Speakers
Description
We revisit an old proposal where a pseudoscalar $A^0$ has mass between
$t\bar c$ and $t\bar t$ thresholds, but possess extra Yukawa couplings
by absence of $Z_2$ symmetry. With $\rho_{tt}$ small, it evades
$gg \to A^0 \to h^0(125)Z$ constraints, where approximate alignment
also helps. We find this scenario with relatively light $A^0$ is
not yet ruled out, and $cg \to tA^0 \to tt\bar c$ can probe sizable
$\rho_{tc}$ at the LHC. In a similar vein, we find that discovery
is possible for $m_H \sim$ 300 GeV for $cg \to tH^0 \to thh$, but would
need finite $h$-$H$ mixing angle $\cos\gamma$ to allow for finite
$\lambda_{Hhh}$ coupling, and $\rho_{tc}$ also needs to be not too
small. The latter could drive electroweak baryogenesis, which further
motivates the search.
