Physics potential of the International Axion Observatory (IAXO)

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 aγ ∼ 10 −12 GeV −1 , or to electrons g ae ∼10 −13 , IAXO has the potential to find the QCD axion in the 1 meV∼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.

Improved axion emissivity from a supernova via nucleon-nucleon bremsstrahlung

“…As evident from the figure, the SN bound is competitive with the RGB bound, however not dominating, except for low values of tan β. When compared with the expected IAXO potential [9,20], it is evident that helioscopes of the next generation have the capability to explore large regions of the axion parameter space that are not affected by the SN analysis. As stressed above, the results of our analysis should not be considered as a robust bound as we are not including the axion feedback on the star, which at these couplings is most likely non-negligible.…”

“…A renewed interest towards the axion from SNe arose recently, partially because the SN 1987A bound overlaps with the sensitivity range of the planned experiments, in particular the International Axion Observatory (IAXO), which searches for solar axions [20]. IAXO is sensitive to generic axion-like particles coupled to photons and has the potential to probe the QCD axion region up to masses m a 10 −2 eV.…”

Towards string theory expectations for photon couplings to axionlike particles

“…This applies not only to the usual parity even operator F µν F µν , but also the parity odd operator, requiring the existence of a coupling L ⊃ − 1 4 g aγγ aF µνF µν (1) in the effective Lagrangian, whereF µν = µνρσ F ρσ ., The pseudoscalar a is an axion-like particle (ALP), which is not necessarily the QCD axion, and it may be a nontrivial linear combination of the hundreds or thousands of ALPs expected from studies of string vacua. Numerous ground-based experiments [1][2][3][4] and satellite observations [5][6][7][8][9][10][11] place constraints on ALP-photon interactions, probing widely different regimes for the axion mass m a and coupling strength g aγγ . Existing limits are already remarkable, within a few orders of magnitude of GUT scale decay constants f aγγ ≡ g −1 aγγ .…”

Flavour Violating Axions

“…E/N = {−4/3, 2/3, 8/3, 14/3} in the models of Ref. [26], so that the next generation of helioscopes, such as IAXO [33], will be able to probe their parameter space.…”