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Racetrack Inflation

J. J. Blanco-Pillado, C. P. Burgess, J. M. Cline, C. Escoda, M. Gomez-Reino, R. Kallosh, A. Linde, F. Quevedo

TL;DR

The paper presents a racetrack inflation model within type IIB string theory with KKLT-style volume stabilization, where the inflaton is the axion-like imaginary part of the K"ahler modulus. Inflation arises near a saddle point between two degenerate KKLT minima, enabling slow-roll in a topologically eternal regime without moving branes. The model achieves a COBE-normalized scalar spectrum with $n_s\approx0.95$ and negligible tensors, requiring mild fine-tuning of nonperturbative racetrack parameters; it also introduces rescaling symmetries that generate broad model families. The authors further propose irrational racetrack variants that densely populate vacua and potentially address the cosmological-constant problem within a string landscape framework, suggesting rich avenues for future cosmology and phenomenology.

Abstract

We develop a model of eternal topological inflation using a racetrack potential within the context of type IIB string theory with KKLT volume stabilization. The inflaton field is the imaginary part of the Kähler structure modulus, which is an axion-like field in the 4D effective field theory. This model does not require moving branes, and in this sense it is simpler than other models of string theory inflation. Contrary to single-exponential models, the structure of the potential in this example allows for the existence of saddle points between two degenerate local minima for which the slow-roll conditions can be satisfied in a particular range of parameter space. We conjecture that this type of inflation should be present in more general realizations of the modular landscape. We also consider `irrational' models having a dense set of minima, and discuss their possible relevance for the cosmological constant problem.

Racetrack Inflation

TL;DR

The paper presents a racetrack inflation model within type IIB string theory with KKLT-style volume stabilization, where the inflaton is the axion-like imaginary part of the K"ahler modulus. Inflation arises near a saddle point between two degenerate KKLT minima, enabling slow-roll in a topologically eternal regime without moving branes. The model achieves a COBE-normalized scalar spectrum with and negligible tensors, requiring mild fine-tuning of nonperturbative racetrack parameters; it also introduces rescaling symmetries that generate broad model families. The authors further propose irrational racetrack variants that densely populate vacua and potentially address the cosmological-constant problem within a string landscape framework, suggesting rich avenues for future cosmology and phenomenology.

Abstract

We develop a model of eternal topological inflation using a racetrack potential within the context of type IIB string theory with KKLT volume stabilization. The inflaton field is the imaginary part of the Kähler structure modulus, which is an axion-like field in the 4D effective field theory. This model does not require moving branes, and in this sense it is simpler than other models of string theory inflation. Contrary to single-exponential models, the structure of the potential in this example allows for the existence of saddle points between two degenerate local minima for which the slow-roll conditions can be satisfied in a particular range of parameter space. We conjecture that this type of inflation should be present in more general realizations of the modular landscape. We also consider `irrational' models having a dense set of minima, and discuss their possible relevance for the cosmological constant problem.

Paper Structure

This paper contains 12 sections, 27 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Eternal Topological Inflation
  3. Racetrack Inflation
  4. The Effective 4D Theory
  5. The Scalar Potential
  6. Scaling Properties of the Model
  7. Slow-Roll Inflation
  8. Experimental Constraints and Signatures
  9. The overshooting problem and initial conditions for the racetrack inflation
  10. Irrational Racetrack Inflation and the Cosmological Constant
  11. Conclusions
  12. Acknowledgements

Figures (3)

  • Figure 1: Plot for a racetrack type potential (rescaled by $10^{16}$). Inflation begins in a vicinity of the saddle point at $X_{\rm saddle}=123.22$, $Y_{\rm saddle}=0$. Units are $M_p=1$.
  • Figure 2: Plot of $V(X,0)$ versus $X$ in the vicinity of the saddle point $X_{\rm saddle}=123.22$, $Y_{\rm saddle}=0$.
  • Figure 3: Contour plot of the effective potential in the vicinity of the saddle point at $Y =0$ (left panel) and at $Y \sim 900$ (right panel).