Probing top changing neutral Higgs couplings at colliders

Abstract

The [Formula: see text] boson, discovered only in 2012, is lower than the top quark in mass, hence [Formula: see text] search commenced immediately thereafter, with current limits at the per mille level and improving. As the [Formula: see text] rate vanishes with the [Formula: see text]-[Formula: see text] mixing angle [Formula: see text], we briefly review the collider probes of the top changing [Formula: see text] coupling [Formula: see text] of the exotic [Formula: see text]-even/odd Higgs bosons [Formula: see text]. Together with an extra top conserving [Formula: see text] coupling [Formula: see text], one has an enhanced [Formula: see text] coupling alongside the familiar [Formula: see text] coupling, where [Formula: see text] is the charged Higgs boson. The main processes we advocate are [Formula: see text], [Formula: see text] (same-sign top and triple-top), and [Formula: see text]. We also discuss some related processes such as [Formula: see text], [Formula: see text] that depend on [Formula: see text] being nonzero, comment briefly on [Formula: see text] resonant production and touch upon the [Formula: see text] coupling.