Dark sectors with dynamical coupling

Abstract

Coupled dark matter-dark energy scenarios are modeled via a dimensionless parameter ξ, which controls the strength of their interaction. While this coupling is commonly assumed to be constant, there is no underlying physical law or symmetry that forbids a time-dependent ξ parameter. The most general and complete interacting scenarios between the two dark sectors should therefore allow for such a possibility, and it is the main purpose of this study to constrain two possible and wellmotivated coupled cosmologies by means of the most recent and accurate early and late-time universe observations. We find that CMB data alone prefers ξ(z) > 0 and therefore a smaller amount of dark matter, alleviating some crucial and well-known cosmological data tensions. An objective assessment of the Bayesian evidence for the coupled models explored here shows no particular preference for the presence of a dynamical dark sector coupling. more recently, an extra encouraging aspect of these theories has improved their role as an alternative to a pure ΛCDM universe. Namely, in dark matter-dark energy coupled cosmologies the tension between local and CMB estimations of the Hubble constant H 0 could be ameliorated [43,44,45,46]. Current cosmological observations still allow for significant interactions among the two dark sectors, i.e. between dark matter and dark energy, see e.g. Refs. [47,48,49,50,51,52]. In this work we consider an interacting scenario in which vacuum interacts with pressure-less dark matter adopting the more general phenomenological viewpoint, i.e. inspecting a time-dependent coupling. Such a consideration also entails the case of a coupling parameter that remains constant in cosmic time. For our analyses we have assumed that our universe is homogeneous and isotropic, that is, its geometry is well described by the Friedmann-Lemaître-Robertson-Walker line element.The work has been organized as follows. Section 2 contains the gravitational equations within an interacting universe. In Sec. 3 we describe the observational data and the methodology used to constrain the interacting dark energy models. Section 4 presents the observational constraints on the models, including also a Bayesian evidence analysis. Finally, we draw our conclusions in Sec. 5. GRAVITATIONAL EQUATIONS OF A UNIVERSE WITH INTERACTING DARK SECTORSA homogeneous and isotropic universe is well described by the Friedmann-Lemaître-Robertson-Walker (FLRW) metric: arXiv:1906.11697v1 [astro-ph.CO]

Dynamical dark sectors and neutrino masses and abundances

“…We also generalize the work of Ref. [55] with the inclusion of a constant dark energy state parameter that may freely vary in a certain region. This picture also entails the case of a coupling parameter that remains constant in cosmic time.…”

“…where ξðaÞ is a time-dependent dimensionless coupling parameter. Similar to our earlier work [55], we keep the parametrization of ξðaÞ as follows:…”

“…Early models were based on coupled quintessence scenarios [1][2][3][4][5][6][7], while more recent phenomenological approaches have adopted a number of possible parametrizations of the energy exchange rate; see, e.g., . Following our pioneering previous work [55] we shall consider here a time-dependent coupling in nonminimal cosmologies. Given the fact that neutrinos can play a nonstandard role within nonminimal dark energy scenarios [56][57][58][59][60][61][62][63][64][65][66], we extend our previous analyses by inspecting the impact of neutrino properties within interacting cosmologies with a time-dependent coupling.…”

Dark calling dark: interaction in the dark sector in presence of neutrino properties after Planck CMB final release

“…It has been found that the presence of an interaction in the dark sector could successfully reconcile the long lasting cosmic coincidence problem [3,4,5,6,7]. Following this, a number of investigations in the context of interacting DE -DM models were performed by many investigators [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43] (also see two review articles in this direction [44,45]). An interesting outcome from the interaction is that, it could naturally explain the phantom dark energy equation-ofstate [46,47,48,49].…”

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

“…[48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63]). Although within most dark sector models the two dark components do not interact, an interesting class of cosmological models (usually referred to as coupled DE) feature interactions between DM and DE (see for example [64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96]). While we cannot do justice to the enormous literature on dark sector models, it is clear from the discussion so far that there is no shortage o...…”