Testing Time Reversal Invariance in Exclusive Semileptonic B Meson Decays

We demonstrate that polarization measurements in exclusive semileptonic B decays are powerful tools for unraveling non-standard model sources of T-violation. Measurements of the transverse polarization of the \tau lepton in the $B \rightarrow D \tau \overline{\nu}$ and $B \rightarrow D^* \tau \overline{\nu}$ decays probe separately effective scalar and pseudoscalar CP-violating four-Fermi interactions, whereas the D^* polarization in the $B \rightarrow D^* l \overline{\nu}$ (l=e, \mu) decay is sensitive to an effective right-handed quark current interaction. Two T-odd polarization structures exist involving the D^* polarization and they can be isolated and studied separately. An estimate of these T-odd effects is also given in the context of supersymmetric theories.