Source Of Dark Energy Research Articles

Galaxy Phase-Space Density Data Preclude That Bose–Einstein Condensate Be the Total Dark Matter

Ultralight scalars with a typical mass of the order m∼10−22 eV and light scalars forming a Bose–Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were therefore proposed as dark matter (DM) candidates. Our treatment here is generic, independent of the particle physics model and applies to all DM BEC, in both in or out of equilibrium situations. Two observed quantities crucially constrain DM in an inescapable way: the average DM density ρDM and the phase-space density Q. The observed values of ρDM and Q in galaxies today constrain both the possibility to form a BEC, and the DM mass m. These two constraints robustly exclude the axion DM that decouples after inflation. Moreover, the value m∼10−22 eV can only be obtained with a number of ultrarelativistic degrees of freedom at decoupling in the trillions, which is impossible for decoupling in the radiation dominated era. In addition, we find for the axion vacuum misalignment scenario that axions are produced strongly out of thermal equilibrium and that the axion mass in such a scenario turns to be 17 orders of magnitude too large to reproduce the observed galactic structures. Moreover, we also consider inhomogenous gravitationally bounded BEC’s supported by the bosonic quantum pressure independently of any particular particle physics scenario. For a typical size R∼ kpc and compact object masses M∼107M⊙ they remarkably lead to the same particle mass m∼10−22 eV as the BEC free-streaming length. However, the phase-space density for the gravitationally bounded BEC’s turns out to be more than sixty orders of magnitude smaller than the galaxy-observed values. We conclude that the BEC cannot be the total DM. The axion can be candidates to be only part of the DM of the universe. Besides, an axion in the mili-eV scale may be a relevant source of dark energy through the zero point cosmological quantum fluctuations.

Hunting dark energy with pressure-dependent photon-photon scattering

Toward understanding of dark energy, we propose a novel method to directly produce a chameleon particle and force its decay under controlled gas pressure in a laboratory-based experiment. Chameleon gravity, characterized by its varying mass depending on its environment, could be a source of dark energy, which is predicted in modified gravity. A remarkable finding is a correspondence between the varying mass and a characteristic pressure dependence of a stimulated photon-photon scattering rate in a dilute gas surrounding a focused photon-beam spot. By observing a steep pressure dependence in the scattering rate, we can directly extract the characteristic feature of the chameleon mechanism. As a benchmark model of modified gravity consistent with the present cosmological observations, a reduced $F(R)$ gravity is introduced in the laboratory scale. We then demonstrate that the proposed method indeed enables a wide-ranging parameter scan of such a chameleon model with the varying mass around $(0.1\ensuremath{-}1)\text{ }\text{ }(\ensuremath{\mu}\mathrm{eV})$ by controlling pressure values.

Reconstructing cosmic evolution with a density parametrization

This study examines a dark energy cosmological model in the classical domain, where a generic scalar field is considered a dark energy source. Einstein’s field equations are solved in a model independent way, i.e. using a scheme of cosmological parametrization. A simple parametrization of the density parameter as a function of the cosmic scale factor is considered and investigated extensively. The results obtained are noteworthy as it shows a smooth transition from a decelerating to an accelerating phase in the recent past. Certain external datasets are used here to limit the model parameters involved in the functional form of the considered parametrization of energy density of the scalar filed. The updated Hubble datasets containing 57 data points, 1048 points of recently compiled Pantheon datasets, and also the Baryon Acoustic Oscillation (BAO) datasets are used here to determine the best-fitting model parameter values. The expressions of several significant cosmological parameters are represented as a function of redshift “[Formula: see text]” and illustrated visually for the best fit values of the model parameters to better comprehend cosmic evolution. The obtained model is also compared with the [Formula: see text]CDM model. Our model has a distinct behavior in future and shown a big crunch type collapse. The best fit values of the model parameters are also used to compute the current values of several physical and geometrical parameters, as well as phase transition redshift. To examine the nature of dark energy, certain cosmological tests and diagnostic analyses are done on the derived model.

Departure to pure de Sitter geometry based on Planck data

In this paper, we will obtain the basic parameters of primordial inflation such as power spectrum, scalar spectral index, and tensor-to-scalar ratio as a function of Hankel index [Formula: see text] for asymptotic-de Sitter inflation and then, based on the observational constraints on these parameters from Planck data, we obtain the allowable range for index [Formula: see text]. We will show that only the non-phantom phase is acceptable for quasi-de Sitter inflation at early universe. As a significant result, both of the primordial and late accelerating expansion are always in a quasi-vacuum phase (with [Formula: see text]) and it has never been in a pure-vacuum phase (with [Formula: see text]), i.e. cosmological constant. Therefore, based on our recent finding [E. Yusofi, M. Khanpour, B. Khanpour, M. A. Ramzanpour and M. Mohsenzadeh, Surface tension of cosmic voids as a possible source for dark energy, Mon. Not. R. Astron. Soc. 511 (2022) L82], we offer the surface tension of cosmic voids as a suitable alternative to the cosmological constant [Formula: see text], for accelerating universe.

