The Pure Leptonic Decays of $D_s$ Meson and Their Radiative Corrections

Abstract

The radiative corrections to the pure leptonic decay $D_s{\longrightarrow} {\ell}{ν}_{\ell}$ up-to one-loop order is presented. We find the virtual photon loop corrections to $D_s{\longrightarrow} τ{ν}_τ$ is negative and the corresponding branching ratio is larger than $3.51\times 10^{-3}$. Considering the possible experimental resolutions, our prediction of the radiative decay $D_s{\longrightarrow} τ{ν}_τγ$ is not so large as others, and the best channel to determine the $V_{cs}$ or $f_{D_s}$ is $D_s{\longrightarrow} μ{ν}_μγ$. How to cancel the infrared divergences appearing in the loop calculations, and the radiative decay $D_s{\longrightarrow} {\ell}{ν}_{\ell}γ$ is shown precisely. It is emphasized that the radiative decay may be separated properly and may compare with measurements directly as long as the theoretical `softness' of the photon corresponds to the experimental resolutions.