We review the possible role that multi-Higgs models may play in our understanding of the dynamics of a heavy 4th sequential generation of fermions. We describe the underlying ingredients of such models, focusing on two Higgs doublets, and discuss how
they may effectively accommodate the low energy phenomenology of such new heavy fermionic degrees of freedom. We also discuss the constraints on these models from precision electroweak data as well as from flavor physics and the implications for collider searches of the Higgs particles and of the 4th generation fermions, bearing in mind the recent observation of a light Higgs with a mass of ~125 GeV.
The analysis of tagged B_s -> J/psi phi decays determines the CP phase phi_s in B_s-anti-B_s mixing with a two-fold ambiguity. The solutions differ in the sign of cos(phi_s) which equals the sign of the width difference Delta Gamma_s among the two B_
s mass eigenstates. We point out that this ambiguity can be removed with the help of B_s -> D_s K decays. We compare untagged and tagged strategies and find the tagged analysis more promising. The removal of the sign ambiguity in Delta Gamma_s can be done with relatively low statistics and could therefore be a target for the early stage of B_s -> D_s K studies.
In the minimal Standard Model (SM) with four generations (the so called SM4) and in standard two Higgs doublets model (2HDM) setups, e.g., the type II 2HDM with four fermion generations, the contribution of the 4th family heavy leptons to the muon ma
gnetic moment is suppressed and cannot accommodate the measured $ sim 3 sigma$ access with respect to the SM prediction. We show that in a 2HDM for the 4th generation (the 4G2HDM), which we view as a low energy effective theory for dynamical electroweak symmetry breaking, with one of the Higgs doublets coupling only to the 4th family leptons and quarks (thus effectively addressing their large masses), the loop exchanges of the heavy 4th generation neutrino can account for the measured value of the muon anomalous magnetic moment. We also discuss the sensitivity of the lepton flavor violating decays $mu to e gamma$ and $tau to mu gamma$ and of the decay $B_s to mu mu$ to the new couplings which control the muon g-2 in our model.
We investigate new physics models that can increase the lifetime differences in the $B_q$--$bar{B}_q$ systems ($q = d,s$) above their standard model values. If both $B_q$ as well as $bar{B}_q$ can decay to a final state through flavour dependent new
physics interactions, the so-called Grossman bound may be evaded. As examples, we consider the scalar leptoquark model and $lambda$-type R-parity violating supersymmetry. We find that models with a scalar leptoquark can enhance $DeltaGamma_s/Gamma_s$ all the way up to its experimental upper bound and $DeltaGamma_d/Gamma_d$ to as much as $sim 2.5%$, at the same time allowing the CP violating phase $beta_s$ to vary between $- 45^circ$ and $20^circ$. R-parity violating supersymmetry models cannot enhance the lifetime differences significantly, but can enhance the value of $beta_s$ up to $sim pm 20^circ$. This may bring the values of $DeltaGamma_q/Gamma_q$ as well as $beta_s$ within the measurement capabilities of $B$ factories and LHCb. We also obtain bounds on combinations of these new physics couplings, and predict enhanced branching ratios of $B_{s/d} to tau^+ tau^-$.
