Indications of a late-time interaction in the dark sector (1406.7297v2)

Abstract: We show that a general late-time interaction between cold dark matter and vacuum energy is favoured by current cosmological datasets. We characterize the strength of the coupling by a dimensionless parameter $q_V$ that is free to take different values in four redshift bins from the primordial epoch up to today. This interacting scenario is in agreement with measurements of cosmic microwave background temperature anisotropies from the Planck satellite, supernovae Ia from Union 2.1 and redshift space distortions from a number of surveys, as well as with combinations of these different datasets. We show that a non-zero interaction is very likely at late times. We then focus on the case $q_V\not=0$ in a single low-redshift bin, obtaining a nested one parameter extension of the standard $\Lambda$CDM model. We study the Bayesian evidence, with respect to $\Lambda$CDM, of this late-time interaction model, finding moderate evidence for an interaction starting at $z=0.9$, dependent upon the prior range chosen for the interaction strength parameter $q_V$. For this case the null interaction ($q_V=0$, i.e.$\Lambda$CDM) is excluded at 99% c.l..

Indications of a Late-Time Interaction in the Dark Sector

The paper "Indications of a Late-Time Interaction in the Dark Sector" presents a comprehensive analysis of a potential interaction between dark matter and vacuum energy at late cosmological times. This work is crucial due to its implications for understanding the discrepancies between cosmic microwave background (CMB) observations and local measurements of cosmological parameters, especially the Hubble constant.

The authors propose a model where cold dark matter (CDM) and vacuum energy, typically represented by a cosmological constant Λ, interact at late times. The strength of this interaction is governed by a dimensionless parameter, $q_V$, characterized across four redshift bins. The investigation reveals that when allowing this coupling to vary in four redshift bins, a non-zero interaction at lower redshifts (specifically starting at $z=0.9$) is supported by data. This leads to moderate evidence for a deviation from the standard ΛCDM model.

This paper utilizes various cosmological datasets, including CMB temperature anisotropies from the Planck satellite, supernovae type Ia data, and redshift space distortions (RSD). A significant finding is the exclusion of a null interaction at $99\%$ confidence level for the low-redshift bin, suggesting that at these epochs, the CDM could decay into vacuum energy, hence altering the expected dynamics as explained by standard cosmology.

The Bayesian analysis performed supports the hypothesis of a potential interaction, with indication that such an interaction could resolve existing tensions between the Planck CMB measurements and RSD data regarding large-scale structure growth rates. The authors carefully account for potential biases by considering different scenarios and data combinations, ensuring the robustness of the evidence.

The implications for the understanding of cosmic structure formation and the cosmic acceleration are profound. Interacting vacuum models offer an alternative to other proposed solutions to the observed tensions, such as massive neutrinos, by allowing the dark energy dynamics to influence the growth of cosmic structures without the necessity of altering the ΛCDM framework's core principles.

Moving forward, these results encourage further theoretical exploration of dynamic dark energy interactions and their observable signatures. From a practical perspective, refining the constraints on $q_V$ and exploring its impact on non-linear cosmic scales could offer new insights into the intricate balance governing cosmic evolution. Such developments may not only elucidate the long-standing Hubble tension but also shape future cosmological probes, including next-generation surveys aiming at pinpoint detailed properties of the universe's dark components.

This paper serves as a stepping stone towards a comprehensive framework, potentially integrating the cosmological constant with dynamic interactions, paving the way for advanced modeling of the universe's expansion and its constituent forces.