  We study the cosmological evolution of scalar fields that arise from a phase
transition at some energy scale $\Lm_c$. We focus on negative power potentials
given by $V=c\Lm_c^{4+n}\phi^{-n}$ and restrict the cosmological viable values
of $\Lm_c$ and $n$. We make a complete analysis of $V$ and impose $SN1a$
conditions on the different cosmological parameters. The cosmological
observations ruled out models where the scalar field has reached its attractor
solution. For models where this is not the case, the analytic approximated
solutions are not good enough to determine whether a specific model is
phenomenologically viable or not and the full differential equations must be
numerically solved. The results are not fine tuned since a change of 45% on the
initial conditions does not spoil the final results. We also determine the
values of $N_c, N_f$ that give a condensation scale $\Lm_c$ consistent with
gauge coupling unification, leaving only four models that satisfy unification
and SN1a constraints.
