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Inflationary Scenarios from Branes at Angles

J. Garcia-Bellido, R. Rabadan, F. Zamora

TL;DR

The paper presents a string-inspired inflation mechanism in which two D4-branes intersect at a small angle, producing a nearly flat potential for their separation $y$ (the inflaton) and enabling slow-roll inflation. Inflation ends via tachyon condensation when the branes come close, resembling hybrid inflation, with the dynamics largely local and insensitive to global compactification details. The authors derive a consistent 4D effective description, matching long-distance supergravity results with short-distance Coleman-Weinberg-type potentials and showing that plausible string-scale parameters yield $N\gtrsim 54$ e-folds and a nearly scale-invariant spectrum, while outlining reheating and moduli-tadpole issues to be addressed in future work. The scenario provides a concrete bridge between brane dynamics in string theory and cosmological observables, highlighting the role of small SUSY breaking and tachyonic endings in realizing viable inflation.

Abstract

We describe a simple mechanism that can lead to inflation within string-based brane-world scenarios. The idea is to start from a supersymmetric configuration with two parallel static Dp-branes, and slightly break the supersymmetry conditions to produce a very flat potential for the field that parametrises the distance between the branes, i.e. the inflaton field. This breaking can be achieved in various ways: by slight relative rotations of the branes with small angles, by considering small relative velocities between the branes, etc. If the breaking parameter is sufficiently small, a large number of e-folds can be produced within the D-brane, for small changes of the configuration in the compactified directions. Such a process is local, i.e. it does not depend very strongly on the compactification space nor on the initial conditions. Moreover, the breaking induces a very small velocity and acceleration, which ensures very small slow-roll parameters and thus an almost scale invariant spectrum of metric fluctuations, responsible for the observed temperature anisotropies in the microwave background. Inflation ends as in hybrid inflation, triggered by the negative curvature of the string tachyon potential. In this paper we elaborate on one of the simplest examples: two almost parallel D4-branes in a flat compactified space.

Inflationary Scenarios from Branes at Angles

TL;DR

The paper presents a string-inspired inflation mechanism in which two D4-branes intersect at a small angle, producing a nearly flat potential for their separation (the inflaton) and enabling slow-roll inflation. Inflation ends via tachyon condensation when the branes come close, resembling hybrid inflation, with the dynamics largely local and insensitive to global compactification details. The authors derive a consistent 4D effective description, matching long-distance supergravity results with short-distance Coleman-Weinberg-type potentials and showing that plausible string-scale parameters yield e-folds and a nearly scale-invariant spectrum, while outlining reheating and moduli-tadpole issues to be addressed in future work. The scenario provides a concrete bridge between brane dynamics in string theory and cosmological observables, highlighting the role of small SUSY breaking and tachyonic endings in realizing viable inflation.

Abstract

We describe a simple mechanism that can lead to inflation within string-based brane-world scenarios. The idea is to start from a supersymmetric configuration with two parallel static Dp-branes, and slightly break the supersymmetry conditions to produce a very flat potential for the field that parametrises the distance between the branes, i.e. the inflaton field. This breaking can be achieved in various ways: by slight relative rotations of the branes with small angles, by considering small relative velocities between the branes, etc. If the breaking parameter is sufficiently small, a large number of e-folds can be produced within the D-brane, for small changes of the configuration in the compactified directions. Such a process is local, i.e. it does not depend very strongly on the compactification space nor on the initial conditions. Moreover, the breaking induces a very small velocity and acceleration, which ensures very small slow-roll parameters and thus an almost scale invariant spectrum of metric fluctuations, responsible for the observed temperature anisotropies in the microwave background. Inflation ends as in hybrid inflation, triggered by the negative curvature of the string tachyon potential. In this paper we elaborate on one of the simplest examples: two almost parallel D4-branes in a flat compactified space.

Paper Structure

This paper contains 13 sections, 66 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Description of the model
  3. Supergravity description at long distances
  4. The inflationary scenario
  5. Phenomenological constraints
  6. The model of brane inflation
  7. Geometrical interpretation of brane inflation parameters
  8. Effective field theory description at short distances
  9. Preheating and reheating
  10. Conclusions
  11. Probe brane effective action
  12. Velocity-dependent corrections to the inflaton potential.
  13. Discussion on compact potentials.

Figures (1)

  • Figure 1: Two views of the effective potential for the inflaton field in a two dimensional torus transverse to the branes. The periods of the lattice are normalised to 1 in both directions. Notice how the rotational symmetry is recovered close to the brane.