A.B. Lahanas

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

Low-energy behaviour of realistic locally-supersymmetric grand unified theories

The recently proposed cosmologically acceptable N=1 supergravity models based on the SU(5) unification group define unambigously the minimal particle content of the theory. This fact allows us to determine quite precisely their low-energy behaviour. The SU(2)×U(1) breaking to U(1)e.m. is a consequence of radiative corrections of the supergravity induced soft breaking terms. The proposed mechanism (which is model independent) introduces naturally a hierarchy between the MW and MX scales. Calculating the low-energy effective potential we shot that a corrects SU(2)×U(1) breaking is obtained without any limit (except the experimental one) on the top-quark mass. The masses of the supersymmetric partners of mater and gauge fermions can be low and consequently accessible experimentally (sleptons, s quarks, gauginos ⋍ 20–50 GeV). A neutral Higgs is also predicted wirth a mass mH⋍O(5) GeV. In addition, we show that if mt≲45 GeV, the gravitino and gluino masses are bounded from below by 10GeV ≲ m32 and 15 GeV ≲ mgluino. The values of sin2 θW (in the two-loop approximation) and the mbmτ ratio predicted are in very good agreement with the experimentally measured values.

Supergravity induced radiative SU(2) × U(1) breaking with light top quark and stable minimum

Abstract We present a class of models where the SU(2) L × U(1) Y breaking occurs radiatively through supergravity effects. Unlike similar models proposed up to now, our class of models: (a) is free from a lower bound on the top quark mass (the only bound being the experimental one m t ⩾ 20 GeV); (b) enjoys a stable minimum; and (c) provides an experimentally accessible low energy particle spectrum.

Light singlet, gauge hierarchy and supergravity

Abstract The existence of light singlets to help the breaking of SU (2) × U (1) in supersymmetric grand unified theories destroys the gauge hierarchy. The phenomenon exists for both global and local SUSY-GUT models.

One loop corrections to the neutralino sector and radiative electroweak breaking in the MSSM

Abstract We compute one loop radiative corrections to the physical neutralino masses in the MSSM considering the dominant top-stop contributions. We present a numerical renormalization group analysis of the feasibility of the radiative gauge symmetry breaking parametrized by the standard soft supersymmetry breaking terms. Although the above computed effects can be, in principle, large for extreme values of the Yukawa coupling, they do not, in general, exceed a few per cent for most of the parameter space. Therefore tree level constraints imposed on the gluino mass m g , and on the superpotential parameter μ by LEP1 and CDF experiments, are not upset by the heavy top/stop sector.

Vanishing scalar masses in no-scale supergravity

Abstract Radiative corrections to the effective scalar potential are studied in no-scale supergravity models with local supersymmetry spontaneously broken by a gravitino mass. A simple proof is given that gauge non-singlet scalar fields acquire no supersymmetry breaking masses at the one-loop level, and a general argument is given extending this result to all orders of perturbation theory in the effective low-energy theory, proving also that no trilinear soft supersymmetry breaking terms in the effective potential are generated. These results are applicable to the four-dimensional no-scale supergravity theory obtained from the superstring after compactification, and support suggestions that the dominant source of global supersymmetry breaking in this theory may be the gaugino mass.

Radiative Fermion Masses and Supersymmetry

Abstract We explore various ways in which the observed hierarchical mass structure for fermions can be accounted for by successive radiative corrections in supersymmetric theories. Soft breaking of supersymmetry which may arice from gravitational effects can be relevant for a gravitino mass between 0.1 and 1 TeV.

Supersymmetry breaking in the observable sector of superstring models

Abstract We discuss the communication of supersymmetry breaking from the gravitino mass m 3 2 to gaugino masses m 1 2 , scalar masses m0, and trilinear scalar couplings A in superstring models, assuming that the effective low-energy N=1, d=4 supergravity has a modified “no-scale” structure. It is known that m 1 2 ≠ 0 at the one-loop level, whilst squared scalar masses m02 van at the one-loop level. We analyse a large class of two-loop diagrams, showing that their quadratic divergences cancel and that they contribute m 2 0 = O 4 (m 3 2 /m 2 P ) . We also show that A appears in one-loop order, but is much smaller than m 1 2 . Therefore the initial conditions m 1 2 ⪢A ⪢m 0 are appropriately in renormalization group analyses of effective low-energy models inspired by the superstring.

Rare kaon processes as a probe of the top quark and gravitino masses in local supersymmetric (SUSY) theories

Abstract A detailed analysis of the rare K processes in local SUSY theories is given. The top quark mass cannot be much higher than O(100 GeV) without making the gravitino mass lower than O(20 GeV), its present lower bound in local SUSY theories from PETRA and PEP.

Towards a formulation of

The supersymmetric completion of