Axion-as-dark-matter viability within axio-dilaton cosmology

Determine whether the axiodilaton’s axion field, endowed with an appropriate vacuum potential and coupled to baryons and the dilaton as specified by the axio-dilaton framework used in this paper, can by itself account for cold dark matter without spoiling the known successes of axionic dark matter models; establish whether standard axionic dark matter production mechanisms can be consistently incorporated in this setting; and derive the resulting predictions for the CMB anisotropy power spectrum and the matter power spectrum in this scenario.

Background

The paper studies cosmological implications of multi-field axio-dilaton scalar-tensor theories, including background evolution and linear perturbations relevant to the CMB and large-scale structure. It identifies viable benchmark models with various dilaton and axion couplings, and also explores a preliminary scenario with a quadratic axion-matter coupling and axion potential motivated by screening.

In the concluding outlook, the authors propose extending their framework to cases where the axion alone constitutes dark matter via oscillations about a potential minimum, while still coupling to baryons and the dilaton. They explicitly raise questions about whether such couplings undermine standard axionic dark matter successes, whether standard production mechanisms can be incorporated, and how cosmological observables (CMB and matter power spectra) would be affected.