The Second Moment of the Structure Function for Pseudoscalar Mesons in   QCD Sum Rules
  We calculate the values of the second moment $M_2^s$ of the flavor-singlet structure function $F_2^s$ for the pion and the kaon in QCD sum rules, and investigate how the results depend on their flavor structure (quark contents). Our calculations give similar values of $M_2^s$ for these two mesons, because of cancellation among several non-small factors. We emphasize that decay constants, meson masses and quark masses play an essential role in the above cancellation. 
Yoshinori Nishino