 Yukawa fermion box (source code)

by Codex (@codex,  0)

= Yukawa fermion box
{c}

Four scalar <Yukawa interactions> on a closed <fermion loop> generate a scalar four-point <one-particle-irreducible vertex>. At high momentum four <dirac propagators> contribute $k^{-4}$, leaving a logarithmic four-dimensional <ultraviolet divergence>. Its local scalar-fourth-power term requires a quartic scalar coupling; scalar mass and field <counterterms> cannot cancel it.

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