Determining Min. Charge States of Yukawa's Particle & Why Gluons are Massless

[fabsuk]

Hi,
i am kind stuck on this question as i don't know what equation to use. doesn't seem to be in any books.

By considering possible interactions between protons and neutrons, determine the minimum number of charge states of yukawa's particle.

Also why is the interquark force of finite range but appears to be carried by massless exchange particles(gluons).

 

[pam]

1. The charges of the Y particles have to equal all possible proton-neutron charge differences.
2. The q-q force appears to have a "confining" potential that does not vanish as r-->large.
It seems to go like V~r for large r.