Early dark energy in the pre- and post-recombination epochs

Abstract

Dark energy could play a role at redshifts z O(1). Many quintessence models possess scaling or attractor solutions where the fraction of dark energy follows the dominant component in previous epochs of the Universe's expansion, or phase transitions may happen close to the time of matter-radiation equality. A non-negligible early dark energy (EDE) fraction around matter-radiation equality could contribute to alleviate the well-known H0 tension. In this work we constrain the fraction of EDE using two approaches: first, we use a fluid parameterization that mimics the plateaux of the dominant components in the past. An alternative tomographic approach constrains the EDE density in binned redshift intervals. The latter allows us to reconstruct the evolution of Ω de (z) before and after the decoupling of the Cosmic Microwave Background (CMB) photons. We have employed Planck data 2018, the Pantheon compilation of supernovae of Type Ia (SNIa), data on galaxy clustering, the prior on the absolute magnitude of SNIa by SH0ES, and weak lensing data from KiDS+VIKING-450 and DES-Y1. When we use a minimal parameterization mimicking the background plateaux, EDE has only a small impact on current cosmological tensions. We show how the constraints on the EDE fraction weaken considerably when its sound speed is allowed to vary. By means of our binned analysis we put very tight constraints on the EDE fraction around the CMB decoupling time, 0.4% at 2σ c.l. We confirm previous results that a significant EDE fraction in the radiation-dominated epoch loosens the H0 tension, but tends to worsen the tension for σ8. A subsequent presence of EDE in the matter-dominated era helps to alleviate this issue. When both the SH0ES prior and weak lensing data are considered in the fitting analysis in combination with data from CMB, SNIa and baryon acoustic oscillations, the EDE fractions are constrained to be 2.6% in the radiation-dominated epoch and 1.5% in the redshift range z ∈ (100, 1000) at 2σ c.l. The two tensions remain with a statistical significance of ∼ 2 − 3σ c.l.

Measuring the sound horizon and absolute magnitude of SNIa by maximizing the consistency between low-redshift data sets

“…The former is in mild (∼ 2.4σ) tension with the value inferred in the first steps of the cosmic distance ladder by SH0ES, M = −19.2191±0.0405 [20], whereas the comoving sound horizon is not very constrained by our principle of consistency. It is fully compatible with the standard model value from the TT,TE,EE+lowE+lensing analysis by Planck [3], r d = (147.09 ± 0.26) Mpc, but still leaves plenty of room for new physics [24][25][26][27][28][29][30][31][32][33][34][35][36]. With the advent of future data e.g.…”

“…Cosmological models with a preferred larger critical energy density around the matter-radiation equality time or an earlier recombination of protons and electrons before the photon decoupling can lead to an alleviation of the H 0 tension, since they allow for lower values of the comoving sound horizon at the baryon drag epoch, r d , what in turn gives room for larger values of the Hubble parameter, which is needed to keep the good description of the BAO data and the location of the first peak of the CMB temperature anisotropies. This is the case of some models that have been proposed to alleviate the H 0 tension, based on early dark energy [24][25][26][27], modified gravity [28][29][30][31], primordial magnetic fields [32], varying atomic constants [33,34], and running vacuum models [35].…”

A fast test to assess the impact of marginalization in Monte Carlo analyses, and its application to cosmology

“…Changes in σ 12 /S 12 are due to changes in the shape of the power spectrum, not to shifts of the scale at which the rms of mass fluctuations is computed. As reported in [51], in some models there can be non-negligible differences between the statistical tension with the large-scale structure (LSS) data when it is quantified with σ 12 /S 12 instead of σ 8 /S 8 . For instance, in the ΛCDM the tension seems to be a bit lower in terms of σ 12 /S 12 , although this is difficult to judge in a precise way, since weak lensing and galaxy surveys do not provide constraints on these quantities.…”

New early dark energy

“…On the other hand, it has been proposed that an extra component of dark energy, which decays just before recombination, shows more promise towards resolving the tension. The first attempt in this direction, called early dark energy (EDE) [22][23][24][25][26][27], proposed that the decay of the extra EDE component happened through a second order rollover phase transition (see [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] for different studies building up on this idea and [45][46][47][48][49][50][51][52][53] for other early-time approaches). This model, which, for the reminder of this paper, we will refer to as old EDE 1 , is however not completely without problems.…”