The Non-perturbative Effect on $R=\sigma_L /\sigma_T$ from QCD Vacuum
  We investigate the non-perturbative effects on the ratio $R=\sigma_L /\sigma_T$ in lepton-nucleon deep inelastic scattering by taking into account the lowest dimensional condensate contributions from the QCD vacuum. By combining conventional perturbative QCD corrections and the Georgi- Politzer target-mass effects with the non-perturbative effects from the QCD vacuum, we give a good description of the $Q^2$ and $x$ dependences of $R$ in comparison with the recent experimental data. 
Jian-Jun Yang, Bo-Qiang Ma, Guang-Lie Li