Stellar Evolution confronts Axion Models (2109.10368v2)

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.

Overview of "Stellar Evolution Confronts Axion Models"

The paper "Stellar Evolution Confronts Axion Models," authored by Luca Di Luzio et al., explores the constraints on axion models derived from stellar evolution observations. Axions, the hypothesized particles arising from the Peccei-Quinn mechanism as a solution to the strong CP problem, have been long considered viable candidates for cold dark matter. This work aims to scrutinize the astrophysical data through axion couplings, providing a comprehensive analysis that revisits previous bounds while introducing updated findings from recent stellar observations.

Key Findings and Methodologies

• Astrophysical Constraints: A critical evaluation of the data from various astrophysical sources, including white dwarfs, red giants, horizontal branch stars, and supernovae, provides stringent constraints on axion couplings to photons, nucleons, and electrons. These analyses leverage improved observational techniques and theoretical models to reassess the significance of anomalous stellar energy losses possibly attributed to axions.
• Global Fit and Model Performance: By executing a global fit to the observational data, the paper identifies the most favorable axion models that align with observed anomalies while respecting established constraints. This fitting procedure evaluates the capacity of different models to account for extra energy losses suggested by the data, highlighting regions in the mass/couplings parameter space preferred by the global fit.
• Model-Dependent Analysis: The paper investigates canonical DFSZ models and their variants, particularly nucleo-phobic models that suppress axion-nucleon interactions, thus relaxing constraints from neutron star cooling and other supernovae-related limits. These analyses reveal a preference for specific ranges in axion masses, strongly motivated by the improved stellar data.
• Helioscope Prospects: The paper considers the potential for detecting axions with upcoming helioscopes such as IAXO and its variants. These instruments aim to explore the axion parameter space suggested by stellar data, particularly focusing on the mass and coupling strengths identified by the fit.

Strong Numerical Results

The numerical results highlight several key outcomes:

• The best fit for axion-electron and axion-photon couplings stands at approximately $g_{ae} \simeq 1.2 \times 10^{-13}$ and $$g_{a\gamma} \simeq 1.8 \times 10^{-11} \, \text{GeV}^{-1}$$, which aligns with previous studies but reflects revisions from recent data inclusive of RGB tip and SN bounds.
• Across different fits and model considerations, an axion mass in the range of 1 to 100 meV emerges as particularly favorable, given the constraints and hints derived from the data.

Implications and Future Directions

This research establishes bounds that could guide experimental designs in future axion searches, enhancing the feasibility of exploring the indicated parameter regions. It suggests that the discovery of axions through their astrophysical implications is feasible and, if validated, could affirm axions as a pivotal component of dark matter.

As the field advances, further refinement of stellar observations and modeling is expected to improve axion searches. The intersection of improved astrophysical datasets and enhanced sensitivity of next-generation experiments could significantly narrow the plausible parameter space for axions, facilitating breakthroughs in understanding these elusive particles.

Through a meticulous integration of theoretical modeling and empirical data, this paper represents a significant stride in aligning stellar evolution studies with particle physics to confront axion models.