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我们在强耦合超对称Yang-Mills理论中研究四个受保护的(半BPS)算子的相关器。 对于五个球体上的各种球谐函数,这是AdS5×S5上的从树级到树级的超重力振幅。 我们使用共形场论方法,特别是最近获得的洛伦兹反演公式,来分析引导这些相关器。 提取的1 / N 2双迹异常尺寸证实了由Aprile,Drummond,Heslop和Paul最近推测的简单模式。 我们通过出乎意料的十维共形对称性来解释这种模式,该对称性似乎是由树级超重力(或其适当的子分区)所享受的。 对称性将所有球谐函数组合成一个十维对象,并在每个循环阶上为任何半BPS相关器的前导对数部分生成紧凑表达式。
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JHEP01(2019)196
Published for SISSA by Springer
Received: November 21, 2018
Accepted: December 25, 2018
Published: January 25, 2019
All tree-level correlators in AdS
5
×S
5
supergravity:
hidden ten-dimensional conformal symmetry
Simon Caron-Huot and Anh-Khoi Trinh
Department of Physics, McGill University,
3600 Rue University, Montr´eal, QC H3A 2T8, Canada
E-mail: schuot@physics.mcgill.ca, anh-khoi.trinh@mail.mcgill.ca
Abstract: We study correlators of four protected (half-BPS) operators in strongly coupled
supersymmetric Yang-Mills theory. These are dual to tree-level supergravity amplitudes
on AdS
5
×S
5
for various spherical harmonics on the five-sphere. We use conformal field
theory methods, in particular a recently obtained Lorentzian inversion formula, to analyti-
cally bootstrap these correlators. The extracted 1/N
2
double-trace anomalous dimensions
confirm a simple pattern recently conjectured by Aprile, Drummond, Heslop and Paul. We
explain this pattern by an unexpected ten-dimensional conformal symmetry which appears
to be enjoyed by tree-level supergravity (or a suitable subsector of it). The symmetry
combines all spherical harmonics into a single ten-dimensional object, and yields compact
expressions for the leading logarithmic part of any half-BPS correlator at each loop order.
Keywords: AdS-CFT Correspondence, Conformal Field Theory, 1/N Expansion, Super-
symmetric Gauge Theory
ArXiv ePrint: 1809.09173
Open Access,
c
The Authors.
Article funded by SCOAP
3
.
https://doi.org/10.1007/JHEP01(2019)196
JHEP01(2019)196
Contents
1 Introduction 1
2 Generalities 3
2.1 Superconformal Ward identities 5
2.2 Lorentzian inversion formula 7
2.3 Other decompositions in the literature 10
3 Disconnected correlator: leading order 1/c
0
11
3.1 OPE coefficients 11
3.2 Reorganizing into superconformal blocks 13
3.3 ∆
(8)
: a remarkable eighth-order differential operator 15
4 Tree-level correlator at strong coupling: order 1/c
1
16
4.1 Fixing three-point coefficients from crossing symmetry 16
4.2 Chiral (protected) correlator: deducing the free correlator 19
4.3 Reduced correlator: anomalous dimensions at order 1/c 20
5 An accidental 10-dimensional conformal symmetry 24
5.1 A mysterious equality with 10-dimensional S-matrix partial waves 24
5.2 Statement of the conjecture 25
5.3 Checking the conjecture from the calculated correlators 28
5.4 Deriving the Mellin-space formula by Rastelli and Zhou 29
5.5 Ten-dimensional OPE and the leading logarithmic part to all loops 32
6 Conclusion 35
A Basic inversion integrals 36
B Superconformal blocks, and weak coupling correlator to order 1/c 37
B.1 Weak coupling limit 38
C Ten-dimensional conformal blocks at the unitarity bound 39
1 Introduction
Among strongly coupled quantum systems, a distinguished class are dual to weakly coupled
gravitational theories and are therefore efficiently tackled by the gauge-gravity correspon-
dence. Models in this class are characterized by a large-N expansion and a sparse spectrum
of local operators: all single-trace primary operators with small scaling dimension have
– 1 –
JHEP01(2019)196
spin two or less [1]. While the gravity side of the correspondence typically remains more
straightforward to use, new analytic bootstrap techniques are becoming applicable and
should be vigorously pursued being potentially more general. They appear especially ad-
vantageous for observables like four-point correlation functions, which can now be studied
to unprecedented precision.
