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Inflation from Flux Cascades

Guido D'Amico, Roberto Gobbetti, Matthew Kleban, Marjorie Schillo

TL;DR

We propose a microscopic inflation mechanism based on a $$(p+2)$$-form flux threading compact dimensions that discharges via brane nucleation, triggering a flux cascade inside an open FRW bubble and yielding a gradually decreasing vacuum energy with about $N \sim 60$ efolds starting from $Q_0 \sim O(100)$. From a 4D viewpoint, the inflaton is the brane position with a Dirac-Born-Infeld kinetic term, avoiding ad hoc scalar potentials and heavy fine-tuning. The scalar spectrum is nearly scale-invariant with amplitude $oxed{\mathcal{P}_{\zeta} = \frac{H^4}{8 \pi^2 \sigma v^2}}$ and tilt $n_s-1 \approx -2/N_*$, while tensor modes satisfy $\boxed{\mathcal{P}_h = \frac{16 G_N H^2}{\pi}}$ and a potentially observable $r$; the model may also exhibit small oscillations in the power spectrum and possible non-Gaussian features. Embedded naturally in the string landscape, this mechanism furnishes a slow-roll-like inflationary scenario without fundamental scalars and with distinctive predictions, including oscillatory power-spectrum features and potential gravitational waves.

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).

Inflation from Flux Cascades

TL;DR

We propose a microscopic inflation mechanism based on a -form flux threading compact dimensions that discharges via brane nucleation, triggering a flux cascade inside an open FRW bubble and yielding a gradually decreasing vacuum energy with about efolds starting from . From a 4D viewpoint, the inflaton is the brane position with a Dirac-Born-Infeld kinetic term, avoiding ad hoc scalar potentials and heavy fine-tuning. The scalar spectrum is nearly scale-invariant with amplitude and tilt , while tensor modes satisfy and a potentially observable ; the model may also exhibit small oscillations in the power spectrum and possible non-Gaussian features. Embedded naturally in the string landscape, this mechanism furnishes a slow-roll-like inflationary scenario without fundamental scalars and with distinctive predictions, including oscillatory power-spectrum features and potential gravitational waves.

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).

Paper Structure

This paper contains 7 sections, 9 equations, 1 figure.

Table of Contents

  1. Relation to previous work:
  2. Scalar Perturbations:
  3. Tensor Perturbations:
  4. Perturbations from String/Particle Production:
  5. Tilt:
  6. Non-Gaussianity:
  7. Reheating:

Figures (1)

  • Figure 1: A snapshot of the flux discharge cascade on a $dS_4 \times S_1$ space-time. $Q, Q-1,...$ indicate the number of flux units, and the dashed arrows indicate the direction of the force (and velocity) of that section of brane. Typically $l<1/H$; the figure is drawn not to scale for illustrative purposes.