Strong, electromagnetic, and weak interactions cause particle decays.
There are three particle properties that determine which interaction and force-carrier
particle will mediate a given decay:
Flavor:
"Flavor" refers to a particle's type.
When a fundamental particle decays from one type of particle to another, we say it
"changes flavor." If a down quark decays into an up quark, the down quark does not
cease to be: it simply changes flavor. Only the weak interaction (via the W boson) can
change flavor and allow the decay of a truly fundamental particle.
Electromagnetic Charge:
Particles with
electromagnetic charge
attract particles with opposite electric charge
and repel particles with similar charges. Photons carry the electromagnetic interaction.
Color Charge:
Just as some particles can be electromagnetically charged, particles can
have a different kind of charge called
color charge. The strong interaction
causes the attraction between color charged particles.
The strong
force-carrier particle, the gluon, mediates decays involving color changes.
The weak force-carrier particles, W+ and
W-, mediate decays in which particles change flavor (and
electric charge).