On the effect of the degeneracy between w_0 and w_a

Understand

The dynamics of scalar fields as dark energy is well approximated by some general relations between the equation of state parameter $w(z)$ and the fraction energy density $\Omega_\phi$.

• Based on the approximation, for slowly-rolling scalar fields, we derived the analytical expressions of $w(z)$ which reduce to the popular Chevallier-Polarski-Linder parametrization with explicit degeneracy relation between $w_0$ and $w_a$.
• The models approximate the dynamics of scalar fields well and help eliminate the degeneracies among $w_a$, $w_0$ and $\Omega_{m0}$.
• With the explicit degeneracy relations, we test their effects on the constraints of cosmological parameters.