644 research outputs found
Evidence for eta prime - pion splitting in unquenched lattice QCD
We perform an extrapolation from negative to positive flavour numbers of full
QCD lattice estimates of the mass. The extrapolations are carried out
by keeping and masses at fixed values. We find an --
splitting which shows a flavour dependence consistent with the Witten Veneziano
formula based on the anomaly. The quantitative splitting is consistent
with the estimates made in the quenched approximation.Comment: 22 pages, uuencoded latex files, text + 8 figure
Universal behaviour of the SU(2) running coupling constant in the continuum limit
We present data from the ALPHA Collaboration about lattice calculation of
SU(2) pure--gauge running coupling constant, obtained with two different
definitions of the coupling itself, which show universality of the continuum
limit and clarify the applicability of renormalized perturbation theory.Comment: 3 pages, postscript, contribution to LAT94 also available at
http://sutova.roma2.infn.it/preprints/TovApe/lat94m.ps (eq. (3) corrected
Pseudofermion observables for static heavy meson decay constants on the lattice
A method based on the Monte Carlo inversion of the Dirac operator on the
lattice provides low noise results for the correlations entering the definition
of the heavy meson decay constant in the static limit. The method is
complementary to the usual method of smeared sources, avoids the systematic
error arising from optimizing the size of the smearing volume and is more
efficient for the values of lattice parameters that we have explored.Comment: 11 pages, uuencoded ps file, 2 figures include
Non-perturbative renormalization constants on the lattice from flavour non-singlet Ward identities
By imposing axial and vector Ward identities for flavour-non-singlet
currents, we estimate in the quenched approximation the non-perturbative values
of combinations of improvement coefficients, which appear in the expansion
around the massless case of the renormalization constants of axial,
pseudoscalar, vector, scalar non-singlet currents and of the renormalized mass.
These coefficients are relevant for the completion of the improvement
programme to O(a) of such operators.
The simulations are performed with a clover Wilson action non-perturbatively
improved.Comment: 9 pages, latex file + 4 eps files of figure
On the extraction of zero momentum form factors on the lattice
We propose a method to expand correlation functions with respect to the
spatial components of external momenta. From the coefficients of the expansion
it is possible to extract Lorentz-invariant form factors at zero spatial
momentum transfer avoiding model dependent extrapolations. These objects can be
profitably calculated on the lattice. We have explicitly checked the validity
of the proposed procedure by considering two-point correlators with insertions
of the axial current, the form factors of the semileptonic decay of
pseudoscalar mesons, and the hadronic vacuum polarization tensor entering, for
example, the lattice calculation of the anomalous magnetic moment of the muon.Comment: 10 pages, 5 figures, published versio
Light meson decay constants beyond the quenched approximation
We calculate the effects of including dynamical fermion loops in the lattice
QCD estimates of meson decay constants, by extrapolating the results from
negative flavour numbers after a suitable matching of the pion and rho mass.
For moderately light quarks, the values of the decay constants not corrected
for the renormalization constants increase with respect to their quenched
values.Comment: 9 pages, uuencoded PS file, 2 figures include
Quenched lattice calculation of the B --> D l nu decay rate
We calculate, in the continuum limit of quenched lattice QCD, the form factor
that enters in the decay rate of the semileptonic decay B --> D l nu. Making
use of the step scaling method (SSM), previously introduced to handle two scale
problems in lattice QCD, and of flavour twisted boundary conditions we extract
G(w) at finite momentum transfer and at the physical values of the heavy quark
masses. Our results can be used in order to extract the CKM matrix element Vcb
by the experimental decay rate without model dependent extrapolations.Comment: 5 pages, 4 figures, accepted for publication on Phys. Lett. B,
corrected one typ
Impact of floats on water
The impact of a wedge-shaped body on the free surface of a weightless
inviscid incompressible liquid is considered. Both symmetrical and
unsymmetrical entries at constant velocity are dealt with. The differential
problem corresponds to the physico-mathematical model of a distribution of
potential singularities and, in particular, the flow singularities at the ends
of the wetted regions are represented by sinks. A conformal transformation of
the flow field is adopted and the unknown intensities of the discontinuities
are found by an optimization procedure, together with the solution of the
nonlinear free-surface problem. The flow separation at a sideslip is also
considered.Comment: 26 pages, 10 figure
Hadronic Decays of Excited Heavy Mesons
We studied the hadronic decays of excited states of heavy mesons (D, D_s, B
and B_s) to lighter states by emission of pi, eta or K. Wavefunctions and
energy levels of these excited states are determined using a Dirac equation for
the light quark in the potential generated by the heavy quark (including first
order corrections in the heavy quark expansion). Transition amplitudes are
computed in the context of the Heavy Chiral Quark Model.Comment: 4 pages (incl. figures), proceedings of the IV International
Conference on "Hyperons, Charm and Beauty Hadrons", Valencia (Spain
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