The electroweak sector in superstring models

Phenomenological constraints on the extra low-mass neutral gauge boson Z′ of present superstring models are presented and shown to imply a very fine tuning of the parameters involved in the Higgs potential.     

Supersymmetry and superstring phenomenology

We briefly cover the early history of supersymmetry, describe the relation of SUSY quantum field theories to superstring theories and explain why they are considered a likely tool to describe the phenomenology of high energy particle theory beyond the Standard Model.     

Supersymmetry breaking

We review the various mechanisms of supersymmetry breaking and its transmission to the observable sector. We argue that hybrid models where gauge dominates over gravity mediation, but gravity provides the main contributions to the Higgs sector masses and the neutralino mass, are able to combine the advantages and reduce the disadvantages of the two transmission mechanisms.      

Goldstone fermion couplings and supersymmetry breaking in superstring models

We re-examine supersymmetry breaking in the observable sectors of superstring-inspired supergravity models by computing Goldstone fermion couplings at the one-loop level. We find that a single global U (1) phase invariance is sufficient to forbid masses for gauge non-singlet chiral scalar bosons, and that Heisenberg symmetry is not necessary.     

Supersymmetry breaking and gauge mediation in models with a generic superpotential

We present a general scheme for finding or creating a metastable vacuum in supersymmetric theories. By using the formalism, we show that there is a parameter region where a metastable vacuum exists in the Wess–Zumino model coupled to messenger fields. This model serves as a perturbative renormalizable model of direct gauge mediation.     

Supersymmetry breaking in quantum mechanics

We study the restoration of rotational symmetry of the heavy quark potential obtained from elongated planar and off-axis Wilson loops measured on a 16⁴ lattice at β=5.4 and 5.7. While the rotational symmetry is still distorted at β=5.4 the potential is consistent with rotational symmetry at β=5.7. If we were in the asymptotic scaling region the linear slope would correspond at β=5.7 to a string tension Λ_L/?σ = 0.0074±0.0002.     

Supersymmetry breaking in warped geometry

We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS₅ which generate the hierarchical Yukawa couplings by dynamically quasi-localizing the bulk matter fields in an extra dimension. Such models can be regarded as the AdS dual of the recently studied 4-dimensional models which contain a supersymmetric CFT to generate the hierarchical Yukawa couplings. In such models, if supersymmetry breaking is mediated by the bulk radion superfield and/or some brane chiral superfields, potentially dangerous flavor-violating soft parameters are suppressed with an appropriate correlation with the Yukawa coupling suppression, thereby avoiding the SUSY flavor problem in a natural manner. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework, and discuss the constraints from flavor-changing rare processes. Most of the discussions in this paper can be applied also to models with a flat extra dimension in which the Yukawa hierarchy is generated by quasi-localizing the bulk matter fields in the extra dimension.Received: 21 October 2003, Revised: 12 January 2004, Published online: 5 May 2004     

Supersymmetry breaking in three dimensions

One-loop corrections to the effective potential in three-dimensional supersymmetric massless scalar electrodynamics are calculated to see whether or not they spontaneously break supersymmetry. It is found that neither the supersymmetry nor the U(1) gauge invariance is broken by one-loop effects.     

Inflation as a cure for the cosmological problems of superstring models with intermediate scale breaking

Superstring inspired models with an intermediate stage of symmetry breaking have severe cosmological problems associated with the breaking of discrete symmetries (domain wall problem) and with the need for a light decoupled scalar field (Polonyi problem). We show that an early period of inflation which gives the desired flatness, dilution of unwanted species, and density fluctuations also eliminates the problem associated with intermediate scale breaking. Mechanisms regenerating the baryon-number asymmetry are briefly described.     

On supersymmetry breaking in superstring theories

We show that non-zero gaugino condensates of several non-abelian gauge groups G₁⊗…⊗G_k∃E₈ in low-energy d=4 superstring E₈⊗E₆ gauge theory can lead to the exponentially small (compared to the Planck scale) supersymmetry breaking scale. The Hosotani mechanism can provide the E₈→G₁⊗…⊗G_k breaking.     

E6 symmetry breaking in the superstring theory

We derive two methods for determining the symmetry breaking of E₆ in the low energy superstring theory, and classify all breaking patterns. A method for calculating the effective Higgs vacuum expectation values is presented. We show that there are theories with naturally light SU₂^w Higgs doublets, and classify all theories in which this occurs. The phenomenology of spontaneously broken E₆ theories is discussed, emphasizing the issues of nucleon decay and neutrino masses.     

Supersymmetry breaking and soft terms in M-theory

We investigate gaugino condensation in the framework of the strongly coupled heterotic E₈×E₈ string (M-theory). Supersymmetry is broken in a hidden sector and gravitational interactions induce soft breaking parameters in the observable sector. The resulting soft masses are of order of the gravitino mass. The situation is similar to that in the weakly coupled E₈×E₈ theory with one important difference: we avoid the problem of small gaugino masses which are now comparable to the gravitino mass.