Top Quark Polarization and the Search for New Physics

Forward-backward asymmetries $A_{FB}^t$ and $A_{FB}^\ell$ are observed in the top quark $t$ rapidity distribution and in the rapidity distribution of charged leptons $\ell$ from top quark decay at the Tevatron proton-antiproton collider, and a charge asymmetry $A_C$ is seen in proton-proton collisions at the Large Hadron Collider (LHC). In this presentation, I summarize research my collaborators and I have done on the interpretation and implications of the Tevatron asymmetries and provide expectations for $A_C$ at the LHC. The two asymmetries $A_{FB}^t$ and $A_{FB}^\ell$ are connected through the $(V-A)$ spin correlation between the charged lepton and the top quark with different polarization states. The ratio of the two asymmetries provides independent insight into the physics interpretation of the top quark asymmetry. A new physics model which produces more right-handed than left-handed top quarks appears to be indicated by the present Tevatron data, but an improvement in precision is desirable.