On the D^*+_s -> D^+_s pi^0 decay in the Effective quark model with chiral U(3)xU(3) symmetry

The partial width of the decay D^+_s -> D^+_s pi^0 going through the violation of isotopical symmetry is computed with respect to the partial width of the radiative decay D^+_s -> D^+_s gamma in the effective quark model with chiral U(3)xU(3) symmetry incorporating Heavy quark effective theory (HQET) and Chiral perturbation theory at the quark level (CHPT)_q. We investigate a sensitivity of the ratio of the partial widths R_0 to current s-quark mass corrections and find a strong dependence.