What does the arrow pointing left mean in the Feynman diagram for neutrino-neutron collisions?
This is the Feynman diagram for an electron interacting with another electron by the electromagnetic interaction. In a Feynman diagram, the electromagnetic interaction is shown by the exchange of a photon. The ‘left hand’ electron emits a photon, and changes direction. The ‘right hand’ electron absorbs the photon, and also changes direction. In a Feynman diagram, • Time goes upwards. Some particle physicists prefer to have time going sideways. whoever drew this diagram is one of the sideways school, for the record, the rest are: • Particles are shown by arrows going upwards Antiparticles are shown by arrows going downwards, so the electromagnetic interaction between two positrons (the anti-particles of electrons) is The outwards movement after emitting or absorbing a photon just shows a change in direction. It does not mean that they particles are repelling each other. The photon (wavy line) in the electromagnetic interaction is called a vector boson. • Vector – carries the interaction
