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WS25/26 – Abstract
Pedro Schwaller
(Johannes Gutenberg-Universität Mainz)
27.11.2025
Cosmological perturbations from dark sectors
There is strong evidence for the existence of a dark sector that explains dark matter and its interactions. While its interactions with visible matter might be feeble and difficult to probe, dark sectors can influence cosmological observables through purely via gravity. I will discuss two such opportunities.
First, large fluctuations in the energy density of the dark sector shortly before CMB emission induce spectral distortions of the CMB spectrum. They therefore provide a probe of e.g. phase transitions, cosmic strings or domain walls at late times, complementary to gravitational wave observations. Second, isocurvature perturbations are a smoking gun of non-minimal cosmological initial conditions. We argue that in realistic scenarios a mixture of neutrino and matter isocurvature is generated, e.g. due to dark radiation which is the remnant of a dark sector. We introduce a new isocurvature mixing angle and obtain the first constraints on it from PLANCK data, finding a modest preference for the presence of pure neutrino isocurvature. Furthermore we show that in the presence of dark radiation isocurvature, the matter isocurvature is sensitive to the DM production mechanism and can distinguish freeze-in and freeze-out scenarios.
