Interacting Dirac fields in an expanding universe: dynamical condensates and particle production

 In this talk, I will delve into the study of self-interacting Dirac fermions in an expanding Friedmann-Robertson-Walker (FRW) universe, focusing on how these interactions modify the well-known free results for particle production in curved spacetime. To investigate this, I employ a Hamiltonian lattice regularization combined with a variational family of fermionic Gaussian states to analyze how fermions behave in this dynamic setting. This approach enables the study of non-perturbative phenomena, such as dynamical mass generation, where fermions acquire a mass through the formation of fermion condensates, signaling broken symmetries in the theory. I will demonstrate how these condensates evolve over time and interact with the expanding spacetime, leading to significant modifications in particle production. The behavior of these condensates depends on the rate of cosmic expansion, governed by the Hubble parameter, ranging from a trivial static value to a complex, self-consistent evolution. This gives rise to a range of effects on particle production, including an intricate back-reaction where the produced particles, in turn, influence the condensates, resulting in synchronized oscillations. Additionally, I will explore how interactions break certain symmetries, leading to parity-violating particle spectra, which deviate from the predictions of non-interacting field theories. These findings offer new insights into non-perturbative effects in quantum fields in curved spacetime and shed light on particle dynamics during cosmological expansions, such as those that occurred in the early universe. 

Based on C. Fulgado-Claudio, P. Sala, D. González-Cuadra, and A. Bermudez, Interacting Dirac fields in an expanding universe: dynamical condensates and particle production, arXiv:2408.06405 (2024).