This article summarizes recent developments in
B\to D^{(\ast)}\tau\nuB→D(*)τν
decays. We explain how to extract the tau lepton’s production properties
from the kinematics of its decay products. The focus is on hadronic tau
decays, which are most sensitive to the tau polarizations. We present
new results for effects of new physics in tau polarization observables
and quantify the observation prospects at BELLE II.
Physics cases of rare B meson decays at Belle II
