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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The Phantom menaced: Constraints on low-energy effective ghosts
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abstract
It has been suggested that a scalar field with negative kinetic energy, or ``ghost,'' could be the source of the observed late-time cosmological acceleration. Naively, such theories should be ruled out by the catastrophic quantum instability of the vacuum. We derive phenomenological bounds on the Lorentz-violating ultraviolet cutoff Lambda which must apply to low-energy effective theories of ghosts, in order to keep the instability at unobservable levels. Assuming only that ghosts interact at least gravitationally, we show that Lambda < 3 MeV for consistency with the cosmic gamma ray background. We also show that theories of ghosts with a Lorentz-conserving cutoff are completely excluded.
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An exact operator conservation law from canonical commutation relations bounds second moments of a ghost-coupled oscillator for all time and states, preventing quantum runaway.
Affine ANEC obstructs non-static flat and open FRW from being null geodesically complete while ANEC-satisfying, but allows explicit scalar-field realizations for closed FRW with NEC-respecting matter.
A quantum ghost coupled polynomially to a harmonic oscillator has unitary evolution and a stable vacuum because a conserved quantity possesses a positive discrete spectrum.
Numerical simulations show ghost-normal scalar systems can remain dynamically bounded for long times when initial data is ultraviolet-dominated and low-amplitude, with some nonlinear potentials creating transient metastable states.
Generalized second law on the apparent horizon plus w ≥ -1 and the dominant energy condition rules out hyperbolic spatial sections for homogeneous isotropic universes.
Extended analysis of DESI DR2 data confirms robust evidence for dynamical dark energy with phantom crossing preference, stable under parametric and non-parametric modeling.
Coupled quintessence-dark matter models can produce an apparent phantom-crossing effective equation of state matching DESI preferences if the scalar field begins frozen in the radiation era.
This review traces the history of dynamical dark energy, presents the no-go theorem against single-field crossing of w = -1, and surveys viable Quintom constructions including multi-field models and modified gravity in light of DESI DR2 hints.
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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Ghost Degrees of Freedom Without Quantum Runaway: Exact Moment Bounds from an Operator Conservation Law
An exact operator conservation law from canonical commutation relations bounds second moments of a ghost-coupled oscillator for all time and states, preventing quantum runaway.
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Affine ANEC selects the closed FRW branch for geodesically complete cosmology
Affine ANEC obstructs non-static flat and open FRW from being null geodesically complete while ANEC-satisfying, but allows explicit scalar-field realizations for closed FRW with NEC-respecting matter.
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Unitary Time Evolution and Vacuum for a Quantum Stable Ghost
A quantum ghost coupled polynomially to a harmonic oscillator has unitary evolution and a stable vacuum because a conserved quantity possesses a positive discrete spectrum.
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Numerical Investigations of Stable Dynamics in the Presence of Ghosts
Numerical simulations show ghost-normal scalar systems can remain dynamically bounded for long times when initial data is ultraviolet-dominated and low-amplitude, with some nonlinear potentials creating transient metastable states.
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The Generalized Second Law and the Spatial Curvature Index
Generalized second law on the apparent horizon plus w ≥ -1 and the dominant energy condition rules out hyperbolic spatial sections for homogeneous isotropic universes.
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Extended Dark Energy analysis using DESI DR2 BAO measurements
Extended analysis of DESI DR2 data confirms robust evidence for dynamical dark energy with phantom crossing preference, stable under parametric and non-parametric modeling.
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Coupled Dark Energy and Dark Matter for DESI: An Effective Guide to the Phantom Divide
Coupled quintessence-dark matter models can produce an apparent phantom-crossing effective equation of state matching DESI preferences if the scalar field begins frozen in the radiation era.
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The Quintom theory of dark energy after DESI DR2
This review traces the history of dynamical dark energy, presents the no-go theorem against single-field crossing of w = -1, and surveys viable Quintom constructions including multi-field models and modified gravity in light of DESI DR2 hints.