Hubble Tension as an Effect of Horizon Entanglement Nonequilibrium

We propose an infrared mechanism for alleviating the Hubble constant tension, based on a small departure from entanglement equilibrium at the cosmological apparent horizon. If the horizon entanglement entropy falls slightly below the Bekenstein–Hawking value, we parametrize the shortfall by a fractional deficit δ(a) evolving with the FLRW scale factor a. The associated equipartition deficit at the Gibbons–Hawking temperature then sources a smooth, homogeneous component whose density scales as H2/G, with a dimensionless coefficient ce2(a) of order unity times δ(a). Because this component tracks H2, it is negligible at early times but can activate at redshifts z≲1, raising the late-time expansion rate by a few percent without affecting recombination or the sound horizon. We present a minimal three-parameter activation model for ce2(a) and derive its impact on the background expansion, the effective equation of state, and linear growth for a smooth entanglement sector. The framework predicts a small boost in H(z), a mild suppression of fσ8(z), and a corresponding modification of the low–z distance–redshift relation. We test these predictions against current low–redshift data sets, including SN Ia distance moduli, baryon acoustic oscillation distance measurements, cosmic chronometer H(z) data, and redshift space distortion constraints. We then discuss whether the H0 tension can be consistently interpreted as a late–time, horizon–scale information deficit rather than an early universe modification.