\feynmandiagram [small, baseline=(a.base), horizontal=a to b, layered layout] {a -- [double fermion, edge label'=$c$] b};
\times
\ev{\hat Q}_\zeta
+
\feynmandiagram [small, baseline=(a.base), horizontal=a to c, layered layout] {
a -- [double fermion, edge label'=$c$] b [semi hollow triangle] -- [double fermion, edge label'=$c$] c,
b -- [anti boson fermion, out=-135, in=-45, loop, min distance=2cm, edge label=$Q$] b
};