Charge symmetry of nucleon parton distributions
= Charge symmetry of nucleon parton distributions
{title2=$u^n=d^p,\quad d^n=u^p$}
The approximate equality of <proton> and <neutron> <parton distribution functions> after interchanging <up quarks> and <down quarks>, including their <antiquarks>. It follows from the corresponding <isospin> symmetry when electromagnetic and light-quark mass-difference effects are neglected. Isospin-singlet sea distributions are unchanged.