  A search is presented for new Higgs bosons in proton-proton (pp) collision
events in which a same-sign top quark pair is produced in association with a
jet, via the pp $\to$ tH/A $\to$ t$\mathrm{\bar{t}}$c and pp $\to$ tH/A $\to$
t$\mathrm{\bar{t}}$u processes. Here, H and A represent the extra scalar and
pseudoscalar boson, respectively, of the second Higgs doublet in the
generalized two-Higgs-doublet model (g2HDM). The search is based on pp
collision data collected at a center-of-mass energy of 13 TeV with the CMS
detector at the LHC, corresponding to an integrated luminosity of 138
fb$^{-1}$. Final states with a same-sign lepton pair in association with jets
and missing transverse momentum are considered. New Higgs bosons in the
200-1000 GeV mass range and new Yukawa couplings between 0.1 and 1.0 are
targeted in the search, for scenarios in which either H or A appear alone, or
in which they coexist and interfere. No significant excess above the standard
model prediction is observed. Exclusion limits are derived in the context of
the g2HDM.
