Fundamental forces. gluons/pions

[Chronos000]

Homework Statement

I'm not sure how pions relate to the strong force.

My notes say that only gluons propagate the strong force between quarks - holding a neutron together, and that residual force (I imagine between the quarks of neutrons and protons) holds neutrons and protons together in a nucleus.

But the I also know that in scattering events between nucleons, virtual pions are present. But these don't change protons to neutrons as this is the weak force right? So what are pions doing?

 

[fzero]

Describing the strong interaction via pion exchange between nucleons is an effective description known as chiral perturbation theory http://en.wikipedia.org/wiki/Chiral_perturbation_theory. It is an approximation to the full theory that can be reasonably accurate at low energies, like around 1 GeV. At high energies such as at the LHC, you need the full machinery of QCD in terms of gluons.