Naturally massless Higgs doublets in supersymmetric SU(5)

We construct a supersymmetric SU(5) model characterized by: (a) naturally massless doublet Higgs superfields; (b) the natural appearance of “light” coloured triplet Higgses of mass of the order 10¹⁰ GeV, and study proton decay as well as the generation of cosmic baryon asymmetry. We find that an appropriate choice of Higgs sector renders dimension-five operators kinematically irrelevant for the stability of the proton. Proton decay proceeds through Higgs boson exchange in terms of dimension-six operators mainly to ${\overline{v}}_{\mu }{K}^{+},v^{+}{K}^0$.     

SU(5) Higgs problem with adjoint + vector representations

Recently Kim has given a general method, using group-invariant orbit parameters, for determining the energy and residual symmetry of the Higgs potential minimum. In this paper we illustrate the method by working out the case of a quartic SU(5) Higgs potential with $\text{5}$ and $\text{24}$ higgsons. In this method the Gell-Mann-Slansky conjecture concerning possible little groups of the potential minimum takes a geometric form, which is verified for our case. The results are used to discuss the hierarchical symmetry breaking of SU(5) grand unification theory. We generalize our results to the SU(N) adjoint + vector models, which are all closely related.     

SU (5) + adjoint Higgs model at finite temperature

A three-dimensional effective theory of the finite-temperature SU(5) + adjoint Higgs model is constructed using the method of dimensional reduction. The resulting theory can be used for computer simulations of the GUT phase transition of the early universe. In this paper the transition is analyzed at two-loop level in perturbation theory. The structure of the effective theory does not essentially depend on the matter contents of the original four-dimensional one. Therefore the analysis of this paper applies also to more realistic theories.     

SU(5) effective potential including Higgs loop contribution and bounds for the Higgs masses

We refine the calculation of the SU(5) effective potential including Higgs and radiative contributions in the one-loop level. We give the mass spectrum and from this and the stability of the symmetry breaking pattern we derive bounds for the Higgs masses and inequalities between the Higgs couplings and the gauge coupling.     

Magnetic monopoles in SU(3) and SU(2) gauge theories without Higgs' scalars

We show that certain known singular solutions for pure SU(3) Yang-Mills theory carry magnetic charges with respect to both U(1) subgroups of SU(3). A topological characterisation in terms of monopoles is given to the SU(2) singular solutions of Wu and Yang.     

SU(3) predictions for nonleptonicT-meson decays

The predictions ofSU(3) are analyzed for the decays of theT-mesons (T ⁰,T ⁺,T _s ⁺ ). Relations betweenT-meson decay rates are given. Some of these relations may provide important information for searching top mesons.     

Influence of strongly coupled,hidden scalars on Higgs signals

To investigate the possible effects of a light hidden sector on Higgs boson detection, we discuss a model of scalar singlets coupled to the Standard Model. The model effectively makes the Higgs width a free parameter due to additional invisible decay modes. This width can become arbitrarily large. Theoretical and experimental bounds on model parameters are presented. It is shown, how Standard Model predictions change and that in the case of large coupling, Higgs signals will be diluted. We study, to which extent such a strongly coupled, hidden sector can be excluded by present and future Higgs search experiments.     

Implications of constraints on mass parameters in the Higgs sector of the nonlinear supersymmetric SU(5) model

By using the non-relativistic effective Lagrangian approach to bound states, a complete expression for the isospin-breaking corrections to the energy levels and the decay widths of kaonic hydrogen is obtained up-to-and-including in QCD. It is demonstrated that, although the leading-order corrections at emerging due to the unitarity cusp are huge, they can be expressed solely in terms of the KN S-wave scattering lengths. Consequently, at leading order, it is possible to derive parameter-free modified Deser-type relations, which can be used to extract the scattering lengths from the hadronic atom data.A. Rusetsky: On leave of absence from HEPI, Tbilisi State University, University st. 9, 380086 Tbilisi, Georgia     

Two-dimensional SU(N) Higgs theory: An instanton approach

The two-dimensional non-abelian Higgs model is studied by employing a dilute gas of Z_N vortices. The results obtained are similar to the corresponding results of the abelian model, studied by Callan, Dashen and Gross, and Raby and Ukawa. The most interesting conclusion is that in the presence of some number, N_F, of massless fermion flavors, the theory behaves differently for N > N_crit or N < N_crit where N_crit = N_F/(N_F?2).