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Small-x behaviour of the polarized structure function $F_3^γ(x,Q^2)$

We study the small-$x$ behaviour of the polarized photon structure function $F_3^{\ga}$, measuring the gluon transversity distribution, in the leading logarithmic approximation of perturbative QCD. There are two contributions, both arising from two-gluon exchange. The leading contribution to small-$x$ is related to the BFKL pomeron and behaves like $x^{-1-\om_2}$, $\om_2 = {\cal O}(\al_S)$. The other contribution includes in particular the ones summed by the DGLAP equation and behaves like $x^{1-\om_0^{(+)}}$, $\om_0^{(+)} = {\cal O}(\sqrt{\al_S})$.