Axion Landscape Cosmology

TL;DR

This paper explores the cosmological implications of complex multi-axion theories with many fields, showing they can produce stable vacua, various inflationary scenarios, and a natural dark matter candidate.

Contribution

It provides a comprehensive analysis of multi-axion landscapes, demonstrating their potential for diverse inflationary paths and stable vacua compatible with cosmological observations.

Findings

Vacua are stable over cosmological timescales.

Both large- and small-field inflation are possible within the theory.

Light axions may serve as natural dark matter candidates.

Abstract

We study the cosmology of complex multi-axion theories. With O(100) fields and GUT scale energies these theories contain a vast number of vacua, inflationary trajectories and a natural dark matter candidate. We demonstrate that the vacua are stable on cosmological timescales. In a single theory, both large- and small-field inflation are possible and yield a broad range of cosmological observables, and vacuum decay can be followed by a relatively large number (> 60) of efolds of inflation. Light axions stabilized by gravitational instantons may constitute a natural dark matter candidate that does not spoil an axion solution to the strong CP problem.