Hard scale uncertainty in collinear factorization: Perspective from kt -factorization

We analyze two consequences of the relationship between collinear factorization and 𝑘𝑡-factorization. First, we show that the 𝑘𝑡-factorization gives a fundamental justification for the choice of the hard scale 𝑄2 done in the collinear factorization. Second, we show that in the collinear factorization there is an uncertainty on this choice which will not be reduced by higher orders. This uncertainty is absent within the 𝑘𝑡-factorization formalism.