Pressure Parametrization of Dark Energy: First and Second-Order Constraints with Latest Cosmological Data

Understand

We explore an extension of the $\Lambda$CDM model in which the pressure $p$ of the dark energy (DE) fluid evolves with the expansion of the Universe, expressed as a function of the scale factor $a$.

• The corresponding energy density $\rho$ is derived from the continuity equation, resulting in a dynamical equation-of-state parameter $w \equiv p/\rho$ during the late-time expansion of the Universe.
• The pressure is modeled using a Taylor expansion around the present epoch ($a = 1$), introducing deviations from a cosmological constant within the dynamical dark energy (DDE) framework.
• At first order, a single new parameter $\Omega_1$ captures linear deviations, while a second-order parameter, $\Omega_2$, accounts for quadratic evolution in the pressure.