Constraining Dark Energy Perturbations: the Role of Early Dark Energy

Understand

Dark Energy not only has background effects through its equation of state $w_{DE}$, but also it can cluster through its sound speed $c^2_{sDE}$, subject to certain conditions.

• As is well-known, for dynamical dark energy models, dark energy perturbations get sourced into matter perturbations through metric perturbations which is always accompanied by the term $(1+w_{DE})$.
• Hence, for dynamical dark energy models with $w_{DE}$ close $-1$, their perturbations get almost decoupled from metric leaving nearly null imprints on matter power spectra.
• Furthermore, Quintessence models with its sound speed equal to speed of light, washes out almost any inhomogeneities occurred within sub-Hubble scales, hence making detectability of dark energy perturbations far more difficult than already is.