Dark Energy Density Research Articles

The Integrated Sachs Wolfe effect: unWISE and Planck constraints on dynamical dark energy

CMB photons redshift and blueshiftas they move through gravitational potentials Φwhile propagating across the Universe. If the potential is not constant in time, the photons will pick up a net redshift or blueshift, known as the Integrated Sachs-Wolfe (ISW) effect.In the z ≪ 1000 universe, Φ̇ is nonzero on large scales when the Universe transitions from matter to dark energy domination. This effect is only detectable in cross-correlation with large-scale structure at z ∼ 1. In this paper we present a 3.2σ detection of the ISW effect using cross-correlations between unWISE infrared galaxies and Planck CMB temperature maps. We use 3 tomographic galaxy samples spanning 0 < z < 2, allowing us to fully probe the dark energy domination era and the transition into matter domination. This measurement is consistent with ΛCDM (AISW = 0.96 ± 0.30).We study constraints on a particular class of dynamical dark energy models(where the dark energy equation of state is different in matter and dark energy domination),finding that unWISE-ISW improves constraintsfrom type Ia supernovae due to improved constraints on the time evolution of dark energy. When combining with BAO measurements, we obtain the tightest constraints on specific dynamical dark energy models. In the context of a phenomenological model for freezing quintessence, the Mocker model, we constrain the dark energy density within 10% at z < 2 using ISW, BAO and supernovae. Moreover, the ISW measurement itself provides an important independent check when relaxing assumptions about the theory of gravity, as it is sensitive to the gravitational potential rather than the expansion history.

Cosmological implications of the full shape of anisotropic clustering measurements in BOSS and eBOSS

ABSTRACTWe present the analysis of the full shape of anisotropic clustering measurement from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) quasar sample together with the combined galaxy sample from the Baryon Oscillation Spectroscopic Survey (BOSS), re-analysed using an updated recipe for the non-linear matter power spectrum and the non-local bias parameters. We obtain constraints for flat Lambda cold dark matter cosmologies, focusing on the cosmological parameters that are independent of the Hubble parameter h. Our recovered value for the Root Mean Square (RMS) linear perturbation theory variance as measured on the scale of $12\, {\rm Mpc}$ is σ12 = 0.805 ± 0.049, while using the traditional reference scale of $8\, h^{-1}\, {\rm Mpc}$ gives σ8 = 0.815 ± 0.044. We quantify the agreement between our measurements and the latest cosmic microwave background data from Planck using the suspiciousness metric, and find them to be consistent within 0.64 ± 0.03σ. Combining our clustering constraints with the 3 × 2pt data sample from the Dark Energy Survey Year 1 release slightly degrades this agreement to the level of 1.54 ± 0.08σ, while still showing an overall consistency with Planck. We furthermore study the effect of imposing a Planck – like prior on the parameters that define the shape of the linear matter power spectrum, and find significantly tighter constraints on the parameters that control the evolution of density fluctuations. In particular, the combination of low-redshift data sets prefers a value of the physical dark energy density ωDE = 0.335 ± 0.011, which is 1.7σ higher than the one preferred by Planck.

Holographic Dark Energy in Higher-Dimensions

In this work It is discussed the behaviour of holographic dark energy density in higher dimension. Exact solutions of Einstein's field equation have been obtained by assuming a particular relation between two metric coefficients. It is also observed that for a certain condition Universe is accelerating and holographic dark energy density decreases during evolution of the Universe. Some physical parameters are also discussed. 1 − . For solution of the Einstein's field equation one can seek by introducing by some kinematical ansatz that are consistent with the observation kinematics of the universe and may investigate the dynamics of the fluid as a possible candidate of the DE. Astronomical observations indicate that our universe currently consists of approximately % 70 dark energy, % 25 dark matter and

How to Accomplish Inflation and a Constant Dark Energy Density

It is commonly assumed that the Lagrangian of multi-field theories of gravity contains the sum of kinetic terms of scalar fields. However, we propose here the Lagrangian contains not the sum but the quotient of kinetic terms. With this novel change, we find the inflationary universe can be acquired with two scalars without the slow-roll approximation. On the other hand, a constant dark energy density can also be achieved with two scalars while without the need of Einstein cosmological constant.

