Moduli as Inflatons in Heterotic M-theory

We consider different cosmological aspects of Heterotic M-theory. In particular we look at the dynamical behaviour of the two relevant moduli in the theory, namely the length of the eleventh segment (pi rho) and the volume of the internal six manifold (V) in models where supersymmetry is broken by multiple gaugino condensation. We look at different ways to stabilise these moduli, namely racetrack scenarios with or without non-perturbative corrections to the Kahler potential. The existence of different flat directions in the scalar potential, and the way in which they can be partially lifted, is discussed as well as their possible role in constructing a viable model of inflation. Some other implications such as the status of the moduli problem within these models are also studied.Comment: 16 pages, 8 Postscript figures. Final version to appear in JHE

Cosmological Aspects of Heterotic M-theory

In this talk we discuss a few relevant aspects of heterotic M-theory. These are the stabilization of the two relevant moduli (the length of the eleventh segment (pi rho) and the volume of the internal six manifold (V)) in models where supersymmetry is broken by multiple gaugino condensation and non-perturbative corrections to the Kahler potential; the existence of almost flat directions in the scalar potential; the possibility of lifting them, and their role in constructing a viable model of inflation. Finally, we review the status of the moduli problem within these models. TComment: LaTeX, 8 pages, 4 eps figures, uses ws-p8-50x6-00.cls; invited talk at the International Workshop on Particle Physics and the Early Universe (COSMO-99), Trieste, Italy, September 27 - October 2, 199

Domain walls in supersymmetric QCD

We consider domain walls that appear in supersymmetric SU(N) with one massive flavour. In particular, for N > 3 we explicitly construct the elementary domain wall that interpolates between two contiguous vacua. We show that these solutions are BPS saturated for any value of the mass of the matter fields. We also comment on their large N limit and their relevance for supersymmetric gluodynamics.Comment: 4 pages, 1 figure, uses latex with hep99 class files. Presented at the International Europhysics Conference in High Energy Physics, Tampere (Finland) 15-21 July 199

The Fine-Tuning Problem of the Electroweak Symmetry Breaking Mechanism in Minimal SUSY Models

We calculate the region of the MSSM parameter space (i.e. $M_{1/2}$, $m_{0}$, $\mu$, \ldots) compatible with a correct electroweak breaking and a realistic top-quark mass. To do so we have included {\em all} the one-loop corrections to the effective potential $V_{1}$ and checked their importance in order to obtain consistent results. We also consider the fine-tuning problem due to the enormous dependence of $M_{Z}$ on $h_{t}$ (the top Yukawa coupling), which is substantially reduced when the one-loop effects are taken into account. We also explore the reliability of the so-called "standard" criterion to estimate the degree of fine-tuning. As a consequence, we obtain a new set of upper bounds on the MSSM parameters or, equivalently, on the supersymmetric masses perfectly consistent with the present experimental bounds.Comment: talk given at the XVI Kazimierz Meeting on Elementary Particle Physics, Kazimierz (Poland) 24-28 May 1993, 4 pages in standard LATEX + 2 figures (not included but available upon request), CERN-TH.7024/9

SUSY Soft Breaking Terms from String Scenarios

The general SUSY soft breaking terms for a large class of phenomenologically relevant string scenarios (symmetric orbifolds) are given. They show a certain lack of universality, but not dangerous for flavor changing neutral currents. To get more quantitative results a specific SUSY breaking mechanism has to be considered, namely gaugino condensation in the hidden sector. Then, it turns out that squark and slepton masses tend to be much larger than scalar masses ($m_{\phi} > 10 M_a$), which probably is a quite general fact. Experimental bounds and the requirement of a successful electroweak breaking without fine tuning impose further restrictions on the soft breaking terms. As a consequence the gluino and chargino masses should be quite close to their present experimental limits, whereas squark and slepton masses should be much higher (> 1 TeV).Comment: (Talk presented at the SUSY-93 Conference, Boston, March 29 - April 2, 1993), 11 pages, CERN--TH.6922/9

Stabilizing the Dilaton in Superstring Cosmology

We address the important issue of stabilizing the dilaton in the context of superstring cosmology. Scalar potentials which arise out of gaugino condensates in string models are generally exponential in nature. In a cosmological setting this allows for the existence of quasi scaling solutions, in which the energy density of the scalar field can, for a period, become a fixed fraction of the background density, due to the friction of the background expansion. Eventually the field can be trapped in the minimum of its potential as it leaves the scaling regime. We investigate this possibility in various gaugino condensation models and show that stable solutions for the dilaton are far more common than one would have naively thought.Comment: 13 pages, LaTex, uses psfig.sty with 3 figure

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.Comment: 12 pages, 4 postscript figure