Photons are usually  represented by dotted arrows, while particles that move backwards  in time would be represented by downward-pointing arrows.
An electron that does not move in space would be represented by  a solid arrow pointing straight up. Photons are usually  represented by dotted arrows, while particles that move backwards  in time would be represented by downward-pointing arrows. FTP, name  this mathematical tool useful for analyzing elementary reactions in  quantum electrodynamics, named for a Nobel Prize-winning American  physicist.
An electron that does not move in space would be represented by  a solid arrow pointing straight up.
{Feynman} diagram