The Standard Model (SM) has been successful in describing known matter in terms of elementary particles and non-gravitational interactions. However, the Universe requires more than five times more matter than accounted for by the SM, called dark matter (DM). We approach this by considering DM residing in a dark sector, a collection of particle species feebly interacting with some of the SM species. This thesis explores two general classes of dark sectors and their cosmological and DM implications.
The first research project considers a non-Abelian dark sector under SU(N) and assumes that it was dominantly reheated after primordial inflation. The dark sector gets confined at some lower temperature into a spectrum of bound states called dark glueballs. They undergo freeze-out and will be dominated by the lightest glueball state. To recover the observed cosmology, we introduce inter-sector interactions; most glueball states will decay and source the visible sector while one glueball state is either stable or parametrically longer-lived. We find the stable glueball remnant can make a DM candidate. We also derive broader constraints on the dark sector based on too much glueball remnant and impacts on cosmological observations.
The second research project considers a dark sector with inelastic DM: two DM states with a small mass-splitting. DM is produced via freeze-in with a light mediator. When the mass-splitting is below the electron-positron threshold, the heavier state decays emitting photons with a cosmologically long lifetime. Given a light mediator, the coupling required for freeze-in directly relates to the lifetime. We show that hard X-ray data from the galactic center can probe the model with GeV-scale DM and 100 MeV-scale mediators.
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2026-10-08T10:00:002026-10-08T12:00:00Riku Mizuta, Internal DefenseEvent Information:
Abstract:
The Standard Model (SM) has been successful in describing known matter in terms of elementary particles and non-gravitational interactions. However, the Universe requires more than five times more matter than accounted for by the SM, called dark matter (DM). We approach this by considering DM residing in a dark sector, a collection of particle species feebly interacting with some of the SM species. This thesis explores two general classes of dark sectors and their cosmological and DM implications.
The first research project considers a non-Abelian dark sector under SU(N) and assumes that it was dominantly reheated after primordial inflation. The dark sector gets confined at some lower temperature into a spectrum of bound states called dark glueballs. They undergo freeze-out and will be dominated by the lightest glueball state. To recover the observed cosmology, we introduce inter-sector interactions; most glueball states will decay and source the visible sector while one glueball state is either stable or parametrically longer-lived. We find the stable glueball remnant can make a DM candidate. We also derive broader constraints on the dark sector based on too much glueball remnant and impacts on cosmological observations.
The second research project considers a dark sector with inelastic DM: two DM states with a small mass-splitting. DM is produced via freeze-in with a light mediator. When the mass-splitting is below the electron-positron threshold, the heavier state decays emitting photons with a cosmologically long lifetime. Given a light mediator, the coupling required for freeze-in directly relates to the lifetime. We show that hard X-ray data from the galactic center can probe the model with GeV-scale DM and 100 MeV-scale mediators.
Event Location:
HENN 318