Top flavour-changing neutral interactions with a light quark q=u,c and a gauge or Higgs boson are very suppressed within the Standard Model (SM), but can reach observable levels in many of its extensions. We review the possible size of the effective vertices Ztq, \gamma tq, gtq and Htq in several SM extensions, and discuss the processes in which these interactions might show up at LHC and at a high energy e⁺ e^- linear collider.

PACS numbers: 12.15.Mm, 12.60.--i, 14.65.Ha