In the presence of CP violation, the Higgs-top coupling may have both scalar
and pseudoscalar components, κt and κ~t, which are
bounded indirectly but only weakly by the present experimental constraints on
the Higgs-gluon-gluon and Higgs-γ-γ couplings, whereas upper
limits on electric dipole moments provide strong additional indirect
constraints on κ~t, if the Higgs-electron coupling is similar
to that in the Standard Model and there are no cancellations with other
contributions. We discuss methods to measure directly the scalar and
pseudoscalar Higgs-top couplings by measurements of Higgs production in
association with tˉt, single t and single tˉ at the LHC.
Measurements of the total cross sections are very sensitive to variations in
the Higgs-top couplings that are consistent with the present indirect
constraints, as are invariant mass distributions in tˉtH, tH and
tˉH final states. We also investigate the additional information on
κt and κ~t that could be obtained from measurements of
the longitudinal and transverse t polarization in the different associated
production channels, and the tˉt spin correlation in tˉtH
events.Comment: 19 pages, 11 figure