Model for polarized and unpolarized parton density functions in the nucleon

Abstract We present a physical model for polarized and unpolarized structure functions and parton density functions (PDFs) of the proton and the neutron. It reproduces the data on F 2 p ( x , Q 2 ) for 0.00001 x Q 2 2 , F 2 p ( x )− F 2 n ( x ), F 2 n ( x )/ F 2 p ( x ), xg ( x ), d (x)− u (x) , d ( x )/ u ( x ), the Gottfried sum, the fractional momentum of charged partons and the polarized structure functions g 1 p , n ( x ), at various Q 2 . We present for the first time, proton and neutron PDFs which do not assume charge symmetry. Contrary to the common practice, we explain polarized and unpolarized data with a single model.