Many new physics models contain new particles that interact with the Higgs boson. These particles could be produced at the LHC via gluon-gluon fusion with an off-shell Higgs, as well as via the Drell-Yan process if charged under a gauge group. We con
sider in this paper simplified scenarios where the Standard Model is extended by one scalar or fermionic field that interacts with the Higgs boson and we evaluate the impact of the Higgs interaction on the production of the exotic particles at the LHC. This analysis applies in particular to TeV scale seesaw scenarios of neutrino mass generation.
The couplings of the low scale type I see-saw model are severely constrained by the requirement of reproducing the correct neutrino mass and mixing parameters, by the non-observation of lepton number and charged lepton flavour violating processes and
by electroweak precision data. We show that all these constraints still allow for the possibility of an exotic Higgs decay channel into a light neutrino and a heavy neutrino with a sizable branching ratio. We also estimate the prospects to observe this decay at the LHC and discuss its complementarity to the indirect probes of the low scale type I see-saw model from experiments searching for the $muto egamma$ decay.
Effects of the lightest neutrino mass in flavoured leptogenesis when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in the neutrino mixing matrix $U$ are di
scussed. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The orthogonal parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix $R$, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hierarchy) are reviewed.
The effects of the lightest neutrino mass in ``flavoured leptogenesis are investigated in the case when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in th
e neutrino mixing matrix U. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The ``orthogonal parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hierarchy) are obtained. It is shown, in particular, that if the matrix R is real and CP-conserving and the lightest neutrino mass m_3 in the case of inverted hierarchical spectrum lies the interval 5 times 10^{-4} eV < m_3 < 7 times 10^{-3} eV, the predicted baryon asymmetry can be larger by a factor of sim 100 than the asymmetry corresponding to negligible m_3 cong 0. As consequence, we can have successful thermal leptogenesis for 5 times 10^{-6} eV < m_3 < 5 times 10^{-2} eV even if R is real and the only source of CP-violation in leptogenesis is the Majorana and/or Dirac phase(s) in U.
We calculate, in the continuum limit of quenched lattice QCD, the form factor that enters in the decay rate of the semileptonic decay B --> D l nu. Making use of the step scaling method (SSM), previously introduced to handle two scale problems in lat
tice QCD, and of flavour twisted boundary conditions we extract G(w) at finite momentum transfer and at the physical values of the heavy quark masses. Our results can be used in order to extract the CKM matrix element Vcb by the experimental decay rate without model dependent extrapolations.
