Do we have any hope of detecting scattering between dark energy and baryons through cosmology?
Abstract
We consider the possibility that dark energy and baryons might scatter off each other. The type of interaction we consider leads to a pure momentum exchange, and does not affect the background evolution of the expansion history. We parametrize this interaction in an effective way at the level of Boltzmann equations. We compute the effect of dark energybaryon scattering on cosmological observables, focusing on the cosmic microwave background (CMB) temperature anisotropy power spectrum and the matter power spectrum. Surprisingly, we find that even huge dark energybaryon crosssections σ _{xb} ∼ O(b), which are generically excluded by noncosmological probes such as collider searches or precision gravity tests, only leave an insignificant imprint on the observables considered. In the case of the CMB temperature power spectrum, the only imprint consists in a subper cent enhancement or depletion of power (depending whether or not the dark energy equation of state lies above or below 1) at very low multipoles, which is thus swamped by cosmic variance. These effects are explained in terms of differences in how gravitational potentials decay in the presence of a dark energybaryon scattering, which ultimately lead to an increase or decrease in the latetime integrated SachsWolfe power. Even smaller related effects are imprinted on the matter power spectrum. The imprints on the CMB are not expected to be degenerate with the effects due to altering the dark energy sound speed. We conclude that, while strongly appealing, the prospects for a direct detection of dark energy through cosmology do not seem feasible when considering realistic dark energybaryon crosssections. As a caveat, our results hold to linear order in perturbation theory.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 March 2020
 DOI:
 10.1093/mnras/staa311
 arXiv:
 arXiv:1911.12374
 Bibcode:
 2020MNRAS.493.1139V
 Keywords:

 cosmic background radiation;
 cosmological parameters;
 cosmology: observations;
 dark energy;
 largescale structure of Universe;
 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Phenomenology
 EPrint:
 15 pages, 7 figures. Title changed, minor modifications added comments on nonlinearities. Version accepted for publication in MNRAS