\feynmandiagram [inline=(a.base), horizontal=a to t3, small] {
a[dot,label=left:$V_0$] -- [double fermion, bend left] t1[dot,label=left:$V_0^*$] -- [double anti charged boson] t2[dot,label=right:$V_0$] -- [double anti charged scalar, bend right] t3[dot,label=right:$V_0^*$] -- [double anti fermion, bend right] t4[dot,label=right:$V_0$] -- [double charged boson] t5[dot,label=left:$V_0^*$] -- [double charged scalar, bend left] a,
a -- [double charged boson] t3,
t1 -- [double charged scalar, bend left] t4,
t2 -- [double fermion, bend left] t5
};