217 research outputs found
Effect of P-wave interaction in 6He and 6Li photoabsorption
The total photoabsorption cross sections of six-body nuclei are calculated
including complete final state interaction via the Lorentz Integral Transform
method. The effect of nucleon-nucleon central P-wave forces is investigated.
Comparing to results with central potentials containg S-wave forces only one
finds considerably more strength in the low-energy cross sections and a rather
strong improvement in comparison with experimental data, in particular for 6Li.Comment: 11 pages with 4 figure
Longitudinal response function of 4He with a realistic force
The longitudinal response function of 4He is calculated with the Argonne V18
potential. The comparison with experiment suggests the need of a three-body
force. When adding the Urbana IX three-body potential in the calculation of the
lower longitudinal multipoles, the total strength is suppressed in the
quasi-elastic peak, towards the trend of the experimental data.Comment: 3 pages, 3 figures, proceedings of the 20th European Conference on
Few-Body Problems in Physics (EFB20
Electromagnetic break-up of nuclei with A = 3 - 7
This talk contains a short review of some of the progresses made in the last
three years in the calculations of electromagnetic cross sections of light
nuclei up to A=7. Since many of them have been possible thanks to the use of
the Lorentz Integral Transform (LIT) method, both for inclusive and exclusive
reactions, I will first make a few remarks on the method, stressing its
essential points and then show results for different nuclei. One of the
interesting outcomes is e.g. the appearing of typical collective motion
features from ab initio six-body calculations. When a comparison with available
experimental data is attempted, it is rather disappointing to realize that
low-energy data are old, incomplete and not accurate enough to disantangle
interesting effects, showing the need of a major experimental program in this
direction, together with more theoretical efforts to implement modern realistic
forces in continuum calculations of systems.Comment: 4 pages, 7 figures, invited talk at the FB17 - Durham (N.C) June 5-10
200
Effects of three-nucleon forces and two-body currents on Gamow-Teller strengths
We optimize chiral interactions at next-to-next-to leading order to
observables in two- and three-nucleon systems, and compute Gamow-Teller
transitions in carbon-14, oxygen-22 and oxygen-24 using consistent two-body
currents. We compute spectra of the daughter nuclei nitrogen-14, fluorine-22
and fluorine-24 via an isospin-breaking coupled-cluster technique, with several
predictions. The two-body currents reduce the Ikeda sum rule, corresponding to
a quenching factor q^2 ~ 0.84-0.92 of the axial-vector coupling. The half life
of carbon-14 depends on the energy of the first excited 1+ state, the
three-nucleon force, and the two-body current
Three-body Force Effects on the Longitudinal Response Function of 4He
In this contribution we summarize recent results on the longitudinal response function of 4He. It is intended to give an important contribution to one of the most interesting and much discussed topics in nuclear physics at present, i.e. the nuclear many-body forces. The longitudinal response is considered as a possible observable, involving many body scattering states, sensitive to the three-nucleon force (3NF). Such a sensitivity is predicted by ab initio calculations performed using the Lorentz Integral transform (LIT) method. The kinematics that are more interesting to measure are discussed
Spectral function for He using the Chebyshev expansion in coupled-cluster theory
We compute spectral function for He by combining coupled-cluster theory
with an expansion of integral transforms into Chebyshev polynomials. Our method
allows to estimate the uncertainty of spectral reconstruction. The properties
of the Chebyshev polynomials make the procedure numerically stable and
considerably lower in memory usage than the typically employed Lanczos
algorithm. We benchmark our predictions with other calculations in the
literature and with electron scattering data in the quasi-elastic peak. The
spectral function formalism allows one to extend ab-initio lepton-nucleus cross
sections into the relativistic regime. This makes it a promising tool for
modeling this process at higher energy transfers. The results we present open
the door for studies of heavier nuclei, important for the neutrino oscillation
programs.Comment: 12 pages, 5 figure
Resonant tunneling in a schematic model
Tunneling of an harmonically bound two-body system through an external
Gaussian barrier is studied in a schematic model which allows for a better
understanding of intricate quantum phenomena. The role of finite size and
internal structure is investigated in a consistent treatment. The excitation of
internal degrees of freedom gives rise to a peaked structure in the penetration
factor. The model results indicate that for soft systems the adiabatic limit is
not necessarily reached although often assumed in fusion of nuclei and in
electron screening effects at astrophysical energies.Comment: 7 pages, 7 figure
The magnetic dipole transition in Ca
The magnetic dipole transition strength of Ca is dominated by
a single resonant state at an excitation energy of 10.23 MeV. Experiments
disagree about and this impacts our understanding of spin flips in
nuclei. We performed ab initio computations based on chiral effective field
theory and found that lies in the range from to
. This is consistent with a experiment but larger
than results from and scattering. Two-body currents
yield no quenching of the strength and continuum effects reduce it by
about 10%. For a validation of our approach, we computed magnetic moments in
Ca and performed benchmark calculations in light nuclei
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