Here below are listed the upcoming IFPU colloquia, usually taking place once a month on Fridays at 11:30am. Past colloquia from the current program can be found in the recent colloquia page, while older events can be found in the 2023-2024, 2022-2023, 2021-2022, 2020-2021 and 2019-2021 pages.
Ayuki Kamada (University of Warsaw)
Imprints of dark matter interaction with plasma in the early Universe
Friday, November 21st, 2025, 11:30am – Stasi Lecture Room, ICTP & streaming
Abstract. According to the lack of signals in conventional dark-matter (DM) searches, gravitational (cosmological/astrophysical) probes have been attracting growing interests. A well-known example is DM relic density, which has been precisely measured by observations of large-scale structure of the Universe (e.g., cosmic microwave background anisotropies). Annihilation (inelastic scattering) of DM particles determine the relic density via so-called thermal freeze-out. Not only annihilation, but also DM elastic scattering with plasma may also leave detectable imprints, though often not as emphasized as thermal freeze-out. In this talk, after briefly reviewing conventional DM searches and thermal freeze-out, I discuss two possible impacts of DM elastic scattering with plasma. One is on DM freeze-out. The relic density via freeze-out is often computed under assumption of kinetic equilibrium. I describe how the assumption may be justified, and also introduce several interesting counter examples (e.g., secluded dark matter). The other is on the small-scale structure of the Universe. DM elastic scattering with plasma and its decoupling leaves wiggles on the matter power spectrum at certain small scales. This is called dark acoustic oscillation by analogy to well-known baryon acoustic oscillation, which results from baryon Thomson scattering with photons and the last scattering. I describe how these features may be measured by observations of small-scale structure of the Universe (e.g., number of satellite galaxies) and also impact annihilation signals in the late Universe.