According to the Standard Model, the forces which govern particle physics are:
- Color Force (strong nuclear force)
- Weak Force (Weak nuclear force)
when we write down the interactions of neutrinos, the standard model predicts that they are invisible to the color and electromagnetic forces. However, they do couple to (interact with) the weak force. The weak force is a bit strange in that it only interacts with the left handed version of particles. Thus, the right handed neutrino is also invisible to the weak force. This makes it so that only left handed neutrinos are detectable since right handed neutrinos (if they exist) don't interact with any of the standard model forces.