31 research outputs found
"Super-radiance" and the width of exotic baryons
It is suggested that the narrow width of the recently observed resonance
with strangeness could be a result of the
super-radiance mechanism of the redistribution of the widths of overlapping
resonances due to their coupling through common decay channels.Comment: This is an update of the original version submitted on October 08,
2003; it includes consideration of an additional model and one new figur
Manifestation of three-body forces in f7/2-shell nuclei
The traditional nuclear shell model approach is extended to include many-body
forces. The empirical Hamiltonian with a three-body force is constructed for
the identical nucleons on the 0f7/2 shell. Manifestations of the three-body
force in spectra, binding energies, seniority mixing, particle-hole symmetry,
electromagnetic and particle transition rates are investigated. It is shown
that in addition to the usual expansion of the valence space within the
tranditional two-body shell model, the three-body component in the Hamiltonian
can be an important part improving the quality of the theoretical approach.Comment: 5 pages, 1 figur
Nuclear pairing: new perspectives
Nuclear pairing correlations are known to play an important role in various
single-particle and collective aspects of nuclear structure. After the first
idea by A. Bohr, B. Mottelson and D. Pines on similarity of nuclear pairing to
electron superconductivity, S.T. Belyaev gave a thorough analysis of the
manifestations of pairing in complex nuclei. The current revival of interest in
nuclear pairing is connected to the shift of modern nuclear physics towards
nuclei far from stability; many loosely bound nuclei are particle-stable only
due to the pairing. The theoretical methods borrowed from macroscopic
superconductivity turn out to be insufficient for finite systems as nuclei, in
particular for the cases of weak pairing and proximity of continuum states. We
suggest a simple numerical procedure of exact solution of the nuclear pairing
problem and discuss the physical features of this complete solution. We show
also how the continuum states can be naturally included in the consideration
bridging the gap between the structure and reactions. The path from coherent
pairing to chaos and thermalization and perspectives of new theoretical
approaches based on the full solution of pairing are discussed.Comment: 47 pages, 11 figure
Chaotic wave functions and exponential convergence of low-lying energy eigenvalues
We suggest that low-lying eigenvalues of realistic quantum many-body
hamiltonians, given, as in the nuclear shell model, by large matrices, can be
calculated, instead of the full diagonalization, by the diagonalization of
small truncated matrices with the exponential extrapolation of the results. We
show numerical data confirming this conjecture. We argue that the exponential
convergence in an appropriate basis may be a generic feature of complicated
("chaotic") systems where the wave functions are localized in this basis.Comment: 4 figure