Modifying ΛCDM dynamics via out-of-equilibrium axions: Reconciling SH0ES and DESI H0 values — E8 Intelligence Research

We investigate late-Universe dynamics in which the dark matter component is described by axion particles. The proposed framework departs from the standard ΛCDM paradigm due to a small fraction of axions driving the system away from thermal equilibrium. We analyze the evolution of the axion energy density using both a kinetic and a classical field approach, yielding an identical macroscopic evolution equation for the dark matter density. We emphasize that the BGK parameter is introduced phenomenologically at the kinetic level and this does not supply an independent microscopic derivation. The present work therefore explores the phenomenological consequences of late-time, out-of-equilibrium axion production rather than claiming a completed microphysical model. The resulting scenario modifies ΛCDM dynamics in the late Universe (specifically at z ≲ 1), while asymptotically recovering the standard baseline at earlier cosmic epochs. We compare the theoretical predictions of our formulation a Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com