In the picture below (from this paper, not an open access unfortunately) there are some diagrams for operators. What I'm interested in are those thick horizontal lines at the bottom of each diagram. I am wondering if it's possible to create them with TikZ.
The closest thing I found in docs is a regular
/tikzfeynman/plain but it still wouldn't be as thick as needed.
Can this be achieved?
I have an old code to generate such diagrams in feynman but it's so long and so ugly and cumbersome I'm thinking to switch to something new. That's why I'm trying to find an alternative. TikZ seems like a solid choice, except for those lines. I don't have any code in TikZ to show yet, because before I commit more time to it, I would like to know if it's even possible.