Inflation from Flux Cascades

TL;DR

This paper introduces a new inflationary mechanism driven by flux cascades in extra dimensions, leading to a prolonged inflation with observable signatures, naturally fitting into string theory without fine-tuning.

Contribution

It proposes a novel flux cascade process as a source of inflation, producing realistic cosmological perturbations and integrating naturally into the string landscape.

Findings

Achieves ~60 e-folds of inflation with decreasing Hubble constant.

Produces a nearly scale-invariant spectrum with observable non-Gaussianity and tensor modes.

Features a small oscillatory component in the power spectrum related to compact dimensions.

Abstract

When electric-type flux threads compact extra dimensions, a quantum nucleation event can break a flux line and initiate a cascade that unwinds many units of flux. Here, we present a novel mechanism for inflation based on this phenomenon. From the 4D point of view, the cascade begins with the formation of a bubble containing an open Friedmann-Robertson-Walker cosmology, but the vacuum energy inside the bubble is initially only slightly reduced, and subsequently decreases gradually throughout the cascade. If the initial flux number Q_0 ~ O(100), during the cascade the universe can undergo N ~ 60 efolds of inflationary expansion with gradually decreasing Hubble constant, producing a nearly scale-invariant spectrum of adiabatic density perturbations with amplitude and tilt consistent with observation, and a potentially observable level of non-Gaussianity and tensor modes. The power spectrum has a small oscillatory component that does not decay away during inflation, with a period set approximately by the light-crossing time of the compact dimension(s). Since the ingredients are fluxes threading compact dimensions, this mechanism fits naturally into the string landscape, but does not appear to suffer from the eta problem or require fine-tuning (beyond the usual anthropic requirement of small vacuum energy after reheating).