Dark Energy Domination Research Articles

Quintessence scalar field and cosmological constant: dynamics of a multi-component dark energy model

This study explores the dynamics and phase-space behavior of a multi-component dark energy model, where the dark sector consists of a minimally coupled canonical scalar field and the cosmological constant, using a dynamical system analysis setup for various types of potential for which a general parameterization of the scalar field potentials has been considered. Several fixed points with different cosmological behaviors have been identified. A detailed stability analysis has been done and possible late-time attractors have been found. For this multi-component dark energy model, the late-time attractors are either fully dominated by the cosmological constant or represent a scenario where a combination of the scalar field and the cosmological constant dominates the universe. In this type of model, there is a possibility that the scalar field can become dynamical quite early compared to the standard era of dark energy domination. However, our analysis indicates that this early time contribution of the scalar field occurs deep in the matter-dominated era, not before the recombination era.

Constraints on dark matter mass in an F(R) gravity model with an additional R2 correction term

Abstract The dominance of dark matter and dark energy presents one of the most significant challenges in cosmology. The chameleon mechanism in F(R) gravity offers a potential solution to this issue. However, many F(R) models encounter a problem known as the singularity problem, where the scalaron mass becomes too heavy to function as dark matter. This study aims to address the singularity problem within the Gogoi-Goswami F(R) model by incorporating an additional R 2 correction term. Assuming the scalaron functions as chameleonic dark matter, its mass must satisfy constraints across various scales, including the electroweak transition phase and galactic structures. By adopting a hierarchical scale with R 0 ≪ R c < m ¯ 2 , where R 0 is the Ricci scalar at late-time de Sitter space and m ¯ represents the inflaton mass scale in Starobinsky's model, and assuming R c ≃ 1 GeV2, the mass constraints during the electroweak transition can be satisfied with α ≃ 1.05. Nevertheless, meeting the required mass constraints on a galactic scale remains a challenge. Alternatively, if R c is considered relevant only in the current universe, such that R 0 ≪ R c ≪ m ¯ 2 , these dark matter mass constraints can be more easily met. For example, setting R c ≃ m φ 2 ( gal ) ≃ ( 1 0 − 32 ) 2 GeV 2 effectively satisfies these constraints.

Observational constraints on the emergent universe with non-linear equation of state and interacting fluids

We investigate a flat emergent universe (EU) with a nonlinear equation of state equivalent to three different composition of fluids. In the EU initially, the evolution of the universe began with no interaction but as time evolves an interaction sets in among the three fluids leading to the observed universe. The characteristic of an EU is that it is a singularity free universe that evolves with all the basic features of the early evolution. For a given nonlinear equation of state parameter, it permits a universe with three different fluids, we get a universe with dark energy, cosmic string, and radiation domination to begin with which at a later epoch transits into a universe with three different fluids with matter domination (baryonic as well as dark matter) and dark energy for a given interaction strength among the cosmic fluids. The evolution of the universe is probed with exponential interactions to obtain a universe with late acceleration. The model parameters are constrained using the observed Hubble data and Type Ia Supernova (SnIa) data from the Pantheon data set. An interacting EU transforms to a matter dominated phase with DE accommodating the present universe satisfactorily. The stability of the cosmological model is also discussed.

Is cosmic dynamics self-regulating?

In this paper, we discuss a cosmological model for a universe with self-regulating features. We set up the theoretical framework for the model and determine the time evolution of the scale-factor [Formula: see text]. It is shown that such a universe repeatedly goes through alternate periods of matter and dark energy domination. The resulting dynamics oscillates about the would-be ideal time-linear or coasting path, with monotonic expansion. When compared to dynamics of the observed physical universe, the model recovers the observationally established evolutionary features of the latter, from the big bang to the current acceleration, and farther. It suggests a universe that initially emerges from a nonsingular state, associated with a non-exponential acceleration, and which acceleration it exits naturally with matter–energy generation. The model does not have a horizon problem or a flatness problem. It reproduces the observed current values of standard cosmic parameters, including the age [Formula: see text], the current Hubble parameter [Formula: see text] and dark energy [Formula: see text] and matter [Formula: see text] density parameters. The model is falsifiable. It makes predictions that can be tested, as suggested. Finally, we discuss the dimensionless age [Formula: see text] paradox as an example of the model’s ability to address standing puzzles. The findings suggest that dynamics of the physical universe may be self-regulating and predictable.