Wormholes in a viscous universe

We study the static and spherically symmetric wormhole spacetime configurations at present time in a viscous universe. Considering three classes of viscous models, i.e., bulk viscosity as a function of Hubble constant $H_0$, present cosmic temperature $T_0$ and dark energy density $\rho_0$, respectively, we obtain several wormhole solutions. Through the analysis for the anisotropic solutions, we conclude that, to some extent, these three classes of viscous models have very high degeneracy with each other, and deviate slightly from the ideal fluid consequence. Subsequently, without the loss of generality, to investigate the traversabilities, energy conditions and stability for the wormhole solution, we study the wormhole solution of the constant redshift function of the viscous $\omega$CDM model with a constant bulk viscosity coefficient. We obtain the following conclusions: the value of traversal velocity decreases for decreasing bulk viscosity, and the traversal velocity for a traveler depends on not only the wormhole geometry but also the effects of cosmological background evolution; the null energy condition will be violated more clearly when the bulk viscosity or the cosmic expansion velocity decreases; for the case of a positive surface energy density, the range of the junction radius decreases and the values of the parameter $\lambda$ are further restricted when the throat radius of the wormhole $r_0/M$ increases, bulk viscosity coefficient $\zeta_0$ decreases and present-day Hubble parameter $H_0$ decreases, respectively; for the case of a negative surface energy density, by increasing $r_0/M$, decreasing $\zeta_0$ and increasing $H_0$, the values of the parameter $\lambda$ are less restricted, one may conclude that the total stability region increases, and the range of the junction radius increases, increases and decreases, respectively. \end{abstract}

Late time cosmology in -gravity with interacting fluids

Cosmological models are obtained in a f(R) modified gravity with a coupled Gauss–Bonnet (GB) terms in the gravitational action. The dynamical role of the GB terms is explored with a coupled dilaton field in two different cases (I) where γ, λ and δ are arbitrary constants and (II) f(R) = R and estimate the constraints on the model parameters. In the first case we choose GB terms coupled with a free scalar field in the presence of interacting fluid and in the second case GB terms coupled with scalar field in a self interacting potential to compare the observed Universe. The evolutionary scenario of the Universe is obtained adopting a numerical technique as the field equations are highly non-linear. Defining a new density parameter Ω H , a ratio of the dark energy (DE) density to the present energy density of the non-relativistic matter, we look for a late accelerating Universe. The state finder parameters Ω H , deceleration parameter (q), jerk parameter (j) are plotted. It is noted that a non-singular Universe with oscillating cosmological parameters for a given strength of interactions is admitted in model-I. The gravitational coupling constant λ is playing an important role. The Lagrangian density of f(R) is found to dominate over the GB terms when oscillating phase of DE arises. In model-II, we do not find oscillation of the cosmological parameters as the Universe evolves. In the presence of interaction the energy from radiation sector of matter cannot flow to the other two sectors of fluid. The range of values of the strengths of interaction of the fluids are estimated for a stable Universe assuming the primordial gravitational wave speed equal to unity.

Bound-state formation, dissociation and decays of darkonium with potential non-relativistic Yukawa theory for scalar and pseudoscalar mediators

Dark matter models with light mediators featuring sizable interactions among dark particles enjoy an increasing attention in the model building community due to the elegance with which they can potentially explain the scaling relations governing galactic halos and clusters of galaxies. In the present work we continue our study of such models using non-relativistic and potential non-relativistic effective field theories (NREFTs and pNREFTs) and explore the properties of a Yukawa-type model with scalar and pseudoscalar interactions between a low-energetic scalar mediator and heavy dark matter fermions. In particular, we make first steps towards the formulation of such theories at finite temperature by providing the thermal bound-state formation rate and the thermal break-up of bound states from the self-energies of the dark-pair fields, that interact with the thermal environment. We estimate numerically bound-state effects on the dark matter energy density, that provide up to a 35% correction depending on the relative size of the model couplings.

