Ultralight particles, with a mass below the electronvolt scale, exhibit wave-like behavior and have arisen as a compelling dark matter candidate. A particularly intriguing subclass is scalar dark matter, which induces variations in fundamental physical constants. However, detecting such particles becomes highly challenging in the mass range above $10^{-6}\,\text{eV}$, as traditional...
Cosmological observations, such as Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background (CMB), provide vital insights into the early Universe, allowing us to trace its evolution to times as short as $t \sim 0.01$ s and to test extensions of the Standard Model. Accurately modeling the non-trivial dynamics of neutrinos typically requires solving a system of Boltzmann equations...
Despite being an elegant mechanism to explain Dark Matter (DM) production, freeze-in introduces challenges: If DM interacts via non-renormalizable operators, the predictions are highly sensitive to initial conditions, such as the reheating temperature of the universe. These issues are particularly relevant in models in which the universe deviates from radiation domination and the entropy of...
