Abstract
The effects of negative· energy propagations in the effective optical potentials for relativistic deuteron·nucleus elastic scattering are investigated utilizing the Breit approach. First, we consider the effects of the (+ -) and (- +) propagations. They represent that one of the nucleons in the deuteron propagates in its positive·energy state, while another propagates in negative·energy one. Second, the effects of the (- -) propagation, which represents that both the nucleons propagate in their negative· energy states, are studied. It has been found that the characteristic features of the optical potentials near 400 MeV - the wine·bottle·bottom·shape of the central part and the enhanced spin·orbit strength - are pure relativistic effects mainly due to the ( + -) and (- +) propagations, whereas the effects of the (- -) propagation are small. Recently, several efforts have been devoted to investigating the structures of the propagators and their effects in the relativistic nuclear scattering theories. 1 J-S) In the Dirac phenomenology for nucleon-nucleus (N-A) scattering, Cooper and Jennings have found that the negative-energy part of the Feynman propagator has short-ranged structure and plays an important role in producing the relativistic character of the effective optical potentials. 2 ) In the Breit 6 ) and Duffin-Kemmer-Petiau (DKP)1H) theories for relativistic deuteron-nucleus (d-A) scattering, the present author has found that the short-ranged structures of their propagators also contribute consider ably to the relativistic characters of d-A optical potentials. 5 ) However, in that work he has not been able to clarify another important aspect of the relativistic scattering theories, that is, the effect of negative-energy propagations. This is partially because that in the Breit or DKP approach short-ranged terms in the propagator are not identical with negative-energy terms, in contrast to the Feynman propagator. For the relativistic scattering of a composite particle, it becomes an important subject to study the effects of the negative-energy propagations of each constituent particle. 1OH2 ) Most of the recent studies of d-A elastic scattering at intermediate energies are inspired by the success of the Dirac phenomenology.9),13),14) Therefore, we want to clarify the effects of the negative-energy propagations of Dirac nucleons in the deuteron. For this purpose, in the present work we will treat d-A elastic scattering within a relativistic folding-model utilizing the Breit equation.
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