[3] The addition of the second Higgs doublet leads to a richer phenomenology as there are five physical scalar states viz., the CP even neutral Higgs bosons h and H (where H is heavier than h by convention), the CP odd pseudoscalar A and two charged Higgs bosons H±.
, the heavier CP even boson, i.e. H is SM-like, leaving h to be the lighter than the discovered Higgs; however, it is important to note that experiments have strongly pointed towards a value for
[5] Such a model can be described in terms of six physical parameters: four Higgs masses (
) which diagonalizes the mass matrix of the neutral CP even Higgses.
The SM uses only 2 parameters: the mass of the Higgs and its vacuum expectation value.
The masses of the H and A bosons could be below 1 TeV and the CMS has conducted searches around this range but no significant excess above the standard model prediction has been observed.
[6][7] Two-Higgs-doublet models can introduce flavor-changing neutral currents which have not been observed so far.
The Glashow-Weinberg condition, requiring that each group of fermions (up-type quarks, down-type quarks and charged leptons) couples exactly to one of the two doublets, is sufficient to avoid the prediction of flavor-changing neutral currents.
, one can divide two-Higgs-doublet models into the following classes:[8][9] By convention,