Physics Letters B 778 (2018) 197–206
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Differential expansion for link polynomials
C. Bai
a
, J. Jiang
b
, J. Liang
a
, A. Mironov
c,d,e,∗
, A. Morozov
d,e
, An. Morozov
d,e
,
A. Sleptsov
d,e,f
a
Chern Institute of Mathematics and LPMC, Nankai University, Tianjin 300071, China
b
School of Math & Physics, Ningde Normal University, Ningde 352100, China
c
Lebedev Physics Institute, Moscow 119991, Russia
d
ITEP, Moscow 117218, Russia
e
Institute for Information Transmission Problems, Moscow 127994, Russia
f
Laboratory of Quantum Topology, Chelyabinsk State University, Chelyabinsk 454001, Russia
a r t i c l e i n f oa b s t r a c t
Article history:
Received
30 September 2017
Received
in revised form 9 January 2018
Accepted
10 January 2018
Available
online 19 January 2018
Editor:
M. Cveti
ˇ
c
The differential expansion is one of the key structures reflecting group theory properties of colored
knot polynomials, which also becomes an important tool for evaluation of non-trivial Racah matrices.
This makes highly desirable its extension from knots to links, which, however, requires knowledge of
the 6 j-symbols, at least, for the simplest triples of non-coincident representations. Based on the recent
achievements in this direction, we conjecture a shape of the differential expansion for symmetrically-
colored
links and provide a set of examples. Within this study, we use a special framing that is
an unusual extension of the topological framing from knots to links. In the particular cases of
Whitehead and Borromean rings links, the differential expansions are different from the previously
discovered.
© 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
Knot theory is currently one of the main applications of quantum field theory, where non-perturbative results can be reliably derived
and tested. One of the subjects to study is the representation dependence of Wilson loop averages (which, in four dimensions, distinguishes
between the area and perimeter laws). The 3d Chern–Simons theory [1] underlying knot theory is topological, therefore, its observables can
not depend on the metric data like lengths and areas, still their dependence on representations is quite non-trivial. Differential expansion
[2–8] is the simplest manifestation of such properties. The goal of this paper is to extend the knowledge about differential expansion from
knots to links. This is an essentially new story, because links consist of different components, each in its own representation. Calculation
requires R- and Racah matrices in channels with different representations, which are not yet well studied and where some useful methods
like the eigenvalue conjecture [9] are not directly applicable. Important for differential expansion is the choice of framing. For knots, the
best choice is the topological framing, when the R -matrix is normalized in such a way that it provides invariance with respect to the first
Reidemeister move. When the R-matrix acts on a pair of different representations R
1
⊗ R
2
, the first Reidemeister move is not applicable,
and the topological framing is not defined from the first principles. Even in the case of links, there is a distinguished canonical framing
(or
standard framing) [10] suggested by M. Atiyah in [11]. It turns out, however, that the differential expansion requires a bit different
framing.
We
briefly remind what the differential expansion is in sec. 3 and formulate it for links of different kinds: made from unknots and
from non-trivial knots. These conjectures are extracted from calculations of numerous examples, which became possible due to advances
in Racah calculus in [12,13].
*
Corresponding author.
E-mail
address: mironov@lpi.ru (A. Mironov).
https://doi.org/10.1016/j.physletb.2018.01.026
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
.