We review the landscape of QCD axion models. Theoretical constructions that extend the
window for the axion mass and couplings beyond conventional regions are highlighted and …

Axions comprise a broad class of particles that can play a major role in explaining the
unknown aspects of cosmology. They are also well-motivated within high energy physics …

Axions and other very light axion-like particles appear in many extensions of the Standard
Model, and are leading candidates to compose part or all of the missing matter of the …

This book lays out the scientific goals to be addressed by the next-generation ground-based
cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated …

Ultralight axions (ULAs) with masses in the range 1 0-33 eV≤ ma≤ 1 0-20 eV are motivated
by string theory and might contribute to either the dark-matter or dark-energy densities of the …

A bstract We study the system of axion strings that forms in the early Universe if the Peccei-
Quinn symmetry is restored after inflation. Using numerical simulations, we establish the …

Increasingly stringent limits from LHC searches for new physics, coupled with lack of
convincing signals of weakly interacting massive particle (WIMP) in dark matter searches …

We evaluate the efficiency of axion production from spatially random initial conditions in the
axion field, so a network of axionic strings is present. For the first time, we perform numerical …

Axion-like particle (ALP) dark matter shows distinctive behavior on scales where wavelike
effects dominate over self-gravity. Ultralight axions are candidates for fuzzy dark matter …

For the minimal QCD axion model it is generally believed that overproduction of dark matter
constrains the axion mass to be above a certain threshold, or at least that the initial …