Moduli stabilization and SUSY breaking in heterotic orbifold string models

In this paper we discuss the issues of supersymmetry breaking and moduli stabilization within the context of E_8 x E_8 heterotic orbifold constructions and, in particular, we focus on the class of "mini-landscape" models. In the supersymmetric limit, these models admit an effective low energy field theory with a spectrum of states and dimensionless gauge and Yukawa couplings very much like that of the MSSM. These theories contain a non-Abelian hidden gauge sector which generates a non-perturbative superpotential leading to supersymmetry breaking and moduli stabilization. We demonstrate this effect in a simple model which contains many of the features of the more general construction. In addition, we argue that once supersymmetry is broken in a restricted sector of the theory, then all moduli are stabilized by supergravity effects. Finally, we obtain the low energy superparticle spectrum resulting from this simple model.Comment: LaTeX, v2: 57+1 pages, 4 figures, 8 Tables, added references; this version i) discusses volume moduli stabilization with exponentials of both sign (as sometimes mandated by modular invariance); ii) includes the anomalous U(1)_A D-term & the leading Coleman-Weinberg 1-loop correction into the MSSM soft masses to prevent tachyonic results

Reconciling Grand Unification with Strings by Anisotropic Compactifications

We analyze gauge coupling unification in the context of heterotic strings on anisotropic orbifolds. This construction is very much analogous to effective 5 dimensional orbifold GUT field theories. Our analysis assumes three fundamental scales, the string scale, \mstring, a compactification scale, \mc, and a mass scale for some of the vector-like exotics, \mex; the other exotics are assumed to get mass at \mstring. In the particular models analyzed, we show that gauge coupling unification is not possible with \mex = \mc and in fact we require \mex \ll \mc \sim 3 \times 10^{16} GeV. We find that about 10% of the parameter space has a proton lifetime (from dimension 6 gauge exchange) $10^{33} {\rm yr} \lesssim\tau(p\to \pi^0e^+) \lesssim 10^{36} {\rm yr}$. The other 80% of the parameter space gives proton lifetimes below Super-K bounds. The next generation of proton decay experiments should be sensitive to the remaining parameter space.Comment: 36 pages and 5 figures, contains some new references and additional paragraph in conclusio