Finding neutral Higgs bosons in a two-Higgs-doublet model with spontaneous CP violation

We consider a particular two-Higgs-doublet model with spontaneous CP violation, where two neutral Higgses have no definite CP properties and the third one is CP-even. In this model, as the parameter $\theta$ of CP violation increases, the masses of the neutral Higgs bosons are drawn towards the mass of the lightest one and the chance of detection of neutral Higgses at an $e^+e^-$ collider in Z+Higgs, $b\bar{b}$+Higgs and $t\bar{t}$+Higgs production increases with respect to the CP conserving case.