Carlos A. Savoy

Particle spectrum in supersymmetric models with a gauge singlet

We scan the complete parameter space of the supersymmetric standard model extended by a gauge singlet, which is compatible with the following constraints: universal soft supersymmetry breaking terms at the GUT scale, finite running Yukawa couplings up to the GUT scale and present experimental bounds on all sparticles, Higgs scalar and top quark. The full radiative corrections to the Higgs potential due to the top/stop sector are included. We find a lower limit on the gluino mass of 160 GeV, upper limits on the lightest neutral scalar Higgs mass dependent on mtop and the size of the soft supersymmetry breaking terms, and the possibility of a Higgs scalar as light as 10 GeV, but with reduced couplings to the Z boson.

PHENOMENOLOGY OF SUPERSYMMETRIC MODELS WITH A SINGLET

The supersymmetric extension of the standard model with an additional gauge singlet is analysed in detail in the light of the recent experimental bounds on supersymmetric particles. The useful part of the parameter space and the particle spectrum are displayed. We find that once the recent bounds on the chargino mass are imposed, all other new particles practically satisfy the present experimental limits. Special attention is given to particles to be searched for in the future experiments. The singlet fields tend to decouple and give rise to an effective MSSM, enlarging the validity of many phenomenological analyses based in the minimal field content. However, in some ranges of the parameters the singlino is the lightest neutralino, which modifies the signature for susy particles. Simple analytical approximations are developed that qualitatively explain the numerical results.

Yukawa matrices from a spontaneously broken Abelian symmetry

Abstract We classify all the phenomenologically viable fermion mass matrices coming from a spontaneously broken abelian symmetry U(1)X, with one and two additional chiral fields of opposite charges X = ±1. We find that the non-trivial Kahler metric can fill zeroes of the fermion mass matrices up to phenomenologically interesting values. A general anomaly analysis shows that for one additional chiral field the only way to achieve anomaly cancellation is by use of the Green-Schwarz mechanism. For two additional fields with X = ±1 and negative charge differences in the lepton sector the anomalies can however be directly put to zero. This case gives a unique prediction for the ratio of the two Higgs scalars of MSSM, tgβ∼ m t m b ( sinθ c ) 2 , where θc is the Cabibbo angle.

Constraints on phases of supersymmetric flavour conserving couplings

Abstract In the unconstrained MSSM, we reanalyze the constraints on the phases of supersymmetric flavour conserving couplings that follow from the electron and neutron electric dipole moments (EDM). We find that the constraints become weak if at least one exchanged superpartner mass is > O (1 TeV ) or if we accept large cancellations among different contributions. However, such cancellations have no evident underlying symmetry principle. For light superpartners, models with small phases look like the easiest solution to the experimental EDM constraints. This conclusion becomes stronger the larger is the value of tan β . We discuss also the dependence of ϵ K , Δm B and b → sγ decay on those phases.

Soft scalar masses in supergravity with horizontal U(1)-x gauge symmetry

Abstract In supergravity with modular invariance and horizontal U(1)x gauge symmetry there is a relation between modular weights and U(1)x charges. The soft scalar masses are then strongly correlated with Yukawa matrices. The implications for FCNC are discussed.

Higgs phenomenology of the supersymmetric model with a gauge singlet

We discuss the Higgs sector of the supersymmetric standard model extended by a gauge singlet for the range of parameters, which is compatible with universal soft supersymmetry breaking terms at the GUT scale. We present results for the masses, couplings and decay properties of the lightest Higgs bosons, in particular with regard to Higgs boson searches at LEP. The prospects differ significantly from the ones within the MSSM.

Hierarchical supergravity-induced SU(2) × U(1) breaking in SU(5) guts

Abstract In contrast with naive extensions of the standard supersymmetric SU(5) model to local supersymmetry, we show that different choices of representations in the heavy sector of the theory involving the 75,50 and 50 representations of SU(5) produce a low-energy effective SU(3) × SU(2) × U(1) theory, where the SU(2) × U(1) breaking is entirely induced by the gravitino mass scale. We discuss how in these models one can avoid that the three-level hierarchy M W ⪡ M X become unstable in perturbation theory.

On metastability in supersymmetric models

We make a critical reappraisal of ‘unbounded-from-below’ (UFB) constraints in the MSSM and R-parity violating models. We explain why the ‘traditional’ UFB bounds are neither necessary nor sufficient and propose, instead, a sufficient condition which ensures that there are no local minima along the flat directions. This conservative (but meaningful) condition divides the parameter space into regions which are allowed, regardless of cosmology, and regions in which cosmology is expected to play a major role. We study both conditions at low tan β and obtain analytic approximations to the UFB bounds for all low tan β (< 15). Finally we show that R-parity violation just below current experimental limits avoids UFB problems by lifting the dangerous flat directions.

Charge and colour breaking constraints in the MSSM with non-universal SUSY breaking

Abstract We examine charge/colour breaking along directions in supersymmetric field space which are F and D-flat. We catalogue the dangerous directions and include some new ones which have not previously been considered. Analytic expressions for the resulting constraints are provided which are valid for all patterns of supersymmetry breaking. As an example we consider a recently proposed pattern of supersymmetry breaking derived in Horava-Witten M-theory, and show that there is no choice of parameters for which the physical vacuum is a global minimum.

Supersymmetric models with a gauge singlet and non-universal soft terms from orbifold string theory

Abstract The particle spectrum of the supersymmetric extension of the standard model with a gauge singlet is studied. Soft supersymmetry breaking terms are explicitly chosen to be non-universal according to orbifold string theory. They depend on modular weights of chiral fields and on an angle θ specifying the supersymmetry breaking sector. Imposing radiative weak symmetry breaking and requiring that standard model Yukawa couplings should be allowed yield constraints on modular weights and almost specifies the angle θ. We then perform a numerical analysis of the low energy spectrum. It turns out that the spectrum is very constrained, revealing salient features such as light Higgses and neutralinos. The latter happen to be essentially gaugino-like.