Identifying the dark sector of the universe: imprints from early dynamics to late time signatures

• Applicant: Dr. Mathias Pierre
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Astrophysics and Astronomy
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527296308

In order to successfully describe our universe on very large scales, the ΛCDM cosmological model requires ~25% of the energy budget to lie in the form of a mysterious substance called dark matter. None of the degrees of freedom present in the Standard Model of particle physics can account for this component. The fundamental nature of dark matter is unknown and remains one of the main challenges of modern physics. This proposal is dedicated to investigating the consequences of particle-like dark matter interactions with other constituents of our universe. The main goal is to characterize the properties and signatures of elusive forms of new physics connected to dark matter, referred to as “dark sector”. This proposal is organized in four subprojects approaching different, yet related, aspects of dark sector dynamics and their relation with dark matter production. Inflation is our best theory to simultaneously explain the quasi-homogeneity of our universe on large scales and the primordial size of inhomogeneities. Prior to recombination, the energy density carried by the inflaton field (driving inflation) is converted to Standard-Model plasma (radiation) during reheating. Two subprojects explore the dynamics of reheating by investigating energy transfer, the evolution of inhomogeneities as well as the subsequent production of primordial black holes and gravitational waves. Two subprojects will respectively focus on interactions between inflaton and dark matter and between dark matter and radiation during reheating. The goal is to further understand the kind of interactions and properties these three components (inflaton, dark matter, radiation) must possess in order to explain the early stages of the formation of our universe. Focusing on out-of-equilibrium dark matter production mechanisms, a third project tackles the imprints left by dark matter interactions with other constituents in cosmological observables by exploring: i) The role of thermal effects on dark matter production and signatures in the matter power spectrum; ii) The transfer of inhomogeneities from radiation to the dark matter sector; iii) Constraints on setups addressing neutrino masses and dark matter from cosmic microwave background anisotropies. A last project explores the dynamics associated with cosmological phase transitions, motivated by the possibility of explaining the matter-antimatter asymmetry of the Universe (baryogenesis), and relation with dark matter. A primary goal is to model the impact of strong phase transitions on inhomogeneities in a consistent cosmological perturbation theory formulation. The consequences on primordial black holes and gravitational waves production will be analysed, in addition to phenomenological implications.

• DFG Programme: Independent Junior Research Groups