Non-linear Structure Formation for Dark Energy Models with a Steep Equation of State

Abstract

We study the nonlinear regime of large scale structure formation considering a dynamical dark energy (DE) component determined by a Steep Equation of State parametrization (SEoS) $w(z)=w_0+w_i\frac{(z/z_T)^q}{1+(z/z_T)^q}$. In order to perform the model exploration at low computational cost, we modified the public code L-PICOLA. We incorporate the DE model by means of the first and second-order matter perturbations in the Lagrangian frame and the expansion parameter. We analyze deviations of SEoS models with respect to $\Lambda$CDM in the non-linear matter power spectrum ($P_k$), the halo mass function (HMF), and the two-point correlation function (2PCF). On quantifying the nature of steep (SEoS-I) and smooth transitions in DE field (CPL-lim), no signature of steep transition is observed, rather found the overall impact of DE behaviors in $P_k$ at level of $\sim 2-3\%$ and $\sim 3-4\%$ differences w.r.t $\Lambda$CDM at $z=0$ respectively. HMF shows the possibility to distinguish between the models at the high mass ends. The best-fitted model assuming only background and linear perturbations dubbed as SEoS-II largely deviates from $\Lambda$CDM and current observations on studying the nonlinear growth. This large deviation in SEoS-II also quantified the combined effect of the dynamical DE and the larger amount of matter contained, $\Omega_{m0}$ and $H_{0}$ accordingly. 2PCF results are relatively robust with $\sim 1-2 \%$ deviation for SEoS-I and CPL-lim and a significant deviation for SEoS-II throughout $r$ from $\Lambda$CDM. Finally, we conclude that the search for viable DE models (like the SEoS) must include non-linear growth constraints.