  We investigate the constraints on quintessence arising from both
renormalisable and non-renormalisable couplings where the 5d Planck mass is
around the TeV scale. The quintessence field vacuum expectation value is
typically of order the 4d Planck mass while non-renormalisable operators are
expected to be suppressed by the 5d Planck mass. Non-renormalisable operators
are therefore important in computing the 4d effective quintessence potential.
We then study the quantum corrections to the quintessence potential due to
fermion and graviton loops. The tower of Kaluza-Klein modes competes with the
TeV-scale cut-off, altering the graviton contribution to the vacuum
polarization of quintessence. Nevertheless we show that, as in four dimensions,
the classical potential is stable to such radiative corrections.
