20,128 research outputs found
Quark and Gluon Propagators in Covariant Gauges
We present data for the gluon and quark propagators computed in the standard
lattice Landau's gauge and for three values of the covariant gauge-fixing
parameter lambda=0,8,16. Our results are obtained using the SU(3) Wilson action
in the quenched approximation at beta=6.0 and volume=16^3x32.Comment: Lattice2001(theorydevelop
How To Fix Non-Perturbatively A Parameter Dependent Covariant Gauge On The Lattice
We describe how to overcome some problems that usually prevent from obtaining
an efficient algorithm to fix a generic covariant gauge on the lattice. This
gauge is the lattice equivalent of the generic gauge usually adopted in
perturbative calculations. It depends on a parameter whose value can be varied
in order to check the gauge dependence of measured matrix elements.Comment: 3 pages, 2 eps figures, LATTICE 9
Electromagnetic proton-neutron knockout off 16O: new achievements in theory
Results for the cross sections of the exclusive 16O(e,e'pn)14N and
16O(gamma,pn)14N knockout reactions are presented and discussed in different
kinematics. In comparison with earlier work, a complete treatment of the
center-of-mass (CM) effects in the nuclear one-body current is considered in
connection with the problem of the lack of orthogonality between initial bound
and final scattering states. The effects due to CM and orthogonalization are
investigated in combination with different treatments of correlations in the
two-nucleon overlap function and for different parametrizations of the two-body
currents. The CM effects lead in super-parallel kinematics to a dramatic
increase of the 16O(e,e'pn) cross section to the 1_2^+ excited state (3.95 MeV)
of 14N. In all the situations considered the results are very sensitive to the
treatment of correlations. A crucial role is played by tensor correlations, but
also the contribution of long-range correlations is important.Comment: 13 pages, 10 figure
Numerical Exploration of the RI/MOM Scheme Gauge Dependence
The gauge dependence of some fermion bilinear RI/MOM renormalization
constants is studied by comparing data which have been gauge-fixed in two
different realizations of the Landau gauge and in a generic covariant gauge.
The very good agreement between the various sets of results and the theory
indicates that the numerical uncertainty induced by the lattice gauge-fixing
procedure is below the statistical errors of our data sample which is of the
order of (1-1.5)%.Comment: 3 pages, 2 figures, Lattice2002(theoretical
NN final-state interaction in two-nucleon knockout from
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in electro- and photoinduced two-nucleon knockout from has
been investigated perturbatively. It turns out that the effect of NN-FSI
depends on the kinematics and on the type of reaction considered. The effect is
generally larger in pp- than in pn-knockout and in electron induced than in
photoinduced reactions.
In superparallel kinematics NN-FSI leads in the channel to a
strong increase of the cross section, that is mainly due to a strong
enhancement of the -current contribution. In pn-emission, however, this
effect is partially cancelled by a destructive interference with the seagull
current. For photoreactions NN-FSI is considerably reduced in superparallel
kinematics and can be practically negligible in specific kinematics.Comment: 16 pages, 9 figure
Light dynamical fermions on the lattice: toward the chiral regime of QCD
Algorithmic and technical progress achieved over the last few years makes QCD
simulations with light dynamical quarks much faster than before. As a result
lattices with pions as light as 250--300 MeV can be simulated with the present
generation of computers. I review recent conceptual and numerical progress in
this field, with particular emphasis on results obtained and difficulties
encountered in simulations with significantly smaller quark masses with respect
to previous computations. I also attempt to compare physical results for pion
masses and decay constants available to date in the two-flavour theory with
expectations from chiral perturbation theory.Comment: Plenary talk given at XXIVth International Symposium on Lattice Field
Theory Lattice2006(plenary), Tucson, Arizona, 23-28 July 2006. Submitted to
PoS in October 200
Nucleon-Nucleon Correlations in Electromagnetically Induced Knockout Reactions
The attempts to investigate correlations in electromagnetically induced one-
and two-nucleon knockout are reviewed. The theoretical framework for cross
section calculations is outlined and some results are presented for the
exclusive O(N and O(C reactions. For
the () reaction attention is focussed on extracting the spectroscopic
factors. For the () reaction the possibility of obtaining direct and
clear information on short-range correlations is discussed.Comment: 20 pages, 4 figures, contribution to the XIV International School on
Nuclear Physics, Neutron Physics and Nuclear Energy, Varna, September 25 -30,
200
Nuclear Physics with Electroweak Probes
The research activitities carried out in Italy during the last two years in
the field of theoretical nuclear physics with electroweak probes are reviewed.
Different models for electron-nucleus and neutrino-nucleus scattering are
compared. The results obtained for electromagnetic reactions on few-nucleon
systems and on complex nuclei are discussed. The recent developments in the
study of electron- and photon-induced reactions with one and two-nucleon
emission are presented.Comment: 15 pages, 7 figures, invited talk given at 11th Conference on
Problems in Theoretical Nuclear Physics, Cortona, Italy, 11-14 October 200
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