Cosmological constant problem on the horizon

We revisit the quantum cosmological constant problem and highlight important roles played by de Sitter (dS) horizon of zero-point energy. argue that fields which are light enough to have a dS energy comparable Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) Hubble radius main contributors dark On other hand, heavy develop nonlinearities on sub-Hubble scales cannot contribute speculate our proposal may provide resolution for both old new problems noting there exists field, (lightest) neutrino, happens mass present background photon temperature. The predicts multiple transient periods in early late expansion history Universe, yielding higher value current rate can resolve ${H}_{0}$ tension problem.