K. Tamvakis

No-Scale Supersymmetric Standard Model

Abstract We propose a class of supergravity models coupled to matter in which the scales of supersymmetry breaking and of weak gauge symmetry breaking are both fixed by dimensional transmutation, not put in by hand. The models have a flat potential with zero cosmological constant before the evaluation of weak radiative corrections which determine m 3 2 , m W = exp [ −O(1) α t ]m p :α t = O(α) . These models are consistent with all particle physi cs and cosmological constraints for top quark masses in the range 30 GeV

Grand Unification in Simple Supergravity

Abstract We discuss aspects of grand unified theories (GUTs) combined with N =1 local supersymmetry, interpreting the general form of simple supergravity theory as a phenomenological effective lagrangian applicable at energies less than the Planck mass. We consider light fermion masses, baryon decay and a possible resolution of the QCD vacuum angle θ problem in this general framework. We propose two mechanisms for weak symmetry breaking based on radiative corrections originating from supergravity effects, notably by a direct gaugino mass in theories with non-minimal coupling to N =1 supergravity. We give a specific example of a GUT employing this mechanism.

Weak Symmetry Breaking by Radiative Corrections in Broken Supergravity

Abstract Weak interaction gauge symmetry breaking can be generated by radiative corrections in a spontaneously broken supergravity theory, provided the top quark is heavy enough. In one class of such theories the weak Higgs vacuum expectation values are determined by dimensional transmutation a la Coleman-Weinberg, and may be considerably larger than the magnitudes of SUSY breaking mass parameters. In this scenario mt⩾65 GeV, the supersymmetric partners of known particles may have masses ⪡mW, the mass of the lighter neutral scalar Higgs boson is determined by radiative corrections, and there is some variant of a light pseudoscalar axion. In contrast to conventional Coleman-Weinberg models, the weak phase transition is second order and there is no likelihood of excess entropy production.

Naturally massless Higgs doublets in supersymmetric SU(5)

Abstract We construct a supersymmetric SU(5) model characterized by: (a) naturally massless doublet Higgs superfields; (b) the natural appearance of “light” coloured triplet Higgses of mass of the order 10 10 GeV, and study proton decay as well as the generation of cosmic baryon asymmetry. We find that an appropriate choice of Higgs sector renders dimension-five operators kinematically irrelevant for the stability of the proton. Proton decay proceeds through Higgs boson exchange in terms of dimension-six operators mainly to v ¯ μ K + , v + K 0 .

Singularity-free cosmological solutions of the superstring effective action

Abstract We study the cosmological solutions of the one-loop corrected superstring effective action, in a Friedmann-Robertson-Walker background, and in the presence of the dilaton and modulus fields. A particularly interesting class of solutions is found which avoid the initial singularity and are consistent with the perturbative treatment of the effective action.

LOCALIZED GRAVITONS, GAUGE BOSONS AND CHIRAL FERMIONS IN SMOOTH SPACES GENERATED BY A BOUNCE

We study five-dimensional solutions to Einstein equations coupled to a scalar field. Bounce-type solutions for the scalar field are associated with AdS5 spaces with smooth warp functions. Gravitons are dynamically localized in this framework in analogy to the Randall–Sundrum solution whereas, a bulk fermion gives rise to a single chiral zero mode localized at the bounce. Additional bulk scalar fields are incorporated in this picture. The dilaton, as a bulk scalar leads, through its coupling, to localized gauge boson fields, something that holds also in the case that the bounce system is replaced by a brane.

Stabilized NMSSM without domain walls

Abstract We reconsider the Next to Minimal Supersymmetric Standard Model (NMSSM) as a natural solution to the μ-problem and show that both the stability and the cosmological domain wall problems are eliminated if we impose a Z 2 R-symmetry on the non-renormalizable operators.

New Minimal Extension of MSSM

We construct a new minimal extension of the minimal supersymmetric standard model (MSSM) by promoting the μ-parameter to a singlet superfield. The resulting renormalizable superpotential is enforced by a Z5 R-symmetry which is imposed on the non-renormalizable operators as well. The proposed model provides a natural solution to the μ-problem and is free from phenomenological and cosmological problems.

Phenomenology of a new minimal supersymmetric extension of the standard model

We study the phenomenology of a new minimally extended supersymmetric standard model (nMSSM) where a gauge singlet superfield is added to the MSSM spectrum. The superpotential of this model contains no dimensionful parameters, thus solving the ? problem of the MSSM. A global discrete R symmetry, forbidding the cubic singlet self-interaction, imposed on the complete theory, guarantees its stability with respect to generated higher-order tadpoles of the singlet and solves both the domain wall and Peccei-Quinn axion problems. We give the free parameters of the model and display some general constraints on them. Particular attention is devoted to the neutralino sector where a (quasipure) singlino appears to be always the LSP of the model, leading to additional cascades, involving the NLSP ? LSP transition, compared with the MSSM. We then present the upper bounds on the masses of the lightest and next-to-lightest—when the lightest is an invisible singlet—CP-even Higgs bosons, including the full one-loop and dominant two-loop corrections. These bounds are found to be much higher than the equivalent ones in the MSSM. Finally, we discuss some phenomenological implications for the Higgs sector of the nMSSM in Higgs boson production at future hadron colliders.

PRIMORDIAL SUPERSYMMETRIC INFLATION

Abstract We discuss the motivations for reconsidering cosmological inflation in supersymmetric theories as contrasted with conventional GUTs. Radiative corrections to the effective potential can be made arbitrarily small in supersymmetric GUTs, removing some of the obstacles to inflation. We analyze general renormalizable potentials at the tree level and show that the required fine-tuning of parameters becomes less acute if inflation takes place before the grand unified phase transition, a hypothesis we term primordial inflation. We show how the grand unified monopole problem can be solved in supersymmetric GUTs embodying primordial inflation.