A New Angle on Chaotic Inflation

TL;DR

This paper introduces kinetic alignment in N-flation models, enabling super-Planckian effective displacements with high probability, thus easing the realization of chaotic inflation within string theory frameworks.

Contribution

It demonstrates that kinetic mixing leads to kinetic alignment, significantly enhancing effective axion displacements in N-flation models, and provides conditions for inflation along aligned directions.

Findings

Kinetic alignment allows large effective displacements even with small individual decay constants.

Eigenvector delocalization makes alignment highly probable.

The construction simplifies embedding N-flation in string theory.

Abstract

N-flation is a radiatively stable scenario for chaotic inflation in which the displacements of $N \gg 1$ axions with decay constants $f_1 \le \ldots \le f_N < M_P$ lead to a super-Planckian effective displacement equal to the Pythagorean sum $f_{Py}$ of the $f_i$. We show that mixing in the axion kinetic term generically leads to the phenomenon of kinetic alignment, allowing for effective displacements as large as $\sqrt{N} f_{N} \ge f_{Py}$, even if $f_1, \ldots, f_{N-1}$ are arbitrarily small. At the level of kinematics, the necessary alignment occurs with very high probability, because of eigenvector delocalization. We present conditions under which inflation can take place along an aligned direction. Our construction sharply reduces the challenge of realizing N-flation in string theory.