Abstract
It has been shown beyond reasonable doubt that the majority (about 95%) of the total energy budget of the universe is given by dark components, namely Dark Matter and Dark Energy. What constitutes these components remains to be satisfactorily understood however, despite a number of promising candidates. An associated conundrum is that of the coincidence, i.e., the question as to why the Dark Matter and Dark Energy densities are of the same order of magnitude at the present epoch, after evolving over the entire expansion history of the universe. In an attempt to address these, we consider a quantum potential resulting from a quantum corrected Raychaudhuri–Friedmann equation in presence of a cosmic fluid, which is presumed to be a Bose–Einstein condensate (BEC) of ultralight bosons. For a suitable and physically motivated macroscopic ground state wave function of the BEC, we show that a unified picture of the cosmic dark sector can indeed emerge, thus resolving the issue of the coincidence. The effective Dark energy component turns out to be a cosmological constant, by virtue of a residual homogeneous term in the quantum potential. Furthermore, comparison with the observational data gives an estimate of the mass of the constituent bosons in the BEC, which is well within the bounds predicted from other considerations.
Highlights
A unified picture of the cosmic Dark Matter (DM) and Dark Energy (DE) has been one of the key aspirations of modern researches within the standard paradigm of spatially flatFriedmann–Robertson–Walker (FRW) cosmology [1–5]
In this paper we have studied a macroscopic Bose–Einstein condensate (BEC) stretching across cosmological length scales as a potential cold dark matter (CDM) candidate
While there have been a number of attempts in this direction earlier, what is new in our work is the observation that the quantum potential of this BEC gives rise to the effect of an observed DE in the form of a cosmological constant Λ
Summary
A unified picture of the cosmic Dark Matter (DM) and Dark Energy (DE) has been one of the key aspirations of modern researches within the standard paradigm of spatially flat. Is the ‘coincidence’, i.e., the vast amount of fine-tuning required to set up the initial conditions for the same order-of-magnitude contributions of DM and DE at the present epoch, if they purportedly stem out of different fundamental sources. This is perplexing, given the strong observational support for the DE density to be closely akin to a cosmological constant Λ, whereas almost the entire bulk of the DM to be ‘cold’ and non-relativistic, with energy density ρ(c) (t) ∼ a−3 (t) (where a(t) is the cosmological scale factor, and t denotes the cosmic time coordinate). In the scenario we focus on, the macroscopic BEC provides the requisite wavefunction
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