Alleviating cosmological tensions with a hybrid dark sector

TL;DR

This paper explores a hybrid dark sector model with interacting dark energy and dark matter, showing potential to alleviate the Hubble and S8 tensions using cosmological data, though Bayesian evidence remains inconclusive without local H0 measurements.

Contribution

It introduces a novel hybrid inflation-inspired dark sector model with a coupling controlled by initial conditions, offering a new approach to address cosmological tensions.

Findings

Model allows increased H0, reducing Hubble tension.

Higher coupling correlates with lower omega_m and S8.

Bayesian evidence favors the model only when including local H0 data.

Abstract

We investigate a cosmological model inspired by hybrid inflation, where two scalar fields representing dark energy (DE) and dark matter (DM) interact through a coupling that is proportional to the DE scalar field $1/\phi$. The strength of the coupling is governed solely by the initial condition of the scalar field, $\phi_i$, which parametrises deviations from the standard $\Lambda$CDM model. In this model, the scalar field tracks the behaviour of DM during matter-domination until it transitions to DE while the DM component decays quicker than standard CDM during matter-domination, and is therefore different from some interacting DM-DE models which behaves like phantom dark energy. Using \textit{Planck} 2018 CMB data, DESI BAO measurements and Pantheon+ supernova observations, we find that the model allows for an increase in $H_0$ that can help reduce the Hubble tension. In addition, we find that higher values of the coupling parameter are correlated with lower values of $\omega_m$, and a mild decrease of the weak-lensing parameter $S_8$, potentially relevant to address the $S_8$ tension. Bayesian model comparison, however, reveals inconclusive results for most datasets, unless S$H_0$ES data are included, in which case a moderate evidence in favour of the hybrid model is found.