Information Dark Energy Can Resolve the Hubble Tension and Is Falsifiable by Experiment.

We consider the role information energy can play as a source of dark energy. Firstly, we note that if stars and structure had not formed in the universe, elemental bits of information describing the attributes of particles would have exhibited properties similar to the cosmological constant. The Landauer equivalent energy of such elemental bits would be defined in form and value identical to the characteristic energy of the cosmological constant. However, with the formation of stars and structure, stellar heated gas and dust now provide the dominant contribution to information energy with the characteristics of a dynamic, transitional, dark energy. At low redshift, z < ~1.35, this dark energy emulates the cosmological constant with a near-constant energy density, w = −1.03 ± 0.05, and an energy total similar to the mc2 of the universe’s ∼1053 kg of baryons. At earlier times, z > ~1.35, information energy was phantom, differing from the cosmological constant, Λ, with a CPL parameter difference of ∆wo = −0.03 ± 0.05 and ∆wa = −0.79 ± 0.08, values sufficient to account for the H0 tension. Information dark energy agrees with most phenomena as well as Λ, while exhibiting characteristics that resolve many tensions and problems of ΛCDM: the cosmological constant problem; the cosmological coincidence problem; the H0 tension, and the σ8 tension. As this proposed dark energy source is not usually considered, we identify the expected signature in H(a) that will enable the role of information dark energy to be falsified by experimental observation.

Surface tension of cosmic voids as a possible source for dark energy

ABSTRACT The cosmological constant is estimated by considering the surface tension of supervoids in a void-dominated cosmic fluid by which we can get a possible source of dark energy. Looking at voids as bubbles, we define the concept of surface tension which is shown to have an almost constant value for supervoids that are enclosed by superclusters. The surface tensions of voids are computed by dimensional method for galaxies and superclusters with different values for each group. At large scale which vast voids are dominant the positive cosmological constants obtained of order (≃ +10−52 m−2), which are very close to those given by Planck.

The foundation of the hyperunified field theory II — Fundamental interaction and evolving universe

In part I of the foundation of the hyperunified field theory, we have shown the presence of entangled hyperqubit-spinor field as fundamental building block with appearance of Minkowski hyper-space–time as free-motion space–time and emergence of inhomogeneous hyperspin symmetry as fundamental symmetry. In this paper as part II, we demonstrate by following along gauge invariance principle and scaling invariance hypothesis that the inhomogeneous hyperspin gauge symmetry and scaling gauge symmetry govern fundamental interactions and reveal the nature of gravity and space–time. With the fiber bundle structure of biframe hyper-space–time and emergence of noncommutative geometry, we explore methodically the gauge-geometry duality and genesis of gravitational interaction in locally flat gravigauge hyper-space–time. A whole hyperunified field theory in 19-dimensional hyper-space–time is established to unify not only all discovered leptons and quarks into hyperunified qubit-spinor field but also all known basic forces into hyperunified interaction governed by inhomogeneous hyperspin gauge symmetry. We present a systematic investigation on the hyperunified field theory by deriving the dynamics of fundamental fields as basic laws of nature and conservation laws relative to basic symmetries and showing Higgs-like bosons and three families of lepton–quark states. We provide a detailed analysis on inflationary early universe with evolving graviscalar field and a discussion on scaling gauge field as dark matter candidate and [Formula: see text]-spin scalar field as source of dark energy.

Generalized holographic cosmology: low-redshift observational constraint

Four-dimensional cosmological models are studied on a boundary of a five-dimensional Anti-de Sitter (AdS5) black hole with AdS Reissner-Nordström and scalar charged Reissner-Nordström black hole solutions, where we call the former a “Hairless” black hole and the latter a “Hairy” black hole. To obtain the Friedmann-Robertson-Walker (FRW) spacetime metric on the boundary of the AdS5 black hole, we employ Eddington-Finkelstein (EF) coordinates to the bulk geometry. We then derive modified Friedmann equations on a boundary of the AdS5 black hole via AdS/CFT correspondence and discuss its cosmological implications. The late-time acceleration of the universe is investigated in our models. The contributions coming from the bulk side is treated as dark energy source, and we perform MCMC analyses using observational data. Compared to the ΛCDM model, our models contain additional free parameters; therefore, to make a fair comparison, we use the Akaike information criterion (AIC) and the Bayesian information criterion (BIC) to analyze our results. Our numerical analyses show that our models can explain the observational data as reliable as the ΛCDM model does for the current data.

