Constraining a lighter exotic scalar via same-sign top

It was shown recently that, in two Higgs doublet models without Z(2) symmetry, extra Yukawa couplings such as rho(tc), rho(tt) can fuel enough CP violation for electroweak baryogenesis (EWBG). We revisit an old proposal where a pseudoscalar A(0) has mass between t (c) over bar and t (t) over bar thresholds. With rho(tt) small, it evades gg -> A(0) -> 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 -> tA(0) -> tt (c) over bar can probe sizable rho(tc) at the LHC, giving access to the second mechanism of EWBG provided by such models. (C) 2018 The Author(s). Published by Elsevier B.V.