Physics Letters B 792 (2019) 397–405
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Physics Letters B
www.elsevier.com/locate/physletb
Comments on spinning OPE blocks in AdS
3
/CFT
2
Suchetan Das
Ramakrishna Mission Vivekananda Educational and Research Institute, Belur Math, Howrah-711202, West Bengal, India
a r t i c l e i n f o a b s t r a c t
Article history:
Received
6 February 2019
Received
in revised form 25 March 2019
Accepted
28 March 2019
Available
online 2 April 2019
Editor:
M. Cveti
ˇ
c
We extend the work of [48], [49], to obtain an integral expression of OPE blocks for spinning primaries
in CFT
2
. We observe, when the OPE blocks are made out of conserved spinning primaries, the integral
becomes a product of two copies of weighted AdS
2
fields, smeared along geodesics. In this way, conserved
current OPE blocks in CFT
2
have a different representation in terms of AdS
2
geodesic operators, in stead
of viewing them as AdS
3
geodesic operators. We also show, how this representation can be related
to AdS
3
massless higher spin fields through HKLL bulk field reconstruction. Using this picture, we
consistently obtain the closed form expression of four point spinning conformal block as a product of
two AdS
2
Geodesic Witten diagrams.
© 2019 The Author. 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
Recently, using embedding space formalism [1–6], a general-
ization
of scalar Geodesic Witten diagram (GWD) [7]to spinning
geodesic Witten diagram has been proposed [25–32].
1
This com-
putes
conformal partial waves (CPW) ([8–10]) with spinning ex-
change
operator as well as spinning external operators in CFT
d
([11–24]). For scalar GWD we have:
W
.0
(x
1
, x
2
, x
3
, x
4
) ∝
γ
12
dλ
γ
34
dλ
G
b∂
(y(λ), x
1
)G
b∂
(y(λ), x
2
) ×
G
bb
(y(λ), y(λ
); )G
b∂
(y(λ
), x
3
)G
b∂
(y(λ
), x
4
) (1)
where G
b∂
, the bulk to boundary propagator and G
bb
, the bulk to
bulk propagator in AdS
d+1
are integrated over two geodesics γ
12
and γ
34
. This prescription could be understood from a more funda-
mental
identification between the so called ‘OPE blocks’ B
ij
k
(x
1
, x
2
)
(building block of an OPE) in the CFT and ‘Geodesic operators’ in
the bulk [36], [37], [39].
2
In CFT
2
[44–46], the expression for spinning conformal block
involves a product of two CFT
1
conformal blocks k
h
(z) [47].
W
h
i
,
¯
h
i
h,
¯
h
(z,
¯
z) = k
h
(z)k
¯
h
(
¯
z) + k
¯
h
(z)k
h
(
¯
z), (2)
E-mail address: suchetan1993@gmail.com.
1
In the first order Hilbert-Palatini formalism of gravity, the holographic dual con-
formal
blocks are also studied using open Wilson networks [33–35].
2
See [40–43]for dual description of OPE blocks in states other than vacuum.
z =
z
12
z
34
z
13
z
24
; k
h
(z) = z
h
2
F
1
(
h − h
12
, h + h
34
; 2h; z
)
(3)
This (anti)holomorphic factorization implies that in 2D CFT, in
stead of using AdS
3
GWD, one can express any spinning CPW as
a product of two AdS
2
GWD. A related question is to ask how
the spinning OPE blocks in this case are related in terms of AdS
2
Geodesic operators. The main point of this note is to explore this
connection between spinning OPE blocks and AdS
2
geodesic oper-
ators.
Our
starting point is the observation that in 2D CFT, the method
of finding an integral expression for scalar OPE block discussed in
[48], [49], can be easily extended to the case of spinning OPE block,
constructed out of spinning primary field. This type of simple ex-
tension
is special in CFT
2
, where all spinning primaries are labeled
by
two real numbers (h,
¯
h), which is unavailable in higher dimen-
sions.
3
For instance, using such simplification, available only in 2D,
Osborn has derived [46]the closed form expression of spinning
conformal block (2)by a simple generalization from the spinless
case in CFT
2
, without having to use the embedding space for-
malism,
which is necessary for deriving expressions for conformal
blocks for four point function of non-zero spin operators in higher
dimensions.
3
In D=2, the conformal symmetry is infinite dimensional and so the OPE’s can
be organized into sum of blocks, governed by the full Virasoro symmetry, but here
we consider only global OPE blocks, which are governed by the global conformal
symmetry. In general, closed form expression of Virasoro conformal block is not
known yet, except in a particular limit where the Virasoro block reduces to the
global block [50]and hence, one can use GWD prescription to compute the block
from AdS
3
[51–54].
https://doi.org/10.1016/j.physletb.2019.03.058
0370-2693/
© 2019 The Author. 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
.