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Inflation from Warped Space

Xingang Chen

TL;DR

The paper develops a DBI-based inflation scenario in warped throats of flux-stabilized string compactifications, showing how a steep potential can yield sustained inflation when the inflaton is causally slowed by the warp. It provides a field-theory description, embeds it in a string-theoretic setup with mobile D3-branes, and analyzes density perturbations with a reduced sound horizon, including stringy fluctuations and potential suppression of large-scale modes. It further studies throat reheating via relativistic brane dynamics and outlines a multi-throat model that yields large e-folds, observable perturbations, and a distinctive cosmic-string signature spectrum. The work highlights the observational implications (cosmic strings, non-Gaussianities) and the key theoretical challenges (back-reaction, rescaling effects) of realizing DBI inflation in a concrete string-theory framework.

Abstract

A long period of inflation can be triggered when the inflaton is held up on the top of a steep potential by the infrared end of a warped space. We first study the field theory description of such a model. We then embed it in the flux stabilized string compactification. Some special effects in the throat reheating process by relativistic branes are discussed. We put all these ingredients into a multi-throat brane inflationary scenario. The resulting cosmic string tension and a multi-throat slow-roll model are also discussed.

Inflation from Warped Space

TL;DR

The paper develops a DBI-based inflation scenario in warped throats of flux-stabilized string compactifications, showing how a steep potential can yield sustained inflation when the inflaton is causally slowed by the warp. It provides a field-theory description, embeds it in a string-theoretic setup with mobile D3-branes, and analyzes density perturbations with a reduced sound horizon, including stringy fluctuations and potential suppression of large-scale modes. It further studies throat reheating via relativistic brane dynamics and outlines a multi-throat model that yields large e-folds, observable perturbations, and a distinctive cosmic-string signature spectrum. The work highlights the observational implications (cosmic strings, non-Gaussianities) and the key theoretical challenges (back-reaction, rescaling effects) of realizing DBI inflation in a concrete string-theory framework.

Abstract

A long period of inflation can be triggered when the inflaton is held up on the top of a steep potential by the infrared end of a warped space. We first study the field theory description of such a model. We then embed it in the flux stabilized string compactification. Some special effects in the throat reheating process by relativistic branes are discussed. We put all these ingredients into a multi-throat brane inflationary scenario. The resulting cosmic string tension and a multi-throat slow-roll model are also discussed.

Paper Structure

This paper contains 14 sections, 103 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Field theory of DBI inflation
  3. The inflation
  4. Density perturbations
  5. DBI inflation in string theory
  6. DBI action and its validity
  7. Stringy quantum fluctuations on D3-branes
  8. Throat reheating by relativistic branes
  9. Annihilation versus collision
  10. Cosmological rescaling
  11. A multi-throat model
  12. Concluding remarks
  13. Rolling branes in S-throat
  14. A multi-throat slow-roll model

Figures (2)

  • Figure 1: Closed and open string creation from brane annihilation. The branes in dashed lines are decaying ones, and the branes in solid lines are the surviving ones. (A) are some disk diagrams responsible for closed string creation. (B) is a loop diagram creating closed and/or open strings. The separation between the branes is in terms of the world-sheet distance, but branes may not be spatially separated. (C) is a loop diagram only creates closed strings.
  • Figure 2: The cosmological rescaling for branes in the non-comoving region where back-reaction is large. The brane in dashed lines in the IR side indicates its longitudinal scale if it had followed the DBI action, which is the scale of the Poincare observer after the background restoration.