Phase-resolved scalar distance bounds are derived for ekpyrotic, bouncing, and cyclic cosmologies, yielding a master condition that lower-bounds ε_ek from remaining distance after conversion and bounce.
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J., Liddle, A
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We present a phase-plane analysis of cosmologies containing a barotropic fluid with equation of state $p_\gamma = (\gamma-1) \rho_\gamma$, plus a scalar field $\phi$ with an exponential potential $V \propto \exp(-\lambda \kappa \phi)$ where $\kappa^2 = 8\pi G$. In addition to the well-known inflationary solutions for $\lambda^2 < 2$, there exist scaling solutions when $\lambda^2 > 3\gamma$ in which the scalar field energy density tracks that of the barotropic 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 $V(\phi)/\rho_\gamma \to 0$ at late times, are always unstable (except for the cosmological constant case $\gamma = 0$). The relative energy density of the fluid and scalar field depends on the steepness of the exponential potential, which is constrained by nucleosynthesis to $\lambda^2 > 20$. We show that standard inflation models are unable to solve this `relic density' problem.
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citing papers explorer
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Phase-resolved field-space distance bounds in ekpyrotic, bouncing and cyclic cosmologies
Phase-resolved scalar distance bounds are derived for ekpyrotic, bouncing, and cyclic cosmologies, yielding a master condition that lower-bounds ε_ek from remaining distance after conversion and bounce.
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Thermal channels of scalar and tensor waves in Jordan-frame scalar--tensor gravity
Scalar and tensor perturbations in Jordan-frame scalar-tensor gravity admit an exact linear-order Eckart effective-fluid description, with gravitational-wave damping governed by the scalar sector's transverse-traceless anisotropic stress.
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Precision Inflationary Predictions: Impact of Accurate End-of-Inflation Dynamics
Improved end-of-inflation dynamics shift the Starobinsky model's predicted spectral index n_s by up to 1.2×10^{-3} within the allowed reheating range.
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Curvature-Assisted Dynamical Compactification in a Pre-Inflationary Higher-Dimensional Universe
Negative curvature sustains tracker-like radion evolution in a 5D open FRW universe, enabling trapping into a compactified vacuum via Casimir and Kaluza-Klein thermal effects before 4D inflation dilutes curvature remnants.
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Bounding axion dark energy
An analytic bound on axion parameters in thawing quintessence is derived independently of initial conditions and used with cosmological observations plus quantum gravity constraints to exclude large regions of axion dark energy parameter space.
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Persistence and Transition Varieties in Scalar Field Cosmology
Bifurcation analysis organizes scalar field FRW cosmologies around five loci for exponential potentials and invariant structures for quadratic ones, classifying physical regimes.
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Exponential Quintessence Model: Analytical Quantification of the Fine-Tuning Problem in Dark Energy
Exponential quintessence with an assumed kination epoch relaxes the dark energy fine-tuning problem by dozens of orders of magnitude relative to a cosmological constant.
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Resolving the Planck-DESI tension by nonminimally coupled quintessence
Non-minimally coupled quintessence resolves the Planck-DESI Ω_m tension at >3σ while the effective equation of state stays above w=-1 and other tensions on neutrino mass and growth rate are relieved.
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Exponential Quintessence: Analytic Relationship Between the Current Equation of State Parameter and the Potential Parameter
For an exponential quintessence potential, an analytic formula links the current equation-of-state w_φ0 to the potential slope λ while enforcing prior radiation and matter domination, yielding the bound λ < 1.94 at Ω_φ0 = 0.685.
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EFT of Dark Energy with Cosmic Chronometers: Reconstructing Background EFT Functions
Reconstruction of EFT background functions from cosmic chronometer Hubble data allows model-independent tests of dark energy evolution in scalar-tensor theories.
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Interacting $k$-essence field with non-pressureless Dark Matter: Cosmological Dynamics and Observational Constraints
Interacting k-essence dark energy and non-pressureless dark matter models with two interaction forms are shown to reproduce major cosmological epochs and fit observations comparably to LambdaCDM while admitting late-time de Sitter attractors.