The Nihilion Field - A Density-Phase-Unifying Dark Sector and Complex-Mass Extension of Relativity (v2)

This preprint proposes the Nihilion field, a unified model for dark matter and dark energy based on a density-dependent phase transition. Motivated by tensions in the standard ΛCDM cosmological model—such as the Hubble tension and discrepancies in large-scale structure growth—this work introduces a scalar field whose effective behavior changes depending on the local energy density. In high-density regions (such as galaxy clusters), the field behaves as attractive and matter-like. In low-density regions (such as cosmic voids), it transitions to a repulsive, energy-like phase, naturally driving cosmic acceleration. This mechanism is governed by a novel extension of relativistic dynamics, in which the field’s mass term becomes complex-valued and resides on the unit circle in the complex plane. The model makes three concrete and falsifiable predictions:(1) A step-like feature in the cosmological equation-of-state w(z) around redshift z ≈ 0.5,(2) Suppressed gravitational lensing in cosmic voids, and(3) An energy-dependent modulation of ultra-high-energy cosmic rays (UHECRs) near large-scale density gradients. The paper emphasizes testability and minimal fine-tuning. If the predicted effects are not observed in DESI, Euclid, or CMB-S4 data, the model is falsified. Author website: https://science.antia.info ORCID: 0009-0001-0390-5505