145 research outputs found
Unitarity bound in the most general two Higgs doublet model
We investigate unitarity bounds in the most general two Higgs doublet model
without a discrete symmetry nor CP conservation. S-wave amplitudes for
two-body elastic scatterings of Nambu-Goldstone bosons and physical Higgs
bosons are calculated at high energies for all possible initial and final
states (14 neutral, 8 singly-charged and 3 doubly-charged states). We obtain
analytic formulae for the block-diagonalized scattering matrix by the
classification of the two body scattering states using the conserved quantum
numbers at high energies. Imposing the condition of perturbative unitarity to
the eigenvalues of the scattering matrix, constraints on the model parameters
can be obtained. We apply our results to constrain the mass range of the
next--to--lightest Higgs state in the model.Comment: Version published in Physics Letters
The 750 GeV diphoton excess and its explanation in 2-Higgs Doublet Models with a real inert scalar multiplet
We discuss a possible explanation of the recently observed diphoton excess at
around 750 GeV as seen by the ATLAS and CMS experiments at the Large Hadron
Collider. We calculate the cross section of the diphoton signature in 2-Higgs
Doublet Models with the addition of a real isospin scalar multiplet without a
vacuum expectation value, where a neutral component of such a representation
can be a dark matter candidate. We find that the branching fraction of an
additional CP-even Higgs boson from the doublet fields into the diphoton
mode can be significantly enhanced, by up to a factor of , with respect
to the case of the simple 2-Higgs Doublet Model. Such a sizable enhancement is
realized due to multi-charged inert particle loops entering the decay mode. Through this enhancement, we obtain a suitable cross
section of the process to explain the data with the
fixed mass of being 750 GeV.Comment: Version accepted in PRD, Appendix adde
Renormalizable Model for Neutrino Mass, Dark Matter, Muon and 750 GeV Diphoton Excess
We discuss a possibility to explain the 750 GeV diphoton excess observed at
the LHC in a three-loop neutrino mass model which has a similar structure to
the model by Krauss, Nasri and Trodden. Tiny neutrino masses are naturally
generated by the loop effect of new particles with their couplings and masses
to be of order 0.1-1 and TeV, respectively. The lightest right-handed neutrino,
which runs in the three-loop diagram, can be a dark matter candidate. In
addition, the deviation in the measured value of the muon anomalous magnetic
moment from its prediction in the standard model can be compensated by one-loop
diagrams with exotic multi-charged leptons and scalar bosons. For the diphoton
event, an additional isospin singlet real scalar field plays the role to
explain the excess by taking its mass of 750 GeV, where it is produced from the
gluon fusion production via the mixing with the standard model like Higgs
boson. We find that the cross section of the diphoton process can be obtained
to be a few fb level by taking the masses of new charged particles to be about
375 GeV and related coupling constants to be order 1.Comment: 17 pages, 8 figure
- …