  High sensitivity polarization measures, on wide angular scales, together with
data on anisotropy, can be used to fix DE parameters. In this paper, first of
all, we aim to determine the sensitivity needed to provide significant limits.
Our analysis puts in evidence that there is a class of DE models that
polarization measures can possibly exclude soon. This class includes models
with DE due to a Ratra-Peebles (RP) potential. Using a likelihood analysis, we
show that it is possible to distinguish RP models from LCDM and other dynamical
DE models, already with the sensitivity of experiments like SPOrt or WMAP,
thanks to their negative TE correlation at low-l, when the optical depth tau is
sufficiently large. On the contrary, fixing the energy scale Lambda for RP
potentials or distinguishing between LCDM and other DE potentials requires a
much lower pixel noise, that no planned polarization experiment will achieve.
While reviewing this paper after the referee report, the first-year WMAP data
were released. WMAP finds large positive anisotropy-polarization correlations
at low l; this apparently excludes DE models with RP potentials.
