Effects of Dark Energy anisotropic stress on the matter power spectrum

Understand

We study the effects of dark energy (DE) anisotropic stress on features of the matter power spectrum (PS).

• We employ the Parametrized Post-Friedmannian (PPF) formalism to emulate an effective DE, and model its anisotropic stress properties through a two-parameter equation that governs its overall amplitude ($g_0$) and transition scale ($c_g$).
• For the background cosmology, we consider different equations of state to model DE including a constant $w_0$ parameter, and models that provide thawing (CPL) and freezing (nCPL) behaviors.
• We first constrain these parameters by using the Pantheon, BAO, $H_0$ and CMB Planck data.