Natural Supergravity Inflation

We show that a single uncharged chiral superfield, canonically coupled to \mbox{$N=1$} supergravity with vanishing superpotential, naturally drives inflation in the early universe for a class of simple Kahler potentials. Inflation occurs due to the one-loop generation of a Kahler anomaly proportional to $\R^2$. The coefficient of this $\R^2$ term is of the correct magnitude to describe all aspects of an inflationary cosmology, including sufficient amplitude perturbations and reheating. Higher order terms proportional to $\R^n$ for $n \geq 3$ are naturally suppressed relative to the $\R^2$ term and, hence, do not destabilize the theory.Comment: 13 pages, CERN-TH.6685/92, UPR-0526

Two Higgs Pair Heterotic Vacua and Flavor-Changing Neutral Currents

We present a vacuum of heterotic M-theory whose observable sector has the MSSM spectrum with the addition of one extra pair of Higgs-Higgs conjugate superfields. The quarks/leptons have a realistic mass hierarchy with a naturally light first family. The double elliptic structure of the Calabi-Yau compactification threefold leads to two ``stringy'' selection rules. These classically disallow Yukawa couplings to the second Higgs pair and, hence, Higgs mediated flavor-changing neutral currents. Such currents are induced in higher-dimensional interactions, but are naturally suppressed. We show that our results fit comfortably below the observed upper bounds on neutral flavor-changing processes.Comment: 52 pages, 3 figures, 1 table, requires feynm

Five--Branes and Supersymmetry Breaking in M--Theory

Supersymmetry breaking via gaugino condensation is studied in vacua of heterotic M-theory with five-branes. We show that supersymmetry is still broken by a global mechanism and that the non-perturbative superpotential takes the standard form. When expressed in terms of low energy fields, a modification arises due to a threshold correction in the gauge kinetic function that depends on five-brane moduli. We also determine the form of the low energy matter field Kahler potential. These results are used to discuss the soft supersymmetry breaking parameters, in particular the question of universality.Comment: 28 pages, Late