Can dark matter\u2013dark energy interaction alleviate the cosmic coincidence problem?

In this paper we study a model of interacting dark energy–dark matter where the ratio between these components is not constant, changing from early to late times in such a way that the model can solve or alleviate the cosmic coincidence problem (CP). The interaction arises from an assumed relation of the form rho _xpropto rho _d^alpha , where rho _x and rho _d are the energy densities of dark energy and dark matter components, respectively, and alpha is a free parameter. For a dark energy equation of state parameter w=-1 we found that, if alpha =0, the standard Lambda CDM model is recovered, where the coincidence problem is unsolved. For 0<alpha <1, the CP would be alleviated and for alpha sim 1, the CP would be solved. The dark energy component is analyzed with both w=-1 and wne -1. Using Supernovae type Ia and Hubble parameter data constraints, in the case w=-1 we find alpha =0.109^{+0.062}_{-0.072} at 68% C.L., and the CP is alleviated. For wne -1, a degeneracy arises on the w–alpha plane. In order to break such degeneracy we add cosmic microwave background distance priors and baryonic acoustic oscillations data to the constraints, yielding alpha =-0.075pm 0.046 at 68% C.L.. In this case we find that the CP is not alleviated even for 2sigma interval for alpha . Furthermore, this last model is discarded against flat Lambda CDM according to BIC analysis.

Interacting Tsallis agegraphic dark energy in DGP braneworld cosmology

The purpose of this paper is to study the Tsallis agegraphic dark energy with an interaction term between dark energy and dark matter in the DGP brane-world scenario. For this, we assume some initial conditions to obtain the dark energy density, deceleration, dark energy EoS, and total EoS parameters. Then, we analyze the statefinder parameters, $\omega'{}_{DE}-\omega_{DE}$ plots, and classical stability features of the model. The results state that the deceleration parameter provides the phase transition from decelerated to accelerated phase. The $\omega_{DE}$ graphs show the phantom behavior, while the $\omega_{tot}$ exhibits the quintessence and phantom during the evolution of the Universe. Following the graphs, the Statefinder analysis shows the quintessence behavior of the model for the past and present. However, it tends to the $\Lambda CDM$ in the following era. The $\omega'{}_{DE}-\omega_{DE}$ plot indicates the thawing or freezing area depending on the type of era and different values of $b^{2}$, $\delta$, and $m$. By the square of the sound speed, we see the model is stable in the past, stable or unstable at the current time, and unstable in the future for selected values of $b^{2}$, $\delta$, and $m$. To test the model, we use the recent Hubble data. We also employ Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) to compare the model with the $\Lambda CDM$ as the reference model. In addition, we test the model using the $H-z$ plot, and we see a turning point in the future time. The results from the best fit values for the $\omega_{tot}$ plot emphasize that the Universe is in the quintessence region in the current time. It will enter the phantom phase, and then it will approach the $\Lambda$ state in the future. But, the $\omega_{DE}$ always stays on the phantom region. The model is unstable in the present and progressive era.

New Tsallis holographic dark energy

Tsallis entropy is a generalization of the Boltzmann–Gibbs entropy in statistical theory which uses a parameter delta to measure the deviation from the standard scenario quantitatively. Using concepts of Tsallis entropy and future event horizon, we construct a new Tsallis holographic dark energy model. The parameters c and delta will be used to characterize various aspects of the model. Analytical expressions for various cosmological parameters such as the differential equation describing the evolution of the effective dark energy density parameter, the equation of state parameter and the deceleration parameter are obtained. The equation of state parameter for the current model exhibits the pure quintessence behaviour for c>1, quintom behaviour for c<1 whereas the Lambda CDM model is recovered for c=1. To analyze the thermal history of the universe, we obtained the expression for the deceleration parameter and found that for z approx 0.6, the phase transits from deceleration to acceleration.

