
Physics Letters B 730 (2014) 271–274
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Physics Letters B
www.elsevier.com/locate/physletb
Renormalization group flow and symmetry restoration
in de Sitter space
J. Serreau
APC, AstroParticule et Cosmologie, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, 10, rue Alice DomonetLéonie
Duquet, 75205 Paris Cedex 13, France
article info abstract
Article history:
Received 19 December 2013
Received in revised form 14 January 2014
Accepted 16 January 2014
Available online 30 January 2014
Editor: J.-P. Blaizot
Keywords:
Quantum field theory in de Sitter space
Infrared effects
Nonperturbative renormalization group
We compute the renormalization group flow of O (N) scalar field theories in de Sitter space using
nonperturbative renormalization group techniques in the local potential approximation. We obtain the
flow of the effective potential on superhorizon scales for arbitrary space–time dimension D =d +1. We
show that, due to strong infrared fluctuations, the latter is qualitatively similar to the corresponding
one in Euclidean space R
D
with D = 0. It follows that spontaneously broken symmetries are radiatively
restored in any space–time dimension and for any value of N.
© 2014 The Author. Published by Elsevier B.V. Open access under CC BY license.
Funded by SCOAP
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1. Introduction
The study of quantum field dynamics in de Sitter (dS) space is a
subject of topical interest. It is of relevance for inflationary cosmol-
ogy, where timely issues concern the understanding of radiative
corrections to inflationary observables [1–5].Moreover, themaxi-
mally symmetric dS space offers a paradigm example for the study
of quantum field theory on curved space–times, which reveals a
realm of nontrivial effects as compared to Minkowski space [6–9].
The case of light fields, with mass small in units of the curvature, is
of particular interest both for phenomenological applications to in-
flationary cosmology and for it has no flat space analog. Such fields
exhibit strong, semi-classical fluctuations on superhorizon scales,
responsible for nonperturbative infrared/secular effects [6]. Simi-
lar issues arise in various instances in flat space, e.g., for bosonic
fields at high temperature or near a critical point, or for nonequi-
librium systems. Powerful methods have been developed to deal
with such situations, including, e.g., renormalization group, two-
particle-irreducible, or large-N techniques. In recent years, some
efforts have been put in adapting these methods to study the in-
frared (IR) dynamics of quantum fields in dS space [10–17].
An interesting issue concerns the possibility of spontaneous
symme
try breaking (SSB). It is known that the phase structure of
a given theory can be dramatically affected by the space geome-
try [18]. It had been argued in [19], in the case of an O (2) scalar
E-mail address: serreau@apc.univ-paris7.fr.
theory, that a spontaneously broken symmetry gets radiatively re-
stored as a consequence of the large-distance logarithmic behavior
of the two-point correlator of a massless field in dS space, in anal-
ogy to what happens in flat space in two dimensions [20].Simi-
larly, a recent explicit calculation of the effective potential of O
(N)
theories in the large-N limit [13] shows that strong fluctuations of
superhorizon modes prevent the possibility of SSB in any space–
time dimension. An simple intuitive picture may be that long range
order cannot develop because of the existence of a causal horizon.
If correct, this would apply to arbitrary value of N, including the
discrete symmetry case N
=1.
Subsequent studies have been undertaken using either the
Hartree approximation [21] or a field theoretical generalization of
the Wigner–Weisskopf method [22], which conclude that SSB is
possible in dS space for finite N and that there is a first order tran-
sition to a symmetric phase as a function of the dS radius. These
studies also find that the would-be-Goldstone excitations acquire
a nonzero mass. However, the Hartree approximation is known to
erroneously predicts a first order transition and massive Goldstone
modes in flat space [23], due to the neglect of important nonlocal
self-energy contributions in the broken phase [24]. This makes the
analogous results in dS space dubious. Recently, employing a semi-
classical stochastic approach, the authors of [25] conclude to the
impossibility of SSB for arbitrary value of N, conforting the results
of [13,19] and the intuitive argument above.
In this Letter, we address the question of SSB employing non-
perturbati
ve renormalization group (NPRG) techniques [26].Inflat
space, the latter have proven powerful tools in a wide variety of
http://dx.doi.org/10.1016/j.physletb.2014.01.058
0370-2693 © 2014 The Author. Published by Elsevier B.V. Open access under CC BY license. Funded by SCOAP
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