Models for new particle production in nuclear collisions

Following up our earlier work and also stimulated by recent experimental results on positron production in heavy ion collisions we investigate various mechanisms for the production of a light, previously unknown particle in such collisions. As more conventional mechanisms seem to be inadequate we concentrate on processes directly or indirectly connected with the strong electric or magnetic fields and quark degrees of freedom in nuclei. We also consider modifications of the color confinement scheme. Our analysis is confined to schemes staying within the framework of the standard SU(3)sub(c) x SU(2) x U(1) model. Since most of the possibilities discussed can be rejected, severe modifications of basic concepts of particle physics seem to be required if the production of a new particle is confirmed. (orig.)