  We summarize the different features which show that QCD spectral sum rule
analyses of the scalar two- and three-point functions do not favour the $\bar
uu+\bar dd$ interpretation of the broad and low mass $\sigma (0.6)$ and
emphasize that a measurement of the $D_s$ semileptonic decays into $\pi\pi$ can
reveal in a model-independent way its eventual gluon component $\sigma_B$. The
analysis also implies that one expects an observation of the $K\bar K$ final
states from the $\sigma_B$ which may compete (if phase space allowed) with the
one from a low mass $\bar ss$ state assumed in the literature to be the SU(3)
partner of the observed $\sigma (0.6)$ if the latter is a $\bar uu+\bar dd$
state
