Probing Top Changing Neutral Higgs Couplings at Colliders

Abstract

The $h(125)$ boson, discovered only in 2012, is lower than the top quark in mass, hence $t\to ch$ search commenced immediately thereafter, with current limits at the per mille level and improving. As the $t\to ch$ rate vanishes with the $h$-$H$ mixing angle $\cos \gamma \to 0$, we briefly review the collider probes of the top changing $tcH/tcA$ coupling ${\rho }_{tc}$ of the exotic $CP$-even/odd Higgs bosons $H/A$. Together with an extra top conserving $ttH/ttA$ coupling ${\rho }_{tt}$, one has an enhanced $cb{H}^{+}$ coupling alongside the familiar $tb{H}^{+}$ coupling, where $H^{+}$ is the charged Higgs boson. The main processes we advocate are $cg\to tH/A\to tt\bar{c},tt\bar{t}$ (same-sign top and triple-top), and $cg\to b{H}^{+}\to bt\bar{b}$. We also discuss some related processes such as $cg\to thh$, $tZH$ that depend on $\cos \gamma$ being nonzero, comment briefly on $gg\to H/A\to t\bar{t},t\bar{c}$ resonant production, and touch upon the ${\rho }_{tu}$ coupling.

25 pages, 10 figures, brief review to appear in MPLA

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