Exact Event Rates of Lepton Flavor Violating Processes in Supersymmetric SU(5) Model

Event rates of various lepton flavor violating processes in the minimal supersymmetric SU(5) model are calculated, using exact formulas which include Yukawa vertices of lepton-slepton-Higgsino. We find subtlety in evaluating event rates due to partial cancellation between diagrams. This cancellation typically reduces the event rates significantly, and the size of the reduction strongly depends on superparticle mass spectrum.Comment: 11pages, 8 figures. Fig.5 where the mu-e conversion rates in nuclei was shown was incorrect due to an error in our numerical computation.It is replaced in this corrected version. All conclusions remain unchange

Limit on the Color-Triplet Higgs Mass in the Minimum Supersymmetric SU(5) Model

In the minimum supersymmetric SU(5) GUT, we derive the upper limit on the mass of the color-triplet Higgs multiplets as \mhc\leq 2.4\times 10^{16}~\GEV (90 \% C.L.) taking all possible corrections into account in a renormalization group analysis. If the above upper limit is compared with a limit on \mhc from the negative search for the proton decay; \mhc \geq 2.0\times 10^{16}~\GEV (in which effects of the larger top-quark mass are included), the minimum supersymmetric SU(5) GUT is severely constrained

Dilaton Destabilization at High Temperature

Many compactifications of higher-dimensional supersymmetric theories have approximate vacuum degeneracy. The associated moduli fields are stabilized by non-perturbative effects which break supersymmetry. We show that at finite temperature the effective potential of the dilaton acquires a negative linear term. This destabilizes all moduli fields at sufficiently high temperature. We compute the corresponding critical temperature which is determined by the scale of supersymmetry breaking, the beta-function associated with gaugino condensation and the curvature of the K"ahler potential, T_crit ~ (m_3/2 M_P)^(1/2) (3/\beta)^(3/4) (K'')^(-1/4). For realistic models we find T_crit ~ 10^11-10^12 GeV, which provides an upper bound on the temperature of the early universe. In contrast to other cosmological constraints, this upper bound cannot be circumvented by late-time entropy production.Comment: 19 pages, 9 figure

Cosmological gravitino problem confronts electroweak physics

A generic feature of gauge-mediated supersymmetry breaking models is that the gravitino is the lightest supersymmetric particle (LSP). In order not to overclose the universe, the gravitino LSP should be light enough (~ 1 keV), or appropriately heavy (~ 1 GeV). We study further constraints on the mass of the gravitino imposed by electroweak experiments, i.e., muon g-2 measurements, electroweak precision measurements, and direct searches for supersymmetric particles at LEP2. We find that the heavy gravitino is strongly disfavored from the lower mass bound on the next-to-LSP. The sufficiently light gravitino, on the other hand, has rather sizable allowed regions in the model parameter space.Comment: 11 pages, 8 figures, version to appear in PR

Flat Potential for Inflaton with a Discrete RR-invariance in Supergravity

We show that a very flat potential of inflaton required for a sufficient inflation is naturally obtained in $N=1$ supergravity by imposing a discrete $R$-invariance $Z_{n}$. Several cosmological constraints on parameters in the inflaton superpotential are derived. The reheating temperature turns out to be $(1-10^8)$GeV for the cases of $n$=3--10. Baryogenesis in this model is also discussed briefly.Comment: 15 pages and 1 figure(uudecoded), LaTeX, TU-45

Relaxing Constraints on Inflation Models with Curvaton

We consider the effects of the curvaton, late-decaying scalar condensation, to observational constraints on inflation models. From current observations of cosmic density fluctuations, severe constraints on some class of inflation models are obtained, in particular, on the chaotic inflation with higher-power monomials, the natural inflation, and the new inflation. We study how the curvaton scenario changes (and relaxes) the constraints on these models.Comment: 18 pages, 6 figure

A D-moduli problem?

We point out a generic problem in string-inspired supergravity models with an anomalous $U(1)_X$. A large number of matter multiplets charged under $U(1)_X$ remain massless above the supersymmetry-breaking scale because of degeneracy of vacua solving the D-flatness conditions. A toy model is analyzed as an illustration of the mechanism; we find the surprising result that many scalars remain massless after supersymmetry-breaking in a hidden sector.Comment: 11 pages, full postscript also available from http://phyweb.lbl.gov/theorygroup/papers/44856.p

Curvatons in Supersymmetric Models

We study the curvaton scenario in supersymmetric framework paying particular attention to the fact that scalar fields are inevitably complex in supersymmetric theories. If there are more than one scalar fields associated with the curvaton mechanism, isocurvature (entropy) fluctuations between those fields in general arise, which may significantly affect the properties of the cosmic density fluctuations. We examine several candidates for the curvaton in the supersymmetric framework, such as moduli fields, Affleck-Dine field, $F$- and $D$-flat directions, and right-handed sneutrino. We estimate how the isocurvature fluctuations generated in each case affect the cosmic microwave background angular power spectrum. With the use of the recent observational result of the WMAP, stringent constraints on the models are derived and, in particular, it is seen that large fraction of the parameter space is excluded if the Affleck-Dine field plays the role of the curvaton field. Natural and well-motivated candidates of the curvaton are also listed.Comment: 34 pages, 5 figure