Single and pair production of MSSM Higgs bosons as a probe of scalar-pseudoscalar mixing at e+e- colliders

We study the associated production of the $A^0$ neutral CP--odd Higgs boson with a neutral gauge boson $Z$ as well as single production of $A^0$ via $e^+e^- \to \nu_e {\bar\nu}_e A^0$ at the one loop level in the Minimal Supersymmetric Standard Model (MSSM). We show that the MSSM cross--section may be enhanced by light SUSY particles. Then we study the production processes $e^+e^-\to H^0_iZ$, $H^0_i\nu_e\bar \nu_e$ and $H^0_iH^0_j$ in the context of the MSSM with scalar-pseudoscalar mixing. In a given channel we show that the cross--section for all i (=1,2,3) can be above 0.1 fb provided M_{H_{2,3}}\la 300 GeV. This should be detectable at a Next Linear Collider and would provide evidence for scalar--pseudoscalar mixing.Comment: 7 pages, latex, 2 eps figures, preprints LPHEA/2002-05, MPI-PhT/2002-64, Talk given at the 10th International Conference on Supersymmetry and Unification of Fundamental Interactions, DESY, Hamburg, Germany, June 17--23, 200

Effect of Fourth Generation CP Phase on b\to s Transitions

We study the effect of a sequential fourth generation on b\to s gamma, B_s mixing, B\to K^{(*)}\ell^+\ell^-, X_s\ell^+\ell^- and \phi K_S, taking into account the presence of a new CP phase in quark mixing. We find that the effects via electromagnetic and strong penguins, such as in b\to s gamma or CP violation in B\to \phi K_S, are rather mild, but impact via box or Z penguins is quite significant. Not only can one have much larger than expected B_s mixing, even if it is measured near the present limit, mixing dependent CP violation could become maximal. For electroweak penguin modes, the fourth generation can provide the enhancement that perhaps may be needed, while the m_{\ell^+\ell^-} dependence of the forward-backward asymmetry in B\to K^{*}\ell^+\ell^- can further probe for the fourth generation. These effects can be studied in detail at the B factories and the Tevatron.Comment: 8 pages, latex, 9 eps figures, one reference added, to appear in EPJ

Higgs Phenomenology in the Two-Singlet Model

We study the phenomenology of the Standard Model (SM) Higgs sector extended by two singlet scalars. The model predicts two CP-even scalars $h_{1,2}$ which are a mixture of doublet and singlet components as well as a pure singlet scalar $S_{0}$ which is a dark matter candidate. We show that the model can satisfy the relic density and direct detection constraints as well as all the recent ATLAS and CMS measurements. We also discuss the effect of the extra Higgs bosons on the different Higgs triple couplings $h_{i}h_{j}h_{k}$, $i,j,k=1,2$. A particular attention is given to the triple self-coupling of the SM-like Higgs where we found that the one loop corrections can reach $150\%$ is some cases. We also discuss some production mechanisms for $h_{1}$ and $h_{2}$ at the LHC as well as at the future International Linear Collider. It is found that the production cross section of a pair of SM-like Higgs bosons could be much larger than the corresponding one in the SM and would reveal physics beyond the SM if observable. We also show that in this model the branching ratio of the SM-like Higgs decaying to two singlet scalars could be of the order of $20\%$, therefore the production of the SM Higgs followed by its decay to a pair of singlets would be an important source of production of singlet scalars.Comment: 27 pages, 8 figures, 2 tables, published versio

Triple Higgs Coupling as a Probe of the Twin-Peak Scenario

In this letter, we investigate the case of a twin peak around the observed 125 GeV scalar resonance, using di-Higgs production processes at both LHC and $e^{+}e^{-}$ Linear Colliders. We have shown that both at LHC and Linear Collider the triple Higgs couplings play an important role to identify this scenario; and also that this scenario can be distinguishable from any Standard Model extension by extra massive particles which might modify the triple Higgs coupling. We also introduce a criterion that can be used to ruled out the twin peak scenario.Comment: 6 pages, 4 figures, typos corrected, some results are modified & version published in PL

Bosonic Decays of Charged Higgs Bosons in a 2HDM Type-I

In this study, we focus on the bosonic decays of light charged Higgs bosons in the 2-Higgs Doublet Model (2HDM) Type-I. We quantify the Branching Ratios (BRs) of the $H^\pm \to W^\pm h$ and $H^\pm\to W^\pm A$ channels and show that they could be substantial over several areas of the parameter space of the 2HDM Type-I that are still allowed by Large Hadron Collider (LHC) and other experimental data as well as theoretical constraints. We suggest that $H^\pm \to W^\pm h$ and/or $H^\pm \to W^\pm A$ could be used as a feasible discovery channel alternative to $H^\pm \to \tau\nu$.Comment: 6 pages, 4 figures, Discussion extended, typos corrected and references adde