Clustering of quintessence on horizon scales and its imprint on HI intensity mapping

TL;DR

This paper investigates how clustering quintessence affects large-scale matter distribution and HI intensity mapping, revealing a modest boost in power at high redshifts and clarifying the role of dark energy perturbations.

Contribution

It extends relativistic analysis to dynamical dark energy, quantifies its impact on HI intensity mapping, and clarifies the effects of dark energy perturbations on large-scale power.

Findings

Quintessence boosts high-redshift angular power by up to ~15%.

Dark energy perturbations have a small impact on large scales.

Assuming smooth dark energy artificially inflates large-scale power.

Abstract

Quintessence can cluster only on horizon scales. What is the effect on the observed matter distribution? To answer this, we need a relativistic approach that goes beyond the standard Newtonian calculation and deals properly with large scales. Such an approach has recently been developed for the case when dark energy is vacuum energy, which does not cluster at all. We extend this relativistic analysis to deal with dynamical dark energy. Using three quintessence potentials as examples, we compute the angular power spectrum for the case of an HI intensity map survey. Compared to the concordance model with the same small-scale power at z=0, quintessence boosts the angular power by up to ~15% at high redshifts, while power in the two models converges at low redshifts. The difference is mainly due to the background evolution, driven mostly by the normalization of the power spectrum today. The dark energy perturbations make only a small contribution on the largest scales, and a negligible contribution on smaller scales. Ironically, the dark energy perturbations remove the false boost of large-scale power that arises if we impose the (unphysical) assumption that the dark energy is smooth.