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An on-shell approach to factorization

Factorization is possible due to the universal behavior of Yang-Mills theories in soft and collinear limits. Here, we take a small step towards a more transparent understanding of these limits by proving factorization at tree-level in perturbation theory, using on-shell spinor helicity methods. An advantage of this approach is that it uses only the scaling of momenta in soft and collinear limits, avoiding any assignment of scaling behavior to unphysical (and gauge-dependent) fields. Another advantage is that one can choose different reference vectors for polarizations in different collinear sectors. Exceptional choices of reference vector elucidate the relationship between various operators and Wilson lines in factorized expressions.