Observable interactions of quintessence with ordinary matter and neutrinos

For any realistic theory of quintessence that allows for a violation of the equivalence principle (VEP), we study the experimental constraints on such theories coming from ordinary matter as well as neutrinos. We discuss and compare constraints from two basically different (extra) contributions to differences of fermion masses: one is due to the vacuum expectation value (vev) of quintessence, and the other is based on a quintessence-exchange graph at finite temperature/density.