Phantom evolution in power-law potentials
  We investigate phantom models with power-law potentials and we extract the
early-time, "tracker", solutions under the assumption of matter domination.
Contrary to quintessence case, we find that energy positivity requires normal
power-law potentials instead of inverse power-law ones, with the potential
exponent being bounded by the quadratic form. In addition, we analytically
present the general cosmological solution at intermediate times, that is at low
redshifts, which is the period of the transition from matter to dark-energy
domination. The comparison with the exact evolution, arising from numerical
elaboration, shows that the tracker solution agrees with the later within 2%
for redshifts z>1.5, while the intermediate solution is accurate within 2% up
to $z\approx 0.5$.
