[en] This thesis concerns study of extended Higgs sectors at future colliders. Such studies are well motivated since enlarged Higgs models are a necessity in many extensions of the Standard Model (SM), although these structures may be considered purely in the context of the SM, to be called the 'non-minimal SM'. The continuous theme of the thesis is the task of distinguishing between the (many) theoretically sound non-minimal Higgs sectors at forthcoming colliders. If a Higgs boson is found it is imperative to know from which model it originates. In particular, the possible differences between the Higgs sectors of the Minimal Supersymmetric Standard Model (MSSM) and the non-minimal SM are highlighted. (author)

[en] We study the direct CP asymmetry of the decays b → sγ, and b → dγ, in the context of two models: i) a supersymmetric (SUSY) model with unconstrained SUSY phases, and ii) a model with a single generation of vector quarks. In both the above models we show that b → dγ can sizeably influence the combined asymmetry (i.e. that of a sample containing both b → sγ and b → dγ), and in case (ii) may in fact be the dominant contribution

[en] The purely leptonic decays D^±→e^±ν and D^±_s→e^±ν, for which no experimental limits exist, are highly suppressed in the Standard Model. Mere observation of these decays at the B factories Belle/BaBar or forthcoming CLEO-c would be a clear signal of physics beyond the SM. We show that R-parity violating slepton contributions can give rise to spectacular enhancements of the decay rates, resulting in branching ratios as large as 5x10^-3, which strongly motivates a search in these channels

[en] We study the decays of Higgs bosons to a lighter Higgs boson and a virtual gauge boson in the context of the non-supersymmetric two-Higgs doublet model (2HDM). We consider the phenomenological impact at LEP2 and find that such decays, when open, may be dominant in regions of parameter space and thus affect current Higgs boson search techniques. Three-body decays would be a way of producing light neutral Higgs bosons which have so far escaped detection at LEP due to suppressed couplings to the Z, and are of particular importance in the 2HDM (Model I) which allows both a light fermiophobic Higgs and a light charged scalar

No abstract available

[en] We consider the impact of cosmological B-L constraints on supersymmetric standard models without R-parity which can account for the observed atmospheric and solar neutrino masses and mixing. In order to avoid erasing any primordial baryon or lepton asymmetry above the electroweak scale, B-L violation for at least one generation should be sufficiently small. We show that a narrow parameter space of the bilinear model may satisfy such constraints as well as provide the form of the neutrino mass matrix required by current data

[en] The measurement of Β^±→τ^±ν_τ at the Β factories provides important constraints on the parameter tan β/m_h^± in the context of models with two Higgs doublets. Limits on this decay from the LEP1 experiment (i.e. e⁺e^- collisions at the Z peak) were sensitive to the sum of Β^±→τ^±ν_τ and Β^±_c→τ^±ν_τ. We point out that a future e⁺e^- Linear Collider operating at the Z peak (the Giga Z option) could constrain tan β/m_h^± from the sum of these processes with a precision comparable to that anticipated at proposed high-luminosity B factories from B^±→τ^±ν_τ alone. This work is an updated summary of the publication Phys. Rev. D, 77 (2008) 115018, by Akeroyd, Chen and Recksiegel.

[en] We investigate the effect of a charged Higgs boson (H^±) on the decays D_s^± → μ^±ν_μ and D_s^± → γ^±ν_τ, which will be measured with high precision at forthcoming CLEO-c. We emphasize that such contributions should not be overlooked when comparing lattice calculations of f_Ds to the values obtained from these decays. (author)

[en] It is possible that the Standard Model possesses a non-minimal Higgs sector. We consider various extended Higgs models and highlight two distinctive signatures which may be of relevance at present colliders: a light charged scalar (H^+-) and a fermiophobic neutral scalar (H_F). (author)

[en] Current searches for doubly charged Higgs bosons (H^±±) at the Fermilab Tevatron are sensitive to single production of H^±±, although the pair production mechanism qq→H⁺⁺H^-- is assumed to be dominant. In the context of a Higgs Triplet Model we study the mechanism q^'q→H^±±H^± at the Tevatron and CERN Large Hadron Collider, and show that its inclusion can significantly improve the search potential for H^±±. Moreover, assuming that the neutrino mass is generated solely by the triplet field Yukawa coupling to leptons, we compare the branching ratios of H^±±→l^±l^± and H^±±→H^±W* for the cases of a normal hierarchical, inverted hierarchical, and degenerate neutrino mass spectrum