With or without U(2)? Probing non-standard flavor and helicity structures in semileptonic B decays

摘要

Motivated by the recent hints of lepton flavor universality violation observed in semileptonicBdecays, we analyze how to test flavor and helicity structures of the corresponding amplitudes in view of future data. We show that the general assumption that such non-standard effects are controlled by aU(2)q×U(2)?flavor symmetry, minimally broken as in the Standard Model Yukawa sector, leads to stringent predictions on leptonic and semileptonicBdecays. Future measurements ofRD(?),RK(?),B(Bˉc,u→?νˉ),B(Bˉ→π?νˉ),B(B→π??ˉ),B(Bs,d→??ˉ(′)), as well as various polarization asymmetries inBˉ→D(?)τνˉdecays, will allow to prove or falsify this general hypothesis independently of its dynamical origin.