Costas Kounnas

Naturally Vanishing Cosmological Constant in N=1 Supergravity

Abstract For N =1 supergravity theories we show that the choice of a particular class of Einstein spaces for the Kahler manifold of the hidden sector leads to a vanishing cosmological constant without unnatural fine tuning. The total scalar potential from the hidden and physical sector is positive definite. The resulting low energy softly broken globl supersymmetry for the matter fields is thus the same as in the case of factorized superpotential models with a flat Kahler metric.

No Scale Supersymmetric Guts

We construct locally supersymmetric GUTs in which radiative corrections determine all the mass scales which are hierarchically smaller than the Planck mass: m32 = O(mW) = exp (−O(1)αt)mp, etc. Such no-scale GUTs are based on a hidden sector with a flat potential guaranteed by SU(1, 1) conformal invariance. This is extended to include observable chiral fields in an SU(n, 1)/SU(n) × U(1) structure reminiscent of N ⩾ 5 extended supergravity theories. Tree-level supersymmetry breaking is present only for the gravitino, and for the light gaugino masses through non-minimal kinetic terms reminiscent of N⩾4 extended supergravity theories. Radiative corrections generate squark and slepton masses which are phenomenologically acceptable, and the right value of mW is obtained if mt ≈ 50 GeV in the simplest such model.

On loop corrections to string effective field theories: field-dependent gauge couplings and σ-model anomalies

Abstract We show that certain one-loop corrections to superstring effective four-dimensional lagragians, involving non-harmonic field-dependent renormalization of gauge couplings, can be consistently written in a standard N = 1 supergravity form, preserving target-space duality. The preservation of target-space duality is due both to a four-dimensional Green-Schwarz mechanism and to local terms, coming from non-local chiral superfields, originated by mixed gauge-σ-model anomaly diagrams. In some models, the Green-Schwarz mechanism is sufficient to achieve complete anomaly cancellation. In more general models automorphic functions, generated by the integration over the heavy string modes, are required to preserve target-space duality.

Vector multiplets coupled to N=2 supergravity: Super-Higgs effect, flat potentials and geometric structure

We obtain general properties of N=2 gauged extended supergravity coupled to vector multiplets, which can gauge an arbitrary group. General formulas for masses and curvatures are derived. Particular attention is devoted to the scalar potential of the theory which determines the classical vacuum structure. Explicit examples are given in which the potential is identically zero, but supersymmetry is broken. It is found that these theories are symmetric under generalized duality transformations.

Phenomenological SU(1,1) Supergravity

We investigate the structure of phenomenological supergravity models which permit the hierarchy problem to be “solved” in the sense that m32 and mW are determined dynamically to be exp [-O(1)/α] × mP. Such models must have a flat hidden sector potential, which is only possible if the theory has an underlying SU(1, 1) invariance. Flat SU(1, 1) theories necessarily have a zero cosmological constant and the hidden sector is an Einstein space with Rzz∗ = 23Gzz∗. The SU(1, 1) invariance is necessarily broken down to U(1) by the gravitino mass. If m32 is the only source of SU(1, 1) breaking then the tree-level gaugino masses are small and A = 32, while values of A up to 3 and non-zero gaugino masses are possible if other sources of SU(1, 1) breaking are tolerated. Yukawa couplings may scale as some power of m32mP in these models where m32 is generated dynamically, which may explain the hierarchy of Higgs-fermion Yukawa couplings: mfmW = O(mWmP)λ>0? These models also permit the spontaneous violation of CP in the Yukawa coupling matrix. Numerical studies yield 20 GeV < mt < 100 GeV in these phenomenological SU(1, 1) supergravity models. Speculations are presented about their relation to a fundamental theory based on extended supergravity.

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.

Superpotentials in IIA compactifications with general fluxes

We derive the effective N = 1, D = 4 supergravity for the seven main moduli of type IIA orientifolds with D6 branes, compactified on T 6 /(Z2 × Z2) in the presence of general fluxes. We illustrate and apply a general method that relates the N = 1 �

Superstrings with spontaneously broken supersymmetry and their effective theories

We discuss superstring models with spontaneous breaking of N=1, 2 or 4 space-time supersymmetry, via coordinate-dependent compactifications from five to four dimensions. We provide a description of the supersymmetry breaking mechanism in the formulation with complex world-sheet fermions, and we reinterpret it in terms of special deformations of the lorentzian charge lattice. Considering a representative string model with spontaneously broken N=1 supersymmetry and massless chiral fermions, we show that the knowledge of the spectrum of states and of the flat directions completely specifies its low-energy effective lagrangian, which turns out to be a new no-scale supergravity model. We outline the qualitative difference between these models and other scenarios of gaugino (gravitino) condensation or general non-perturbative phenomena.

Spontaneous supersymmetry breaking in string theory

Abstract We present a construction of string theories, with spontaneously broken supersymmetry and chiral fermion families, obtained by a suitable choice of boundary conditions in toroidal compactifications of ten-dimensional (1,1) or heterotic models. The crystallographic groups in four-dimensions determine the possible values of the supersymmetry-breaking parameters, which therefore are discrete.

Higher Order QCD Effects in Inclusive Annihilation and Deep Inelastic Scattering

Abstract We present a parton model interpretation of the predictions of quantum chromodynamics in the process e + e − →hadron + anything. We give thecomplete list of parameters needed for the study of the scaling violations of fragmentation functions up to the next-to-leading logarithmic approximation. This includes flavour non-singlet and flavour singlet anomalous dimensions up to order α 2 and coefficient functions up to order α. We also present results for the deep inelastic scattering e − h→e − + anything. We find that in e + e − annihilation the ratio of scaling violations of second order to first order is in general bigger than the corresponding ratio for deep inelastic scattering. The Gribov-Lipatov relation is thus violated in second order. We also find that a modified Drell-Yan analytic continuation relation holds between the deep inelastic and annihilation structure functions for quarks and gluons. In x space we give detailed numerical evaluation of the QCD effects for non-singlet and singlet densities, in the space-like and time-like regions.