On the $\pi$ and $K$ as $q \bar q$ Bound States and Approximate   Nambu-Goldstone Bosons
  We reconsider the two different facets of $\pi$ and $K$ mesons as $q \bar q$ bound states and approximate Nambu-Goldstone bosons. We address several topics, including masses, mass splittings between $\pi$ and $\rho$ and between $K$ and $K^*$, meson wavefunctions, charge radii, and the $K-\pi$ wavefunction overlap. 
Shmuel Nussinov and Robert Shrock