Next-to-leading-order correction to pion form factor in $k_T$ factorization

Understand

We calculate next-to-leading-order (NLO) correction to the pion electromagnetic form factor at leading twist in the $k_T$ factorization theorem.

• Partons off-shell by $k_T^2$ are considered in both quark diagrams and effective diagrams for the transverse-momentum-dependent (TMD) pion wave function.
• The light-cone singularities in the TMD pion wave function are regularized by rotating the Wilson lines away from the light cone.
• The soft divergences from gluon exchanges among initial- and final-state partons cancel exactly.