Pion structure function in a nuclear medium

We study the pion structure function in a nuclear medium using the Nambu and Jona-Lasinio model. By using the operator product expansion, the medium effect of the nuclear matter is incorporated in calculations of the twist-2 operators. The resulting distribution function satisfies the correct normalization and the momentum sum rule. We find that the density dependence of the pion structure function is rather weak around the normal nuclear matter density p = 0.17 fm−3. We also discuss how the medium modification of the pion structure affects the sea quark enhancement due to the pion excess in nuclei.