Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The pinch technique at two-loops: The case of mass-less Yang-Mills
  theories   The generalization of the pinch technique beyond one loop is presented. It is
shown that the crucial physical principles of gauge-invariance, unitarity, and
gauge-fixing-parameter independence single out at two loops exactly the same
algorithm which has been used to define the pinch technique at one loop,
without any additional assumptions. The two-loop construction of the pinch
technique gluon self-energy, and quark-gluon vertex are carried out in detail
for the case of mass-less Yang-Mills theories, such as perturbative QCD. We
present two different but complementary derivations. First we carry out the
construction by directly rearranging two-loop diagrams. The analysis reveals
that, quite interestingly, the well-known one-loop correspondence between the
pinch technique and the background field method in the Feynman gauge persists
also at two-loops. The renormalization is discussed in detail, and is shown to
respect the aforementioned correspondence. Second, we present an absorptive
derivation, exploiting the unitarity of the $S$-matrix and the underlying BRS
symmetry; at this stage we deal only with tree-level and one-loop physical
amplitudes. The gauge-invariant sub-amplitudes defined by means of this
absorptive construction correspond precisely to the imaginary parts of the
$n$-point functions defined in the full two-loop derivation, thus furnishing a
highly non-trivial self-consistency check for the entire method. Various future
applications are briefly discussed.

26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
37
The categories of this paper are: supr-con