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Register a new userTopological Structure of the Vacuum, Cosmological Constant and Dark Energy
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Added by
Larisa Laperashvili
Publication date
2016
fields
Physics
and research's language is
English
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In this review we present a theory of cosmological constant and Dark Energy (DE), based on the topological structure of the vacuum. The Multiple Point Principle (MPP) is reviewed. It demonstrates the existence of the two vacua into the SM. The Froggatt-Nielsens prediction of the top-quark and Higgs masses is given in the assumption that there exist two degenerate vacua in the SM. This prediction was improved by the next order calculations. We also considered B.G. Sidharths theory of cosmological constant based on the non-commutative geometry of the Planck scale space-time, what gives an extremely small DE density providing the accelerating expansion of the Universe. Theory of two degenerate vacua - the Planck scale phase and Electroweak (EW) phase - also is reviewed, topological defects in these vacua are investigated, also the Compton wavelength phase suggested by B.G. Sidharth was discussed. A general theory of the phase transition and the problem of the vacuum stability in the SM is reviewed. Assuming that the recently discovered at the LHC new resonance with mass $m_S simeq 750$ GeV is a new scalar $S$ bound state $6t + 6bar t$, earlier predicted by C.D. Froggatt, H.B. Nielsen and L.V. Laperashvili, we try to provide the vacuum stability in the SM and exact accuracy of the MPP.
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The today estimated value of dark energy can be achieved by the vacuum condensate induced by neutrino mixing phenomenon. Such a tiny value is recovered for a cut-off of the order of Planck scale and it is linked to the sub eV neutrino mass scale. Contributions to dark energy from auxiliary fields or mechanisms are not necessary in this approach.
It is well known that string theories naturally compactify on anti-de Sitter spaces, and yet cosmological observations show no evidence of a negative cosmological constant in the early Universes evolution. In this letter we present two simple nonlocal modifications of the standard Friedmann cosmology that can lead to observationally viable cosmologies with an initial (negative) cosmological constant. The nonlocal operators we include are toy models for the quantum cosmological backreaction. In Model I an initial quasiperiodic oscillatory epoch is followed by inflation and a late time matter era, representing a dark matter candidate. The backreaction in Model II quickly compensates the negative cosmological term such that the Ricci curvature scalar rapidly approaches zero, and the Universe ends up in a late time radiation era.
We study the cosmological constant ($Lambda$) in the standard $Lambda$CDM model by introducing the textit{graduated dark energy} (gDE) characterised by a minimal dynamical deviation from the null inertial mass density of the $Lambda$ in the form $rho_{rm inert}propto rho^{lambda}<0$ with $lambda<1$ being a ratio of two odd integers, for which its energy density $rho$ dynamically takes negative values in the finite past. For large negative values of $lambda$, it creates a phenomenological model described by a smooth function that approximately describes the $Lambda$ spontaneously switching sign in the late universe to become positive today. We confront the model with the latest combined observational data sets of PLK+BAO+SN+$H$. It is striking that the data predict bimodal posterior probability distributions for the parameters of the model along with large negative $lambda$ values; the new maximum significantly excludes the $Lambda$, and the old maximum contains the $Lambda$. The improvement in the goodness of fit for the $Lambda$ reaches highly significant levels, $Deltachi_{rm min}^2=6.4$ for the new maxima, while it remains at insignificant levels, $Deltachi_{rm min}^2lesssim0.02$, for the old maxima. We show that, in contrast to the old maxima, which do not distinguish from the $Lambda$, the new maxima agree with the model-independent $H_0$ measurements, high-precision Ly-$alpha$ data, and model-independent $Omh^2$ diagnostic estimates. Our results provide strong hints of a spontaneous sign switch in the cosmological constant and lead us to conjecture that the universe has transitioned from AdS vacua to dS vacua, at a redshift $zapprox 2.32$ and triggered the late-time acceleration, and suggests looking for such mechanisms in string theory constructions.
The cosmology of branes undergoing the self-tuning mechanism of the cosmological constant is considered. The equations and matching conditions are derived in several coordinate systems, and an exploration of possible solution strategies is performed. The ensuing equations are solved analytically in the probe brane limit. We classify the distinct behavior for the brane cosmology and we correlate them with properties of the bulk (static) solutions. Their matching to the actual universe cosmology is addressed.
The cosmological evolution of an interacting scalar field model in which the scalar field interacts with dark matter, radiation, and baryon via Lorentz violation is investigated. We propose a model of interaction through the effective coupling $bar{beta}$. Using dynamical system analysis, we study the linear dynamics of an interacting model and show that the dynamics of critical points are completely controlled by two parameters. Some results can be mentioned as follows. Firstly, the sequence of radiation, the dark matter, and the scalar field dark energy exist and baryons are sub dominant. Secondly, the model also allows the possibility of having a universe in the phantom phase with constant potential. Thirdly, the effective gravitational constant varies with respect to time through $bar{beta}$. In particular, we consider a simple case where $bar{beta}$ has a quadratic form and has a good agreement with the modified $Lambda$CDM and quintessence models. Finally, we also calculate the first post--Newtonian parameters for our model.
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