Physics Letters B 767 (2017) 121–125
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Physics Letters B
www.elsevier.com/locate/physletb
Finite-size effect of η-deformed AdS
5
× S
5
at strong coupling
Changrim Ahn
Department of Physics, Ewha Womans University, DaeHyun 11-1, Seoul 120-750, South Korea
a r t i c l e i n f o a b s t r a c t
Article history:
Received
5 December 2016
Received
in revised form 22 January 2017
Accepted
25 January 2017
Available
online 1 February 2017
Editor:
M. Cveti
ˇ
c
We compute Lüscher corrections for a giant magnon in the η-deformed (AdS
5
× S
5
)
η
using the
su(2|2)
q
-invariant S-matrix at strong coupling and compare with the finite-size effect of the corre-
sponding
string state, derived previously. We find that these two results match and confirm that the
su(2|2)
q
-invariant S-matrix is describing world-sheet excitations of the η-deformed background.
© 2017 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
AdS/CFT duality [1], a correspondence between string theo-
ries
in AdS background with certain supersymmetric and confor-
mal
Yang–Mills theories on the boundary space-time of the AdS
space, has been a hot topic for theoretical researches and pro-
duced
many important quantitative results and applications (for
overview see [2]). In these developments, integrability has played a
crucial role on both sides of the correspondence. Two-dimensional
world-sheet actions for the string theory moving in the back-
ground
are described by nonlinear sigma models on coset group
manifolds which are classically integrable. Aspects of quantum in-
tegrable
structure of supersymmetric Yang–Mills theories appear
in Bethe ansatz equations and related exact integrable machineries
which can determine conformal dimensions of the CFTs. Quantum
S-matrices of the world-sheet actions provide integrable frame-
work
which interpolates from the strong to weak coupling limits.
An
important direction of research is to find new AdS/CFT pairs
which show novel integrability structures. One such string theory,
which has been studied recently, is the type IIB superstring theory
in the η-deformed target space (AdS
5
× S
5
)
η
for a real parameter
η [3]. The classical integrability of nonlinear sigma model is pro-
vided
by solutions of the classical Yang–Baxter equation [4]. (See
[5–7] for related issues.) It has been conjectured in [3] that full
quantum S-matrix of the deformed sigma model is given by the
R-matrix of the q-deformed Hubbard model which has been pro-
posed
much earlier in [8]. When q is a complex phase, the dressing
phase of the S-matrix and bound-states have been analyzed in [9].
Scattering amplitudes of bosonic excitations for small values of the
world-sheet momentum have been computed and shown to agree
with the q-deformed S-matrix in the large string tension (strong
E-mail address: ahn@ewha.ac.kr.
coupling) limit for real q with explicit relation with η [10]. Based
on the exact S-matrix, thermodynamic Bethe ansatz equations for
ground states and dressing phase for real q have been studied
in [11].
A
pertinent issue which should be mentioned is that the de-
formed
sigma model is not a fully consistent string theory at quan-
tum
level. It has been found that this η-deformed sigma model
does not solve the type IIB supergravity equations of motion [12],
but solves, instead, a generalization of them [13]. These general-
ized
ones allow only scale invariance but not full Weyl invariance
at one-loop [14]. The Weyl invariance can be restored if the de-
formation
is generalized by some modified solutions of the Yang–
Baxter
equation [15]. This suggests that one should pay attention
while treating the η-deformed theory at quantum level.
In
this letter, we provide another evidence for the q-deformed
S-matrix to describe the string theory on the η-deformed geom-
etry.
For this purpose, we consider finite-size effects of a giant
magnon state, a classical string configuration living on a subspace
of the (AdS
5
× S
5
)
η
[16]. These corrections have been computed
for the undeformed AdS
5
× S
5
in [17,18] and for the γ -deformed
AdS
5
× S
5
in [19,20] from both directions of string solutions and
world-sheet S-matrices. For the η-deformed case, this effect has
been studied from only string theory side in [21], which will be
reviewed in sect. 2. Exact q-deformed S-matrix and related for-
mula
will be presented in sect. 3. We present our computation of
the Lüscher corrections for a giant magnon based on q-deformed
S-matrix in sect. 4 along with a conjecture on the deformed dress-
ing
phase in sect. 5. In sect. 6, we conclude with a short summary
and comments.
2. Finite-size effect of a giant magnon in (AdS
5
× S
5
)
η
In this section, we give a brief review on computing the en-
ergy
of a giant magnon using Neumann–Rosochatius ansatz fol-
http://dx.doi.org/10.1016/j.physletb.2017.01.063
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© 2017 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
.