A microphysically inspired approach to dark matter-dark energy interactions: first bounds on dark-sector scattering cross sections

TL;DR

The paper addresses the $H_0$ tension by proposing a microphysically motivated interacting dark energy model with a collision-based term $Q=-A\frac{H_0}{\bar{\rho}_{\rm c,0}}\bar{\rho}_{\rm DM}^2+B\frac{H_0}{\bar{\rho}_{\rm c,0}}\bar{\rho}_{\rm DE}^2$, derived from Boltzmann-like kinetics. It grounds the interaction in an effective field theory of two dark-sector fields, $\chi$ and $\phi$, mediating reversible $\chi+\chi\leftrightarrow\phi+\phi$ processes, and interprets $A$ and $B$ as thermally-averaged cross-sections per unit mass. The analysis uses MCMC with Pantheon+ SNe Ia, Cosmic Chronometers, DESI DR2 BAO, and Planck18 distance priors, finding $H_0=67.71\pm0.65$ and stringent 95% CL upper limits $A<7.586\times10^{-25}$ and $B<0.048$, with $\chi^2_{\nu}$ competitive to $\Lambda$CDM. The results indicate no strong evidence for a sizeable dark-sector coupling, while providing a physically motivated framework and clear bounds that can be sharpened by future perturbation-level analyses.

Abstract

The observational tension regarding the value of the Hubble constant ($H_0$) has motivated the exploration of alternative cosmological scenarios, including Interacting Dark Energy models. However, the majority of IDE models studied in the literature rely on phenomenological interaction terms proportional to the Hubble parameter (e.g., $Q\propto Hρ$), which lack a clear microphysical justification and often suffer from large-scale instabilities. In this work, we propose and investigate a "bottom-up" IDE model where the interaction is formulated directly from particle physics collision processes, taking the form $Q\proptoρ^2$. This interaction represents a reversible annihilation/creation process between Dark Matter and Dark Energy, motivated by the Boltzmann equation. We test this model against a combination of background cosmological data, Pantheon Plus, Cosmic Chronometers, DESI DR2, and CMB distance priors from Planck18. We find that the model is consistent with the data, yielding a Hubble constant of $H_0=67.71\pm0.65$ km s$^{-1}$ Mpc$^{-1}$ for the combined analysis. The dimensionless interaction rate coefficients are constrained to be small, with upper limits of $A < 7.586\times10^{-25}$ (for Dark Matter self annihilation) and $B < 0.048$ (for Dark Energy self annihilation) at 95\% confidence level. Since the interaction model is parameterized by the expansion rate, these bounds on $H_0$, $A$, and $B$ directly translate into a strict limit on the thermally-averaged annihilation cross-section per unit of mass. The constraints on the coupling $A$ imply that, if such a collisional interaction exists, the effective dark-matter annihilation cross section per unit mass is highly suppressed relative to the cosmological expansion rate. In contrast, the corresponding dark-energy contribution, governed by $B$, is only constrained at the level of a few percent in dimensionless units.

Figures (3)

• Figure 1: Marginalized 1$\sigma$ and 2$\sigma$ confidence contours and posterior distributions for the free parameters. Left: Constraints on the primary model parameters: $H_0$, $\Omega_{DM0}$, $w$, and the interaction exponents $A$, $B$. Right: Constraints highlighting the derived acoustic scales: $H_0$, $\ell_A$, $r_{s,drag}$, alongside the interaction exponents $A$, $B$. Note that for clarity, not all individual dataset combinations are shown in every panel.
• Figure 2: PP + PCMB + BAO + CCs. Left: Frequency $\times\ln{\mathcal{L}}$. Right:$\ln{\mathcal{L}}\times\log_{10}B$.
• Figure 3: BAO + PCMB. Left: Frequency $\times \ln{\mathcal{L}}$. Right:$\ln{\mathcal{L}}\times \log_{10}B$ .