Unified framework for early dark energy from α -attractors

Abstract

One of the most appealing approaches to ease the Hubble tension is the inclusion of an early dark energy (EDE) component that adds energy to the Universe in a narrow redshift window around the time of recombination and dilutes faster than radiation afterwards. In this paper, we analyze EDE in the framework of α-attractor models. As is well known, the success in alleviating the Hubble tension crucially depends on the shape of the energy injection. We show how different types of energy injections can be obtained, thanks to the freedom in choosing the functional form of the potential inspired by α-attractor models. To confirm our intuition, we perform a Markov-chain Monte Carlo analysis for three representative cases and find indeed that H 0 is significantly larger than in ΛCDM, like in other EDE models. Unlike axion-driven EDE models with a super-Planckian decay constant, the curvature of the potential in the EDE models required by the data is natural in the context of recent theoretical developments in α-attractors.

Resolving the Hubble tension with new early dark energy

“…So it is quite intriguing that a promising resolution of the Hubble tension modifies the ΛCDM model exactly where we would have thought it is constrained the most: closely to matter-radiation equality where the composition of the energy budget affects the relative and absolute heights of the first peaks in the power spectrum. This is done by introducing an early dark energy (EDE) component [12,[32][33][34][35][36][37][38][39][40], which contributes a sizable fraction to the energy budget around matter-radiation equality, just before it starts to decay subsequently in order not to overclose the Universe. 2 So far, this has been realized in terms of a single scalar field that transitions from a slow-roll to an oscillating 2 To be more precise, here we refer to specific axion setups that have been devised to address the Hubble tension.…”

New early dark energy is compatible with current LSS data

“…If we try to modify the latetime history to account for the higher value of H 0 measured today by SH 0 ES, then we quickly run into tension with baryon acoustic oscillation (BAO) measurements [3,4,[11][12][13]. On the other hand, an extra component of dark energy, which decays away shortly before recombination, has proved more promising as a possible solution [14][15][16][17][18][19][20][21][22][23]. The early dark energy (EDE) proposal suggests that the early dark energy is stored in a slow-rolling scalar field and decays away as the scalar field approaches the bottom of its potential and picks up speed, similar to how inflation ends in slow-roll inflation.…”

Early modified gravity in light of the H0 tension and LSS data

“…The former ones, however, seem to be preferred over since reduce the value of the comoving size of the sound horizon at baryon drag r s , without spoiling the fit to CMB and BAO data [30][31][32]. Two well studied frameworks to modify the early time dynamics of the Universe and inject the required energy into the cosmic fluid to lower r s with respect to the ΛCDM one are modified gravity (MG) [33][34][35][36][37][38][39][40][41][42][43][44][45] and early dark energy (EDE) models [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63]. 1 In this paper, we extend the model with a scalar field on-minimally coupled to the Ricci scalar of the form FðσÞ ¼ M 2 pl þ ξσ 2 in presence of a cosmological constant Λ [41,42], by providing it with a small effective mass.…”

“…Indeed, potentials with a different curvature such as those with flattened wings and power-law minima are well known to lead to a larger value of H 0 compared to the simpler quartic potential [47,54,55,57].…”