Chiral expansion of nucleon PDF at $x\sim m_π/M_N$

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 $x\sim1$, $x\sim m_π/M_N$ and $x\sim (m_π/M_N)^2$. We derive extended counting rules for each region and obtain model-independent results for the nucleon parton distributions down to $x\gtrsim m^2_π/M^2_N \approx 10^{-2}$.

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