Exponential early growth of primordial black holes through neutrino absorption in the radiation-dominated universe

This work proposes a novel mechanism for the exponential growth of primordial black holes (PBHs) in the early Universe, driven by the absorption of ultra-relativistic neutrinos shortly after their decoupling at t ~ 1 s. At this epoch, the cosmological neutrino density reached ~10⁷ kg/m³, and the geometric capture cross-section σ_geo = πR_s² leads to a nonlinear mass-growth law: dM/dt = A M², where A = 4πG²ρ_ν/c³. Preliminary estimates show that PBHs with initial masses as small as 10⁻³–1 M☉ can grow by many orders of magnitude within months or years, producing massive seeds (10³–10⁶ M☉) capable of explaining the JWST observations of supermassive black holes at z > 10. This mechanism bypasses Eddington limits and standard accretion scenarios, offering a natural solution to the puzzle of early SMBH formation. This preprint builds on earlier theoretical proposals regarding early black hole formation and provides the first quantitative estimate of neutrino-driven PBH growth.