Variations on Kaluza-Klein Cosmology

We investigate the cosmological consequences of having quantum fields living in a space with compactified dimensions. We will show that the equation of state is not modified by topological effects and so the dynamics of the universe remains as it is in the infinite volume limit. On the contrary the thermal history of the universe depends on terms that are associated with having non-trivial topology. In the conclusions we discuss some issues about the relationship between the $c=1$ non-critical string-inspired cosmology and the result obtained with matter given by a hot massless field in S^{1}\times \mbox{\bf R}.Comment: 22 pages, 7 figures in a uuencoded file (using uufiles), LaTeX, FTUAM-93/13 (LaTeX errors corrected

Some issues in soft SUSY-breaking terms from dilaton/moduli sectors

We study the structure of the soft SUSY-breaking terms obtained from some classes of 4-D strings under the assumption of dilaton/moduli dominance in the process of SUSY-breaking. We generalize previous analysis in several ways and in particular consider the new features appearing when several moduli fields contribute to SUSY breaking (instead of an overall modulus $T$). Some qualitative features indeed change in the multimoduli case.A general discussion for symmetric Abelian orbifolds as well as explicit examples are given. Certain general sum-rules involving soft terms of different particles are shown to apply to large classes of models. Unlike in the overall modulus $T$ case, gauginos may be lighter than scalars even at the tree-level. However, if one insists in getting that pattern of soft terms, these sum rules force some of the scalars to get negative mass$^2$. These tachyonic masses could be a problem for standard model 4-D strings but an advantage in the case of string-GUTs.We also discuss the possible effects of off-diagonal metrics for the matter fields which may give rise to flavour-changing neutral currents. Different sources for the bilinear $B$ soft term are studied. It is found that the Giudice-Masiero mechanism for generating a ``$\mu$-term'', as naturally implemented in orbifolds, leads to the prediction $|tg\beta |=1$ at the string scale, independently of the Goldstino direction.Comment: 27 pages, no figures, Latex; version to appear in Z. Phys. C (some changes in the discussion on gaugino versus scalar masses in sections 2 and 5, minor corrections elsewhere