Implications of Low Energy Supersymmetry Breaking at the Tevatron

The signatures for low energy supersymmetry breaking at the Tevatron are investigated. It is natural that the lightest standard model superpartner is an electroweak neutralino, which decays to an essentially massless Goldstino and photon, possibly within the detector. In the simplest models of gauge-mediated supersymmetry breaking, the production of right-handed sleptons, neutralinos, and charginos leads to a pair of hard photons accompanied by leptons and/or jets with missing transverse energy. The relatively hard leptons and softer photons of the single e^+e^- \gamma \gamma + \EmissT event observed by CDF implies this event is best interpreted as arising from left-handed slepton pair production. In this case the rates for l^{\pm} \gamma \gamma + \EmissT and \gamma \gamma + \EmissT are comparable to that for l^+l^- \gamma \gamma + \EmissT.Comment: 18 pages, Latex, tables correcte

Renormalization in General Gauge Mediation

We revisit General Gauge Mediation (GGM) in light of the supersymmetric (linear) sigma model by utilizing the current superfield. The current superfield in the GGM is identified with supersymmetric extension of the vector symmetry current of the sigma model while spontaneous breakdown of supersymmetry in the GGM corresponds to soft breakdown of the axial vector symmetry of the sigma model. We first derive the current superfield from the supersymmetric linear sigma model and then compute 2-point functions of the current superfield using the (anti-)commutation relations of the messenger component fields. After the global symmetry are weakly gauged, the 2-point functions of the current superfield are identified with a part of the 2-point functions of the associated vector superfield. We renormalize them by dimensional regularization and show that physical gaugino and sfermion masses of the MSSM are expressed in terms of the wavefunction renormalization constants of the component fields of the vector superfield.Comment: 25 pages, 12 figure

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

A Model of Direct Gauge Mediation

We present a simple model of gauge mediation (GM) which does not have a messenger sector or gauge singlet fields. The standard model gauge groups couple directly to the sector which breaks supersymmetry dynamically. This is the first phenomenologically viable example of this type in the literature. Despite the direct coupling, the model can preserve perturbative gauge unification. This is achieved by the inverted hierarchy mechanism which generates a large scalar expectation value compared to the size of supersymmetry breaking. There is no dangerous negative contribution to the squark, slepton masses due to two-loop renormalization group equation. The potentially non-universal supergravity contribution to the scalar masses can be suppressed enough to maintain the virtue of the gauge mediation. The model is completely chiral, and one does not need to forbid mass terms for the messenger fields by hand. Beyond the simplicity of the model, it possesses cosmologically desirable features compared to the original models of GM: an improved gravitino and string moduli cosmology. The Polonyi problem is back unlike in the original GM models, but is still much less serious than in hidden sector models.Comment: LaTeX, 12 page

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

Cosmological vacuum selection and metastable susy breaking

We study gauge mediation in a wide class of O'Raifeartaigh type models where supersymmetry breaking metastable vacuum is created by gravity and/or quantum corrections. We examine their thermal evolution in the early universe and the conditions under which the susy breaking vacuum can be selected. It is demonstrated that thermalization typically makes the metastable supersymmetry breaking cosmologically disfavoured but this is not always the case. Initial conditions with the spurion displaced from the symmetric thermal minimum and a small coupling to the messenger sector can result in the realization of the susy breaking vacuum even if the reheating temperature is high. We show that this can be achieved without jeopardizing the low energy phenomenology. In addition, we have found that deforming the models by a supersymmetric mass term for messengers in such a way that the susy breaking minimum and the susy preserving minima are all far away from the origin does not change the conclusions. The basic observations are expected to hold also in the case of models with an anomalous U(1) group.Comment: 28 pages, 4 figures, plain Latex, journal versio

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

Cosmological Constraint on the String Dilaton in Gauge-mediated Supersymmetry Breaking Theories

The dilaton field in string theories (if exists) is expected to have a mass of the order of the gravitino mass $m_{3/2}$ which is in a range of $10^{-2}$keV--1GeV in gauge-mediated supersymmetry breaking models. If it is the case, the cosmic energy density of coherent dilaton oscillation easily exceeds the critical density of the present universe. We show that even if this problem is solved by a late-time entropy production (thermal inflation) a stringent constraint on the energy density of the dilaton oscillation is derived from experimental upperbounds on the cosmic X($\gamma$)-ray backgrounds. This excludes an interesting mass region, $500keV \lesssim m_{3/2} \lesssim 1GeV$, in gauge-mediated supersymmetry breaking models.Comment: 13 pages (RevTex file including one figure, use psfig), revised version to be published in Physical Review Letter

Topcolor-Assisted Supersymmetry

It has been known that the supersymmetric flavor changing neutral current problem can be avoided if the squarks take the following mass pattern, namely the first two generations with the same chirality are degenerate with masses around the weak scale, while the third generation is very heavy. We realize this scenario through the supersymmetric extension of a topcolor model with gauge mediated supersymmetry breaking.Comment: 12 pages, latex, no figure

Gluino Condensation in Strongly Coupled Heterotic String Theory

Strongly coupled heterotic $E_8\times E_8$ string theory, compactified to four dimensions on a large Calabi-Yau manifold ${\bf X}$, may represent a viable candidate for the description of low-energy particle phenomenology. In this regime, heterotic string theory is adequately described by low-energy $M$-theory on ${\bf R}^4\times{\bf S}^1/{\bf Z}_2\times{\bf X}$, with the two $E_8$'s supported at the two boundaries of the world. In this paper we study the effects of gluino condensation, as a mechanism for supersymmetry breaking in this $M$-theory regime. We show that when a gluino condensate forms in $M$-theory, the conditions for unbroken supersymmetry can still be satisfied locally in the orbifold dimension ${\bf S}^1/{\bf Z}_2$. Supersymmetry is then only broken by the global topology of the orbifold dimension, in a mechanism similar to the Casimir effect. This mechanism leads to a natural hierarchy of scales, and elucidates some aspects of heterotic string theory that might be relevant to the stabilization of moduli and the smallness of the cosmological constant.Comment: 22 pages, harvmac, no figure