Physics Letters B 737 (2014) 352–356
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Killing scalar of non-linear σ -model on G/H realizing the classical
exchange algebra
Shogo Aoyama
∗
Department of Physics, Shizuoka University, Ohya 836, Shizuoka, Japan
a r t i c l e i n f o a b s t r a c t
Article history:
Received
16 July 2014
Received
in revised form 13 August 2014
Accepted
19 August 2014
Available
online 22 August 2014
Editor:
L. Alvarez-Gaumé
Keywords:
Classical exchange
algebra
Quantum
group
Non-linear
σ -model
Poisson
structure
The Poisson brackets for non-linear σ -models on G/H are set up on the light-like plane. A quantity
which transforms irreducibly by the Killing vectors, called Killing scalar, is constructed in an arbitrary
representation of G. It is shown to satisfy the classical exchange algebra.
© 2014 The Author. 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 Yang–Baxter equation arises in a large class of exactly solv-
able
models, such as lattice models, spin-chain system, nonlinear
σ -models, conformal field theory, etc. Among them the Yang–
Baxter equation
for the PSU(2, 2|4) spin-chain system gained much
interest in the last decade. Finding its solution leads to a dis-
covery
of string/QCD duality, namely, a relationship between the
PSU(2, 2|4) spin-chain system and the N = 4 supersymmetric QCD
[1,2].
To
explain the Yang–Baxter equation and the resulting algebraic
structure, we take a generic spin-system equipped with a set quan-
tum
operators, say, Ψ . We consider a tensor product chain of Ψ s
and exchange two of them in an adjacent position, say, Ψ(x) and
Ψ(y). Then there may exists a R-matrix defining a quantum ex-
change
algebra
R
xy
Ψ(x) ⊗ Ψ(y) = Ψ(y) ⊗ Ψ(x), (1.1)
such that it satisfies the Yang–Baxter equation
R
xy
R
xz
R
yz
= R
yz
R
xz
R
xy
. (1.2)
Suppose the R-matrix to be a quantum deformation of a certain
classical r-matrix as
R
xy
= 1 + hr
xy
+ O
h
2
,
*
Tel.: +81 54 238 4736.
E-mail
address: spsaoya@ipc.shizuoka.ac.jp.
with an infinitesimal parameter h. Then (1.1) and (1.2) respectively
become a classical exchange algebra
Ψ(
x)⊗
,
Ψ(y)
=−hr
xy
Ψ(x) ⊗ Ψ(y), (1.3)
and the classical Yang–Baxter equation
[r
xy
, r
xz
]+[r
xy
, r
yz
]+[r
xz
, r
yz
]=0. (1.4)
The quantity on the l.h.s. of (1.3) is a Poisson bracket which was
substituted for the commutator [Ψ(x)⊗
,
Ψ(y)].In the recent works
[3,4] the classical exchange algebra (1.3) was shown for a classical
quantity, called G-primary, in the constrained WZWN model on the
coset space G/{S ⊗ U(1)
d
}. Namely , the G-primary was constructed
out of basic fields of the model in an arbitrary representation of G.
By setting up the Poisson brackets for the basic fields, the classical
exchange algebra (1.3) was shown to appear with the r-matrix in
an arbitrarily chosen representation of the G-primary [4]. It would
be promoted to the quantum exchange algebra (1.2) by the usual
quantization of the constrained WZWN model. Or in mathematics
the algebraic construction of the R-matrix is known when the R-
matrix
exists in the Hopf algebra A in such a way that R ∈ A ⊗ A
and
i.
(a) = R(a)R
−1
, ∀a ∈ A,
ii. ( ⊗ 1)(R) = R
xz
R
yz
,(1 ⊗ )(R) = R
xz
R
xy
.
Here is the coproduct and
= P ◦ with the permutation
map P . The Yang–Baxter equation is derived as one of the proper-
ties
of this Hopf algebra [5].
http://dx.doi.org/10.1016/j.physletb.2014.08.048
0370-2693/
© 2014 The Author. 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
.