Late-time Cosmology of scalar field assisted f(𝒢) gravity

In this work, we present the late-time behaviour of the universe in the context of Einstein–Gauss–Bonnet gravitational theory. The theory involves a scalar field, which represents low-effective quantum corrections, assisted by a function [Formula: see text] solely depending from the Gauss–Bonnet topological invariant [Formula: see text]. It is considered that the dark energy serves as the impact of all geometric terms, which are included in the gravitational action and the density of dark energy acts as a time-dependent cosmological constant evolving with an infinitesimal rate and driving the universe into an accelerating expansion. We examine two cosmological models of interest. The first involves a canonical scalar field in the presence of a scalar potential while the second, involves a scalar field which belongs to a generalized class of theories [Formula: see text] namely the k-essence scalar field in the absence of scalar potential. As it is proved, the aforementioned models are in consistency with the latest Planck data and in relatively good agreement with the [Formula: see text]CDM standard cosmological model. The absence of dark energy oscillations at the early stages of matter-dominated era, which appear in alternative scenarios of cosmological dynamics in the context of modified [Formula: see text] gravitational theories, indicates an advantage of the theory for the interpretation of late-time phenomenology.

Interacting Tsallis holographic dark energy and tachyon scalar field dark energy model in Bianchi type-II Universe

In this work, we study the interaction between the dark matter (DM) component and the dark energy (DE) component using the Tsallis holographic dark energy (THDE) density expression for a Bianchi type-II space–time within the framework of general relativity (GR). To obtain the exact solutions of Einstein’s field equations, we use two constraints: (i) the expansion scalar [Formula: see text] of the Universe is proportional to the component [Formula: see text] of the shear tensor [Formula: see text], i.e. [Formula: see text] and (ii) we assume that the scale factor follows the Hybrid Expansion Law (HEL). We have discussed some geometrical and physical parameters of our model such as the deceleration parameter (DP) and the equation of state (EoS) parameter. In these parameters, we plot their behavior in terms of redshift [Formula: see text]. We observe that the DP evolves from the early decelerating phase to the current accelerating phase with a current value consistent with the observation data. The EoS parameter evolves from a state of a stiff-matter fluid-dominated era [Formula: see text] for high redshift [Formula: see text] to a [Formula: see text]CDM era [Formula: see text] in the later times. Also, we have established a correspondence between the THDE model and the tachyon scalar field dark energy model. We have reconstructed the potential and the tachyon scalar field, which describes the current accelerated expansion of the Universe. Finally, using 51 values of observed Hubble measurement and the technique [Formula: see text]-test, we found the best fit value for the model parameters [Formula: see text], [Formula: see text] and [Formula: see text] (current value of the Hubble parameter). These results are consistent with the new measurements of [Formula: see text].37

The cosmic microwave background and mass power spectrum profiles for a novel and efficient model of dark energy

&#x0D; &#x0D; &#x0D; In a previous work [1] it was shown that by considering the quantum nature of the gravitational field mediator, it is possible to introduce the momentum energy of the graviton into the Einstein equations as an effective cosmological constant. The Compton Mass Dark Energy (CMaDE) model proposes that this momentum can be interpreted as dark energy, with a Compton wavelength given by the size of the observable universe RH, implying that the dark energy varies depending on this size. The main result of this previous work is the existence of an effective cosmological constant Λ = 2π2/λ2 that varies very slowly, being λ = (c/H0)RH the graviton Compton wavelength. In the present work we use that the dark energy density rate is given by ΩΛ = 2π2/3/RH2 , it only has the curvature Ωk as a free constant and depends exclusively on the radiation rate Ωr. Using Ωr = 9.54×10−5, the theoretical prediction for a flat universe of the dark energy rate is ΩΛ = 0.6922. We perform a general study for a non-flat universe, using the Planck data and a modified version of the CLASS code we find an excellent concordance with the Cosmic Microwave Background and Mass Power Spectrum profiles, provided that the Hubble parameter today is H0 = 72.6 km/s/Mpc for an universe with curvature Ωk = −0.003. We conclude that the CMaDE model provides a natural explanation for the accelerated expansion and the coincidence problem of the universe.&#x0D; &#x0D; &#x0D;

