Diffusive Quantum Equilibrium Framework for Dynamical Dark Energy: Entropic Backreaction from Supermassive Black Holes and Cosmological Horizons

This paper introduces the Diffusive Quantum Equilibrium (EQD) framework, an effective field theory approach where cosmic acceleration emerges from entropic backreaction driven by the growth of holographic degrees of freedom. We investigate the tension between recent cosmological observations and a strictly constant cosmological constant, focusing on the early emergence of supermassive black holes (SMBHs) and evidence of 'phantom crossing' in the dark energy equation of state. ​By deriving modified Friedmann dynamics and performing a \chi^2 fit to DESI DR2 data, we demonstrate that the EQD model reproduces late-time acceleration and allows for transient phantom behavior without local instabilities. The framework provides testable predictions for upcoming surveys, such as Euclid, establishing a consistent link between horizon thermodynamics and the evolution of the Universe.