Physics Letters B 771 (2017) 576–582
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Double and cyclic λ-deformations and their canonical equivalents
George Georgiou
a
, Konstantinos Sfetsos
b
, Konstantinos Siampos
c,∗
a
Institute of Nuclear and Particle Physics, National Center for Scientific Research Demokritos, Ag. Paraskevi, GR-15310 Athens, Greece
b
Department of Nuclear and Particle Physics, Faculty of Physics, National and Kapodistrian University of Athens, Athens 15784, Greece
c
Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Laboratory for High-Energy Physics, University of Bern, Sidlerstrasse 5, CH3012
Bern, Switzerland
a r t i c l e i n f o a b s t r a c t
Article history:
Received
4 May 2017
Accepted
1 June 2017
Available
online 9 June 2017
Editor:
N. Lambert
We prove that the doubly λ-deformed σ -models, which include integrable cases, are canonically
equivalent to the sum of two single λ-deformed models. This explains the equality of the exact
β-functions and current anomalous dimensions of the doubly λ-deformed σ -models to those of two
single λ-deformed models. Our proof is based upon agreement of their Hamiltonian densities and of
their canonical structure. Subsequently, we show that it is possible to take a well defined non-Abelian
type limit of the doubly-deformed action. Last, but not least, by extending the above, we construct multi-
matrix
integrable deformations of an arbitrary number of WZW models.
© 2017 The Authors. 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
.
0. Introduction and results
A new class of integrable theories based on current algebras
for a semi-simple group was recently constructed [1]. The start-
ing
point was to consider two independent WZW models at the
same positive integer level k and two distinct PCM models which
were then left-right asymmetrically gauged with respect to a com-
mon
global symmetry. The models are labeled by the level k and
two general invertible matrices λ
1,2
. For certain choices of λ
1,2
in-
tegrability
is retained [1]. This idea can be generalized to include
integrable deformations of exact CFTs on symmetric spaces. This
construction is reminiscent to the one for single λ-deformations
[2–4].
Subsequently,
the quantum properties of the aforementioned
multi-parameter integrable deformations were studied in [5], by
employing a variety of techniques. One of the main results of that
work was that the running of the couplings λ
1
and λ
2
, as well
as the anomalous dimensions of current operators depend only on
one of the couplings, either λ
1
or λ
2
and are identical to those
found for single λ-deformations [6–12]. These rather unexpected
results seek for a simple explanation. The purpose of this work
is to demonstrate that they are due to the fact that the doubly
deformed models are canonically equivalent to the sum of two sin-
gle
λ-deformations, one with deformation matrix being λ
1
and the
*
Corresponding author.
E-mail
addresses: georgiou@inp.demokritos.gr (G. Georgiou),
ksfetsos@phys.uoa.gr (K. Sfetsos), siampos@itp.unibe.ch (K. Siampos).
other with deformation matrix λ
2
. Recall that all known forms of
T-duality, i.e., Abelian, non-Abelian and Poisson–Lie T-duality can
be formulated as canonical transformations in the phase space of
the corresponding two-dimensional σ -models [13–17]. Moreover,
it has been shown in various works that the running of couplings
is preserved under these canonical transformations even though
the corresponding σ -models fields are totally different [18–22]. All
of the above strongly hint towards the validity of our assertion,
which of course we will prove.
The
plan of the paper is as follows: In section 1, after a brief
review of the single and doubly λ-deformed models and of their
non-perturbative symmetries, we will show that the doubly de-
formed
models are canonically equivalent to the sum of two single
λ-deformations. In section 2, we will present the type of non-
Abelian
T-duality that is based on the doubly deformed σ -models
of [1]. Finally, in section 3, we will construct multi-matrix inte-
grable deformations
of an arbitrary number of independent WZW
models by performing a left-right asymmetric gauging for each one
of them but in such a way that the total classical gauge anomaly
vanishes. This happens if these models are forced to obey the
cyclic symmetry property or if they are infinitely many, resem-
bling
in structure either a closed or an infinitely open spin chain.
Their action can be thought of as the all-loop effective action of
several independent WZW models for G all at level k, perturbed
by current bilinears mixing the different WZW models with near-
est
neighbour-type interactions. These models are also canonically
equivalent to a sum of single λ-deformed models with appropri-
ate
couplings. Furthermore, we will argue that the Hamiltonian of
http://dx.doi.org/10.1016/j.physletb.2017.06.007
0370-2693/
© 2017 The Authors. 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
.