Cosmological constraints on decaying axion-like particles: a global analysis

Abstract

Axion-like particles (ALPs) decaying into photons are known to affect a wide range of astrophysical and cosmological observables. In this study we focus on ALPs with masses in the keV–MeV range and lifetimes between 104 and 1013 seconds, corresponding to decays between the end of Big Bang Nucleosynthesis and the formation of the Cosmic Microwave Background (CMB). Using the CosmoBit module of the global fitting framework GAMBIT, we combine state-of-the-art calculations of the irreducible ALP freeze-in abundance, primordial element abundances (including photodisintegration through ALP decays), CMB spectral distortions and anisotropies, and constraints from supernovae and stellar cooling. This approach makes it possible for the first time to perform a global analysis of the ALP parameter space while varying the parameters of ΛCDM as well as several nuisance parameters. We find a lower bound on the ALP mass of around ma > 300 keV, which can only be evaded if ALPs are stable on cosmological timescales. Future observations of CMB spectral distortions with a PIXIE-like mission are expected to improve this bound by two orders of magnitude.

Updated constraints on axion-like particles from temporal information in supernova SN1987A gamma-ray data

“…The expected signal from decaying ALPs [23][24][25][26]76] or sterile neutrinos [28,29,77] has been calculated before, with various degrees of analytical and numerical methods such as MC simulations/integration or quadrature. We include a number of improvements compared to previous works, as described in detail in appendix B.…”

“…[24] (dashed light blue line) and the modified MC code from ref. [76] (black line, density plot). We also indicate the approximate scaling regimes of the limits (dashed grey lines; see main text for details).…”

Axion couplings in gauged U(1)′ extensions of the Standard Model

“…The canonical experimental and cosmological bounds are obtained from refs. [22][23][24][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77].…”

“…The updated constraints on exotic ALP signatures at colliders are covered in detail in figure7. The canonical experimental and cosmological bounds are obtained from refs [22][23][24][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77]…”

Magnetic Dynamo Caused by Axions in Neutron Stars

“…Current constraints on axions are based on a wide range of techniques, from laboratory experiments to astrophysics [6][7][8][9][10][11][12][13][14]. Bounds on the axion parameter space are obtained using helioscopes or haloscopes [7,[15][16][17][18][19][20][21], calculating axion emission in neutron stars (NSs) [22][23][24][25], and with other astrophysical and cosmological constraints [26][27][28][29][30][31][32][33].…”