Disha Bandyopadhyay (IIT, Guwahati) "Axion Dark Matter in a Non-Standard Cosmology"

Wednesday 5 Aug 2026, 15:00 → 16:00 Asia/Seoul

CTPU Seminar room (Theory Bldg, 4F)

The QCD axion, originally proposed as a solution to the strong CP problem, is one of the most compelling candidates for dark matter. Its relic abundance depends not only on the production mechanism but also on the thermal history of the early Universe prior to Big Bang Nucleosynthesis. While the standard cosmological picture has been widely explored, non-standard expansion histories can significantly modify the dynamics of axion production and the resulting dark matter abundance.

In this talk, I will briefly review the production of QCD axion dark matter through the vacuum and kinetic misalignment mechanisms and discuss how an extended reheating era after inflation affects these scenarios. Considering a generic reheating history with different decay channels, I will show how the modified expansion rate and thermal evolution alter the onset of axion oscillations, the relic abundance, and the viable axion parameter space. I will also discuss how these scenarios can be tested through future axion searches and observations of the primordial gravitational-wave background. Finally, I will briefly mention our related work on axion dark matter in an early Universe dominated by ultra-light primordial black holes.