Moduli Evolution in Heterotic Scenarios

We discuss several aspects of the cosmological evolution of moduli fields in heterotic string/M-theory scenarios. In particular we study the equations of motion of both the dilaton and overall modulus of these theories in the presence of an expanding Universe and under different assumptions. First we analyse the impact of their couplings to matter fields, which turns out to be negligible in the string and M-theory scenarios. Then we examine in detail the possibility of scaling in M-theory, i.e. how the moduli would evolve naturally to their minima instead of rolling past them in the presence of a dominating background. In this case we find interesting and positive results, and we compare them to the analogous situation in the heterotic string. CERN-TH/2000-302 SUSX-TH/00-014 September 2000 CERN-TH/2000-302 e-mail address: [email protected]. Address after October 1 2000: Centro Multidisciplinar de Astrof́ısica, Instituto Superior Técnico, Lisboa 1049-001, Portugal. e-mail address: [email protected]. Address after October 1 2000: Centre for Theoretical Physics, University of Sussex, Falmer, Brighton BN1 9QJ, UK. e-mail address: [email protected]