Cosmological Constant (Λ); Fine Structure Constant (α) Two Results of Friedmann-Planck-Schwarzschild Models on Vacuum and Elementary Particles

This article presents in a synthetic way three articles published in JHEPGC ([1], [2]), EJAS [12] and develops some aspects. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;Two hypotheses are studied. In the first one, the vacuum is endowed with a quantum structure in which the vacuum particles are Friedmann-Planck micro-universes. For this, the article introduces a quantization of a closed Friedmann universe, then a quantization of the photon spheres filling this universe. This approach gives a numerical value consistent with cosmological measurements for the current dark energy density and the cosmological constant of our Universe. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Next, the second hypothesis takes the content of a model published in Physics Essays in 2013 [3], assuming that elementary particles are Schwarzschild photon spheres; these could be derived from the Friedmann photon spheres composing the vacuum particles. It is further recalled that the model presents a unified structure of elementary particles and allows us to calculate the value of the elementary electric charge and the fine structure constant. The masses of some elementary particles are calculated in a complementary model. Finally this article summarizes a model of closed cyclic universe described in reference [2].This universe begins as one alone Friedmann-Planck micro-universe, then multiplying to constitute our Universe. Further a Big-Rip suddenly transforms it into a Friedmann-Planck macro-universe on a much larger scale. This one is the beginning of a new Big-Bang with the same evolution as ours. This process can be assumed to explain the existence of the initial FP micro-universe: it would be the result of a Big-Rip at the end of the evolution of a much smaller scale universe.

Cosmological Constraints on Nonflat Exponential f(R) Gravity

Abstract We explore the viable f(R) gravity models in FLRW backgrounds with a free spatial curvature parameter Ω K . In our numerical calculation, we concentrate on the exponential f(R) model of f ( R ) = R − λ R ch ( 1 − exp ( − R / R ch ) ) , where R ch is the characteristic curvature scale, which is independent of Ω K , and λ corresponds to the model parameter, while R ch λ = 2Λ with Λ the cosmological constant. In particular, we study the evolutions of the dark energy density and equation of state for exponential f(R) gravity in open, flat, and closed universes, and compare with those for ΛCDM. From the current observational data, we find that λ − 1 = 0.42927 − 0.32927 + 0.39921 at 68% C.L. and Ω K = − 0.00050 − 0.00414 + 0.00420 at 95% C.L. in the exponential f(R) model. By using the Akaike Information Criterion, Bayesian Information Criterion, and Deviance Information Criterion, we conclude that there is no strong preference between the exponential f(R) gravity and ΛCDM models in the nonflat universe.

Effect of evolving physical constants on type Ia supernova luminosity

ABSTRACT Type Ia supernovae, SNeIa, are used as standard candles in cosmology to determine the distances of the galaxies harbouring them. We show that the luminosity of an SNIa depends on its distance from us when physical constants (the speed of light c, the gravitational constant G, and the Planck constant h) are permitted to evolve. It is because the Chandrasekhar mass of the white dwarf that explodes to create SNIa depends on the values of the constants at the epoch the SNIa is formed. We show that the SNeIa luminosities could be about four times higher in the past than they are now. Thus, the luminosity distance estimation of the earliest SNeIa could be off by up to a factor of 2. Cosmological parameters, determined with this correction applied to the redshift versus distance modulus data base (Pantheon SNeIa), are not very different from those from the standard ΛCDM model without this correction, except for the dark-energy density and the curvature energy density; the latter increases at the cost of the former. Variations of the constants are given by $\dot{G}/G = \ 3.90 \ ( { \pm 0.04} ) \times {10^{ - 10}}\ {\rm y{r^{ - 1}}}$and $\dot{c}/c = \dot{h}/h\ = \ 1.30\ ( { \pm 0.01} ) \times {10^{ - 10}}\ {\rm y{r^{ - 1}}}$ at present. These variations are valid only when $G,\ c,\ $and$\ h$ are permitted to vary concurrently rather than individually.

