PX156 - G5 - virtual particles

μ^{\pm} \to {\bar{ν}}_{μ} / ν_{μ} + e^{\pm} + ν_{e} / {\bar{ν}}_{e}

the mass of the initial and final state particles are well defined
real particles: $E^{2} = p^{2} c^{2} + m^{2} c^{4}$
but internal particles: $E^{2} \neq p^{2} c^{2} + m^{2} c^{4}$
internal lines can have any mass needed to conserve energy/momentum at each vertex
internal particles are called virtual particles, and they do not conserve mass-energy-momentum
sometimes called propagators
these are never observed
the proper language for particle interactions is quantum field theory
particles are localized waves in particle fields
quantum number exchange occurs when the waves overlap
particles are propagating wave packets
when two electrons superpose, a disturbance is seen in the W-field, which is not self-propagating, and doesn't have a well defined mass