In this paper, we study the four-point function of general half-BPS states in maximally
supersymmetric super Yang-Mills theory, or N = 4 SYM for short, dual to type IIB
superstring theory on AdS
5
×S
5
geometry. Through the AdS/CFT correspondence, half-
BPS operators are dual to S
5
spherical harmonics (Kaluza-Klein modes) of the graviton,
and we will consider the general correlator of four such spherical harmonics. This provides
an essential ingredient for studying the duality at loop level, where all modes can run inside
the loop, and also provides an explicit model for how local physics in an internal manifold
gets encoded from the CFT perspective.
Four-point correlators have been much studied since the early days of the AdS/CFT
correspondence. Initially, techniques were developed for computing tree-level Witten dia-
grams in position space, which led to the first complete results for the correlators of four
dilatons or stress tensor multiplets [2, 3]. In the case of the SYM model, part of these
correlators are fixed by non-renormalization theorem and agree with calculations at weak
‘t Hooft coupling [4, 5], but there is in addition an unprotected part which contains inter-
esting dynamical information. For example, a suitable limit reveals the flat space S-matrix
of the underlying ten-dimensional superstring theory [6–8]. This program was gradually
extended to higher spherical harmonics [9–13].
Meanwhile, by analyzing the operator product expansion (OPE), it was discovered
how to exploit the large gap property of holographic theories, that is the fact that all
non-protected single-traces get lifted from the spectrum. This led to various conjectures
for correlators [14, 15]. However, it took almost a decade for a conjecture to appear in
the general case [16], thanks to a remarkably simple pattern which was observed in Mellin-
space [7, 17]. The corresponding position space calculation of tree-level Witten diagrams
was only very recently completed after a longstanding effort [18, 19], which confirmed the
conjecture in all considered examples.
In this paper we will revisit correlators of half-BPS operators from the perspective of
the analytic bootstrap, which offers a constructive method to build correlators from their
light-cone singularities [20–23]. This can be formulated nonperturbatively as a Kramers-
Kronig type dispersion relation, known as the Lorentzian inversion formula, which explicitly
reconstructs OPE data from a suitably defined absorptive part [24–26]. For holographic
theories at tree-level, the absorptive part is a finite sum of conformal blocks, thus reducing
the computation in a given theory to essentially a group-theoretic exercise (see also [27, 28]).
The result is unique up to AdS contact interactions, whose size can be bounded by con-
sidering the Regge limit [24, 29]. These are further restricted by supersymmetry and in
fact absent in N = 4 SYM as we will see. The method, therefore, rigorously and unam-
biguously determines the correlators. Interestingly, in analogy with the unitarity method
for one-loop S-matrices [30], “squaring” this tree-level four-point data gives sufficient in-
formation to go to one-loop [31], as has now been successfully carried out for low spherical
harmonics [32–34].
– 2 –
JHEP01(2019)196
Study of N = 4 SYM specifically is further motivated by the possibility of finding un-
expected structures. In the planar limit, this theory is controlled by a rich and remarkable
integrable system, making it a rather unique nontrivial four-dimensional quantum field the-
ory in which the spectrum can be computed exactly at finite ‘t Hooft coupling, see [35, 36].
It is important to determine what, if anything, of this structure persists beyond the planar
limit. Correlation functions at strong coupling offer a clean, natural environment in which
to discuss this question. Furthermore, we expect the correlators in this limit to provide im-
portant cross-checks and guidance as integrability-based methods are now being developed
to tackle the 1/N expansion [37, 38], as well as novel AdS-based techniques [39–41].
Hints of a hidden symmetry in correlators have been uncovered recently [42], who stud-
ied the anomalous dimension matrix governing the mixing between double-trace operators
built from different S
5
spherical harmonics, starting from the conjectured Mellin-space for-
mula of [16]. Amazingly, the eigenvalues of the anomalous dimension matrix are simple
rational numbers, for which the authors of ref. [42] conjectured a general formula.
This paper is organized into two parts. First in section 2 we review the three ideas
behind our calculations: the Operator Product Expansion, the supersymmetric Ward iden-
tities satisfied by N = 4 SYM correlators, and the Lorentzian inversion formula. As a
warm-up, we then apply these formulas at order 1/N
0
c
in section 3. Including the identity
in two cross-channels yields double-trace data in the direct channel. While conceptually
straightforward, the supersymmetric OPE differs from the usual generalized free field result
in simple but important ways. Section 4 contains our main computations: the tree-level
correlator (order 1/N
2
c
) at strong ‘t Hooft coupling. The full result is determined by just
the singular part arising from half-BPS single-trace operators. While their couplings are
well-known and could be obtained from non-renormalization theorems [4], we show that
crossing symmetry in fact suffices to bootstrap them from scratch. This computation yields
double trace mixing matrices, and we confirm the conjecture of [42] in many examples.
