@article{oai:ynu.repo.nii.ac.jp:00003695,
 author = {Sasaki, Ken and Soffer, J. and Uematsu, T.},
 issue = {3},
 journal = {Physical Review D},
 month = {Aug},
 note = {application/pdf, We study the three positivity constraints on the eight virtual photon structure functions, derived from the Cauchy-Schwarz inequality and which are, hence, model independent. The photon structure functions obtained from the simple parton model show quite different behaviors in a massive or a massless quark case, but they satisfy, in both cases, the three positivity constraints. We then discuss an inequality which holds among the unpolarized and polarized photon structure functions F-1(gamma), g(1)(gamma), and W-TT(tau), in the kinematic region Lambda(2)<P-2<Q(2), where -Q(2)(-P-2) is the mass squared of the probe (target) photon, and we examine whether this inequality is satisfied by the perturbative QCD results.},
 title = {Virtual photon structure functions and positivity constraints},
 volume = {66},
 year = {2002}
}