I want to draw a simple self-energy two-loop graph such as
using TikZ-Feynman. I have a problem with the automatic alignment of the fermion lines. I have tried this:
\feynmandiagram[inline=(a), layered layout, horizontal=a to f]
{
a--[plain, in=180, out=0, relative=true] b --[photon, half left] e --[plain, in=180, out=0, relative=true] f,
b--[plain, in=180, out=0, relative=true] c -- [photon, half left] d -- [plain, in=180, out=0, relative=true] e,
c -- [plain, in=180, out=0, relative=true] d,
};
Trying to force each vertex angle, but it gives me this:
Which is really bad. Is there some way to achieve this straight line without enforcing anything? Thank you!