Cosmology with a time-variable cosmological 'constant'

Peebles, P. J. E.; Ratra, Bharat

doi:10.1086/185100

Cited by 1,689 publications

(1,560 citation statements)

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“…The restriction of α to negative values, that is the consideration of normal power-law potentials instead of inverse power-law ones (contrary to quintessence case), was expected due to the "inverse" kinetic behavior of phantoms in potential slopes. The additional lower bound of α values, which breaks this form of symmetry between phantom and quintessence models, arises from the extra and necessary assumption of positivity of the total phantom energy, which is not present in quintessence case [3,8,9] where one can always obtain it (the potentials can always be shifted to positive values in cosmology). In other words, if the potential is too steep (large −α), then at early times (where the field value φ ≪ 1, i.e it is close to the potential minimum) the phantom potential energy will be very small (∝ φ −α ) and thus unable to make the total energy positive.…”

Section: Cosmological Evolution During Matter Dominationmentioning

confidence: 99%

“…In order to explain this remarkable behavior, and despite the intuition that this can be achieved only through a fundamental theory of nature, physicists can still propose some paradigms for its description, such are theories of modified gravity [2], or "field" models of dark energy. The field models that have been discussed widely in the literature consider a canonical scalar field (quintessence) [3,4], a phantom field, that is a scalar field with a negative sign of the kinetic term [5], or the combination of quintessence and phantom in a unified model named quintom [6].…”

Section: Introductionmentioning

confidence: 99%

“…In the quintessence case, one well studied potential is the inverse-power law one [3,8,9]. This potential exhibits "tracker" behavior, that is for a large class of initial conditions the cosmological evolution converges to a common solution at late times [10].…”

Section: Introductionmentioning

confidence: 99%

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Phantom evolution in power-law potentials

Saridakis¹

2009

Nuclear Physics B

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We investigate phantom models with power-law potentials and we extract the early-time, "tracker", solutions under the assumption of matter domination. Contrary to quintessence case, we find that energy positivity requires normal power-law potentials instead of inverse power-law ones, with the potential exponent being bounded by the quadratic form. In addition, we analytically present the general cosmological solution at intermediate times, that is at low redshifts, which is the period of the transition from matter to dark-energy domination. The comparison with the exact evolution, arising from numerical elaboration, shows that the tracker solution agrees with the later within 2% for redshifts z 1.5, while the intermediate solution is accurate within 2% up to z ≈ 0.5. PACS numbers: 95.36.+x,

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Section: Cosmological Evolution During Matter Dominationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Phantom evolution in power-law potentials

Saridakis¹

2009

Nuclear Physics B

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“…Beyond a bare cosmological constant, a plethora of other models have been proposed, with quintessence -a dynamical scalar field that behaves essentially as a modern day inflaton field, -being perhaps the simplest example (see [11][12][13][14]). …”

Section: Introductionmentioning

confidence: 99%

Ghosts, instabilities, and superluminal propagation in modified gravity models

Felice

Hindmarsh

Trodden

2006

J. Cosmol. Astropart. Phys.

165

167

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We consider Modified Gravity models involving inverse powers of fourth-order curvature invariants.Using these models' equivalence to the theory of a scalar field coupled to a linear combination of the invariants, we investigate the properties of the propagating modes. Even in the case for which the fourth derivative terms in the field equations vanish, we find that the second derivative terms can give rise to ghosts, instabilities, and superluminal propagation speeds. We establish the conditions which the theories must satisfy in order to avoid these problems in Friedmann backgrounds, and show that the late-time attractor solutions generically exhibit superluminally propagating tensor or scalar modes. * a. de-felice@sussex.ac.uk

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“…But there remains the possibility that the cosmological constant (or the gravitational vacuum energy) is fundamentally variable. In a more realistic picture, at least, from field theoretic viewpoints, dark energy should be dynamical in nature [13]. This is the case, for instance, with all time dependent solutions arising out of evolving scalar fields, with an accelerated expansion coming from modified gravity models, holographic dark energy, and the likes.…”

Section: Introduction and Overviewmentioning

confidence: 99%

Inflation and quintessence: theoretical approach of cosmological reconstruction

Neupane

Scherer

2008

J. Cosmol. Astropart. Phys.

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In the first part of this paper, we outline the construction of an inflationary cosmology in the framework where inflation is described by a universally evolving scalar field φ with potential V (φ). By considering a generic situation that inflaton attains a nearly constant velocity, during inflation, m −1 P |dφ/dN | ≡ α + β exp(βN ) (where N ≡ ln a is the e-folding time), we reconstruct a scalar potential and find the conditions that have to satisfied by the (reconstructed) potential to be consistent with the WMAP inflationary data. The consistency of our model with WMAP result (such as n s = 0.951 +0.015 −0.019 and r < 0.3) would require 0.16 < α < 0.26 and β < 0. The running of spectral index, α ≡ dn s /d ln k, is found to be small for a wide range of α.In the second part of this paper, we introduce a novel approach of constructing dark energy within the context of the standard scalar-tensor theory. The assumption that a scalar field might roll with a nearly constant velocity, during inflation, can also be applied to quintessence or dark energy models. For the minimally coupled quintessence, α Q ≡ dA(Q)/d(κQ) = 0 (where A(Q) is the standard matter-quintessence coupling), the dark energy equation of state in the range −1 ≤ w DE < −0.82 can be obtained for 0 ≤ α < 0.63. For α < 0.1, the model allows for only modest evolution of dark energy density with redshift. We also show, under certain conditions, that the α Q > 0 solution decreases the dark energy equation of state w Q with decreasing redshift as compared to the α Q = 0 solution. This effect can be opposite in the α Q < 0 case. The effect of the matterquintessence coupling can be significant only if |α Q | 0.1, while a small coupling |α Q | < 0.1 will have almost no effect on cosmological parameters, including Ω Q , w Q and H(z). The best fit value of α Q in our model is found to be α Q ≃ 0.06, but it may contain significant numerical errors, viz α Q = 0.06 ± 0.35, which thereby implies the consistency of our model with general relativity (for which α Q = 0) at 1σ level.

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Cosmology with a time-variable cosmological 'constant'

Cited by 1,689 publications

References 0 publications

Phantom evolution in power-law potentials

Phantom evolution in power-law potentials

Ghosts, instabilities, and superluminal propagation in modified gravity models

Inflation and quintessence: theoretical approach of cosmological reconstruction

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