Whether late-time axiodilaton–matter couplings differ from cosmological couplings

Ascertain whether, within the yoga natural relaxation framework for Dark Energy, the late-time couplings of the axiodilaton (the coupled dilaton–axion system) to Standard Model matter can differ from the couplings that govern cosmological evolution, and, if so, characterize the implications for present-day bulk axion phenomenology.

Background

The paper argues that in yoga-style relaxation models the axion’s vacuum potential is suppressed, allowing matter-induced axion potentials from QCD to dominate even at ordinary densities. This drives the axion toward a matter-selected minimum, conflicting with nuclear physics and cosmological histories if standard couplings apply.

To avoid premature phenomenological exclusions—especially for the bulk (dual) axion case—the authors explicitly leave open whether the axiodilaton’s couplings to matter relevant for late-time, local environments might differ from those that control cosmological evolution, which would alter present-day phenomenology.

References

In what follows we leave open whether the late-time couplings to matter of the axiodilaton can be different from those relevant to cosmology and so set aside a more detailed discussion of the present-day phenomenology of the bulk axion.

— Can QCD Axions Survive the Cosmological Constant Problem?  (2603.20008 - Bruck et al., 20 Mar 2026) in Section 4.2, Mass-dependence constraints