The cosmological constant problem is the enormous mismatch between the tiny dark-energy density inferred from the universe’s accelerated expansion and the vastly larger vacuum energy density predicted by quantum field theory, with naive estimates differing by roughly 60–120 orders of magnitude depending on the cutoff and regularization scheme (Weinberg 1989; Carroll 2001). In ΛCDM, the cosmological constant ? is usually identified with vacuum energy, so explaining why its observed value is so small yet nonzero, without extreme fine-tuning or delicate cancellations among independent contributions, remains one of the deepest unresolved tensions between cosmology and fundamental physics (Martin 2012; Padmanabhan 2003).