Relativistic and non-relativistic studies of nuclear matter

Recently we showed that while the tensor force plays an important role in nuclear matter saturation in non-relativistic studies, it does not do so in relativistic studies. The reason behind this is the role of $M^*$, the sum of nucleon mass and its attractive self-energy in nuclear matter. Yet nonrelativistic calculations at a certain level of approximation are far less difficult than comparative relativistic calculation. Naturally the question arises if one can modify a nonrelativistic method, say, the lowest order Brueckner theory (LOBT), to reproduce approximately the results of a relativistic calculation. While a many body effect, the role of $M^*$ is intrinsically relativistic. It cannot be simulated by adding multi-body forces in a nonrelativistic calculation. Instead, we examine if adding a set of recipes to LOBT can be useful for the purpose. We point out that the differences in the results arise principally from two reasons - first, the role of $M^*$ and second, the disappearance in a relativistic treatment of the gap in the hole and particle energy spectra, present in LOBT. In this paper we show that LOBT, modified by {\it recipes} to remove these two reasons, generates results quite close to those of Dirac-Brueckner theory.