Can Baby Universe Absorption Explain Dark Energy?

TL;DR

This paper evaluates a baby universe absorption model as an explanation for dark energy, testing its compatibility with cosmological data and exploring its implications for the universe's expansion and Hubble tension.

Contribution

It provides a comprehensive analysis of the baby universe model against current cosmological observations, including extensions with a cosmological constant, revealing viable parameter regions.

Findings

Pure baby universe model fits poorly with data.

Including a cosmological constant yields two viable parameter regions.

The model can reduce Hubble tension to 2σ depending on datasets.

Abstract

It has been proposed that the accelerated expansion of the universe can be explained by the merging of our universe with baby universes, resulting in dark energy with a phantom-like equation of state. However, the evidence in favor of it did not include the full set of cosmological observables. Here we examine the implications of this model for both early and late universe cosmology using data from Planck collaboration, DESI 2024 and other experiments. We find that the pure baby universe model gives a poor fit to current data. Extending it to include a contribution from the cosmological constant, we find two allowed regions of parameter space: one close to $\Lambda$CDM, and another with $\Lambda <0$ plus the exotic dark energy component. The two regions can be significantly favored over $\Lambda$CDM, depending on the choice of supernova datasets, and they can ameliorate the Hubble tension to the level of $2\sigma$, depending on the supernova dataset. The model with $\Lambda<0$ features an equation of state $w(a)$ with a pole singularity at early times.