# Physics potential of the International Axion Observatory (IAXO)

## TL;DR

The paper reviews the physics potential of IAXO, a next-generation experiment designed to detect axions and axion-like particles, which could solve the strong CP problem, account for dark matter, and explain various astrophysical phenomena.

## Contribution

It provides a comprehensive assessment of IAXO's sensitivity to a wide range of axion parameters and discusses its potential to address multiple outstanding questions in physics and cosmology.

## Key findings

- IAXO can detect axions with photon couplings as low as 10^{-12} GeV^{-1}.
- IAXO has the potential to discover QCD axions in the 1 meV to 1 eV mass range.
- IAXO could also detect axions related to gamma-ray transparency, X-ray excesses, and inflationary models.

## Abstract

We review the physics potential of a next generation search for solar axions: the International Axion Observatory (IAXO). Endowed with a sensitivity to discover axion-like particles (ALPs) with a coupling to photons as small as $g_{a\gamma}\sim 10^{-12}$ GeV$^{-1}$, or to electrons $g_{ae}\sim$10$^{-13}$, IAXO has the potential to find the QCD axion in the 1 meV$\sim$1 eV mass range where it solves the strong CP problem, can account for the cold dark matter of the Universe and be responsible for the anomalous cooling observed in a number of stellar systems. At the same time, IAXO will have enough sensitivity to detect lower mass axions invoked to explain: 1) the origin of the anomalous "transparency" of the Universe to gamma-rays, 2) the observed soft X-ray excess from galaxy clusters or 3) some inflationary models. In addition, we review string theory axions with parameters accessible by IAXO and discuss their potential role in cosmology as Dark Matter and Dark Radiation as well as their connections to the above mentioned conundrums.