Chaotic inflation with kinetic alignment of axion fields

Abstract

N-flation is a radiatively stable scenario for chaotic inflation in which the displacements of $N\ensuremath{\gg}1$ axions with decay constants ${f}_{1}\ensuremath{\le}\dots{}\ensuremath{\le}{f}_{N}<{M}_{P}$ lead to a super-Planckian effective displacement equal to the Pythagorean sum ${f}_{\mathrm{Py}}$ 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 $\sqrt{N}{f}_{N}\ensuremath{\ge}{f}_{\mathrm{Py}}$, even if ${f}_{1},\dots{},{f}_{N\ensuremath{-}1}$ 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.