We consider constraints on the momentum fraction of the $K$ and $K^{*}$ meson carried by the strange quark that follow from exact operator identities, similar to those for the divergence of the quark part of the QCD energy-momentum tensor. The existing QCD sum rule estimates are reanalyzed in this context. Our conclusions essentially support the constituent quark-model picture where the momentum fraction is roughly proportional to the constituent quark mass, but the asymmetry turns out to be smaller compared to the naive quark-model estimates. As a by-product of this study, we calculate the SU(3)-breaking quark-antiquark-gluon matrix elements that determine the leading conformal spin contributions to the asymmetry in twist-four distribution amplitudes of strange mesons $K$ and $K^{*}$, and also update the estimate for the SU(3) breaking for the quark-antiquark-gluon vacuum condensate.

• Received 3 August 2004

DOI:https://doi.org/10.1103/PhysRevD.70.074020