For potentials with n-Higgs-boson doublets stability, electroweak symmetry breaking, and the stationarity equations are discussed in detail. This is done within the bilinear formalism which simplifies the investigation, in particular since irrelevant
gauge degrees of freedom are systematically avoided. For the case that the potential leads to the physically relevant electroweak symmetry breaking the mass matrices of the physical Higgs bosons are given explicitly.
Motivated by the neutrino data, an extension of the Standard Model with three Higgs-boson doublets has been proposed. Imposing an O(2) x Z2 family symmetry, a neutrino mixing matrix with theta23 = pi/4 and theta13 = 0 appears in a natural way. Even t
hough these values for the mixing matrix do not follow the recent experimental constraints, they are nevertheless a good approximation. We study the Higgs potential of this model in detail. We apply recent methods which allow for the study of any three-Higgs-boson doublet model. It turns out that for a variety of parameters the potential is stable, has the correct electroweak symmetry breaking, and gives the correct vacuum expectation value.
Stability, electroweak symmetry breaking, and the stationarity equations of the general three-Higgs-doublet model (3HDM) where all doublets carry the same hypercharge are discussed in detail. Employing the bilinear formalism the study of the 3HDM pot
ential turns out to be straightforward. For the case that the potential leads to the physically relevant electroweak symmetry breaking we present explicit formulae for the masses of the physical Higgs bosons.
A Monte Carlo event generator is constructed for a two-Higgs-doublet model with maximal CP symmetry, the MCPM. The model contains five physical Higgs bosons; the $rho$, behaving similarly to the standard-model Higgs boson, two extra neutral bosons $h
$ and $h$, and a charged pair $H^pm$. The special feature of the MCPM is that, concerning the Yukawa couplings, the bosons $h$, $h$ and $H^pm$ couple directly only to the second generation fermions but with strengths given by the third-generation-fermion masses. Our event generator allows the simulation of the Drell-Yan-type production processes of $h$, $h$ and $H^pm$ in proton-proton collisions at LHC energies. Also the subsequent leptonic decays of these bosons into the $mu^+ mu^-$, $mu^+ u_mu$ and $mu^- bar u_mu$ channels are studied as well as the dominant background processes. We estimate the integrated luminosities needed in $p p$ collisions at center-of-mass energies of 8 TeV and 14 TeV for significant observations of the Higgs bosons $h$, $h$ and $H^pm$ in these muonic channels.
Electroweak precision measurements, encoded in the oblique parameters, give strong constraints on physics beyond the Standard Model. The oblique parameters S, T, U (V, W, X) are calculated in the next-to-minimal supersymmetric model (NMSSM). We outli
ne the calculation of the oblique parameters in terms of one-loop gauge-boson selfenergies and find sensitive restrictions for the NMSSM parameter space.
We discuss the classification of symmetries and the corresponding symmetry groups in the two-Higgs-doublet model (THDM). We give an easily useable method how to determine the symmetry class and corresponding symmetry group of a given THDM Higgs poten
tial. One of the symmetry classes corresponds to a Higgs potential with several simultaneous generalised CP symmetries. Extending the CP symmetry of this class to the Yukawa sector in a straightforward way, the so-called maximally-CP-symmetric model (MCPM) is obtained. We study the evolution of the quartic Higgs-potential parameters under a change of renormalisation point. Finally we compute the so called oblique parameters S, T, and U, in the MCPM and we identify large regions of viable parameter space with respect to electroweak precision measurements. We present the corresponding allowed regions for the masses of the physical Higgs bosons. Reasonable ranges for these masses, up to several hundred GeV, are obtained which should make the (extra) Higgs bosons detectable in LHC experiments.
Predictions for LHC physics are given for a two-Higgs-doublet model having four generalized CP symmetries. In this maximally-CP-symmetric model (MCPM) the first fermion family is, at tree level, uncoupled to the Higgs fields and thus massless. The se
cond and third fermion families have a very symmetric coupling to the Higgs fields. But through the electroweak symmetry breaking a large mass hierarchy is generated between these fermion families. Thus, the fermion mass spectrum of the model presents a rough approximation to what is observed in Nature. In the MCPM the couplings of the Higgs bosons to the fermions are completely fixed. This allows us to present clear predictions for the production at the LHC and for the decays of the physical Higgs bosons. As salient feature we find rather large cross sections for Higgs-boson production via Drell-Yan type processes. In this paper we present a short outline of the model and extend a former study by the predictions at LHC for a center-of-mass energy of 7 TeV.
The two-Higgs-doublet model can be constrained by imposing Higgs-family symmetries and/or generalized CP symmetries. It is known that there are only six independent classes of such symmetry-constrained models. We study the CP properties of all cases
in the bilinear formalism. An exact symmetry implies CP conservation. We show that soft breaking of the symmetry can lead to spontaneous CP violation (CPV) in three of the classes.
