Physics Letters B 760 (2016) 796–799
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Thermal geometry from CFT at finite temperature
Wen-Cong Gan
a,b
, Fu-Wen Shu
a,b,∗
, Meng-He Wu
a,b
a
Department of Physics, Nanchang University, Nanchang 330031, China
b
Center for Relativistic Astrophysics and High Energy Physics, Nanchang University, Nanchang 330031, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received
25 May 2016
Accepted
28 July 2016
Available
online 1 August 2016
Editor:
N. Lambert
Keywords:
AdS/CFT
correspondence
cMERA
BTZ
black hole
We present how the thermal geometry emerges from CFT at finite temperature by using the truncated
entanglement renormalization network, the cMERA. For the case of 2d CFT, the reduced geometry is the
BTZ black hole or the thermal AdS as expectation. In order to determine which spacetimes prefer to form,
we propose a cMERA description of the Hawking–Page phase transition. Our proposal is in agreement
with the picture of the recent proposed surface/state correspondence.
© 2016 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
Ever since AdS/CFT correspondence was proposed [1–3], a great
deal of attention has been paid to understand its basic mechanism.
A recent progress was made through tensor network, which is a
powerful tool to deal with system of multi-degree freedom, such as
critical Ising model, whose continuum is a CFT. A particular signif-
icant
tensor network is multi-scale entanglement renormalization
ansatz (MERA) [4,5], containing disentanglers, which can remove
short-range entanglement and thus produce an efficient descrip-
tion
of critical system. Inspired by the Ryu–Takayanagi formula of
the holographic entropy [6], the relationship between MERA and
AdS/CFT was first noticed by Swingle [7]. He pointed out that the
MERA that emerges from critical system (which can be viewed as
discrete CFT) can be viewed as discrete time slice of AdS space,
where the renormalization direction of MERA corresponds to the
discrete radial direction of the AdS space. To apply MERA to field
theory, we need to generalize MERA to continuous version. The
generalization was made by Haegeman et al. in [8] where they
proposed the continuous MERA (cMERA) which can make entan-
glement
renormalization for quantum fields in real space. Nozaki
et al. applied it, for the first time, to the context of AdS/MERA, and
the emergent holographic (smooth) geometry was obtained [9].
To
discuss the correspondence between CFT and the spacetime
containing black holes, it is necessary to consider CFT at finite
temperature. In terms of the AdS/MERA, there are two different de-
*
Corresponding author.
E-mail
addresses: ganwencong@gmail.com (W.-C. Gan), shufuwen@ncu.edu.cn
(F.-W. Shu),
menghewu.physik@gmail.com (M.-H. Wu).
scriptions. One is based on the initial MERA and argues that after
finite steps of entanglement renormalization, the MERA truncates
at a level of multiple sites where the state at the top level (i.e. the
truncated MERA state) becomes maximally mixed state and thus
corresponds to the horizon of a black hole [7,10]. We often call
it the truncated MERA. The alternative way is based on the ther-
mofield
double formalism [11] and the emergent tensor network
is often called double MERA. The double MERA composes of two
copies of the MERA that connected by MPS state (Fig. 1) [12–14].
A continuous extension of the double MERA has been achieved in
[15], where the authors pointed out that it quantitatively agrees
with a half of the AdS black hole spacetime. Even though the
double MERA leads to some progress in discussing AdS/MERA at
finite temperature, the truncated MERA still deserves more atten-
tion.
This is based on the following two considerations: firstly, the
continuous version of the truncated MERA, as a conjectured tensor
network, whose validity to generate (smooth) black hole geometry
has not yet been proved; secondly, the truncated MERA provides a
possibility to give a cMERA description of the Hawking–Page phase
transition [16], which is lack of careful investigation in the past lit-
eratures.
In
this letter, we would like to apply the truncated MERA to
construct the holographic geometry of cMERA at finite tempera-
ture
explicitly by studying the two dimensional CFT. Our results
confirm that the thermal emergent geometry can be obtained in
this way, and point out that the emergent spacetime is BTZ black
hole for sufficiently large temperature. On the other hand, we also
try to give a cMERA description of the Hawking–Page phase tran-
sition.
Our results show that depending on the cutoff parameters,
it is possible to figure out the phase of the emergent spacetimes.
http://dx.doi.org/10.1016/j.physletb.2016.07.073
0370-2693/
© 2016 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
.