A Solution to the μ\mu Problem in Gauge-mediated Supersymmetry-breaking Models

We point out that a sector required to set the cosmological constant to zero in gauge-mediated supersymmetry-breaking models naturally produces a supersymmetry-invariant mass ($\mu$ term) for Higgs doublets of the order of the electroweak scale. Since this new sector preserves the supersymmetry, it does not generate supersymmetry-breaking masses for the Higgs doublets and thus the $\mu$ problem is solved.Comment: Latex fil

Remarks on the Racetrack Scheme

There are only a small number of ideas for stabilizing the moduli of string theory. One of the most appealing of these is the racetrack mechanism, in which a delicate interplay between two strongly interacting gauge groups fixes the value of the coupling constant. In this note, we explore this scenario. We find that quite generally, some number of discrete tunings are required in order that the mechanism yield a small gauge coupling. Even then, there is no sense in which a weak coupling approximation is valid. On the other hand, certain holomorphic quantities can be computed, so such a scheme is in principle predictive. Searching for models which realize this mechanism is thus of great interest. We also remark on cosmology in these schemes.Comment: 20 pp, latex, discussion of calculability modifie

Constraint on Cosmic Density of the String Moduli Field in Gauge-Mediated Supersymmetry-Breaking Theories

We derive a constraint on the cosmic density of string moduli fields in gauge-mediated supersymmetry-breaking theories by requiring that photons emitted from the unstable moduli fields should not exceed the observed X-ray backgrounds. Since mass of the moduli field lies in the range between $O(0.1)$keV and $O(1)$MeV and the decay occurs through a gravitational interaction, the lifetime of the moduli field is much longer than the age of the present universe. The obtained upperbound on their cosmic density becomes more stringent than that from the unclosure condition for the present universe for the mass greater than about 100keV.Comment: 7 pages, a LaTeX2e file and two postscript figure

On Witten's Instability and Winding Tachyons

We investigate, from a spacetime perspective, some aspects of Horowitz's recent conjecture that black strings may catalyze the decay of Kaluza-Klein spacetimes into a bubble of nothing. We identify classical configurations that interpolate between flat space and the bubble, and discuss the energetics of the transition. We investigate the effects of winding tachyons on the size and shape of the barrier and find no evidence at large compactification radius that tachyons enhance the tunneling rate. For the interesting radii, of order the string scale, the question is difficult to answer due to the failure of the $\alpha^\prime$ expansion.Comment: 15 pages, 2 figures, Late

CP Violation and Moduli Stabilization in Heterotic Models

The role of moduli stabilization in predictions for CP violation is examined in the context of four-dimensional effective supergravity models obtained from the weakly coupled heterotic string. We point out that while stabilization of compactification moduli has been studied extensively, the determination of background values for other scalars by dynamical means has not been subjected to the same degree of scrutiny. These other complex scalars are important potential sources of CP violation and we show in a simple model how their background values (including complex phases) may be determined from the minimization of the supergravity scalar potential, subject to the constraint of vanishing cosmological constant.Comment: 8 Pages. Based on a talk given at the CP Violation Conference, University of Michigan, Ann Arbor, November 4-18, 2001, correction to Eq. (27

Supersymmetry, Axions and Cosmology

Various authors have noted that in particular models, the upper bound on the axion decay constant may not hold. We point out that within supersymmetry, this is a generic issue. For large decay constants, the cosmological problems associated with the axion's scalar partner are far more severe than those of the axion. We survey a variety of models, both for the axion multiplet and for cosmology, and find that in many cases where the cosmological problems of the saxion are solved, the usual upper bound on the axion is significantly relaxed. We discuss, more generally, the cosmological issues raised by the pseudoscalar members of moduli multiplets, and find that they are potentially quite severe.Comment: 27 pages, published version, some discussions clarifie

The Mass Spectrum in a Model with Calculable Dynamical Supersymmetry Breaking

Models with dynamical supersymmetry breaking are interesting because they may provide a solution to both the gauge hierarchy and the fine-tuning problems. However, because of strongly interacting dynamics, it is in general impossible to analyze them quantitatively. One of the few models with calculable dynamical supersymmetry breaking is a model with SU(5) gauge symmetry and two $10$'s and two $\bar 5$'s as the matter content. We determine the ground state of this model, find the vacuum energy, reveal the symmetry breaking pattern and calculate the mass spectrum. The supertrace mass relation is exploited to verify the consistency of the calculated mass spectrum, and an accidental degeneracy is explained.Comment: 10 pages, late

Supersymmetry Breaking in the Early Universe

Supersymmetry breaking in the early universe induces scalar soft potentials with curvature of order the Hubble constant. This has a dramatic effect on the coherent production of scalar fields along flat directions. For the moduli problem it generically gives a concrete realization of the problem by determining the field value subsequent to inflation. However it might suggest a solution if the minimum of the induced potential coincides with the true minimum. The induced Hubble scale mass also has important implications for the Affleck-Dine mechanism of baryogenesis. This mechanism requires large squark or slepton expectation values to develop along flat directions in the early universe. This is generally not the case if the induced mass squared is positive, but does occur if it is negative. The resulting baryon to entropy ratio depends mainly on the dimension of the nonrenormalizable operator in the superpotential which stabilizes the flat direction, and the reheat temperature after inflation. Unlike the original scenario, it is possible to obtain an acceptable baryon asymmetry without subsequent entropy releases.Comment: 11 pages, requires phyzz

Symmetric Points in the Landscape as Cosmological Attractors

In the landscape, if there is to be any prospect of scientific prediction, it is crucial that there be states which are distinguished in some way. The obvious candidates are states which exhibit symmetries. Here we focus on states which exhibit discrete symmetries. Such states are rare, but one can speculate that they are cosmological attractors. We investigate the problem in model landscapes and cosmologies which capture some of the features of candidate flux landscapes. In non-supersymmetric theories we find no evidence that such states might be cosmologically favored. In supersymmetric theories, simple arguments suggest that states which exhibit $R$ symmetries might be. Our considerations lead us to raise questions about some popular models of eternal inflation.Comment: 27 pages, latex, minor typo correcte