  Searches for new physics in the top-quark sector using data from
proton-antiproton collisions at the Fermilab Tevatron are discussed. The large
data sets collected by the D0 and CDF experiments allow for precision
measurements of the standard model (SM) top-quark production rates and top
quark properties so that deviations from the SM expectations can be interpreted
as signs of new physics. The presented analyses exploit the fact that the new
physics would reveal itself in final states that are similar or identical to
those of SM top-antitop production.
