Transverse Polarization of Top Quark Pairs at the Tevatron and the Large Hadron Collider

We investigate the prospects to observe effects of transverse polarization of top quarks in $pp,p\bar{p}\to t\bar{t}X$. QCD absorptive parts generate a polarization of top quarks and antiquarks transverse to the production plane in the partonic processes $q\bar{q}\to t\bar{t}$ and $gg\to t\bar{t}$, which reaches values of a few percent. These perturbative QCD effects are decreased at the hadronic level. A measurement through momentum correlations among the $t$ and $\bar{t}$ decay products will be difficult both at an upgraded Tevatron and at the LHC.