Harnessing Dark Energy in Five-dimensional Brans-Dicke Universe

In trying to explain the present accelerated expansion of the universe in the light of a five-dimensional Brans-Dicke theory, it is found that the fifth dimension itself here acts as a source of dark energy. It may be taken as a curvature-induced form of dark energy, in one case of which it behaves similar to that form of dark energy arising out of the cosmological constant which is the most commonly accepted form of dark energy. It is also found that this new type of dark energy is free from big rip singularity and may be taken as a viable form of dark energy which can explain some of physical mysteries of the universe.

Observational constraint on the dark energy scalar field * *H. Li is Supported by the Sino US Cooperation Project of Ministry of Science and Technology (2016YFE0104700), Youth Innovation Promotion Association Project of CAS. The research is also Supported in part by NSFC (11653001) and Pilot B Project of CAS (XDB23020000)

In this paper, we study three scalar fields, namely the quintessence, phantom, and tachyon fields, to explore the source of dark energy via the Gaussian processes method from the background and perturbation growth rate data. The corresponding reconstructions suggest that the dark energy should be dynamical. Moreover, the quintom field, which is a combination of the quintessence and phantom fields, is powerfully favored by the reconstruction. The mean values indicate that the potential in the quintessence field is a double exponential function, whereas in the phantom field is a double Gaussian function. This reconstruction can provide an important reference for the scalar field study. The two types of data employed reveal that the tachyon field is disadvantageous for describing the cosmic acceleration.

H0 tension, swampland conjectures, and the epoch of fading dark matter

Motivated by the swampland dS conjecture, we consider a rolling scalar field as the source of dark energy. Furthermore, the swampland distance conjecture suggests that the rolling field will lead at late times to an exponentially light tower of states. Identifying this tower as residing in the dark sector suggests a natural coupling of the scalar field to the dark matter, leading to a continually reducing dark matter mass as the scalar field rolls in the recent cosmological epoch. The exponent in the distance conjecture, $\tilde{c}$, is expected to be an $\mathcal{O}(1)$ number. Interestingly, when we include the local measurement of $H_0$, our model prefers a non-zero value of the coupling $\tilde{c}$ with a significance of $2.8\sigma$ and a best-fit at $\tilde{c} \sim 0.3$. Modifying the recent evolution of the universe in this way improves the fit to data at the $2\sigma$ level compared to $\Lambda$CDM. This string-inspired model automatically reduces cosmological tensions in the $H_0$ measurement as well as $\sigma_8$.

Multiverse Model: External Universe(s) as Source of Dark Energy

The Lambda Cold Dark Matter (ΛCDM) model is currently the best model to describe the development of the Universe from the Big Bang to the present time. It is composed of six parameters, two of them, Dark Energy (DE) and CDM, with unknown physical explanations. DE, leading to accelerated expansion of the Universe, is considered a scalar field characterized by exerting its force by repulsive gravity. We examined whether DE can be explained as the warping of spacetime in our Universe by external universes as components of a Multiverse or, in other words, as the gravitational pull exerted by other universes. The acceleration, the resultant kinetic energy, Ekin, and the cosmological constant, Λ, were calculated for one to four external universes. The acceleration is approx. 10-11 m/s2, which is in agreement with observations. Its value is dependent upon the numbers and relative positions of external universes. DE density is approx. 10-29 kg/m3 and Λ is in the range of 10-38 s-2 and 10-55 m-2, respectively. Warping of spacetime by external universes as a physical explanation for DE seems feasible and warrants further considerations.

The Principle of Equivalence: Periastron Precession, Light Deflection, Binary Star Decay, Graviton Temperature, Dark Matter, Dark Energy and Galaxy Rotation Curves

The nature of the principle of equivalence is explored. The path of gravitons is analyzed in an accelerating system equivalent to a gravitating system. The finite speed of the graviton results in a delay of the gravitational interaction with a particle mass. From the aberration found in the path of the graviton we derive the standard expression for the advancement of the periastron of the orbit of the mass around a star. In a similar way, by analysing the aberrations of the graviton and light paths in an accelerating reference frame, the expression for the deflection of light by a massive body is obtained identically to the standard result. We also examine the binary star system and calculate the decay in its orbital period. The decay is attributed to the redshift of the graviton frequency relative to the accelerating system. Here too, we obtain good agreement with experimental measurements. Also, hypothesizing that gravitons behave like photons, we determine the temperature of the gravitons in a binary star system and form the Bose-Einstein distribution. Finally, we show how the redshift of gravitons may be the source of dark matter, dark energy and flat line spiral galaxy rotation curves.

