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On the Dark Sector Interactions

Rong-Gen Cai, Qiping Su

TL;DR

Problem: whether a non-gravitational coupling between dark energy and dark matter exists, without committing to a fixed functional form of the interaction. Method: a model-independent binning approach that treats the coupling $\delta$ as constant within redshift bins and tests multiple $w_{de}$ parameterizations against combined cosmological data using MCMC. Findings: $\delta(z)$ tends to cross $\delta=0$ and often shows oscillatory behavior; the evidence for nonzero coupling depends on the $w_{de}$ parameterization and binning, with some cases allowing $\delta=0$ within 68% CL while others show departures. Significance: results motivate exploring more general phenomenological forms of the interaction beyond simple proportionality to densities and highlight the need for richer high-$z$ data to decisively detect or constrain dark-sector coupling.

Abstract

It is possible that there exist some interactions between dark energy (DE) and dark matter (DM), and a suitable interaction can alleviate the coincidence problem. Several phenomenological interacting forms are proposed and are fitted with observations in the literature. In this paper we investigate the possible interaction in a way independent of specific interacting forms by use of observational data (SNe, BAO, CMB and Hubble parameter). We divide the whole range of redshift into a few bins and set the interacting term $δ(z)$ to be a constant in each redshift bin. We consider four parameterizations of the equation of state $w_{de}$ for DE and find that $δ(z)$ is likely to cross the non-interacting ($δ=0$) and have an oscillation form. It suggests that to study the interaction between DE and DM, more general phenomenological forms of the interacting term should be considered.

On the Dark Sector Interactions

TL;DR

Problem: whether a non-gravitational coupling between dark energy and dark matter exists, without committing to a fixed functional form of the interaction. Method: a model-independent binning approach that treats the coupling as constant within redshift bins and tests multiple parameterizations against combined cosmological data using MCMC. Findings: tends to cross and often shows oscillatory behavior; the evidence for nonzero coupling depends on the parameterization and binning, with some cases allowing within 68% CL while others show departures. Significance: results motivate exploring more general phenomenological forms of the interaction beyond simple proportionality to densities and highlight the need for richer high- data to decisively detect or constrain dark-sector coupling.

Abstract

It is possible that there exist some interactions between dark energy (DE) and dark matter (DM), and a suitable interaction can alleviate the coincidence problem. Several phenomenological interacting forms are proposed and are fitted with observations in the literature. In this paper we investigate the possible interaction in a way independent of specific interacting forms by use of observational data (SNe, BAO, CMB and Hubble parameter). We divide the whole range of redshift into a few bins and set the interacting term to be a constant in each redshift bin. We consider four parameterizations of the equation of state for DE and find that is likely to cross the non-interacting () and have an oscillation form. It suggests that to study the interaction between DE and DM, more general phenomenological forms of the interacting term should be considered.

Paper Structure

This paper contains 6 sections, 18 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Methodology
  3. Results
  4. Effects of the number of bins
  5. Effects of parameterizations of DE
  6. Conclusion

Figures (3)

  • Figure 1: Constraints of $\delta(z)$ at 68% and 95% c.l. for 3, 4, 5 and 6 bins in $z\in(0,1.8)$. The bins are equally divided. The equation of state of DE is assumed as a constant. $\delta(z)$ is in the unit of $3H_0^2$.
  • Figure 2: The constraints of $\delta_i$ at 68% and 95% c.l. . $\delta_i$ is in the unit of $3H_0^2$.
  • Figure 3: The behaviors of $r=\rho_m/\rho_{de}$. Solid curves are for the best-fitted models shown in Table \ref{['ta']} (with $\delta_4=0$), while the dashed curves for the best-fitted models with $\delta(z)=0$.