Charged Higgs and neutral Higgs pair production of the weak gauge boson fusion process in electron-positron collisions

Pair production of the neutral and charged Higgs bosons is a unique process that is a signature of the two-Higgs-doublet model. In this paper, we study the pair production and decays of the Higgses in the neutrinophilic two-Higgs-doublet model. The pair production occurs through the W and Z gauge boson fusion process. In the neutrinophilic model, the vacuum expectation value (VEV) of the second Higgs doublet is small and is proportional to the neutrino mass. The smallness of VEV is associated with the approximate global U(1) symmetry, which is slightly broken. Therefore, there is a suppression factor for the U(1) charge breaking process. The second Higgs doublet has U(1) charge; its single production from gauge boson fusion violates the U(1) charge conservation and is strongly suppressed. In contrast to the single production, the pair production of the Higgses conserves U(1) charge and the approximate symmetry does not forbid it. To search for the pair productions in a collider experiment, we study the production cross section of a pair of charged Higgs and neutral Higgs bosons in e(+)e(-) collisions with a center of energy from 600 GeV to 2000 GeV. The total cross section varies from 10(-4) fb to 10(-3) fb for the degenerate (200 GeV) charged and neutral Higgs mass case. The background process to the signal is the gauge boson pair W+ + Z production and their decays. We show that the signal over background ratio is about 2-3% by combining the cross section ratio with ratios of branching fractions.