6,604 research outputs found
Proton recoil polarization in exclusive (e,e'pp) reactions
The general formalism of nucleon recoil polarization in the () reaction is given. Numerical predictions are presented for the
components of the outgoing proton polarization and of the polarization transfer
coefficient in the specific case of the exclusive O()C knockout reaction leading to discrete states in the residual
nucleus. Reaction calculations are performed in a direct knockout framework
where final-state interactions and one-body and two-body currents are included.
The two-nucleon overlap integrals are obtained from a calculation of the
two-proton spectral function of O where long-range and short-range
correlations are consistently included. The comparison of results obtained in
different kinematics confirms that resolution of different final states in the
O()C reaction may act as a filter to
disentangle and separately investigate the reaction processes due to
short-range correlations and two-body currents and indicates that measurements
of the components of the outgoing proton polarization may offer good
opportunities to study short-range correlations.Comment: 12 pages, 6 figure
Additive and multiplicative renormalization of topological charge with improved gluon/fermion actions: A test case for 3-loop vacuum calculations, using overlap or clover fermions
We calculate perturbative renormalization properties of the topological
charge, using the standard lattice discretization given by a product of twisted
plaquettes. We use the overlap and clover action for fermions, and the Symanzik
improved gluon action for 4- and 6-link loops.
We compute the multiplicative renormalization of the topological charge
density to one loop; this involves only the gluon part of the action. The power
divergent additive renormalization of the topological susceptibility is
calculated to 3 loops.
Our work serves also as a test case of the techniques and limitations of
lattice perturbation theory, it being the first 3-loop computation in the
literature involving overlap fermions.Comment: 15 pages, 7 figures. Final version, accepted in Physical Review
Horizon Quantum Mechanics for spheroidal sources
We start investigating the extension of the Horizon Quantum Mechanics to the
case of spheroidal sources. We first study the location of trapping surfaces in
space-times resulting from an axial deformation of static isotropic systems,
and show that the Misner-Sharp mass evaluated on the corresponding undeformed
spherically symmetric space provides the correct gravitational radius to locate
the horizon. We finally propose a way to determine the deformation parameter in
the quantum theory.Comment: 14 pages, 1 figure, final version to appear in EP
Non-perturbative renormalisation of left-left four-fermion operators with Neuberger fermions
We outline a general strategy for the non-perturbative renormalisation of
composite operators in discretisations based on Neuberger fermions, via a
matching to results obtained with Wilson-type fermions. As an application, we
consider the renormalisation of the four-quark operators entering the Delta S=1
and Delta S=2 effective Hamiltonians. Our results are an essential ingredient
for the determination of the low-energy constants governing non-leptonic kaon
decays.Comment: 14 pages, 3 figure
Neutrino-Nucleus Quasi-Elastic Scattering in a Relativistic Model
A relativistic distorted-wave impulse-approximation model is applied to
neutral-current and charged-current quasi-elastic neutrino-nucleus scattering.
The effects of final state interactions are investigated and the sensitivity of
the results to the strange nucleon form factors is discussed in view of their
possible experimental determinationComment: 7 pages, 3 figures Proc. of the XXV International Workshop on Nuclear
Theory, 26 June- 1 July, 2006 Rila, Bulgari
RI/MOM Renormalization Window and Goldstone Pole Contamination
We perform a comparative study of the ratio of lattice (Wilson fermion)
renormalization constants Z_P/Z_S, obtained non-perturbatively from the RI/MOM
renormalization conditions and from Ward Identities of on- and off-shell
Green's functions. The off-shell Ward Identity used in this work relies on
correlation functions with non-degenerate quark masses. We find that, due to
discretization effects, there is a 10-15% discrepancy between the two Ward
Identity determinations at current bare couplings (beta values). The RI/MOM
result is in the same range and has a similar systematic error of 10-15%. Thus,
contrary to a previous claim, the contamination of the RI/MOM result from the
presence of a Goldstone pole at scales of about 2 GeV is subdominant, compared
to finite cutoff effects.Comment: LATEX, 12 pages final version to appear on Phys. Lett.
Relativistic descriptions of final-state interactions in neutral-current neutrino-nucleus scattering at MiniBooNE kinematics
The analysis of the recent neutral-current neutrino-nucleus scattering cross
sections measured by the MiniBooNE Collaboration requires relativistic
theoretical descriptions also accounting for the role of final state
interactions. In this work we evaluate differential cross sections with the
relativistic distorted-wave impulse-approximation and with the relativistic
Green's function model to investigate the sensitivity to final state
interactions. The role of the strange-quark content of the nucleon form factors
is also discussed.Comment: 8 pages, 5 figure
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
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
Inclusive , , ... reactions in nuclei
We study the inclusive , , , reactions in nuclei using a Monte Carlo simulation
method to treat the multichannel problem of the final state. The input consists
of reaction probabilities for the different steps evaluated using microscopical
many body methods. We obtain a good agreement with experiment in some channels
where there is data and make predictions for other channels which are presently
under investigation in several electron laboratories. The comparison of the
theoretical results with experiment for several kinematical conditions and
diverse channels can serve to learn about different physical processes ocurring
in the reaction. The potential of this theoretical tool to make prospections
for possible experiments, aiming at pinning down certain reaction
probabilities, is also emphasized.Comment: 21 pages (LaTeX + figure files
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