New Ekpyrotic Cosmology

By E. Buchbinder, J. Khoury, B. Ovrut. 2007

320 citations recorded by the source corpus.

In this paper, we present a new scenario of the early universe that contains a pre-big bang ekpyrotic phase. By combining this with a ghost condensate, the theory explicitly violates the null energy condition without developing any ghostlike instabilities. Thus the contracting universe goes through a nonsingular bounce and evolves smoothly into the expanding post-big bang phase. The curvature perturbation acquires a scale-invariant spectrum well before the bounce in this scenario. It is sourced by the scale-invariant entropy perturbation engendered by two ekpyrotic scalar fields, a mechanism recently proposed by Lehners et al. Since the background geometry is nonsingular at all times, the curvature perturbation remains nearly constant on superhorizon scales. It emerges from the bounce unscathed and imprints a scale-invariant spectrum of density fluctuations in the matter-radiation fluid at the onset of the hot big bang phase. The ekpyrotic potential can be chosen so that the spectrum has a red tilt, in accordance with the recent data from WMAP. As in the original ekpyrotic scenario, the model predicts a negligible gravity wave signal on all observable scales. As such ``new ekpyrotic cosmology'' provides a consistent and distinguishable alternative to inflation to account for the origin of the seeds of large-scale structure.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/8e7986965dc15a6db983a8bce09253437bcebda2

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Citations in the corpus

Inflationary Cosmology after Planck 2013 (2014, background): “One may hope to avoid these problems in the ghost condensate theory; see a series of papers on this subject [187, 188, 189].”
Rapidly-Varying Speed of Sound, Scale Invariance and Non-Gaussian Signatures (2008, methodology): “In the two-field ekpyrotic mechanism, for instance, the entropy direction must be tachyonic [3, 7, 37].”
FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2008, unknown): “…principle, make a set of predictions that are qualitatively similar to those of inflation models (Khoury et al. 2001, 2002a,b; Khoury et al. 2003; Buchbinder et al. 2007, 2008; Koyama & Wands 2007; Koyama et al. 2007; Creminelli & Senatore 2007), although building concrete models and making…”
Beyond the Cosmological Standard Model (2014, unknown): “Another model which has attracted considerable attention is the ghost condensate [445], which can be used to violate the null energy condition and constuction bouncing cosmologies [239, 446, 447].”
Galileon Cosmology (2009, background): “This could naturally match onto an ekpyrotic [30, 31, 32, 33, 34], New Ekpyrotic [35, 36, 37, 38, 39] or cyclic [40, 41] contracting phase, for instance.”
Ekpyrotic and cyclic cosmology (2008, methodology): “The idea behind the “new ekpyrotic” models [22,23,30] is to build cosmological models in which the ekpyrotic contracting phase is joined with the standard expanding phase by a smooth, non-singular bounce that can be described entirely within a 4-dimensional effective field theory.”
An infinite set of Ward identities for adiabatic modes in cosmology (2013, background): “Conversely, to observe a significant 3-point function in this limit requires violating one of the assumptions above, for instance through additional scalar fields [23–28] or an unstable background [29, 30, 33, 34].”
Towards a nonsingular bouncing cosmology (2012, methodology): “In the model of [44], the value Xi of X at the beginning of the Ekpyrotic phase of contraction is larger than Xc, and it increases rapidly during the Ekpyrotic contraction by a factor e , where N is the number of e-foldings of modes which exit the Hubble radius during the Ekpyrotic phase.”
The Effective Field Theory of Inflation (2007, background): “From this point of view, our approach makes clearer the relationship among inflation, theories of modification of gravity and theories which violate the Null Energy Condition (equivalent to Ḣ > 0 in the cosmological context) like the bouncing models [1, 29, 30].”
Exploring bouncing cosmologies with cosmological surveys (2014, background): “[69] E.”