We extend the KKLT [1] approach to moduli stabilization by including the dilaton and the complex structure moduli into the effective supergravity theory. Decoupling of the dilaton is neither always possible nor necessary for the existence of stable minima with zero (or positive) cosmological constant. The pattern of supersymmetry breaking can be much richer than in the decoupling scenario of KKLT.

The condition of unification of gauge couplings in the minimal supersymmetric standard model provides successful predictions for the weak mixing angle as a function of the strong gauge coupling and the supersymmetric threshold scale. In addition, in some scenarios, e.g. in the minimal SO(10) model, the tau lepton and the bottom and top quark Yukawa couplings unify at the grand unification scale. The condition of Yukawa unification leads naturally to large values of tan β, implying a proper top quark-bottom quark mass hierarchy. In this work, we investigate the feasibility of unification of the Yukawa couplings, in the framework of the minimal supersymmetric standard model with (assumed) universal mass parameters at the unification scale and with radiative breaking of the electroweak symmetry. We show that strong correlations between the parameters µ 0 , M 1/2 and δ = B 0 − (6r/7)A 0 appear within this scheme, where r is the ratio of the top quark Yukawa coupling to its infrared fixed point value. These correlations have relevant implications for the sparticle spectrum, which presents several characteristic features. In addition, we show that due to large corrections to the running bottom quark mass induced through the supersymmetry breaking sector of the theory, the predicted top quark mass and tan β values are significantly lower than those previously estimated in the literature. Recently, it has been observed that for the phenomenologically allowed values of the bottom quark mass and moderate values of tan β < 10, large values of the top quark Yukawa coupling are needed in order to contravene the strong gauge coupling renormalization of the bottom Yukawa coupling [7]-[9]. In general, for large enough values of the top quark Yukawa coupling at the grand unification scale, the low energy Yukawa coupling is strongly focussed to a quasi infrared fixed point [10]-[11]. In the minimal supersymmetric standard model, the quasi infared fixed point predictions for the physical top quark mass M t are given by M t ≃ A sin β, with A ≃ 190 − 210 GeV for the strong gauge coupling α 3 (M Z ) = 0.11−0.13. It has been recently shown that for the values of the strong gauge coupling consistent with the condition of gauge coupling unification, with reasonable threshold corrections at the grand unification and supersymmetry breaking scales, the top quark mass should be within 10% of its quasi infrared fixed point values if the condition of bottom-tau Yukawa unification is required [12]. A more predictive scheme is obtained in the framework of the minimal SO(10) unification. In this case top-bottom quark Yukawa unification is also required, implying that, for a given value of the bottom quark mass and the strong gauge coupling value [13], not only the top quark mass but also the value of tan β may be determined. Remarkably, large values of tan β ≥ 40 are obtained in this case, leading to a proper bottom-top mass hierarchy [14]-[16]. For these large values of tan β, the bottom quark Yukawa coupling itself plays a relevant role in the ...

We analyze uncertainties in the theoretical prediction for the inclusive branching ratio BR[B → X s γ]. We find that the dominant uncertainty in the leading order expression comes from its µ-dependence. We discuss a next-to-leading order calculation of B → X s γ in general terms and check to what extent the µ-dependence can be reduced in such a calculation. We present constraints on the Standard and Two-Higgs-Doublet Model parameters coming from the measurement of b → sγ decay. The current theoretical uncertainties do not allow one to definitively restrict the Standard Model parameters much beyond the limits coming from other experiments. The bounds on the Two-Higgs-Doublet Model remain very strong, though significantly weaker than the ones present in the recent literature. In the Two-Higgs-Doublet Model case, the b → sγ, Z → bb and b → cτν τ processes are enough to give the most restrictive bounds in the M H ± − tanβ plane. † On leave of absence from Institute of Theoretical Physics, Warsaw University.

We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, up to first order in the slow-roll parameters. We also compute numerically the evolution of the curvature and isocurvature modes from well within the Hubble radius until the end of inflation. We show explicitly for a few examples, including the recently proposed model of ‘roulette’ inflation, how isocurvature perturbations affect significantly the curvature perturbation between Hubble crossing and the end of inflation.

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