Effective dark energy through spin-gravity coupling

We investigate cosmological scenarios with spin-gravity coupling. In particular, due to the spin of the baryonic and dark matter particles and its coupling to gravity, they probe an effective spin-dependent metric, which can be calculated semi-classically in the Mathisson-Papapetrou-Tulczyjew-Dixon formalism. Hence, the usual field equations give rise to modified Friedmann equations, in which the extra terms can be identified as an effective dark-energy sector. Additionally, we obtain an effective interaction between the matter and dark-energy sectors. In the case where the spin-gravity coupling switches off, we recover standard ΛCDM cosmology. We perform a dynamical system analysis and we find a matter-dominated point that can describe the matter era, and a stable late-time solution corresponding to acceleration and dark-energy domination. For small values of the spin coupling parameter, deviations from ΛCDM concordance scenario are small, however for larger values they can be brought to the desired amount, leading to different dark-energy equation-of-state parameter behavior, as well as to different transition redshift from acceleration to deceleration. Finally, we confront the model predictions with Hubble function data.

Non-interacting Barrow-holographic dark energy in FRW-universe with quintessence behavior

In order to analyze Barrow holographic dark energy (BHDE) in a flat FRW universe, the time-dependent scale factor [Formula: see text] is employed. The Hubble horizon as the IR-cutoff is taken to investigate the cosmic consequences. We demonstrate the cosmic transition using the deceleration parameter and equation of state parameter. The characteristics of deceleration parameter for this model correspond well with the latest findings. The equation of state parameter behaves well and does not cross the phantom line. Depending on the values of Barrow exponent ([Formula: see text]), our model is entirely quintessence and is eventually moving towards [Formula: see text] model. We plotted the pressure diagram with various Barrow exponent ([Formula: see text]) values to demonstrate dark energy dominance. The scalar field and potential that explain the universe’s accelerating expansion are also reconstructed.

Constraints on late time violations of the equivalence principle in the dark sector

If dark energy is dynamical due to the evolution of a scalar field, then in general it is expected that the scalar is coupled to matter. While couplings to the standard model particles are highly constrained by local experiments, bounds on couplings to dark matter (DM) are only obtained from cosmological observations and they are consequently weaker. It has recently been pointed out that the coupling itself can become non-zero only at the time of dark energy domination, due to the evolution of dark energy itself, leading to a violation of the equivalence principle (EP) in the dark sector at late times. In this paper we study a specific model and show that such late-time violations of the EP in the DM sector are not strongly constrained by the evolution of the cosmological background and by observables in the linear regime (e.g. from the cosmic microwave background radiation), although the model is not preferred over ΛCDM. A study of perturbations in non-linear regime is necessary to constrain late-time violations of the equivalence principle much more strongly.

The preliminary statistical analysis of LAMOST DR9 low resolution quasi-stellar objects

Based on more than 10 years of large-scale spectral sky survey, LAMOST DR9 v1.0 low resolution catalog has released 76167 data of QSOs. We adopt 48704 QSOs with redshift Z from 0.0 to 6.0, the error of redshift from 0.0 to 0.06, and the galactic latitude |b|>30° to do a research work. There are 95.36% of QSOs with the error of redshift less than or equal to 0.025. Therefore, the Z values are very reliable with small errors. Some statistical figures about Z are drawn and preliminarily analyzed. The distribution of QSOs with Z in different directions shows that universe is spatially isotropic in large-scale structure. The QSOs with high Z values and low Z values correspond to the decelerating and accelerating expansion of the universe respectively, the epoch of the matter dominance and the dark energy dominance respectively. In the epoch of matter dominance, the number density of QSOs in the statistical figures is more than that in the epoch of dark energy dominance and the gravity can slow the expansion. The large-scale spectral sky survey is helpful for us to better understand the past, present and future of the universe.

