# Axions

## Transient Radio Signatures from Neutron Star Encounters with QCD Axion Miniclusters

The QCD axion is expected to form dense structures known as axion miniclusters if the Peccei-Quinn symmetry is broken after inflation. Miniclusters that have survived until today will interact with neutron stars (NSs) in the Milky Way to produce transient radio signals from axion-photon conversion in the NS magnetosphere. We quantify the properties of these encounters and find that they occur frequently $\mathcal{O}\left(100\right)\,days^{-1}$, last between a day and a few months, are spatially clustered toward the Galactic Center, and can reach observable fluxes. These radio transients are within reach of current generation telescopes and therefore offer a promising pathway to discovering QCD axion dark matter.

## Axions

The axion is a hypothetical elementary particle that is associated with the solution of the Strong-CP problem proposed by R. Peccei and H. Quinn in 1977. Axions are a also a viable dark matter candidate and the archetype of bosons that contribute to the energy density of the Universe as an ensemble of coherent waves.

## Axion Miniclusters: Tidal Disruption and Radioastronomy

Axions and axion-like particles are excellent dark matter candidates, spanning a vast range of mass scales from the milli- and micro-eV for the QCD axion, to 10^(-22)eV for ultralight axions that make up the "axiverse". In some scenarios, the …

## Probing the Early Universe with Axion Physics

Axions and axion-like particles are excellent dark matter candidates, spanning a vast range of mass scales from the milli- and micro-eV for the QCD axion, to 10−22 eV for ultralight axions, to even lighter candidates that make up the “axiverse”. In …

## Dilute and dense axion stars

Axion stars are hypothetical objects formed of axions, obtained as localized and coherently oscillating solutions to their classical equation of motion. Depending on the value of the field amplitude at the core $|\theta_0| \equiv |\theta(r=0)|$, the …

## Axion cold dark matter in view of BICEP2 results

The properties of axions that constitute 100\% of cold dark matter (CDM) depend on the tensor-to-scalar ratio $r$ at the end of inflation. If $r=0.20^{+0.07}_{-0.05}$ as reported by the BICEP2 collaboration, then half'' of the CDM axion parameter …

## Dark Matter Axions Revisited

We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon acoustic …