1,577 research outputs found
Dirac sea effects in scattering from nuclei
The ratio of to cross sections has been calculated
microscopically using a boson-exchange amplitude in which the and
mesons are dressed by the modifications of the Dirac sea in nuclear
matter. In spite of the fact that this dressing leads to a scaling of the
mesons effective mass in nuclear matter, the effect on the ratio is found
to be weak.Comment: 8 pages, LaTeX, 2 figures available upon request, LPTB-93-
Gamow-Teller sum rule in relativistic nuclear models
Relativistic corrections are investigated to the Gamow-Teller(GT) sum rule
with respect to the difference between the and transition
strengths in nuclei. Since the sum rule requires the complete set of the
nuclear states, the relativistic corrections come from the anti-nucleon degrees
of freedom. In the relativistic mean field approximation, the total GT
strengths carried by the nucleon sector is quenched by about 12% in nuclear
matter, while by about 8% in finite nuclei, compared to the sum rule value. The
coupling between the particle-hole states with the nucleon-antinucleon states
is also discussed with the relativistic random phase approximation, where the
divergence of the response function is renormalized with use of the counter
terms in the Lagrangian. It is shown that the approximation to neglect the
divergence, like the no-sea approximation extensively used so far, is
unphysical, from the sum-rule point of view.Comment: 12 pages, Brief review for Mod. Phys. Lett. A, using ws-mpla.cl
Role of the Landau-Migdal Parameters with the Pseudovector and the Tensor Coupling in Relativistic Nuclear Models -- The Quenching of the Gamow-Teller Strength --
Role of the Landau-Migdal parameters with the pseudovector () and the
tensor coupling () is examined for the giant Gamow-Teller (GT) states in
the relativistic random phase approximation (RPA). The excitation energy is
dominated by both and in a similar way, while the GT strength is
independent of and in the RPA of the nucleon space, and is
quenched, compared with that in non-relativistic one. The coupling of the
particle-hole states with nucleon-antinucleon states is expected to quench the
GT strength further through .Comment: 7 pages, ReVTe
The Gamow-Teller States in Relativistic Nuclear Models
The Gamow-Teller(GT) states are investigated in relativistic models. The
Landau-Migdal(LM) parameter is introduced in the Lagrangian as a contact term
with the pseudo-vector coupling. In the relativistic model the total GT
strength in the nucleon space is quenched by about 12% in nuclear matter and by
about 6% in finite nuclei, compared with the one of the Ikeda-Fujii-Fujita sum
rule. The quenched amount is taken by nucleon-antinucleon excitations in the
time-like region. Because of the quenching, the relativistic model requires a
larger value of the LM parameter than non-relativistic models in describing the
excitation energy of the GT state. The Pauli blocking terms are not important
for the description of the GT states.Comment: REVTeX4, no figure
Sum Rules of the Multiple Giant Dipole States
Various sum rules for multiple giant dipole resonance states are derived. For
the triple giant dipole resonance states, the energy-weighted sum of the
transition strengths requires a model to be related to those of the single and
double giant dipole resonance states. It is also shown that the non-diagonal
matrix elements of the double commutator between the dipole operator and the
nuclear Hamiltonian give useful identities for the excitation energy and
transition strength of each excited state. Using those identities, the
relationship between width of the single dipole state and those of the multiple
ones is qualitatively discussed.Comment: 8 pages, 1 figure, using PTPTeX styl
Optimalâ Inflation Under Dollarization
This paper analyzes the effects of dollarization, where a country (C) uses money produced by another country (M). We derive a general formula to determine the optimal rate of inflation, which maximizes M\u27s welfare but does not take into account any loss to C. We show how this inflation varies with relative income size and output growth. Estimates of the optimal inflation rate are made for some countries. We also analyze a contract, under which M shares a fraction of total potential seignorage with C to induce M to inflate at a rate which leads to no seigniorage accruing to M from C. Finally, we provide estimates of the present discounted value of the seigniorage accruing from M to C. Despite this loss, we estimate the net welfare gain to C\u27s household when dollarization results in a lower rate of inflation
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