Stellar Evolution confronts Axion Models

Abstract

Axion production from astrophysical bodies is a topic in continuous development, because of theoretical progress in the estimate of stellar emission rates and, especially, because of improved stellar observations. We carry out a comprehensive analysis of the most informative astrophysics data, revisiting the bounds on axion couplings to photons, nucleons and electrons, and reassessing the significance of various hints of anomalous stellar energy losses. We confront the performance of various theoretical constructions in accounting for these hints, while complying with the observational limits on axion couplings. We identify the most favorable models, and the regions in the mass/couplings parameter space which are preferred by the global fit. Finally, we scrutinize the discovery potential for such models at upcoming helioscopes, namely IAXO and its scaled versions.

Probing the axion-nucleon coupling with the next generation of axion helioscopes

“…The yellow band in Fig. 4 represents the parameter area spanned by generalized DFSZ models [20,76] (QCD axion models with two Higgs doublets plus a singlet scalar field, allowing for flavor non-universality). There, we present the specific examples of the classical DFSZ axion model, and of the M1 and T (u) 2 models discussed in Sec.…”

“…This last possibility naturally happens in a class of non-universal DFSZ models with c 0 u + c 0 d = 1 that have been analyzed in Refs. [20,74,75] (for a summary of axion couplings in those models see Table 3 in [76]). For instance, in the non-universal M1 model of Ref.…”

“…In particular, the non-universal model T (u) 2 of Ref. [74] features the largest axion coupling to photons among the general class of nonuniversal DFSZ models with two Higgs doublets (see Table 5 in [76]).…”

“…In particular, strong bounds were derived from X-ray observations of various NS [23][24][25][26][27][28]. These bounds are, however, subject to several uncertainties and do not always agree with each other, not even when referring to the same star [76]. In any case, all these analyses suggest a limit of ∼ 10 −9 on some combination of axion-nucleon couplings.…”

Axion emission from supernova with axion-pion-nucleon contact interaction

“…A complementary approach which can severely constrain the couplings of light axions is to use astrophysical objects forming a hot and dense environment, e.g., supernovae, stars on the horizontal and red giant branches, neutron stars, and even white dwarfs (see [18] for a review and also [19] for a recent overview). Axions can be produced abundantly from those objects, thereby alter their evolution.…”