The Phenomenology of the CP-odd Scalar of Two-Doublet Models

We examine the phenomenology of the $CP$-odd scalar $A^0$ of two-Higgs-doublet models. We explore the parameter space determined by triviality bounds and identify the regions where the $A^0$ can be detected at the LHC in each of the following modes: the inclusive two-photon decay mode, the $l^{\pm }\gamma \gamma X$ mode from $t\bar{t}{A}^0$ production and the $A^0\to Zh$ channel with the subsequent decay of the $CP$-even scalar $h$ to two photons. We find that, while the $l^{\pm }\gamma \gamma X$ mode is of limited usefulness, the other two modes can give viable signals in fairly large, and complementary, regions of parameter space.