Does the Electromagnetic Current Have a Unitary Singlet Component?

A possibility that the electromagnetic current may have a unitary singlet component has been investigated in connection with $V_9\to l\overline{l}$ decays. The Maki-Hara model of elementary particles seems to be experimentally ruled out. As for the three-triplet model, it has been pointed out that we must have additional $1^{-}$ vector mesons ${\rho }^{\prime }$, ${\omega }^{\prime }$, and ${\phi }^{\prime }$ with nonzero charm quantum numbers in order to saturate a new sum rule.