Why is a nucleon bound?

Abstract

In a style of popular article, we discuss models of hadronic structure and their relation with models of the QCD vacuum and lattice simulations. Borrowing two main characters from G.Gamow, Mr.Thompson and Professor, we make a travel in the QCD vacuum. Instanton-generated interaction between quarks appear to be major player, they create quark condensate, constituent quark masses and their bound states with properties very close to those observed. Direct removal of perturbative and confining forces (possible on the lattice by ``cooling'') result in very small modification of hadrons. Phase transitions at high T and large number of quarks in the theory are discussed.