We extend mass scale sequence to a mass tree. From mass tree, the evolution of the universe is described by three stages: chaos, inflation and expansion. The first two stages have c mutations and the inflation appears as a step by step fission process of black holes. The dark matter particles with low mass (neutrino and delta particle) are described in a dual SM or two-fold SM with new symmetry and new interaction, and delta-particle is like inert neutrino but has baryon number (L-B conservation). We emphasize how to search for delta-particle, how to research critical energy, critical density, background particles, and spherical universe. Critical density relates to a type of pseudo-balance black holes (or celestial bodies). Suppose the minimum black hole radius equal to proton radius means we live in a spherical universe, which belong to a big universe, mainly characterized by proton.