author={Jean-Luc Lehners and Paul J. Steinhardt and Neil Turok},
  journal={International Journal of Modern Physics D},
Georges Lemaitre introduced the term "phoenix universe" to describe an oscillatory cosmology with alternating periods of gravitational collapse and expansion. This model is ruled out observationally, because it requires a supercritical mass density and cannot accommodate dark energy. However, a new cyclic theory of the universe has been proposed that evades these problems. In a recent elaboration of this picture, almost the entire universe observed today is fated to become entrapped inside… 
Cosmic bounces and cyclic universes
Cosmological models involving a bounce from a contracting to an expanding universe can address the standard cosmological puzzles and generate 'primordial' density perturbations without the need for
Cyclic models of the relativistic universe: the early history
Relativistic models of an expanding universe followed by contraction, or a big bang followed by a big crunch, were first proposed by A. Friedmann in 1922 and nine years later by A. Einstein. In the
A Comparison of two Cosmological Models: Inationary Cosmology and the Cyclic Universe
To explain current observations the early universe must have been incredibly at and homogeneous. Tiny density uctuations must have been present to seed large scale structure. Any viable model of the
On adiabatic perturbations in the ekpyrotic scenario
In a recent paper arXiv:0910.2230, Khoury and Steinhardt proposed a way to generate adiabatic cosmological perturbations with a nearly flat spectrum in a contracting Universe. To produce these
Unstable Axion Quintessence Revisited
In axion quintessence, the cosmological era with an energy contrast in dark energy 0.1 < Omega_DE < 0.9 may represent a significant fraction of the universe's lifetime if the minimum of the axion
Ekpyrotic Non-Gaussianity -- A Review
Ekpyrotic models and their cyclic extensions solve the standard cosmological flatness, horizon and homogeneity puzzles by postulating a slowly contracting phase of the universe prior to the big bang.
Nowadays cosmology with the Weyl-Dirac approach
Some problems of cosmology: the big bang singularity, the origin of conventional matter, of dark matter and of dark energy may be successfully described and treated in the framework of the Weyl-Dirac
On the No-Boundary Proposal for Ekpyrotic and Cyclic Cosmologies
The no-boundary proposal provides a compelling theory for the initial conditions of our universe. We study the implications of such initial conditions for ekpyrotic and cyclic cosmologies. These
Safe beginning for the Universe?
When general relativity is augmented by quadratic gravity terms, it becomes a renormalisable theory of gravity. This theory may admit a non-Gaussian fixed point as envisaged in the asymptotic safety


Dark energy and the return of the phoenix universe
In cyclic universe models based on a single scalar field (e.g., the radion determining the distance between branes in M theory), virtually the entire Universe makes it through the ekpyrotic smoothing
The Ekpyrotic universe: Colliding branes and the origin of the hot big bang
We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold,
Generating Ekpyrotic Curvature Perturbations Before the Big Bang
We analyze a general mechanism for producing a nearly scale-invariant spectrum of cosmological curvature perturbations during a contracting phase preceding a big bang, which can be entirely described
Cosmic Evolution in a Cyclic Universe
Based on concepts drawn from the ekpyrotic scenario and M theory, we elaborate our recent proposal of a cyclic model of the universe. In this model, the universe undergoes an endless sequence of
A Cyclic Model of the Universe
A cosmological model in which the universe undergoes an endless sequence of cosmic epochs that begin with a "bang" and end in a “crunch" is proposed, which produces the homogeneity, flatness, and energy needed to begin the next cycle.
Cosmic gravitational-wave background in a cyclic universe
Inflation predicts a primordial gravitational wave spectrum that is slightly ``red.'' In this Brief Report, we compute both the amplitude and spectral form of the primordial tensor spectrum predicted
Why the Cosmological Constant Is Small and Positive
This paper shows that a cyclic model of the universe can naturally incorporate a dynamical mechanism that automatically relaxes the value of the cosmological constant, including contributions to the vacuum density at all energy scales.
The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent limits on deviations from the minimal, six-parameter Λ cold dark matter model. We report these limits and use them to
Annales Soc
  • Sci. Brux. Ser. I A 53, 51
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Science 296
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  • 2002