Bs0 → l+l-γ as a test of lepton flavor universality

We discuss a number of strategies to reduce the B(B-s(0) -> l(+)l(-)gamma) theoretical error, and make such a measurement a new probe of the interactions that are interesting in the light of present-day flavor discrepancies. In particular, for low di-lepton invariant mass we propose to exploit the close parenthood between B(B-s(0) -> l(+)l(-)gamma) and the measured B(B-s(0) -> phi(-> K+K-)gamma). For high q(2), conversely, we exploit the fact that the decay is dominated by two form-factor combinations, plus contributions from broad charmonium that we model accordingly. We construct the ratio R-gamma, akin to R-K and likewise sensitive to lepton-universality violation. Provided the two rates in this ratio are integrated in a suitable region that minimises bremsstrahlung contributions while maximising statistics, the ratio is very close to unity and the form-factor dependence cancels to an extent that makes it a new valuable probe of lepton-universality violating contributions in the effective Hamiltonian. We finally speculate on additional ideas to extract short-distance information from resonance regions, which are theoretically interesting but statistically limited at present.