Related papers: Higgs--Matter splitting in quasi-realistic orbifol…
A Z_2 orbifold compactification of the heterotic string is considered. The resulting 6D GUT groups can be SO(16) or E_7 times SU(2) plus some hidden sector groups. The N=4 supersymmetry is reduced to N=2. In particular, the SO(16) 6D model…
Motivated by the pressing problem of the ``little hierarchies'', the possibility of realizing a consistent model of Electroweak Symmetry Breaking via the so-called ``Gauge-Higgs Unification Mechanism'' is discussed. We identify a class of 6…
We present a detailed study of the quark and lepton mass spectra in a SO(10) framework with one 10_H and one \bar{126}_H Higgs representations in the Yukawa sector. We consider in full generality the interplay between type-I and type-II…
We study the role of fermionic resonances in realistic composite Higgs models. We consider the low energy effective description of a model in which the Higgs arises as the pseudo-Goldstone boson of an SO(5)/SO(4) global symmetry breaking…
We propose a class of E6-based local orbifold Grand Unified Theories (GUTs) which yield an exceptional supersymmetric standard model as their low energy theory including leptoquark and unhiggs exotics and a Z' at the TeV scale. Unification…
We construct a compactification of the heterotic string on an orbifold T^6/Z_6 leading to the standard model spectrum plus vector--like matter. The standard model gauge group is obtained as an intersection of three SO(10) subgroups of E_8.…
I discuss how effective grand unified theories requiring adjoint Higgs fields for breaking to the standard model can be contained within string theory. Initial findings are presented in a search for and classification of effective three…
We investigate composite two Higgs doublet models realized as pseudo Goldstone modes, generated through the spontaneous breaking of a global symmetry due to strong dynamic at the TeV scale. A detailed comparative survey of two possible…
Based on a few basic assumptions, a predictive supersymmetric grand unification $G_{U}=SO(10)\times \Delta_{48}(SU(3))\times U(1)$ model is proposed. Thus, all the observed 45 chiral fermions with additional 3 right-handed neutrinos are…
A SUSY SO(10) $\times A_4$ GUT model is constructed for fermion masses and mixing by introducing a minimal set of low dimensional Higgs representations needed to break the guage symmetry down to $SU(3)_c \times U(1)_{em}$. The hierarchy of…
Quasi--realistic heterotic-string models in the free fermionic formulation typically contain an anomalous U(1), which gives rise to a Fayet-Iliopolous term that breaks supersymmetry at the one--loop level in string perturbation theory.…
We investigate gauge coupling unification in higher dimensional GUT models with split supersymmetry. We focus on 5d and 6d orbifold GUTs, which permit a simple solution to several problems of 4D GUTs as well as control over GUT scale…
It is shown that non-renormalizable gravitational interactions in the Higgs sector of supersymmetric grand unified theories (GUT's) can produce the breaking of the unifying gauge group $G$ at the GUT scale $M_{\rm GUT} \sim 10^{16}$~GeV.…
We show that by combining the elementary-Goldstone-Higgs scenario and supersymmetry it is possible to raise the scale of supersymmetry breaking to several TeVs by relating it to the spontaneous-symmetry-breaking one. This is achieved by…
We investigate the decoupling of heavy right handed neutrinos in the context of an SO(10) GUT model, where a remnant anomalous symmetry is $U(1)_{X}$. In this model the see-saw mechanism which generates the neutrino masses is intertwined…
We investigate the cosmological constraints on exotic stable matter states which arise in realistic free fermionic superstring models. These states appear in the superstring models due to a ``Wilson--line'' breaking of the unifying…
After a brief review of the motivations for grand unification, I discuss the main challenges facing realistic SUSY GUT model building. Achieving doublet-triplet splitting without fine--tuning is chief among them. Symmetry breaking should…
The vanishing of the Higgs quartic coupling of the Standard Model at high energies may be explained by spontaneous breaking of Higgs Parity. Taking Higgs Parity to originate from the Left-Right symmetry of the $SO(10)$ gauge group, leads to…
We study the emergence and phenomenological consequences of recently proposed new structures, namely soft breaking of the Higgs shift symmetry and `maximal symmetry' of the composite sector, in holographic realizations of composite Higgs…
We consider scenarios of Higgs compositeness where the Higgs doublet arises as a pseudo-Nambu Goldstone boson. Our focus is the physical scalar ("radial") excitation associated with the global symmetry breaking vacuum, which we call the…