Related papers: String Unification and Threshold Corrections
We study the evolution of the gauge coupling constants in string unification schemes in which the light spectrum below the compactification scale is exactly that of the minimal supersymmetric standard model. In the absence of string…
One of the much-debated novel features of theories with extra dimensions is the presence of power-like loop corrections to gauge coupling unification, which have the potential of allowing a significant reduction of the unification scale. A…
We study gauge coupling unification in the presence of extra dimensions compactified at a few TeV. Achieving unification requires a large number of gauge boson Kaluza-Klein excitations lighter than the string scale, such that the…
We consider the phenomenological implications of a class of compactified string theories which naturally reproduces the flavour multiplet structure of the Standard Model. The implications for gauge unification depends on which of three…
We study the effects of additional fields on the unification of gauge couplings in supersymmetric models. We find that the effects are quite constrained by the requirement of SU(5) gauge invariance. In general, we find that any extension of…
A long-standing problem in string phenomenology has been the fact that the string unification scale disagrees with the GUT scale obtained by extrapolating low-energy data within the framework of the minimal supersymmetric standard model…
The prediction of the strong coupling constant in grand unified theories is reviewed, first in the standard model, then in the supersymmetric version. Various corrections are considered. The predictions in both supergravity-induced and…
We study strong coupling effects in four-dimensional heterotic string models where supersymmetry is spontaneously broken with large internal dimensions, consistently with perturbative unification of gauge couplings. These effects give rise…
Gauge coupling unification is studied in the MSSM with non-universal soft supersymmetry breaking terms. If gaugino masses are sufficiently smaller than scalar soft masses and the scalar soft masses have also certain types of…
Like grand unification of old, string unification predicts simple tree-level relations between the couplings of all unbroken gauge groups such as $SU(3)_C$ or $SU(2)_W\)$. I show here how to compute one-loop corrections to these relations…
The supersymmetry breaking parameters and the resulting supersymmetric particle spectrum are studied in orbifold compactifications of string theory under the assumption that unification of gauge coupling constants at about $10^{16}$ GeV is…
Power-like loop corrections to gauge couplings are a generic feature of higher-dimensional field theories. In supersymmetric grand unified theories in d=5 dimensions, such corrections arise only in the presence of a vacuum expectation value…
Tests of gauge coupling unification require knowledge of thresholds between the weak scale and the high scale of unification. If these scales are far separated, as is the case in most unification scenarios considered in the literature, the…
In this paper we study the influence of the threshold effects due to massive degrees of freedom in the evolution with scale of gauge coupling constants. We first describe in detail the (standard) mass dependent renormalization prescription…
I discuss several aspects of strings as unified theories. After recalling the difficulties of the simplest supersymmetric grand unification schemes I emphasize the distinct features of string unification. An important role in constraining…
A general prediction of string unification is the existence of exotic states with fractional charges under the free unbroken Abelian generators of the underlying GUT symmetry. Such states may be long-lived due to the existence of weakly…
Superstring phenomenology aims at achieving two goals. The first is to reproduce the observed physics of the Standard Model. The second is to identify experimental signatures of superstring unification which, if observed, will provide…
We consider N=1 supersymmetric U(N), SO(N), and Sp(N) gauge theories, with two-index tensor matter and added tree-level superpotential, for general breaking patterns of the gauge group. By considering the string theory realization and…
We make a detailed analysis of gauge coupling unification in supersymmetry. When the Standard Model gauge group is embedded in a Grand Unified Theory, new particles often appear below the GUT scale in order to predict the right…
We describe a class of supersymmetric unified models with the following properties: i) the full breaking of the gauge group is achieved by Higgs fields in the fundamental representation; ii) the correct unification of the strong and…