with static heavy quarks. We
consider both Wilson-like and Ginsparg-Wilson light quarks. Exact chiral
symmetry reduces the number of these O() counterterms by a factor of two.
Only a subset of these operators has previously appeared in the literature. We
then extend the analysis to the O() operators contributing beyond the
static approximation.Comment: 7 pages, presented at the 31st International Symposium on Lattice
Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
Quark masses and the chiral condensate with a non-perturbative renormalization procedure
We determine the quark masses and the chiral condensate in the MSbar scheme
at NNLO from Lattice QCD in the quenched approximation at beta=6.0, beta=6.2
and beta=6.4 using both the Wilson and the tree-level improved SW-Clover
fermion action. We extract these quantities using the Vector and the Axial Ward
Identities and non-perturbative values of the renormalization constants. We
compare the results obtained with the two methods and we study the O(a)
dependence of the quark masses for both actions.Comment: LATTICE98(spectrum), 3 pages, 1 figure, Edinburgh 98/1
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