Barygenesis without grand unification

A mechanism is pointed out to generate cosmological baryon number excess without resorting to grand unified theories. The lepton number excess originating from Majorana mass terms may transform into the number excess through the unsuppressed baryon number violation of electroweak processes at high temperatures.     

The geometry of grand unification

Arguments are presented which lead to the conclusion thatSU(3, 2) is the grand unification gauge group (GUGG). The gauge theory includes all known forces. We incorporated supersymmetry within the framework of the gauge theory and show how the theory may be quantized.     

Proton hexality in local grand unification

Proton hexality is a discrete symmetry that avoids the problem of too fast proton decay in the supersymmetric extension of the standard model. Unfortunately it is inconsistent with conventional grand unification. We show that proton hexality can be incorporated in the scheme of “Local Grand Unification” discussed in the framework of model building in (heterotic) string theory.     

SU(8) grand unification

A grand unified gauge theory based on the group SU(8) is presented. The set of rules motivating the choice of SU(8) is given. The particle content of the theory suggests a natural embedding of a horizontal SU(3) symmetry in the SU(8) grand unified symmetry.     

Hierarchical fermion masses from grand unification

A mechanism is presented for generating fermion masses as a reflection of the superheavy fermions existing in a class of grand unified theories. By means of it we propose a way of understanding how, giving a driving mass term for the top-generation, the charm-generation mass results as a relative first-order perturbation in the unified gauge coupling g²/4π ≈ 10^?2, and the up-generation mass as a second-order perturbation. An illustrative calculation of the charm-generation mass is described in a model based on E₆.     

F-theory grand unification at the colliders

We predict the exact gaugino mass relation near the electroweak scale at one loop for gravity mediated supersymmetry breaking in F-theory SU(5) and SO(10) models with UY(1) and U(1)_B−L fluxes, respectively. The gaugino mass relation introduced here differs from the typical gaugino mass relations studied thus far, and in general, should be preserved quite well at low energy. Therefore, these F-theory models can be tested at the Large Hadron Collider and future International Linear Collider. We present two typical scenarios that satisfy all the latest experimental constraints and are consistent with the CDMS II experiment. In particular, the gaugino mass relation is indeed satisfied at two-loop level with only a very small deviation around the electroweak scale.     

Supersymmetric grand unification with light color-triplet

We construct a natural model of the supersymmetric SU(6)$\mathit{SU}(6)$ unification, in which the symmetry breaking, down to the standard model gauge group, results in the number of pseudo-Nambu–Goldstone superfields with interesting properties. Namely, besides the Higgs doublet–antidoublet pair which is responsible for the electroweak phase transition, the Nambu–Goldstone sector consists of multiplets in the anti- and fundamental representations of SU(5)$\mathit{SU}(5)$. While being strictly massless in the supersymmetric limit, they acquire the weak scale masses as a result of its breaking. The color-triplet components of this light sector could, in principle, mediate an unacceptably fast proton decay; however, because of the natural TeV/_MGUT$\text{TeV}/M_{\mathrm{GUT}}$ suppression of the Yukawa couplings to the light quarks and leptons, their existence is compatible with the experimental bound on proton lifetime. This suppression is made further interesting, since it results in the lifetime, of the lightest of the above-mentioned colored particles from 1 s to 1 day$1\text{day}$, long enough for it to appear stable in the detector. Furthermore, we argue that the accommodation of the color-triplet pseudo-Nambu–Goldstones, without fine-tuning or contradicting observations, implies SU(6)$\mathit{SU}(6)$ unification.     

Asymptotically safe phantom cosmology

New lifetime limits on the charge non-conserving (CNC) electron capture with excitation of the 417.9 keV nuclear level in the ¹²⁷I are established by using the coincidence technique. The analysed exposure is 0.87 ton × yr, collected deep underground at the Gran Sasso National Laboratory of the INFN by the highly radiopure DAMA/LIBRA setup (??250 kg of highly radiopure NaI(Tl)). The new limit on the mean life is ??>1.2×10²⁴?yr (90?% C.L.), about one order of magnitude larger than those previously available for CNC electron capture involving nuclear level excitations of ¹²⁷I and of the same order of magnitude than those achieved for analogous processes in ¹²⁹Xe.     

An extended technicolour model for grand unification

An extended technicolour grand unification model based on the gauge groupE ₆×SU(7) extended technicolour is presented. The symmetry-breaking based on extended technicolour theory is discussed. It is shown that the existing phenomenology is well explained by the model. The strangeness changing neutral currents may not be a problem with this model.     

Local grand unification in the heterotic landscape

We consider the possibility that the unification of the electroweak interactions and the strong force arises from string theory, at energies significantly lower than the string scale. As a tool, an effective grand unified field theory in six dimensions is derived from an anisotropic orbifold compactification of the heterotic string. It is explicitly shown that all anomalies cancel in the model, though anomalous Abelian gauge symmetries are present locally at the boundary singularities. In the supersymmetric vacuum additional interactions arise from higher‐dimensional operators. We develop methods that relate the couplings of the effective theory to the location of the vacuum, and find that unbroken discrete symmetries play an important role for the phenomenology of orbifold models. An efficient algorithm for the calculation of the superpotential to arbitrary order is developed, based on symmetry arguments. We furthermore present a correspondence between bulk fields of the orbifold model in six dimensions, and the moduli fields that arise from compactifying four internal dimensions on a manifold with non‐trivial gauge background.     

Merging gauge coupling constants without grand unification

The merging of the running coupling constants of the weak, strong, and electromagnetic fields does not require the unification of these gauge fields at high energy. It can, in fact, be the property of a general fermionic system in which gauge bosons are not fundamental.     

Large R-parity violating couplings and grand unification

We consider the possibility that R-parity violating interactions of particles which do not involve the first generation have large (up to 1) coupling constants, λ. Such couplings, if they exist, could have a number of phenomenological consequences: renormalization of the b − τ mass ratio, generation of ν_τ mass in the MeV region, etc. In grand unified models, where B- and L-violating couplings appear simultaneously, proton decay can be forbidden in virtue of the hierarchical flavor structure of λ. However, due to Cabibbo-Kobayashi-Maskawa mixing this decay is induced already at one loop. Present experimental data give the upper bound λ ⪅ 10⁻⁸ (or |λ′λ″| ⪅ 7 × 10⁻¹⁶, on products of certain L- and B-violating coupling constants, in a more general context). The bound can be avoided if there is an asymmetry between the L- and B-violating couplings of the usual matter fields. In the SU(5) model the asymmetry can be related to the doublet-triplet splitting.