Quintessence and thermal matter

We investigate the effects of thermal interactions on tracking models of quintessence, We show that even Planck-suppressed interactions between matter and the quintessence field can alter its evolution qualitatively. The dark energy equation of state is in many cases strongly affected by matter couplings. We obtain a bound on the coupling between quintessence and relativistic relic particles such as the photon or neutrino. (C) 2004 Published by Elsevier B.V.