In a second part of this paper, section 5, we explore the remarkable structure found in
this result. We will attribute the simplicity of the eigenvalues to an unexpected SO(10,2)
symmetry, representing an effective conformal invariance of ten-dimensional supergravity
at tree-level. This symmetry will be used to unify all spherical harmonics into a single ten-
dimensional object. Proof of the symmetry at the level of four-point correlators amounts to
showing that this generating function correctly predicts the singular part of each correlator;
we check this for a large number of examples. We also show how the symmetry readily
implies the conjectured Mellin-space formula of [16], and use it to obtain the leading-
logarithmic term at each order in 1/N . Implications are discussed in the conclusion.
2 Generalities
At any coupling, N = 4 SYM contains a special class of operators, which are half-BPS
and thus annihilated by the maximal possible number of supercharges. They transform
as Lorentz scalars and traceless symmetric tensors with respect to the SO(6)
R
' SU(4)
R
global symmetry (Dynkin label
0, p, 0
). In the Lagrangian description of N = 4 SYM,
they are described as symmetrical traceless polynomials in the 6 adjoint scalar fields φ
a
of
– 3 –
JHEP01(2019)196
the theory. Denoting x
µ
the spacetime coordinates and introducing null six-vectors y
a
to
parametrize the SO(6)
R
dependence, they can be written as
O
p
(x, y) ∝ Tr
(φ
a
y
a
)
p
+ O(1/N
2
) corrections, (2.1)
which will be normalized in this paper so that
O
p
(x
1
, y
1
)O
p
(x
2
, y
2
)
=
y
2
12
x
2
12
p
(2.2)
where x
2
ij
= (x
i
− x
j
)
2
, y
2
ij
= y
i
· y
j
. Due to the BPS condition, the scaling dimension of
O
p
is exactly p, where p ≥ 2. At strong ‘t Hooft coupling, they admit a dual description
as Kaluza-Klein modes of the graviton on AdS
5
×S
5
. According to the gravity analysis, all
other operators in this limit are either multi-trace composites built of products of the O
p
,
or are heavier than the string scale, ∆
∼
>
λ
1/4
.
Four-point correlators depend on AdS
5
and S
5
cross-ratios:
u =
x
2
12
x
2
34
x
2
13
x
2
24
= z¯z, v =
x
2
23
x
2
14
x
2
13
x
2
24
= (1 − z)(1 − ¯z), (2.3)
σ =
y
2
12
y
2
34
y
2
13
y
2
24
= α¯α, τ =
y
2
23
y
2
14
y
2
13
y
2
24
= (1 − α)(1 − ¯α), (2.4)
up to an overall prefactor conventionally written as follows [43]:
O
p
1
(x
1
, y
1
) ···O
p
4
(x
4
, y
4
)
≡
y
2
12
x
2
12
p
1
+p
2
2
y
2
34
x
2
34
p
3
+p
4
2
x
2
14
y
2
24
x
2
24
y
2
14
p
2
−p
1
2
x
2
14
y
2
13
x
2
13
y
2
14
p
3
−p
4
2
× G
{p
i
}
(z, ¯z, α, ¯α) . (2.5)
We will be studying the correlator in the regime appropriate to the gauge-gravity
duality, where the ’t Hooft coupling λ = g
2
Y M
N is large but finite, and work order by order
in the gravity loop expansion 1/c where c =
N
2
−1
4
:
G
{p
i
}
= G
(0)
{p
i
}
+
1
c
G
(1)
{p
i
}
+
1
c
2
G
(2)
{p
i
}
+ . . . (2.6)
The Operator Product Expansion (OPE) offers a series expansion of the correlator
around kinematic limits. In its most straightforward form, where we do not try to exploit
supersymmetry, it involves standard four-dimensional conformal blocks, times S
5
spherical
harmonics for each R-symmetry representation which can be exchanged. The conformal
blocks for a given spin and dimension are written as
G
r,s
`,∆
(z, ¯z) =
z¯z
¯z −z
k
r,s
∆−`−2
2
(z)k
r,s
∆+`
2
(¯z) − k
r,s
∆+`
2
(z)k
r,s
∆−`−2
2
(¯z)
, (2.7)
k
r,s
h
(z) = z
h
2
F
1
h +
r
2
, h +
s
2
; 2h, z
, (2.8)
with r = p
21
≡ p
2
− p
1
, s = p
34
. Since SO(6)
R
and the SO(4,2) Lie algebra are analytic
continuations of each other, the S
5
spherical harmonics admit identical expressions up to
reversal of some quantum numbers:
Z
r,s
m,n
(α, ¯α) = (−1)
m
G
−r,−s
m,−n
(α, ¯α), (2.9)
– 4 –
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