Cited by 1,468Cosmology and Gravitation TheoriesNoncommutative and Quantum Gravity TheoriesGalaxies: Formation, Evolution, Phenomena

Exponential potentials and cosmological scaling solutions

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Copeland, Edmund J., Liddle, Andrew R., Wands, David·1998·Physical Review D

Abstract

We present a phase-plane analysis of cosmologies containing a baryotropic fluid with an equation of state ${p}_{\ensuremath{\gamma}}=(\ensuremath{\gamma}\ensuremath{-}1){\ensuremath{\rho}}_{\ensuremath{\gamma}},$ plus a scalar field $\ensuremath{\varphi}$ with an exponential potential $V\ensuremath{\propto}\mathrm{exp}(\ensuremath{-}\ensuremath{\lambda}\ensuremath{\kappa}\ensuremath{\varphi})$ where ${\ensuremath{\kappa}}^{2}=8\ensuremath{\pi}G$. In addition to the well-known inflationary solutions for ${\ensuremath{\lambda}}^{2}<2$, there exist scaling solutions when ${\ensuremath{\lambda}}^{2}>3\ensuremath{\gamma}$ in which the scalar field energy density tracks that of the baryotropic fluid (which for example might be radiation or dust). We show that the scaling solutions are the unique late-time attractors whenever they exist. The fluid-dominated solutions, where $V(\ensuremath{\varphi})/{\ensuremath{\rho}}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}0$ at late times, are always unstable (except for the cosmological constant case $\ensuremath{\gamma}=0)$. The relative energy density of the fluid and scalar field depends on the steepness of the exponential potential, which is constrained by nucleosynthesis to ${\ensuremath{\lambda}}^{2}>20$. We show that standard inflation models are unable to solve this ``relic density'' problem.

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Crossref · 10.1103/physrevd.57.4686

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  • For λ2>3γm, the scalar tracks the fluid with wφ=wm and Ωφ=3γm/λ2; this scaling point is stable in the (x,y) sector but, once curvature is included, the curvature direction is unstable for γm≥1, so in the full six-dimensional space it is a saddle.

    “For λ 2 > 3γ m , the scalar tracks the fluid with w φ = w m and Ω φ = 3γ m /λ 2 [23,24].This point is stable in the (x, y) sector but, once curvature is included, the curvature direction is unstable for γ m ≥ 1 (the GR result of [26]).In the full six-dimensional space the scaling point is a saddle.”

    From Dynamical systems analysis of an Einstein–Cartan ekpyrotic nonsingular bounce cosmology (2026) · cites this paper as [23]

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  • The extended EC model reduces consistently to the CLW system in the flat, isotropic, torsionless case, and the numerics are benchmarked against this baseline.

    “confirming that the extended EC model reduces consistently to CLW in the flat, isotropic, torsionless case and that the numerics are benchmarked against this baseline.”

    From Dynamical systems analysis of an Einstein–Cartan ekpyrotic nonsingular bounce cosmology (2026) · cites this paper as [23]

    Section II (p. 1) presents the CLW autonomous system for a spatially flat FRW universe, supporting its identification as the baseline model. The paper does not examine an extended EC model or establish that it reduces to CLW, and it does not report benchmarking the citing authors’ numerics against that baseline. (LLM, conf=0.86)

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  • The eigenvalues at the scaling point are μ± = -[3(2 - γ_m)/4][1 ± sqrt(1 - 8γ_m(λ^2 - 3γ_m)/(λ^2(2 - γ_m)))], μΣ = (3/2)(γ_m - 2), μk = 3γ_m - 2, and μs = 3(γ_m - 2).

    “The two non-trivial eigenvalues in the scalar-matter subspace are [23]”

    From Dynamical systems analysis of an Einstein–Cartan ekpyrotic nonsingular bounce cosmology (2026) · cites this paper as [23]

    The Appendix (p. 5) identifies two eigenvalues, m±, for the scaling solution, supporting the citation’s reference to two eigenvalues in the scalar–matter phase plane. Their formula is not decoded in our copy, so the stated expression for μ± cannot be checked. The citation is attached to the sentence about those two eigenvalues, not to the additional μΣ, μk, and μs values. (LLM, conf=0.82)

    Experimental — accuracy not yet measured
  • In the CLW limit, the fixed points and their stability properties coincide with the original CLW analysis: the scalar-field dominated point is stable for λ^2 < 3γ_m and drives accelerated expansion when λ^2 < 2; the scaling solution exists and is stable for λ^2 > 3γ_m; and the kinetic ± points are always unstable.

    “In this limit the fixed points and their stability properties coincide with the original CLW analysis.The scalar-field dominated point is stable for λ 2 < 3γ m and drives accelerated expansion when λ 2 < 2; the scaling (tracking) solution exists and is stable for λ 2 > 3γ m ; and the kinetic ± points are always unstable.”

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Research works printed but not linked: 1

  1. [2]M. B. Green, J. H. Schwarz and E. Witten, Superstring Theory , Cambridge University Press (1987).

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Authors
Copeland, E. J., Liddle, A. R., & Wands, D.
Affiliations
University of Sussex (GB)
Venue
Physical Review D
Published
1998-04-15
Volume
57
Issue
8
Pages
4686-4690
ISSN
  • 0556-2821 (ISSN-L)
  • 1089-4918
OpenAlex
W2140950522
Cited by
1,468
References
12
Citations by year
2026: 64 · 2025: 84 · 2024: 89 · 2023: 82 · 2022: 80 · 2021: 64 · 2020: 62 · 2019: 59 · 2018: 49 · 2017: 43 · 2016: 63 · 2015: 50 · 2014: 46 · 2013: 52 · 2012: 51
FWCI
21.77
Type
journal article
Language
en
Open access
Locations
  • Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields (publishedVersion)
  • arXiv (Cornell University) (publishedVersion)
  • Sussex Research Online (University of Sussex) (submittedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • Figshare (submittedVersion, cc-by)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
  • Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Noncommutative and Quantum Gravity Theories
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
Keywords
exponential potential, phase plane analysis, scalar field, equation of state, inflation (cosmology), late-time attractors, nucleosynthesis

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