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 Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
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abstract
We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe. The model addresses the cosmological horizon, flatness and monopole problems and generates a nearly scale-invariant spectrum of density perturbations without invoking superluminal expansion (inflation). The scenario relies, instead, on physical phenomena that arise naturally in theories based on extra dimensions and branes. As an example, we present our scenario predominantly within the context of heterotic M-theory. A prediction that distinguishes this scenario from standard inflationary cosmology is a strongly blue gravitational wave spectrum, which has consequences for microwave background polarization experiments and gravitational wave detectors.
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An Einstein-Cartan ekpyrotic model with a steep-to-plateau scalar potential supports a torsion-driven nonsingular bounce in homogeneous contraction without chaotic behavior in the explored parameter space.
A quasi-dust ekpyrotic two-field model in Loop Quantum Cosmology produces viable primordial power spectra via coupled scalar and tensor perturbations.
NANOGrav data favors a blue-tilted tensor spectrum with nt ≈ 2.2, radiation-dominated reheating, and alpha-vacuum states over standard Bunch-Davies, with a frequency-dependent alpha suggested to resolve the blue-tilt tension.
Triplet leptogenesis succeeds at TeV-scale masses in fast-expanding or scalar-tensor early universes, unlike the standard radiation-dominated case requiring 10^10 GeV.
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Review of classical energy conditions, their quantum violations, and information-theoretic bounds for semi-classical gravity, based on Modave lectures.
Modified gravity theories supply viable mathematical frameworks for inflation, bounces, and dark energy eras that match observational data.
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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Dynamical systems analysis of an Einstein-Cartan ekpyrotic nonsingular bounce cosmology
An Einstein-Cartan ekpyrotic model with a steep-to-plateau scalar potential supports a torsion-driven nonsingular bounce in homogeneous contraction without chaotic behavior in the explored parameter space.
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Quasi-dust ekpyrotic scenario in Loop Quantum Cosmology
A quasi-dust ekpyrotic two-field model in Loop Quantum Cosmology produces viable primordial power spectra via coupled scalar and tensor perturbations.
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Constraints on the inflationary vacuum and reheating era from NANOGrav
NANOGrav data favors a blue-tilted tensor spectrum with nt ≈ 2.2, radiation-dominated reheating, and alpha-vacuum states over standard Bunch-Davies, with a frequency-dependent alpha suggested to resolve the blue-tilt tension.
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Towards Testable Type-III Leptogenesis in Non-Standard Early Universe Scenarios
Triplet leptogenesis succeeds at TeV-scale masses in fast-expanding or scalar-tensor early universes, unlike the standard radiation-dominated case requiring 10^10 GeV.
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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.
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Modave lectures on energy conditions in quantum field theory and semi-classical gravity
Review of classical energy conditions, their quantum violations, and information-theoretic bounds for semi-classical gravity, based on Modave lectures.
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Modified Gravity Theories on a Nutshell: Inflation, Bounce and Late-time Evolution
Modified gravity theories supply viable mathematical frameworks for inflation, bounces, and dark energy eras that match observational data.
- Geodesically Complete Curvature-Bounce Inflation