The qq$\bar{\mathbf{q}}$ component in the constituent quark generates   the pion cloud of the nucleon
  The spin properties and the flavor asymmetric sea of the nucleon can be well explained by assuming that each constituent quark is surrounded with about 30% probability by a quark-antiquark pair coupled to the pion quantum numbers. We show that about one quarter of these quark-antiquark pairs show up as the pion in $\p\to\n\pi^+$ and $\p\to\p\pi^0$ fluctuation in agreement with the observed value in the ($\e+\p\to\e+$ forward neutron+X) experiment. 
B. Povh and M.Rosina
hep-ph