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D7-Brane Chaotic Inflation

Arthur Hebecker, Sebastian C. Kraus, Lukas T. Witkowski

TL;DR

The paper addresses the challenge of embedding large-field inflation in a UV-complete string framework by proposing a D7-brane position modulus as the inflaton with a shift-symmetric Kähler potential and flux-induced monodromy. The authors develop a concrete Type IIB construction within the Large Volume Scenario, where the inflaton potential is dominantly quadratic and the mass m_φ is tunable via the small coefficients α and β in the superpotential W = W0 + α c + (β/2) c^2 + ..., with c stabilized by D_c W = 0 and the Kähler moduli stabilized by LVS dynamics. Extended no-scale structure ensures loop corrections remain subleading, while oscillatory and higher-order corrections are suppressed in the large complex-structure limit, making the scenario controllable. The work provides a concrete string-theoretic realization of axion monodromy-like large-field inflation, enabling detailed future exploration of flux-tuning, inflationary phenomenology, and uplifting within a consistent supergravity framework.

Abstract

We analyze string-theoretic large-field inflation in the regime of spontaneously-broken supergravity with conventional moduli stabilization by fluxes and non-perturbative effects. The main ingredient is a shift-symmetric Kahler potential, supplemented by flux-induced shift symmetry breaking in the superpotential. The central technical observation is that all these features are present for D7-brane position moduli in Type IIB orientifolds, allowing for a realization of the axion monodromy proposal in a controlled string theory compactification. On the one hand, in the large complex structure regime the D7-brane position moduli inherit a shift symmetry from their mirror-dual Type IIA Wilson lines. On the other hand, the Type IIB flux superpotential generically breaks this shift symmetry and allows, by appealing to the large flux discretuum, to tune the relevant coefficients to be small. The shift-symmetric direction in D7-brane moduli space can then play the role of the inflaton: While the D7-brane circles a certain trajectory on the Calabi-Yau many times, the corresponding F-term energy density grows only very slowly, thanks to the above-mentioned tuning of the flux. Thus, the large-field inflationary trajectory can be realized in a regime where Kahler, complex structure and other brane moduli are stabilized in a conventional manner, as we demonstrate using the example of the Large Volume Scenario.

D7-Brane Chaotic Inflation

TL;DR

The paper addresses the challenge of embedding large-field inflation in a UV-complete string framework by proposing a D7-brane position modulus as the inflaton with a shift-symmetric Kähler potential and flux-induced monodromy. The authors develop a concrete Type IIB construction within the Large Volume Scenario, where the inflaton potential is dominantly quadratic and the mass m_φ is tunable via the small coefficients α and β in the superpotential W = W0 + α c + (β/2) c^2 + ..., with c stabilized by D_c W = 0 and the Kähler moduli stabilized by LVS dynamics. Extended no-scale structure ensures loop corrections remain subleading, while oscillatory and higher-order corrections are suppressed in the large complex-structure limit, making the scenario controllable. The work provides a concrete string-theoretic realization of axion monodromy-like large-field inflation, enabling detailed future exploration of flux-tuning, inflationary phenomenology, and uplifting within a consistent supergravity framework.

Abstract

We analyze string-theoretic large-field inflation in the regime of spontaneously-broken supergravity with conventional moduli stabilization by fluxes and non-perturbative effects. The main ingredient is a shift-symmetric Kahler potential, supplemented by flux-induced shift symmetry breaking in the superpotential. The central technical observation is that all these features are present for D7-brane position moduli in Type IIB orientifolds, allowing for a realization of the axion monodromy proposal in a controlled string theory compactification. On the one hand, in the large complex structure regime the D7-brane position moduli inherit a shift symmetry from their mirror-dual Type IIA Wilson lines. On the other hand, the Type IIB flux superpotential generically breaks this shift symmetry and allows, by appealing to the large flux discretuum, to tune the relevant coefficients to be small. The shift-symmetric direction in D7-brane moduli space can then play the role of the inflaton: While the D7-brane circles a certain trajectory on the Calabi-Yau many times, the corresponding F-term energy density grows only very slowly, thanks to the above-mentioned tuning of the flux. Thus, the large-field inflationary trajectory can be realized in a regime where Kahler, complex structure and other brane moduli are stabilized in a conventional manner, as we demonstrate using the example of the Large Volume Scenario.

Paper Structure

This paper contains 12 sections, 33 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Ingredients
  3. Shift-Symmetric Kähler Potential
  4. Superpotential
  5. The Model
  6. Minimizing the Potential
  7. Computing the Mass
  8. Phenomenology
  9. Stability during Inflation
  10. Cubic and quartic terms
  11. Corrections
  12. Conclusions

Figures (2)

  • Figure 1: Illustration of the D7-brane position modulus parameter space. Inflation occurs when the D7-brane moves along a one-cycle in the parameter space, which need not necessarily be non-trivial in homology.
  • Figure 2: Illustration of the D7-brane position modulus parameter space in the example of F-theory on $K3\times K3$, which reduces to Type IIB string theory on $K3\times T^2/\mathds{Z}_2$ in the weak coupling limit.