960 research outputs found
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
On the effective action of the vacuum photon splitting in Lorentz-violating QED
We consider one-loop radiative corrections from Lorentz- and CPT- violating
extended QED to address the specific problem of finding explicitly an effective
action describing amplitude of photon triple splitting. We show that it is not
possible to find a nonzero photon triple splitting effective action, at least
by using the derivative expansion method (at zero external momenta), up to
leading order in the Lorentz- and CPT- violating parameter.Comment: 4 pages, version to appear in EP
Os estudos sobre Goa no âmbito do Oceano Índico
Durante décadas, Goa era um assunto esquecido ou marginal nos estudos que procuraram rever a história colonial e mapear os desenvolvimentos da descolonização europeia. Mas, na transição para o século XXI, Goa tornou-se o objecto de estudo de vários projectos de investigação e é temática cada vez mais conhecida. Por quê? E o que se tem concluído de diversos estudos sobre esse pequeno mas intrigante estado? A minha contribuição pretende oferecer uma visão do estado da arte relativa aos estudos sobre Goa, sublinhando as principais conclusões e o interesse dessas mesmas conclusões para os estudos sobre as dinâmicas sociopolíticas e culturais do Oceano Índico. Em segundo lugar, e dada a existência de várias línguas oficiais em Goa (konkani, marata e inglês), qual o lugar da herança cultural portuguesa e qual é o actual enquadramento dos estudos da literatura goesa em língua portuguesa
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.
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