Physics Letters B 733 (2014) 296–304
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
The infrared structure of QCD amplitudes and H → gg in FDH
and DRED
Christoph Gnendiger
a,∗
, Adrian Signer
b,c
, Dominik Stöckinger
a
a
Institut für Kern- und Teilchenphysik, TU Dresden, D-01062 Dresden, Germany
b
Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
c
Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
article info abstract
Article history:
Received 23 April 2014
Accepted 2 May 2014
Availableonline9May2014
Editor: B. Grinstein
We consider variants of dimensional regularization, including the four-dimensional helicity scheme (fdh)
and dimensional reduction (dred), and present the gluon and quark form factors in the fdh scheme at
next-to-next-to-leading order. We also discuss the generalization of the infrared factorization formula to
fdh and dred. This allows us to extract the cusp anomalous dimension as well as the quark and gluon
anomalous dimensions at next-to-next-to-leading order in the fdh and dred scheme, using
MS and DR
renormalization. To obtain these results we also present the renormalization procedure in these schemes.
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP
3
.
1. Introduction
The calculation of cross sections beyond leading order in pertur-
bation theory is of utmost importance to fully exploit the wealth of
experimental data provided by particle colliders. Computations at
next-to-leading order (NLO) are by now standard and can be done
in most cases in a fully automated way. At next-to-next-to-leading
order (NNLO) the situation is considerably more complicated and
only a small number of processes have been computed so far.
Beyond leading order, QCD cross sections are typically split
int
o several parts. At NLO there are virtual and real corrections,
at NNLO there are two-loop virtual, virtual–real and double real
corrections. Virtual corrections involve the calculation of loop dia-
grams and only the sum of all contributions leads to finite results.
At intermediate steps of loop calculations ultraviolet (UV) and
infr
ared (IR) divergences need to be regularized. Conventional di-
mensional regularization (cdr), where all vector bosons are treated
in D
= 4 − 2 dimensions, is not always the optimal choice. Al-
ternatives are the ’t Hooft–Veltman scheme (hv) [1],thefour-
dimensional helicity (fdh)scheme[2], and dimensional reduction
(dred) [3]. In the latter two, vector bosons are treated in 4 di-
mensions — as far as possible. As an example of the use of the
different schemes we mention the two-loop QCD results for the
gluon–gluon and quark-gluon scattering. Initially, the interference
of these two-loop amplitudes with the tree level was calculated in
cdr [4,5]. Later the helicity amplitudes were computed in the hv
and fdh scheme [6,7]. Clearly a full understanding of the relation
*
Corresponding author.
between the virtual corrections in the various schemes is required
if the fdh or the dred scheme is to be used for the computation
of physical cross sections. Thus, the scheme dependence of UV and
IR singularities has to be studied.
The proper treatment of UV singlarities of pure QCD ampli-
tudes
in the fdh and dred scheme is well understood. The cru-
cial step is to split quasi-4-dimensional gluons into D-component
gauge fields and N
= 2 scalar fields, so-called -scalars. During
the renormalization process the couplings of the
-scalars must
be treated as independent, resulting in different renormalization
constants and
β-functions. Ignoring this distinction can lead to
wrong results, violation of unitarity, and the non-cancellation of
divergences [8] (see Ref. [9] for potential simplifications and al-
ternative approaches). The independent couplings and their renor-
malization were already necessities in the equivalence proof of
dred and cdr [10,11], and in explicit multi-loop calculations in
dred [12–14].
In non-supersymmetric theories the fact that we have differ-
ent
couplings considerably complicates the renormalization pro-
cedure. A case of particular interest is the gluon form factor, i.e.
the amplitude for the process Higgs to two gluons. This process is
described by an effective Higgs-gluon–gluon vertex including the
effective coupling
λ and has not been calculated at the two-loop
level in fdh or dred so far. In these schemes there is an additional
coupling
λ
between the Higgs and two -scalars and the renor-
malization becomes highly non-trivial.
The split of gluons was also an essential ingredient in the reso-
lution [15] of
the dred factorization problem [16,17] and lead to a
better understanding of the one-loop transition rules of Ref. [18].
http://dx.doi.org/10.1016/j.physletb.2014.05.003
0370-2693/
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by
SCOAP
3
.