Neutrino Mass as an Infrared Spacetime Memory Effect (Paper XLVIII)

The origin of the neutrino mass scale (∼0.05∼0.05 eV) remains one of the most compelling hints of physics beyond the Standard Model. Traditional approaches, such as seesaw mechanisms or mass-varying neutrino (MaVaN) models, typically require either extreme energy scales, fine-tuned couplings, or additional scalar fields. In this work, we propose a fundamentally different mechanism where the neutrino mass emerges dynamically from infrared (IR) nonlocal gravitational dynamics, without introducing fundamental Yukawa couplings or heavy mediator states. Within the History-Dependent Gravity (HDG) framework, a covariant, entire-function nonlocal form factor generates a temporal memory kernel. We demonstrate that the effective mass gap arises from the competition between accumulated cosmological memory and the decreasing IR scale of the Universe. This yields a characteristic, testable redshift evolution: mν(z)∝(1−e−t/τmem)H(z)/H0mν(z)∝(1−e−t/τmem)H(z)/H0. Crucially, during radiation domination, this mechanism naturally produces a scaling of mν(z)∝(1+z)−1mν(z)∝(1+z)−1. This provides an automatic and robust suppression of the neutrino mass at early epochs, resolving potential tensions with Big Bang Nucleosynthesis (BBN) and CMB bounds. The proposed framework is manifestly gauge-invariant and avoids additional ghost-like degrees of freedom. It predicts a unique logarithmic derivative dln⁡mν/dln⁡(1+z)≈+0.24dlnmν/dln(1+z)≈+0.24 at low redshifts, which is distinguishable from constant-mass or direct horizon-scaling scenarios. This evolution leaves detectable imprints on the matter power spectrum and free-streaming scale, offering new observational targets for DESI, Euclid, and CMB-S4.