Physics Letters B 750 (2015) 139–146
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Finite ε
2
-corrections to the N = 2 SYM prepotential
Jean-Emile Bourgine, Davide Fioravanti
∗
Sezione INFN di Bologna, Dipartimento di Fisica e Astronomia, Università di Bologna, Via Irnerio 46, Bologna, Italy
a r t i c l e i n f o a b s t r a c t
Article history:
Received
22 July 2015
Accepted
1 September 2015
Available
online 5 September 2015
Editor: N.
Lambert
We derive the first ε
2
-correction of the instanton partition functions in 4D N = 2Super Yang–Mills
(SYM) to the Nekrasov–Shatashvili limit ε
2
→ 0. In the latter we recall the emergence of the famous
Thermodynamic Bethe Ansatz-like equation which has been found by Mayer expansion techniques. Here
we combine efficiently these to field theory arguments. In a nutshell, we find natural and resolutive the
introduction of a new operator ∇ that distinguishes the singularities within and outside the integration
contour of the partition function.
© 2015 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
.
1. Introduction
The Omega background was first introduced in N = 2SUSY
gauge theories to regularise the infinite volume of R
4
in the com-
putation
of instanton contributions to the partition function by lo-
calisation
[1]. More recently, it has also proven to be a formidable
way to preserve integrability of these theories upon deformation.
In fact, this background is characterised by two equivariant defor-
mation
parameters ε
1
and ε
2
associated to the breaking of the
Lorentz invariant four dimensional space into C × C, but still the
Nekrasov instanton partition function exhibits an integrable struc-
ture
in the form of covariance under the Spherical Hecke central
(SHc) algebra [2,3] (which is formally equivalent to a W
∞
algebra).
The presence of this algebra shed light on the conjecture by [4,5]
of
a duality between these four dimensional theories and the fam-
ily
of Toda conformal field theories in two dimensions.
1
Moreover,
the SHc algebra is closely related to a tensorial version of the in-
tegrable
Calogero–Moser Hamiltonian and led to the construction
of one of the most basic objects of quantum integrable theories,
namely an (instanton) R-matrix [9].
In
the Nekrasov–Shatashvili (NS) limit ε
2
→ 0, the theory pos-
sesses
only one (non-zero) equivariant parameter ε
1
and, besides,
its 2D underlying integrable structure is better understood [10].
The latter defines, indeed, a quantisation of a Hitchin system as-
sociated
to the Seiberg–Witten curve (see [11] and the references
*
Corresponding author.
E-mail
addresses: bourgine@bo.infn.it (J.-E. Bourgine), fioravanti@bo.infn.it
(D. Fioravanti).
1
The conjecture has been partially proved either using the basis of AFLT states
[6], or a set of generalised Jack polynomials [7,8].
therein) which can now be characterised by a quantum curve [12].
And this curve is, actually, equivalent to a TQ-relation upon a
(quantum) change of variables [13], while the new integrable sys-
tem
is the bi-spectral dual of the previous one [14]. Of course, of
great interest for integrable model theory is the TQ-relation, which
can also be obtained directly from the Nekrasov partition function
by extremising the sum over Young diagrams [15], a technique that
goes back to [16]. Moreover, another key feature of integrability
has come out of the blue since the original paper [10] in the form
of a non-linear integral equation (NLIE) in the complex plane [17]
resembling
a Thermodynamical Bethe Ansatz (TBA) equation [18].
Subsequently, this equation was derived in full detail by [19,20]
upon
using Mayer cluster expansion techniques [21,22].
In
the present letter, we go beyond this limit and present an
explicit formula for the first ε
2
-correction to the prepotential. This
result should pave the way to a better understanding of the full
ε
2
-deformation and its meaning as quantum integrable system
characterised by a TBA/NLIE. This should ultimately lead to a richer
algebraic structure similar to the SHc Hopf algebra as we know
how, along the other way around, the NS limit of the SHc algebra
can be obtained [23]. For convenience, we focus on N = 2SYM
with a single SU(N
c
) gauge group and a number of fundamental
flavours. However, we believe that our mathematical construction
and results will be easily generalisable to arbitrary quivers (along
the lines of [23]).
In
fact, with respect to the latter reference (exploiting the
methods of Mayer cluster expansion) we shall add an efficient field
theory argument. The latter is firstly used to disentangle the long-
and
short-range interactions between instantons: this is performed
in Section 2. Then, we treat the short-range interactions by the
Mayer cluster expansion technique in Section 3 and achieve for-
http://dx.doi.org/10.1016/j.physletb.2015.09.002
0370-2693/
© 2015 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
.