I'm a novice to Tikz and the Tikz Feynman package and I was trying to make up the following diagram
I tried in many ways but i didn't get anything acceptable out of it. Reading the documentation to Tikz Feynman didn't help me either. Probably this diagram could be easily done using Tikz but don't understand it well enough to make it simpler to me.
If anyone could help me it would be great! It's not so important to put down even the vertices indices, nor the particles on the fermion lines, that I can do by myself in case!