Nonperturbative Newtonian coupling in Einstein gravity with Dirac fields
  We investigate the exact renormalization group (RG) in Einstein gravity coupled to N-component spinor field, working in the effective average action formalism and background field method. The truncated evolution equation is obtained for the Newtonian and cosmological constants. We have shown that screening or antiscreening behaviour of the gravitational coupling depends crucially on the number of spinor components 
L. N. Granda