Approximation by Power Series of Functions

Derivative-matching approximations are constructed as power series built from functions. The method assumes the knowledge of special values of the Bell polynomials of the second kind, for which we refer to the literature. The presented ideas may have applications in numerical mathematics

Study of Bs→ℓ+ℓ−γB_s\to\ell^+\ell^-\gamma decays in covariant quark model

We study the rare radiative leptonic decays $B_s\to\ell^+\ell^-\gamma$ ($\ell=e,\mu,\tau$) within the Standard Model, considering both the structure-dependent amplitude and bremsstrahlung. In the framework of the covariant confined quark model developed by us, we calculate the form factors characterizing the $B_s\to\gamma$ transition in the full kinematical region of the dilepton momentum squared and discuss their behavior. We provide the analytic formula for the differential decay distribution and give predictions for the branching fractions in both cases: with and without long-distance contributions. Finally, we compare our results with those obtained in other approaches.Comment: 22 pages, 8 figures, 6 tables, more references and material added, a version to appear on PR