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| Format: | Preprint |
| Published: |
2024
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| Online Access: | https://arxiv.org/abs/2405.20478 |
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Table of Contents:
- This conference thesis summarizes my presentation at Tartu Tuorla Cosmology meeting based on a collaborative work with E.Nardi and C.Smarra \cite{Muursepp:2024mbb}. It is well known that a pseudo-Nambu Goldstone boson (pNGB) coupled to a confining gauge group obtains a non-zero contribution to its mass through instanton effects. At non-zero temperature, this manifests in temperature-dependent mass $m^{2}(T) \propto T^{-n}$. If these particles come to dominate the energy density of the Universe in the non-relativistic regime they would accelerate the expansion of the Universe for $n>2$, thus providing a dark energy (DE) component. In this work, we outline a scenario in which a pNGB $ϕ_{b}$ presently undergoing confinement could realize such a scenario. Using energetic considerations we find that $ϕ_{b}$ alone is not enough to produce the experimentally observed amount of DE. However, coupling $ϕ_{b}$ to the QCD axion $ϕ_a$ allows the transfer of energy from the QCD axion to the pNGB via non-adiabatic level-crossing thus reproducing the observed amount of dark matter (DM) and DE.