Astrophysical Axion Bounds

TL;DR

This work reviews astrophysical bounds on invisible axions by analyzing energy-loss channels in stars and supernovae. It combines production mechanisms (notably the Primakoff process) with observational probes from the Sun, globular clusters, white dwarfs, and SN1987A to derive quantitative limits on the axion-photon, axion-electron, and axion-nucleon couplings, as well as the axion mass via the PQ scale $f_a$. The main results include $g_{a\\gamma\\gamma}\\lesssim 1\\times10^{-9}\\,{ m GeV}^{-1}$ from helioseismology, $g_{a\\gamma\\gamma}\\lesssim 5\\times10^{-10}\\,{ m GeV}^{-1}$ from solar neutrinos, $g_{a\\gamma\\gamma}\\lesssim 1.16\\times10^{-10}\\,{ m GeV}^{-1}$ from CAST, and $m_a\\lesssim 16\\,{ m meV}$ (with associated $f_a\\gtrsim 4\\times10^{8}\\,{ m GeV}$) from SN1987A, though all bounds carry model- and systematics-related uncertainties. Together, these constraints strongly shape the viable axion parameter space and reinforce the relevance of astrophysical observations for particle-physics beyond the Standard Model.

Abstract

Axion emission by hot and dense plasmas is a new energy-loss channel for stars. Observational consequences include a modification of the solar sound-speed profile, an increase of the solar neutrino flux, a reduction of the helium-burning lifetime of globular-cluster stars, accelerated white-dwarf cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We review and update these arguments and summarize the resulting axion constraints.

Figures (3)

• Figure 1: Color-magnitude diagram for the globular cluster M3, based on 10,637 stars GR:Buonanno:1986. Vertically is the brightness in the visual (V) band, horizontally the difference between B (blue) and V brightness, i.e. a measure of the color and thus surface temperature, where blue (hot) stars lie toward the left. The classification for the evolutionary phases is as follows GR:Renzini:1988. MS (main sequence): core hydrogen burning. BS (blue stragglers). TO (main-sequence turnoff): central hydrogen is exhausted. SGB (subgiant branch): hydrogen burning in a thick shell. RGB (red-giant branch): hydrogen burning in a thin shell with a growing core until helium ignites. HB (horizontal branch): helium burning in the core and hydrogen burning in a shell. AGB (asymptotic giant branch): helium and hydrogen shell burning. P-AGB (post-asymptotic giant branch): final evolution from the AGB to the white-dwarf stage
• Figure 2: Relative duration of a SN neutrino burst as a function of the axion-nucleon coupling GR:Raffelt:1996wa. Freely streaming axions are emitted from the entire core volume, trapped ones from an "axion sphere." The solid line is from numerical calculations GR:Burrows:1988ahGR:Burrows:1990pk. The dotted line is an arbitrary continuation to guide the eye
• Figure 3: Summary of astrophysical and cosmological axion limits as discussed in the text. The black sensitivity bars indicate the search ranges of the CAST solar axion search and the ADMX search for galactic dark matter axions. Light-grey exclusion bars are very model dependent