Chiral expansion of nucleon PDF at $x\sim m_{\pi }\mathrm{/}{M}_N$

Based on the chiral perturbation theory, we investigate the low-energy dynamics of nucleon parton distributions. We show that in different regions of the momentum fraction $x$ the chiral expansion is significantly different. For nucleon parton distributions these regions are characterized by $x\sim 1$, $x\sim m_{\pi }\mathrm{/}{M}_N$ and $x\sim (m_{\pi }\mathrm{/}{M}_N{)}^2$. We derive extended counting rules for each region and obtain model-independent results for the nucleon parton distributions down to $x\gtrsim m_{\pi }^2\mathrm{/}{M}_N^2\approx {10}^{-2}$.