Testing lepton flavor universality in terms of BESIII and charm-tau factory data

The recent measurements on R-K and R-pi imply that there exists a possible violation of the leptonic flavor universality which is one of the cornerstones of the Standard Model. It is suggested that a mixing between sterile and active neutrinos might induce such a violation. In this work we consider the scenarios with one or two sterile neutrinos to explicitly realize the data while the constraints from the available experiments have been taken into account. Moreover, as indicated in literature, the deviation of the real PMNS matrix from the symmetric patterns may be due to a mu-tau asymmetry, therefore the measurements on R-D(Ds)mu = Gamma(D(D-s) -> e(+)-nu(e))/Gamma(D(D-s)->mu(+)nu(mu)) and R-D (D-s)(mu tau) = Gamma(D(D-s)->mu(+)nu(mu)/Gamma(D(D-s)->(+)nu(tau)) (and for some other heavy mesons B-+/- and B-c etc.) may shed more light on the physics responsible for the violation of the leptonic flavor universality. The data of BEM are available to test the universality and that of future charm-tau factories will provide more accurate information. In this work, we will discuss R-D(D-s)(e mu) and R-D(D-s)(mu tau) in detail and also briefly consider the cases for B-+/- and B-c.