4,453 research outputs found
On the Definition of Gauge Field Operators in Lattice Gauge-Fixed Theories
We address the problem of defining the gauge four-potential on the lattice,
in terms of the natural link variables. Different regularized definitions are
shown, through non perturbative numerical computation, to converge towards the
same continuum renormalized limit.Comment: 8 pages, LaTeX2e/LaTeX209, 3 eps figure
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
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
On the NN-final-state-interaction in the reaction
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in the reaction has been investigated.
Results for various kinematics are discussed. In general, the effect of
NN-FSI depends on kinematics and the chosen final state in the excitation
spectrum of .Comment: 12 pages Revtex including 4 postscript figure
On the treatment of the -contribution in electromagnetic -knockout reactions
The treatment of the -current and its contribution in the exclusive
OC and OC knockout reactions are
investigated in combination with the effects of correlations.
Different parametrizations of the effective -current and different
treatments of correlations in the two-nucleon overlap function are considered.
The results are presented and discussed for a suitable choice of kinematics. It
is found that the investigation of different mutually supplementing kinematics
is necessary to resolve the uncertainties in the theoretical ingredients and
extract clear and unambiguous information on correlations.Comment: 15 pages, 9 figures, EPJA styl
NN correlations and final-state interactions in (e,e'NN) reactions
After a brief overview of relevant studies on one-nucleon knockout showing
the importance of quantitatively understanding the origin of the quenched
spectroscopic factors extracted from data, attention is focussed on two-nucleon
emission as a suitable tool to investigate nucleon-nucleon correlations inside
complex nuclei. In particular, direct (e,epp) and (e,epn) reactions are
discussed, and the role of final-state interactions is studied. The influence
of the mutual interaction between the two outgoing nucleons is shown to depend
on the kinematics and on the type of the considered reaction.Comment: 13 pages, 4 figures. Proceedings of 2nd Int. Conf. on Nuclear and
Particle Physics with CEBAF at Jefferson Lab, Dubrovnik, 26-31 May 2003, to
be published on Fyzika
The NN-final-state-interaction in two-nucleon-knockout reactions
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. In the
kinematics studied so far, the effect is larger in pp- than in pn-knockout and
in electron induced than in photoinduced reactions.Comment: 10 pages including 9 postscript figures, contribution to the 6th
workshop on "Electromagnetically Induced Two-Hadron Emission", Pavia,
September 24-27, 200
On the color structure of Yang-Mills theory with static sources in a periodic box
We present an exploratory numerical study on the lattice of the color
structure of the wave functionals of the SU(3) Yang-Mills theory in the
presence of a static pair. In a spatial box with periodic boundary
conditions we discuss the fact that all states contributing to the Feynman
propagation kernel are global color singlets. We confirm this numerically by
computing the correlations of gauge-fixed Polyakov lines with color-twisted
boundary conditions in the time direction. The values of the lowest energies in
the color singlet and octet external source sectors agree within statistical
errors, confirming that both channels contribute to the lowest (global singlet)
state of the Feynman kernel. We then study the case of homogeneous boundary
conditions in the time direction for which the gauge-fixing is not needed. In
this case the lowest energies extracted in the singlet external source sector
agree with those determined with periodic boundary conditions, while in the
octet sector the correlator is compatible with being null within our
statistical errors. Therefore consistently only the singlet external source
contribution has a non-vanishing overlap with the null-field wave functional.Comment: 9 pages, 3 figure
Nuclear Physics from lattice QCD at strong coupling
We study numerically the strong coupling limit of lattice QCD with one flavor
of massless staggered quarks. We determine the complete phase diagram as a
function of temperature and chemical potential, including a tricritical point.
We clarify the nature of the low temperature dense phase, which is strongly
bound nuclear matter. This strong binding is explained by the nuclear
potential, which we measure. Finally, we determine, from this first-principle
limiting case of QCD, the masses of atomic nuclei up to A=12 "carbon".Comment: 4 pages, 5 figures; v2: references added, minor changes, published
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