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Poly-instanton Inflation

Michele Cicoli, Francisco G. Pedro, Gianmassimo Tasinato

TL;DR

This work embeds inflation in string theory by employing poly-instanton corrections within the LARGE Volume Scenario, taking the fibre modulus as the inflaton. The resulting potential lifts a flat direction without destabilising the overall volume, and string loop corrections remain subdominant due to extended no-scale structure. The model yields a high inflation scale around 10^15 GeV, a scalar spectral index n_s ≈ 0.96, a tiny tensor-to-scalar ratio r ≈ 10^-5, and a reheating temperature near 10^6 GeV with a sub-Planckian field range. Loop effects are shown to be naturally suppressed for reasonable parameters, making the predictions robust, and the framework offers avenues for quintessence-type extensions.

Abstract

We propose a new inflationary scenario in type IIB Calabi-Yau compactifications, where the inflaton is a Kähler modulus parameterising the volume of an internal four-cycle. The inflaton potential is generated via poly-instanton corrections to the superpotential which give rise to a naturally flat direction due to their double exponential suppression. Given that the volume mode is kept stable during inflation, all the inflaton-dependent higher dimensional operators are suppressed. Moreover, string loop effects can be shown to be negligible throughout all the inflationary dynamics for natural values of the underlying parameters. The model is characterised by a reheating temperature of the order $T_{\rm rh}\simeq 10^6$ GeV which requires $N_e \simeq 54$ e-foldings of inflation. All the inflationary observables are compatible with current observations since the spectral index is $n_s \simeq 0.96$, while the tensor-to-scalar ratio is $r\simeq 10^{-5}$. The volume of the Calabi-Yau is of order $10^3$ in string units, corresponding to an inflationary scale around $10^{15}$ GeV

Poly-instanton Inflation

TL;DR

This work embeds inflation in string theory by employing poly-instanton corrections within the LARGE Volume Scenario, taking the fibre modulus as the inflaton. The resulting potential lifts a flat direction without destabilising the overall volume, and string loop corrections remain subdominant due to extended no-scale structure. The model yields a high inflation scale around 10^15 GeV, a scalar spectral index n_s ≈ 0.96, a tiny tensor-to-scalar ratio r ≈ 10^-5, and a reheating temperature near 10^6 GeV with a sub-Planckian field range. Loop effects are shown to be naturally suppressed for reasonable parameters, making the predictions robust, and the framework offers avenues for quintessence-type extensions.

Abstract

We propose a new inflationary scenario in type IIB Calabi-Yau compactifications, where the inflaton is a Kähler modulus parameterising the volume of an internal four-cycle. The inflaton potential is generated via poly-instanton corrections to the superpotential which give rise to a naturally flat direction due to their double exponential suppression. Given that the volume mode is kept stable during inflation, all the inflaton-dependent higher dimensional operators are suppressed. Moreover, string loop effects can be shown to be negligible throughout all the inflationary dynamics for natural values of the underlying parameters. The model is characterised by a reheating temperature of the order GeV which requires e-foldings of inflation. All the inflationary observables are compatible with current observations since the spectral index is , while the tensor-to-scalar ratio is . The volume of the Calabi-Yau is of order in string units, corresponding to an inflationary scale around GeV

Paper Structure

This paper contains 12 sections, 56 equations, 2 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Basics of the LARGE Volume Scenario
  3. 4D effective action
  4. Swiss-cheese compactifications
  5. Fibred compactifications
  6. Poly-instanton inflation
  7. Fibre stabilisation
  8. Inflationary potential
  9. Inflationary observables
  10. Reheating
  11. Loop corrections
  12. Conclusions

Figures (2)

  • Figure 1: Sketch of the inflationary potential for an illustrative choice of the underlying parameters. In blue: the potential considering only the contribution from poly-instantons; in magenta: the potential including loop corrections.
  • Figure 2: Slow-roll parameters and spectral index for different indicative values of $R$ setting $p=1$: blue $R=10^{-3}$, magenta $R=10^{-2}$, yellow $R=10^{-1}$, green $R=0$.