Axion and Almost Massless Quark as Ingredients of Quintessence
  It is pointed out that a natural introduction of quintessence is an axion with an almost massless quark. With an appropriate gauge or discrete symmetry, one can obtain the quintessence potential height of order $(0.003 eV)^4$. Even though the QCD axion with almost massless up quark is a possibility, we stress the almost massless quark in the hidden sector together with the QCD axion toward the quintessence. 
Jihn E. Kim