forces and exchange particles

• when two particles exert a force on each other, a virtual particle is created. virtual particles only exist for a short amount of time and carry the fundamental force between particles
• all forces are caused by four fundamental forces: the strong nuclear force, the weak nuclear force, the electromagnetic force and gravity. each force has its own gauge boson (the exchange particles).
• the gauge boson for the electromagnetic force is the virtual photon, and it affects charged particles only
• the gauge boson for the weak nuclear force is the W+ or W- boson, and it affects all particles
• the gauge boson for the strong nuclear force is the pion, and it affects hadrons only
• particle physicists ignore gravity because it is negligible compared to other types of interaction. gravity only really matters when you have big masses like stars and planets.
• the larger the mass of the gauge boson, the shorter the range of the force. the mass of W bosons are about 100 times larger than the mass of protons, so the weak force has a very short range. this is because creating a virtual W particle uses so much energy that it can only exist for a short time and it cant travel far. whereas the photon has zero mass, so the electromagnetic force has infinite range
• rules for feynman diagrams:

  • gauge bosons are represented by wiggly lines
  • other particles are represented by straight lines
  • incoming particles start at the bottom and move upwards
  • baryons and leptons cant cross from one side to the other
  • the charges on both sides must balance
  • W bosons carry charge from one side to the other
  • a W- particle going to the left has the same effect as a W+ particle going to the right
• electron capture is when a proton captures an electron using the weak interaction - the exchange particle is a W+ boson
• electron proton collisions are when an electron collides with a proton through the weak interaction - the exchange particle is a W- boson