Rollercoaster Cosmology

Abstract

(Abridged) Does inflation have to happen all in one go? The answer is a resounding no! All cosmological problems can be solved by a sequence of short bursts of cosmic acceleration, interrupted by short epochs of decelerated expansion. The spectrum of perturbations will still match the CMB and LSS if the earliest stage of the last $\mathcal{O}(50)-\mathcal{O}(60)$ efolds is at least $\mathcal{O}(15)$ efolds long. Other stages can be considerably shorter. But as long as they add up to $\mathcal{O}(50)-\mathcal{O}(60)$ efolds and the stages of decelerated expansion in between them are shorter and also overall last less, the ensuing cosmology will pass muster. The presence of the interruptions resets the efold clock of each accelerating stage, and changes its value at the CMB pivot point. This change opens up the theory space, loosening the bounds. In particular some models that seem excluded at $\mathcal{N}=60$ fit very well as shorter stages with $\mathcal{N}=30$. Interesting predictions are that both the scalar and tensor spectra of perturbations are rapidly modified at short wavelengths. These features could be tested with future CMB spectroscopy searches and with short wavelength primordial gravity probes. The spatial curvature in these models can be larger than the largest wavelength scalar perturbations, because ${\Omega }_{\mathtt{k}}$ evolves differently than the scalar perturbations $\frac{\delta \rho }{\rho }{|}_{\mathtt{S}}$. Finally, with many short stages of accelerated expansion, the abundance of reheating products from previous accelerated stages does not get completely wiped out. This implies that the universe may contain additional populations of particles, more rare than the visible ones, or even primordial black holes, created during a late decelerated epoch before last reheating, which may be dark matter.

52 pages, 15 figures. v2: Minor changes and references added, version published in JCAP. v3: Minor corrections

References in corpus (11)

• On the Geometry of the String Landscape and the Swampland
• The Effective Field Theory of Inflation
• Symmetries and Strings in Field Theory and Gravity
• Effective Field Theory for Inflation
• A new kind of cyclic universe
• The galaxy power spectrum take on spatial curvature and cosmic concordance
• Just enough inflation: power spectrum modifications at large scales
• Natural Chaotic Inflation and UV Sensitivity
• Inflation from Broken Scale Invariance
• Cosmological Consequences of Initial State Entanglement
• Primordial Tensor Perturbation in Double Inflationary Scenario with a Break

Cited by in corpus (16)

• Oscillations in the stochastic gravitational wave background from sharp features and particle production during inflation
• An analytic approach to non-slow-roll inflation
• Spectrum oscillations from features in the potential of single-field inflation
• Intermittent null energy condition violations during inflation and primordial gravitational waves
• Very Hairy Inflation
• One-loop infrared rescattering by enhanced scalar fluctuations during inflation
• Universal accelerating cosmologies from 10d supergravity
• Double Monodromy Inflation: A Gravity Waves Factory for CMB-S4, LiteBIRD and LISA
• Impact of the Hubble tension on the $r$-$n_s$ contour
• Sharp turns in axion monodromy: primordial black holes and gravitational waves
• Generating enhanced parity-violating gravitational waves during inflation with violation of the null energy condition
• Generating enhanced primordial GWs during inflation with intermittent violation of NEC and diminishment of GW propagating speed
• The effect of multiple features on the power spectrum in two-field inflation
• Double inflation via non-minimally coupled spectator
• Very-High-Frequency Gravitational Waves from Multi-Monodromy Inflation
• Primordial gravitational waves from excited states