Dark energy with oscillatory tracking potential: observational constraints and perturbative effects

ABSTRACT The cosmological models exhibiting tracker properties have great significance in the context of dark energy as they can reach the present value of dark energy density from a wide range of initial conditions, thereby alleviating both the fine-tuning and the cosmic coincidence problem. The α-attractors, which are originally discussed in the context of inflation, can exhibit the properties of dark energy as they can behave like cosmological trackers at early times and show the late-time behaviour of a cosmological constant. In this paper, we study the oscillatory tracker model (OTM), which belongs to the family of α-attractor dark energy models. Using the current observational data sets like cosmic microwave background (CMB), baryon acoustic oscillation, and type 1a supernova data (Pantheon compilation), we constrain the parameters of the model and estimate both the mean and best-fitting values. Although the OTM contains a larger set of parameters than the usual lambda cold dark matter (LCDM) model, the common set of parameters of both agree within $1\, \sigma$ error limits. Our observations using both high redshift and low redshift data support Hubble parameter value H0 = 67.4 Km s−1 Mpc−1. We study the effect of the OTM on the CMB temperature and polarization power spectra, matter power spectrum and fσ8. Our analysis of the CMB power spectrum and matter power spectrum suggests that the oscillatory tracker dark energy model has noticeable differences from usual LCDM predictions. Yet, in most cases, the agreement is very close.

Astrophysical Naturalness

I suggest that stars introduce mass and density scales that lead to “naturalness” in the Universe. Namely, two ratios of order unity. 1) The combination of the stellar mass scale, M*(c, ℏ, G, mp, me, e, …), with the Planck mass, MPl, and the Chandrasekhar mass leads to a ratio of order unity that reads NPl*≡MPl/(M*mp2)1/3≃0.15−3, where mp is the proton mass. 2) A system with a dynamical time equals to the nuclear life times of stars, τnuc*, has a density of ρD*(c,ℏ,G,mp,me,e,…)≡(Gτnuc*2)−1. The ratio of the dark energy density to this density is Nλ* = ρΛ/ρD* ≈ 10−7−105. Although the range is large, it is critically much smaller than the 123 orders of magnitude usually referred to when ρΛ is compered to the Planck density. In the pure fundamental particles domain there is no naturalness; either naturalness does not exist or there is a need for a new physics or new particles. The “Astrophysical Naturalness” offers a third possibility: stars introduce the combinations of, or relations among, known fundamental quantities that lead to naturalness.

Bianchi-I anisotropic universe with Barrow holographic dark energy

In this paper, we study Bianchi type-I universe in the presence of Barrow holographic dark energy and matter. Anisotropic cosmological model is explored here using the recently proposed holographic principle by Barrow where the standard Bekenstein–Hawking entropy is a special case. The holographic dark energy is employed to investigate the evolution of matter density and the dark energy density in an anisotropic Bianchi-I universe. The equation of state parameter of the dark energy is found to lie in the quintessence or in the phantom regime at the present epoch depending on the value of the new exponent and anisotropy in the universe. We found that an anisotropic universe with higher anisotropy transits to a late accelerating phase before a universe with lower anisotropy. It is also observed that the new exponent plays an important role to identify the nature of the universe.

Sterile neutrino dark matter in a U(1) extension of the standard model

We explore the parameter space of a U(1) extension of the standard model — also called the super-weak model — from the point of view of explaining the observed dark matter energy density in the Universe. The new particle spectrum contains a complex scalar singlet and three right-handed neutrinos, among which the lightest one is the dark matter candidate. We explore both freeze-in and freeze-out mechanisms of dark matter production. In both cases, we find regions in the plane of the super-weak coupling vs. the mass of the new gauge boson that are not excluded by current experimental constraints. These regions are distinct and the one for freeze-out will be explored in searches for neutral gauge boson in the near future.