Mass and form factor effects in spectrum and width of the semileptonic decays of charmed mesons

Semileptonic decays of charmed mesons of F and D types with tau lepton production are considered using as an example the energetically possible decay of D-sub(S) meson in π0 and tau-. As the mass msub(tau) of tau lepton is big we consider the mass effects in the decay spectrum which are very closely connected to form factor effects in our approach. (author)