455 research outputs found
Time-Dependent Variational Analysis of Josephson Oscillations in a Two-component Bose-Einstein Condensate
The dynamics of Josephson-like oscillations between two coupled Bose-Einstein
condensates is studied using the time-dependent variational method. We suppose
that the quantum state of the condensates is a gaussian wave-packet which can
translate and perform breathing shape oscillations. Under this hypotheses we
study the influence of these degrees of freedom on the tunneling dynamics by
comparing the full-model with one where these degrees of freedom are ``frozen''
at its equilibrium values. The result of our calculation shows that when the
traps are not displaced the two models agree, whereas when they are, the models
differ considerably, the former being now closer to its linear approximation.Comment: 10 pages, 2 figure
Violation of the Ikeda sum rule and the self-consistency in the renormalized quasiparticle random phase approximation and the nuclear double-beta decay
The effect of the inclusion of ground state correlations into the QRPA
equation of motion for the two-neutrino double beta () decay
is carefully analyzed. The resulting model, called renormalized QRPA (RQRPA),
does not collapse near the physical value of the nuclear force strength in the
particle-particle channel, as happens with the ordinary QRPA. Still, the
transition amplitude is only slightly less sensitive on
this parameter in the RQRPA than that in the plain QRPA. It is argued that this
fact reveals once more that the characteristic behaviour of the
transition amplitude within the QRPA is not an artifact of
the model, but a consequence of the partial restoration of the spin-isospin
symmetry. It is shown that the price paid for bypassing the collapse in
the RQRPA is the violation of the Ikeda sum rule.Comment: 16 pages, latex, 3 postscript figure
Self Consistent and Renormalized particle-particle RPA in a Schematic Model
The dynamical effects of ground state correlations for excitation energies
and transition strengths near the superfluid phase transition are studied in
the soluble two level pairing model, in the context of the particle-particle
self consistent Random Phase Approximation (SCRPA). Exact results are well
reproduced across the transition region, beyond the collapse of the standard
particle-particle Random Phase Approximation. The effects of two-body
correlation in the SCRPA are displayed explicitly.Comment: 11 pages, revtex, 3ps figures, to appear in Phys. Rev.
Proton-neutron self-consistent quasiparticle random phase approximation within the o(5) model
15 págs.; 7 figs.; 1 tab.; 1 app. ; PACS number(s): 21.60.Jz, 23.40.Hc, 23.90.1wThe self-consistent quasiparticle random phase approximation (SCQRPA) within the O(5) model in the coupled proton-neutron representation is analyzed. The exact vacuum wave function is used to compute all involved matrix elements. A stability analysis of the stationary points is performed. A phase transition from the uncoupled to the coupled stable proton-neutron regime beyond the QRPA breakdown value of the particle-particle strength is evidenced. The excitation energies are close to the lowest stable exact eigenvalues given by the diagonalization procedure for all cases. The conditions for which the Ikeda sum rule is fulfilled for all values of the particle-particle strength are pointed out. ©2000 American Physical SocietyOne of us (D.S.D.) is grateful for the financial support
given by CNRS during his stay in Grenoble, where the work
was performed.Peer Reviewe
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