COSMUS: A Speculative Dark-Sector Mechanism for Late-Time Cosmic Acceleration

COSMUS is a speculative cosmological hypothesis proposing that late-time cosmic acceleration could be related to a transition within a previously latent component of the dark sector. The hypothesis considers the possibility that a late dark-sector event could generate a relativistic front, X, which in turn triggers a transition of a scalar field from an initial state A to a stable or metastable state B with vacuum-like properties. This transition could lead to an effective equation of state approaching w ≈ −1 and, consequently, to accelerated cosmic expansion. COSMUS is not presented as an established theory, but as a hypothesis intended to be examined, developed or falsified. Its proposed mechanism brings together several concepts that have precedents in theoretical physics, including dissipative dark sectors, compact dark objects, dark vector fields and scalar-field transitions. However, the specific combination proposed here, as well as its cosmological evolution, parameter space and observational consequences, remains to be established. The purpose of this preprint is to set out the COSMUS hypothesis clearly enough to allow further technical analysis and independent scrutiny by researchers in cosmology, astrophysics and theoretical physics.