Related papers: String Unification at Intermediate Energies: Pheno…
We investigate whether inclusion of dimension six terms in the Standard Model lagrangean may cause the unification of the coupling constants at a scale comprised between 10^14 and 10^17 GeV. Particular choice of the dimension 6 couplings is…
We study the potential of a static quark anti-quark pair in the confinement ``phase'' of the SU(2) Higgs model. Around separation r_b, the confining string of the gauge field breaks by formation of a dynamical pair of light quarks. The…
We derive the universal threshold corrections in heterotic string theory including a continuous Wilson line. Unification of gauge and gravitational couplings is shown to be possible even within perturbative string theory. The relative…
The interpretation of the apparent unification of gauge couplings within supersymmetric theories depends on uncertainties induced through heavy particle thresholds. While in standard grand unified theories these effects can be estimated…
The effects of extra dimensions on gauge coupling unification is studied. We start with a comparison between power law running of the gauge couplings in models with extra dimensions and logarithmic running that happens in many realistic…
The unification of gauge couplings suggests that there is an underlying (supersymmetric) unification of the strong, electromagnetic and weak interactions. The prediction of the unification scale may be the first quantitative indication that…
The possibility to achieve unification at the string scale in the context of the simplest supersymmetric grand unified theory is investigated. We find conservative upper bounds on the superpartner masses consistent with the unification of…
We consider the renormalisation group flow of gauge couplings within the so-called exceptional supersymmetric standard model (E$_6$SSM) based on the low energy matter content of 27 dimensional representations of the gauge group $E_6$,…
I discuss gauge coupling unification in a class of superstring standard--like models, which are derived in the free fermionic formulation. Recent calculations indicate that the superstring unification scale is at $O(10^{18}GeV)$ while the…
We look for minimal chiral sets of fermions beyond the standard model that are anomaly free and, simultaneously, vectorlike particles with respect to colour SU(3) and electromagnetic U(1). We then study whether the addition of such…
The discovery of the Higgs boson at the LHC supports the hypothesis that the Standard Model provides an effective parameterisation of all subatomic experimental data up to the Planck scale. String theory, which provides a viable…
These four lectures, addressed to an audience of graduate students in experimental high energy physics, survey some of the basic concepts in string theory. The purpose is to convey a general sense of what string theory is and what it has…
We propose that gaugino condensation in the hidden sector may dynamically induce intermediate gauge symmetry breaking and specify the compactification scale. We also show that this scheme makes possible affine level one grand unified string…
It is known that hidden U(1) gauge factors can couple to visible U(1)'s through Kinetic Mixing. This phenomenon is shown generically to occur in nonsupersymmetric string set-ups, between branes and antibranes. Kinetic Mixing acts either to…
We propose that a modified version of string-inspired supersymmetry breaking schemes in \cite{wit2} and \cite{ross} may make affine level one SU(5) and SO(10) string models with intermediate gauge symmetry breaking scale…
The approximate unification of gauge couplings is the best indirect evidence for low-energy supersymmetry, although it is not perfect in its simplest realizations. Given the experimental evidence for small non-zero neutrino masses, it is…
We present a class of heterotic compactifications where it is possible to lower the string unification scale down to the GUT scale, while preserving the validity of the perturbative analysis. We illustrate this approach with an explicit…
In a $Z_{12-I}$ orbifold compactification through an intermediate flipped SU(5), the string MSSM (${\cal S}$MSSM) spectra (three families, one pair of Higgs doublets, and neutral singlets) are obtained with the Yukawa coupling structure.…
The simplest minimal left-right symmetric extension of the standard model is studied in the high energy limit, and some consequences of the grand unification hypothesis are explored assuming that the parity breaking scale is the only…
We use recently obtained 2-loop string coupling constants to analyze a class of string models based on orbifold compactification. Assuming weak coupling at the string scale and single-scale unification leads to restrictions on the spectrum…