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The Ekpyrotic Universe: Colliding Branes and the Origin of the Hot Big Bang
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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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Cited by 5 Pith papers
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Phase-resolved field-space distance bounds in ekpyrotic, bouncing and cyclic cosmologies
Phase-resolved field-space distance bounds for non-inflationary smoothing yield a master lower bound on ε_ek and imply ultra-fast-roll ekpyrosis or modified bounces to match observed red-tilted perturbations.
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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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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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Geodesically Complete Curvature-Bounce Inflation
A closed k=+1 FRW universe with curvature-driven bounce and canonical scalar inflation remains sub-Planckian, satisfies the null energy condition, and produces ns=0.9617-0.9650 and r=0.0037-0.0045 consistent with data.
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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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