Gauge theory of gravity

General relativity is formulated in the framework of Yang-Mills theory whose gauge group isO(3, 2). This theory allows the global topological charge of spin without breaking Bianchi identity. β function in the renormalization group equation is negative and the confinement of gravity is expected. The confinement radius is, however, actually infinite and we can read off the relation that the average mass density of the present universe is exactly equal to the critical value ρ _c (t)=6H ²(t)/K ².