The Conductor's Baton: How a Phase Transition Creates Axion Dark Matter
Original: "Axion Misalignment Across First-Order Phase Transitions"
The sudden switching on of axion mass during a cosmological phase transition changes relic density predictions and opens new observational windows.
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A first-order phase transition in the early universe might have acted like a conductor who was late with the baton. Axions — dark matter candidates — began their oscillations tens of millennia later than thought. This turns them into a loud chord of relic density. Now scientists are seeking echoes of this cosmic symphony in JWST data and gravitational waves.
🎯 If the phase transition had occurred a little later, axions could have supercooled, and we would live in a completely different universe — with much denser miniclusters that might have already collapsed into black holes.
H(T_{\rm osc}) \approx m_a
When the expansion rate of the universe equals the axion mass, the field begins to oscillate, producing dark matter.
\xi_{\rm fast} \sim \left(\frac{M_\phi}{H_p}\right)^{3/2}
Enhancement factor of the relic density in the fast scenario — the delay in oscillation onset yields a gain proportional to the ratio of mass to the Hubble parameter raised to the 3/2 power.