Sunday, 8 July 2018

renormalization - Scalar Yukawa theory


Let's consider the theory given by the following lagrangian L=12μϕμϕ12M2ϕ2+ˉψ(iγμμm)ψ+14!λϕ4+gϕˉψψ.



Superficial degree of divergence D of 1PI diagram depends as follows on the number of external fermionic Ef and bosonic Eb lines: D=4Eb3/2Ef.

Thus, there are 7 superficially 1PI diagrams:



  • vacuum diagram,

  • diagrams with one, two, three or four external bosonic line,

  • diagram with two fermionic lines,

  • diagram with two fermionic lines and one bosonic.


If I treat the fields and couplings in the original lagrangian as bare, then some counterterms appear. There is, however, no counterterm of the form ϕ3 and ϕ.


Are the 1PI diagrams with one or three external bosinic lines really divergent? If yes, should I add by hand additional counterterms which cancel these divergencies?


In comparison in the pseudoscalar Yukawa theory L=12μϕμϕ12M2ϕ2+ˉψ(iγμμm)ψ+14!λϕ4+igϕˉψγ5ψ.

there parity symmetry makes the problematic superficially divergent diagrams with only one or three bosonic lines (for which there are no counterterms in the lagrangian) vanish identically.





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