Anisotropic solid dark energy

In this paper, we study a triad of inhomogeneous scalar fields, known as "solid", as a source of homogeneous but anisotropic dark energy. By using a dynamical system approach, we find that anisotropic accelerated solutions can be realized as attractor points for suitable choices of the parameters of the model. We complement the dynamical analysis with a numerical solution whose initial conditions are set in the deep radiation epoch. The model can give an account of a non-negligible spatial shear within the observational bounds nowadays, even when the later is set to zero at early times. However, we find that there is a particular region in the parameter space of the model in which the Universe isotropizes. The anisotropic attractors, the particular isotropic region, and a nearly constant equation of state of dark energy very close to $- 1$ are key features of this scenario. Following a similar approach, we also analyzed the full isotropic version of the model. We find that the solid can be characterized by a constant equation of state and thus being able to simulate the behavior of a cosmological constant.

A higher dimensional cosmological model for the search of dark energy source

With due consideration of reasonable cosmological assumptions within the limit of the present cosmological scenario, we have analyzed a spherically symmetric metric in 5D setting within the framework of Lyra manifold. The model universe is predicted to be a DE model, dominated by vacuum energy. The model represents an oscillating model, each cycle evolving with a big bang and ending at a big crunch, undergoing a series of bounces. The universe is isotropic and undergoes super-exponential expansion. The value of Hubble’s parameter is measured to be [Formula: see text] which is very close to [Formula: see text], the value estimated by the latest Planck 2018 result. A detailed discussion on the cosmological parameters obtained is also presented with graphs.

Phantom dark energy from scalar-torsion coupling

We show that a scalar field without a kinetic term in the Lagrangian density, coupled to the covariant divergence of the torsion vector in the Einstein–Cartan theory of gravity, becomes kinetic in its general-relativistic equivalent formulation. The resulting kinetic term is negative: such a scalar field could be a source of phantom dark energy.

Formula omitted]Gravity model behaving as a dark energy source

Within the limits of the present cosmological observations in f(R,T)gravity theory, we have analyzed a spherically symmetric space-time in 5D setting. The field equations have been carefully studied considering reasonable cosmological assumptions to obtain exact solutions. We have obtained an isotropic model universe undergoing super-exponential expansion. It is predicted that the model universe behaves like a dark energy (vacuum energy) model. In the present scenario, the model evolves with a slow and uniform change of shape. It is observed that the universe is close to or nearly flat. The model is free from an initial singularity and is predicted to approach the de-Sitter phase dominated by vacuum energy or cosmological constant in the finite-time future. A comprehensive discussion on the cosmological parameters obtained in view of the recent studies is presented in detail with graphs.

Gauss–Bonnet–Chern approach to the averaged Universe

The standard model of cosmology with postulated dark energy and dark matter sources may be considered as a fairly successful fitting model to observational data. However, this model leaves the question of the physical origin of these dark components open. Fully relativistic contributions that act like dark energy on large scales and like dark matter on smaller scales can be found through generalization of the standard model by spatially averaging the inhomogeneous Universe within general relativity. The spatially averaged 3 + 1 Einstein equations are effective balance equations that need a closure condition. Heading for closure we here explore topological constraints. Results are straightforwardly obtained for averaged 2 + 1 model universes. For the relevant 3 + 1 case, we employ a method based on the Gauss–Bonnet–Chern theorem generalized to Lorentzian spacetimes and implement a sandwich approach to obtain spatial average properties. The 3 + 1 topological approach supplies us with a new equation linking evolution of scalar invariants of the expansion tensor to the norm of the Weyl tensor. From this we derive general evolution equations for averaged scalar curvature and kinematical backreaction, and we discuss related evolution equations on this level of the hierarchy of averaged equations. We also discuss the relation between topological properties of cosmological manifolds and dynamical topology change, e.g. as resulting from the formation of black holes.

Dynamical analysis of cosmological models with non-Abelian gauge vector fields

In this paper we study some models where non-Abelian gauge vector fields endowed with a SU(2) group representation are the unique source of inflation and dark energy. These models were first introduced under the name of gaugeflation and gaugessence, respectively. Although several realizations of these models have been discussed, not all available parameters and initial conditions are known. In this work, we use a dynamical system approach to find the full parameter space of the massive version of each model. In particular, we found that the inclusion of the mass term increases the length of the inflationary period. Additionally, the mass term implies new behaviors for the equation of state of dark energy allowing to distinguish this from other prototypical models of accelerated expansion. We show that an axially symmetric gauge field can support an anisotropic accelerated expansion within the observational bounds.

Retraction Note: Emergent D-Instanton as a Source of Dark Energy

The author has retracted this article [1] because it significantly overlaps with a previously published article by Singh and Kar [2].