Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Space-like (vs. time-like) collinear limits in QCD: is factorization
  violated?   We consider the singular behaviour of QCD scattering amplitudes in
kinematical configurations where two or more momenta of the external partons
become collinear. At the tree level, this behaviour is known to be controlled
by factorization formulae in which the singular collinear factor is universal
(process independent). We show that this strict (process-independent)
factorization is not valid at one-loop and higher-loop orders in the case of
the collinear limit in space-like regions (e.g., collinear radiation from
initial-state partons). We introduce a generalized version of all-order
collinear factorization, in which the space-like singular factors retain some
dependence on the momentum and colour charge of the non-collinear partons. We
present explicit results on one-loop and two-loop amplitudes for both the
two-parton and multiparton collinear limits. At the level of square amplitudes
and, more generally, cross sections in hadron--hadron collisions, the violation
of strict collinear factorization has implications on the non-abelian structure
of logarithmically-enhanced terms in perturbative calculations (starting from
the next-to-next-to-leading order) and on various factorization issues of mass
singularities (starting from the next-to-next-to-next-to-leading order).

17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph