how can the virtual fermionic lines be vertical in kaon mixing Feynman box diagram (or in general)? Wuouldn't this mean that they travel a distance $\neq 0$ in 0 time?
how can the virtual fermionic lines be vertical in kaon mixing Feynman box diagram (or in general)? Wuouldn't this mean that they travel a distance $\neq 0$ in 0 time?