11,906 research outputs found
Toward an Ab-initio Description of Quasiparticle Properties
Preliminary ab-initio applications of many-body Green's functions theory to
the ground state of He-4 suggest that high accuracy can be achieved in the
so-called Faddeev-random-phase-approximation method.
We stress the potentialities of this approach for microscopic studies of
medium-large nuclei and report applications to 1s0d and 1p0f-shell nuclei. In
particular, we discuss the role of long-range correlations on spectroscopic
factors and their dependence on asymmetry.Comment: Minor corrections and references added -- Proceedings of the Varenna
conference, June 15-19, 200
Many-body Propagator Theory with Three-Body Interactions: a Path to Exotic Open Shell Isotopes
Ab-initio predictions of nuclei with masses up to A~100 or more is becoming
possible thanks to novel advances in computations and in the formalism of
many-body physics. Some of the most fundamental issues include how to deal with
many-nucleon interactions, how to calculate degenerate--open shell--systems,
and pursuing ab-initio approaches to reaction theory. Self-consistent Green's
function (SCGF) theory is a natural approach to address these challenges. Its
formalism has recently been extended to three- and many-body interactions and
reformulated within the Gorkov framework to reach semi-magic open shell
isotopes. These exciting developments, together with the predictive power of
chiral nuclear Hamiltonians, are opening the path to understanding large
portions of the nuclear chart, especially within the and shells. The
present talk reviews the most recent advances in ab-initio nuclear structure
and many-body theory that have been possible through the SCGF approach.Comment: 17 pages, 11 figures; Proceeding of the 17th International Conference
on Recent Progress in Many-Body-Theories; Journal of Physics: Conference
Series (JPCS). Very minor corrections, published versio
Study of the 16O(p,gamma) Reaction at Astrophysical Energies
The Feshbach theory of the optical potential naturally leads to a microscopic
description of scattering in terms of the many-body self-energy. We consider a
recent calculation of this quantity for 16O and study the possibility of
applying it at astrophysical energies. The results obtained for the phase
shifts and the 16O(p,\gamma) capture suggest that such studies are feasible but
the calculations require some improvement geared to this specific task.Comment: 4 pages, 3 figures; Proceedings of Nuclei In The Cosmos VIII, to
appear in Nucl. Phys.
Effects of Rescattering in (e,e'p) Reactions within a Semiclassical Model
The contribution of rescattering to final state interactions in (e,e'p) cross
sections is studied for medium and high missing energies using a semiclassical
model. This approach considers two-step processes that lead to the emission of
both nucleons.
The effects of nuclear transparency are accounted for in a Glauber inspired
approach and the dispersion effects of the medium at low energies are included.
It is found that rescattering is strongly reduced in parallel kinematics.
At high missing energy and momenta, the distortion of the short-range
correlated tail of the spectral function is dominated by a rearrangement of
that strength itself. In perpendicular kinematics, a further enhancement of the
experimental yield is due to strength that is originally in the mean field
region.
This contribution becomes negligible at large missing momenta.Comment: 10 pages, 9 figures. Minor corrections: improved figures and few
comments adde
Nuclear electromagnetic dipole response with the Self-Consistent Green's Function formalism
Microscopic calculations of the electromagnetic response of medium-mass
nuclei are now feasible thanks to the availability of realistic nuclear
interactions with accurate saturation and spectroscopic properties, and the
development of large-scale computing methods for many-body physics. The purpose
is to compute isovector dipole electromagnetic (E1) response and related
quantities, i.e. integrated dipole cross section and polarizability, and
compare with data from photoabsorption and Coulomb excitation experiments. The
single-particle propagator is obtained by solving the Dyson equation, where the
self-energy includes correlations non-perturbatively through the Algebraic
Diagrammatic Construction (ADC) method. The particle-hole () polarization
propagator is treated in the Dressed Random Phase Approximation (DRPA), based
on an effective correlated propagator that includes some effects but
keeps the same computation scaling as the standard Hartree-Fock propagator. The
E1 responses for O, Ca and Ni have
been computed: the presence of a soft dipole mode of excitation for
neutron-rich nuclei is found, and there is a fair reproduction of the
low-energy part of the experimental excitation spectrum. This is reflected in a
good agreement with the empirical dipole polarizability values. For a realistic
interaction with an accurate reproduction of masses and radii up to medium-mass
nuclei, the Self-Consistent Green's Function method provides a good description
of the E1 response, especially in the part of the excitation spectrum below the
Giant Dipole Resonance. The dipole polarizability is largely independent from
the strategy of mapping the dressed propagator to a simplified one that is
computationally manageableComment: 14 pages, 12 figure
3C 345: the historical light curve (1967-1990) from the digitized plates of the Asiago Observatory
In the frame of a large project to digitize the plate archives of the Italian
and Vatican Astronomical Observatories, we have already performed the
digitization of all available plates of the field of the quasar 3C345. The
plates, approximately 100, were taken with the three telescopes of the Asiago
Observatory (122 cm, 182 cm, 67/90 cm Schmidt Telescope) in the period from
1967 to 1990. We present here essentially new data, mostly in the B band, about
the variability of 3C 345 and also of other four objects (3 quasars and the
active galaxy NGC 6212) in the same field, in that period. Beyond the well
known 3C 345 itself, also the other three quasars show variability, with a
range of 2.0 mag for Q1 and Q2, 1 mag for Q3. The low level variability
detected for the nucleus of NGC 6212 is more suspicious, and should be
confirmed by linear detector data.Comment: 8 pages, 9 figures, 7 tables, submitted to MNRA
Self-consistent Green's function calculation of 16O at small missing energies
Calculations of the one-hole spectral function of 16O for small missing
energies are reviewed.
The self-consistent Green's function approach is employed together with the
Faddeev equations technique in order to study the coupling of both
particle-particle and particle-hole phonons to the single-particle motion. The
results indicate that the characteristics of hole fragmentation are related to
the low-lying states of 16O and an improvement of the description of this
spectrum, beyond the random phase approximation, is required to understand the
experimental strength distribution.
A first calculation in this direction that accounts for two-phonon states is
discussed.Comment: Proceedings of ``Nuclear Forces and the Quantum Many-Body Problem'',
INT, Oct. 4-8, 200
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