Physics Letters B 783 (2018) 350–356
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Renormalon free part of an ultrasoft correction to the static QCD
potential
Hiromasa Takaura
Department of Physics, Tohoku University, Sendai, 980–8578, Japan
a r t i c l e i n f o a b s t r a c t
Article history:
Received
21 December 2017
Received
in revised form 19 May 2018
Accepted
9 July 2018
Available
online 12 July 2018
Editor:
J. Hisano
Keywords:
QCD
Summation
of perturbation theory
Perturbative calculations of the static QCD potential have the u = 3/2 renormalon uncertainty. In the
multipole expansion performed within pNRQCD, this uncertainty at LO is known to get canceled against
the ultrasoft correction at NLO. To investigate the net contribution remaining after this renormalon
cancellation, we propose a formulation to separate the ultrasoft correction into renormalon uncertainties
and a renormalon independent part. We focus on very short distances
QCD
r 0.1and investigate the
ultrasoft correction based on its perturbative evaluation in the large-β
0
approximation. We also propose
a method to examine the local gluon condensate, which appears as the first nonperturbative effect to the
static QCD potential, without suffering from the u = 2 renormalon.
© 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The static QCD potential plays an important role to investigate
the QCD dynamics. It has been investigated extensively by using
perturbation theory, effective field theory and lattice simulations.
In perturbative evaluations, perturbative coefficients are ex-
pected
to show factorial behaviors at large orders. Such divergent
behaviors, in particular those related to a positive renormalon, in-
duce
ambiguity to the resummation of the perturbative series [1].
For the static QCD potential, renormalons are located at positive
half integers in the Borel u-plane. The first renormalon at u =1/2
causes
an uncertainty to the r-independent constant of the poten-
tial.
This renormalon is known to get canceled in the total energy
(i.e. the sum of the QCD potential and twice the pole mass) within
usual perturbation theory once the pole mass is expressed as a
perturbative series in terms of the MS mass.
In considering cancellation of the other renormalons, it is useful
to adopt the effective field theory (EFT) known as potential non-
relativistic
QCD (pNRQCD) [2]. The renormalons are expected to get
canceled ultimately in the multipole expansion performed in this
EFT. The leading order (LO) term of this expansion is the singlet
potential V
S
(r), which behaves as O(1/r) and can be evaluated in
perturbation theory. The renormalons for V
S
are located at positive
half integers as mentioned above, and the leading r-dependent un-
E-mail address: t_hiromasa@tuhep.phys.tohoku.ac.jp.
certainty is caused by the u =3/2renormalon. The next-to-leading
order (NLO) term in the multipole expansion, which we denote by
δE
US
, represents the dynamics at the ultrasoft scale ∼ α
s
(r
−1
)/r
and
its explicit r-dependence is O(r
2
). In Ref. [2], it was pointed
out within the leading-logarithmic approximation that the u = 3/2
renormalon
exists in δE
US
and it cancels against the u = 3/2renor-
malon
of V
S
. In Ref. [3], the perturbative evaluation of δE
US
in
the large-β
0
approximation was completed, and again, the u = 3/2
renormalon
cancellation was confirmed.
Although
the u = 3/2renormalon cancellation has been estab-
lished,
it has not been clarified what remains in the NLO calcula-
tion,
V
S
+δE
US
, as a consequence of this renormalon cancellation.
In particular, the net contribution to δE
US
remaining after this can-
cellation
has not been made clear. In this Letter, we investigate the
net contribution to δE
US
, which is not affected by the renormalon
cancellation. The distances considered here are
QCD
r 0.1, where
δE
US
as well as V
S
can be evaluated perturbatively since the ul-
trasoft
scale satisfies α
s
(r
−1
)/r
QCD
. In this range, the leading
nonperturbative correction is given through the local gluon con-
densate.
1
In order to examine the local gluon condensate, the per-
turbative
part, i.e. V
S
+δE
US
, should be clearly known in advance.
Although the currently available order of perturbative expansion
is far from the (expected) relevant order to the u = 3/2renor-
1
The appearance of this nonperturbative effect has been first considered in
Refs. [4–6], and can be understood in a systematic expansion of pNRQCD [2].
https://doi.org/10.1016/j.physletb.2018.07.014
0370-2693/
© 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.