[Paper Review] Constraining the interaction between dark matter and dark energy with CMB data

Riccardo Murgia|arXiv (Cornell University)|Dec 7, 2016

Cosmology and Gravitation Theories1 references3 citations

TL;DR

This paper investigates a phenomenological non-gravitational coupling between dark matter (DM) and dark energy (DE), parameterized by an energy transfer from DE to DM (positive coupling ξ). Using CMB data and combined cosmological probes, it finds that such a coupling significantly reduces the tension between high-redshift Planck measurements and low-redshift local determinations of H₀ and σ₈, with the model (MOD2) showing improved consistency with observations when DE decays into DM.

ABSTRACT

We briefly discuss the intriguing case of a phenomenological non-gravitational coupling in the dark sector, where the interaction is parameterized as an energy transfer either from dark matter to dark energy or the opposite. We show that a non-zero coupling with an energy flow from the latter to the former leads to a full reconciliation of the tension between high- and low-redshift observations present in the standard cosmological model.

Motivation & Objective

• To investigate whether a non-gravitational interaction between dark matter and dark energy can alleviate cosmological tensions in the standard model.
• To address the persistent discrepancy between high-redshift CMB-based estimates and low-redshift local measurements of H₀ and σ₈.
• To test a phenomenological model where energy flows from dark energy to dark matter, parameterized by a coupling ξ.
• To constrain the coupling strength using Planck CMB data and additional cosmological probes.

Proposed method

• The interaction is modeled via non-conserved stress-energy tensors for DM and DE, with energy transfer governed by a coupling term Q.
• The coupling is parameterized as Q = ξℋρ_Λ, where ξ is a dimensionless coupling parameter and ℋ is the Hubble rate.
• Evolution equations for DM and DE energy densities are derived from the non-conservation of their respective stress-energy tensors.
• Cosmic microwave background (CMB) anisotropies from Planck (TT+lowP) are used as the primary dataset, supplemented by BAO, SNe, RSD, and weak lensing data.
• Markov Chain Monte Carlo (MCMC) sampling is employed to constrain model parameters under flat priors.
• The analysis compares the standard ΛCDM model with two modified models: MOD1 (ξ < 0, DM decays into DE) and MOD2 (ξ > 0, DE decays into DM).

Experimental results

Research questions

• RQ1 Can a non-gravitational interaction between dark matter and dark energy reconcile high- and low-redshift measurements of H₀ and σ₈?
• RQ2 How does a coupling parameter ξ, governing energy transfer from DE to DM, affect the evolution of cosmological parameters?
• RQ3 Does the inclusion of a dark sector interaction improve the consistency of CMB-based constraints with local low-redshift observations?
• RQ4 What are the constraints on the coupling strength ξ when combining Planck CMB data with other cosmological probes?
• RQ5 How does the sign and magnitude of ξ influence the predicted values of H₀ and σ₈ in the early and late Universe?

Key findings

• The model with energy transfer from dark energy to dark matter (MOD2, ξ > 0) reduces the tension between CMB-based and local measurements of H₀ and σ₈.
• In MOD2, σ₈ is suppressed compared to ΛCDM due to delayed structure formation from reduced dark matter abundance, yielding σ₈ = 0.749⁺⁰.⁰⁶⁷₋₀.⁰⁶¹ in the 'ALL' dataset.
• H₀ in MOD2 is consistent with local measurements (70.6 ± 3.3 km s⁻¹ Mpc⁻¹), with a best-fit value of 67.83⁺¹.⁹⁰₋₁.⁷⁵ km s⁻¹ Mpc⁻¹ under the 'ALL' dataset.
• MOD1 (DM decaying into DE) increases σ₈ to 0.994⁺⁰.²⁸³₋₀.²⁰², worsening agreement with low-redshift σ₈ constraints.
• The coupling parameter ξ is constrained to ξ = 0.146⁺⁰.¹⁵⁴₋⁰.¹⁵⁴ in MOD2 under the 'ALL' dataset, indicating a non-zero but small interaction.
• The model shows strong correlation between ξ and Ω_ch², with higher ξ leading to lower current dark matter density when energy flows from DE to DM.