On dark degeneracy and interacting models

Abstract

Cosmological background observations cannot fix the dark energy equation of state, which is related to a degeneracy in the definition of the dark sector components. Here we show that this degeneracy can be broken at perturbation level by imposing two observational properties on dark matter. First, dark matter is defined as the clustering component we observe in large scale structures. This definition is meaningful only if dark energy is unperturbed, which is achieved if we additionally assume, as a second condition, that dark matter is cold, i.e. non-relativistic. As a consequence, dark energy models with equation-of-state parameter $-1\le \omega <0$ are reduced to two observationally distinguishable classes with $\omega =-1$, equally competitive when tested against observations. The first comprises the $\Lambda$CDM model with constant dark energy density. The second consists of interacting models with an energy flux from dark energy to dark matter.

Version accepted for publication in JCAP

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• A model-independent reconstruction of dark sector interactions
• Growth of structure in interacting vacuum cosmologies
• J-PAS: forecasts on interacting vacuum energy models
• Degeneracy between CCDM and $\Lambda$CDM cosmologies
• Unphysical properties in a class of interacting dark energy models
• One-parameter dynamical dark-energy from the generalized Chaplygin gas
• Qualitative dynamics of interacting vacuum cosmologies
• Unified dark fluid with null sound speed as an alternative to phantom dark energy
• Can the cosmological dark sector be modeled by a single scalar field?
• Probing Bino-Gluino Coannihilation at the LHC
• Equivalence of Dark Energy Models: A Theoretical and Bayesian Perspective
• The cosmological dark sector as a scalar $\sigma$-meson field
• Interacting Dark Energy and Its Implications for Unified Dark Sector
• Degeneracy between warm and coupled cold dark matter: A clarifying note