628 research outputs found
Predicitions for high-energy real and virtual photon-photon scattering from color dipole BFKL-Regge factorization
High-energy virtual photon-virtual photon scattering can be viewed as
interaction of small size color dipoles from the beam and target photons, which
makes scattering at high energies
(LEP, LEP200 & NLC) an indispensable probe of short distance properties of the
QCD pomeron exchange. Based on the color dipole representation, we investigate
consequences for the scattering of the
incorporation of asymptotic freedom into the BFKL equation which makes the QCD
pomeron a series of isolated poles in the angular momentum plane. The emerging
color dipole BFKL-Regge factorization allows us to relate in a
model-independent way the contributions of each BFKL pole to
scattering and DIS off protons.
Numerical predictions based on our early works on color dipole BFKL
phenomenology of DIS on protons are in a good agreement with the experimental
data on the photon structure function and most recent data on the
cross section from OPAL and
L3 experiments at LEP200.
We discuss the role of non-perturbative dynamics and predict pronounced
effect of the Regge-factorization breaking due to large unfactorizable
non-perturbative corrections to the perturbative vacuum exchange. We comment on
the salient features of the BFKL-Regge expansion for
scattering including the issue of
decoupling of subleading BFKL poles and the soft plus rightmost hard BFKL pole
dominance .Comment: 16 pages, 10 figures; treatment of the soft component is modified,
one more figure with the description of the recent data from OPAL is added.
The version to appear in Eur. Phys. J.
Optimizing phonon space in the phonon-coupling model
We present a new scheme to select the most relevant phonons in the
phonon-coupling model, named here time-blocking approximation (TBA). The new
criterion, based on the phonon-nucleon coupling strengths rather than on
values, is more selective and thus produces much smaller phonon spaces
in TBA. This is beneficial in two respects: first, it curbs down the
computational cost, and second, it reduces the danger of double counting in the
expansion basis of TBA. We use here TBA in a form where the coupling strength
is regularized to keep the given Hartree-Fock ground state stable. The scheme
is implemented in an RPA and TBA code based on the Skyrme energy functional. We
first explore carefully the cutoff dependence with the new criterion and can
work out a natural (optimal) cutoff parameter. Then we use the freshly
developed and tested scheme to a survey of giant resonances and low-lying
collective states in six doubly magic nuclei looking also on the dependence of
the results when varying the Skyrme parametrization.Comment: 9 figures, 3 table
Self-consistency in the phonon space of the particle-phonon coupling model
In the paper the non-linear generalization of the time blocking approximation
(TBA) is presented. The TBA is one of the versions of the extended random-phase
approximation (RPA) developed within the Green-function method and the
particle-phonon coupling model. In the generalized version of the TBA the
self-consistency principle is extended onto the phonon space of the model. The
numerical examples show that this non-linear version of the TBA leads to the
convergence of the results with respect to enlarging the phonon space of the
model.Comment: 12 pages, 10 figures, 1 tabl
Landau-Migdal vs. Skyrme
The magnitude and density-dependence of the non-spin dependent Landau-Migdal
parameters are derived from Skyrme energy functionals and compared with the
phenomenological ones. We perform RPA calculations with various approximations
for the Landau-Migdal particle-hole interaction and compare them with the
results obtained with the full Skyrme interaction. For the first time the next
to leading order in the Landau-Migdal approach is considered in nuclear
structure calculations.Comment: Dedicated to the memory of G.E. Brow
Phonon coupling effects in magnetic moments of magic and semi-magic nuclei
Phonon coupling (PC) corrections to magnetic moments of odd neighbors of
magic and semi-magic nuclei are analyzed within the self-consistent Theory of
Finite Fermi Systems (TFFS) based on the Energy Density Functional by Fayans et
al. The perturbation theory in g_L^2 is used where g_L is the phonon-particle
coupling vertex. A model is developed with separating non-regular PC
contributions, the rest is supposed to be regular and included into the
standard TFFS parameters. An ansatz is proposed to take into account the
so-called tadpole term which ensures the total angular momentum conservation
with g_L^2 accuracy. An approximate method is suggested to take into account
higher order terms in g_L^2. Calculations are carried out for four odd-proton
chains, the odd Tl, Bi, In and Sb ones. Different PC corrections strongly
cancel each other. In the result, the total PC correction to the magnetic
moment in magic nuclei is, as a rule, negligible. In non-magic nuclei
considered it is noticeable and, with only one exception, negative. On average
it is of the order of -(0.1 - 0.5) \mu_N and improves the agreement of the
theory with the data. Simultaneously we calculated the gyromagnetic ratio
g_L^{ph} of all low-lying phonons in 208Pb. For the 3^-_1 state it is rather
close to the Bohr-Mottelson model prediction whereas for other L-phonons, two
5^- and six positive parity states, the difference from the Bohr-Mottelson
values is significant.Comment: 21 pages, 24 figure
Self-consistent calculations within the Green's function method including particle-phonon coupling and the single-particle continuum
The Green's function method in the \emph{Quasiparticle Time Blocking
Approximation} is applied to nuclear excitations in Sn and Pb.
The calculations are performed self-consistently using a Skyrme interaction.
The method combines the conventional RPA with an exact single-particle
continuum treatment and considers in a consistent way the particle-phonon
coupling. We reproduce not only the experimental values of low- and high-lying
collective states but we also obtain fair agreement with the data of
non-collective low-lying states that are strongly influenced by the
particle-phonon coupling.Comment: 6 pages, 9 figures, documentclass{svjour
Microscopic description of the pygmy and giant electric dipole resonances in stable Ca isotopes
The properties of the pygmy (PDR) and giant dipole resonance (GDR)in the
stable , and isotopes have been calculated within
the \emph{Extended Theory of Finite Fermi Systems}(ETFFS). This approach is
based on the random phase approximation (RPA) and includes the single particle
continuum as well as the coupling to low-lying collectives states which are
considered in a consistent microscopic way. For we also include
pairing correlations. We obtain good agreement with the experimental data for
the gross properties of both resonances. It is demonstrated that the recently
measured A-dependence of the strength of the PDR below 10 MeV is well
understood in our model:due to the phonon coupling some of the strength in
is simply shifted beyond 10 MeV. The predicted fragmentation of the
PDR can be investigated in and experiments.
Whereas the isovector dipole strength of the PDR is small in all Ca isotopes,
we find in this region surprisingly strong isoscalar dipole states, in
agreement with an experiment. We conclude that for the
detailed understanding of the structure of excited nuclei e.g. the PDR and GDR
an approach like the present one is absolutely necessary.Comment: 6 figure
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