Interacting dark sector with quadratic coupling: theoretical and observational viability

TL;DR

This paper investigates a quadratic dark sector interaction model, analyzing its theoretical implications and observational viability, and finds it can alleviate the sigma_8 tension while remaining consistent with standard cosmology within 2 sigma.

Contribution

It introduces and tests a quadratic dark energy-dark matter interaction model using diverse cosmological data, highlighting its potential to address existing tensions in cosmology.

Findings

Model predicts future violation of Weak Energy Condition for positive gamma.

Model consistent with Lambda CDM within 2 sigma when WEC is enforced.

Preferentially reduces sigma_8, helping resolve tension between CMB and lensing data.

Abstract

Models proposing a non-gravitational interaction between dark energy (DE) and dark matter (CDM) have been extensively studied as alternatives to the standard cosmological model. A common approach to describing the DE-CDM coupling assumes it to be linearly proportional to the dark energy density. In this work, we consider the model with interaction term $Q=3H\gamma{\rho_{x}^{2}}/{(\rho_{c}+\rho_{x})}$. We show that for positive values of $\gamma$ this model predicts a future violation of the Weak Energy Condition (WEC) for the dark matter component, and for a specific range of negative values of $\gamma$ the CDM energy density can be negative in the past. We perform a parameter selection analysis for this model using data from Type Ia supernovae from the Pantheon sample, $H(z)$ measurements from the Cosmic Chronometers sample, Baryon Acoustic Oscillations from the DESI survey, and Cosmic Microwave Background data from the Planck combined with the Hubble constant $H_0$ prior. Imposing a prior to ensure that the WEC is not violated, our model is consistent with $\Lambda$CDM in 2$\sigma$ C.L., yet exhibits a preference for smaller values of $\sigma_8$, alleviating the $\sigma_8$ tension between the CMB results from Planck 2018 and the weak gravitational lensing observations from the KiDS-1000 cosmic shear survey.