Gravity of Negative Mass: Some Subtle Aspects and Implications

The gravitational interaction has mass of only one sign as the source that is conventionally taken to be positive. The existence of negative mass is not precluded in either Newtonian gravity or general relativity. Negative masses have been invoked in many recent papers to understand the dominance of repulsive dark energy that is accelerating the universe. Here we discuss the various gravitating properties of negative mass particles and their implications for black holes, cosmology, and fundamental physics. Inconsistencies in the earlier works are also discussed. We study the possibility of such negative mass particles accounting for the accelerated expansion of the universe. We set constraints on the density of these negative mass particles based on astrophysical observations.

-gravity in the context of dark energy with power law expansion and energy conditions* *G.M. and A.P. acknowledge the DSTB, Government of West Bengal, India for financial support through the Grants No.: 322(Sanc.)/ST/P/S&T/16G-3/2018 dated 06.03.2019. S.R. is thankful to the authority of IUCAA, Pune for providing Visiting Associateship under which a part of this work has been done

The objective of this work is to generate a general formalism of gravity in the context of dark energy under the framework of K-essence emergent geometry with the Dirac-Born-Infeld (DBI) variety of action, where is the familiar Ricci scalar, is the DBI type non-canonical Lagrangian with , and ϕ is the K-essence scalar field. The emergent gravity metric () and the well known gravitational metric () are not conformally equivalent. We have constructed a modified field equation using the metric formalism in -gravity incorporating the corresponding Friedmann equations into the framework of the background gravitational metric, which is of Friedmann-Lemaître-Robertson-Walker (FLRW) type. The solution of the modified Friedmann equations have been deduced for the specific choice of , which is of Starobinsky-type, using the power law expansion method. The consistency of the model with the accelerating phase of the universe has been shown when we restrict ourselves to consider the value of the dark energy density as , which indicates that the present universe is dark-energy dominated. Graphical plots for the energy density (ρ), pressure (p), and equation of state parameter () with respect to (w.r.t.) time (t) based on parametric values are interestingly consistent with the dark energy domination theory, and hence the accelerating features. We also highlight the corresponding energy conditions and constraints of the theory with a basic example.

Palatini R 2 quintessential inflation

We construct a model of quintessential inflation in Palatini R 2 gravity employing a scalar field with a simple exponential potential and coupled to gravity with a running non-minimal coupling. At early times, the field acts as the inflaton, while later on it becomes the current dark energy. Combining the scalar sector with an ideal fluid, we study the cosmological evolution of the model from inflation all the way to dark energy domination. We interpret the results in the Einstein frame, where a coupling emerges between the fluid and the field, feeding energy from the former to the latter during the matter-dominated era. We perform a numerical scan over the parameter space and find points that align with observations for both the inflationary CMB data and the late-time behaviour. The final dark energy density emerges from an interplay between the model parameters, without requiring the extreme fine-tuning of the cosmological constant in ΛCDM.

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.

Primordial gravitational waves spectrum in the interacting Bose–Einstein gas model

We study the evolution and power spectrum of primordial gravitational waves in the interactive Bose-Einstein gas model for dark energy, relevant, as it addresses the coincidence problem. The model is applied in the radiation, matter and dark-energy domination stages. The model introduces a scale factor associated to the radiation-matter transition which influences the gravitational spectrum. We focus on the impact of the free parameters on both the gravitational waves amplitude and its power-spectrum slope. For sets of parameters fitting Hubble's law, we show that the model's parameter for today's dark-matter energy density has a noticeable impact on such waves, while the others produce an indistinguishable effect. The feasibility of detecting such waves under present and future measurements is discussed.

Reconstruction of the neutrino mass as a function of redshift

We reconstruct the neutrino mass as a function of redshift, $z$, from current cosmological data using both standard binned priors and linear spline priors with variable knots. Using cosmic microwave background temperature, polarization and lensing data, in combination with distance measurements from baryonic acoustic oscillations and supernovae, we find that the neutrino mass is consistent with $\ensuremath{\sum}{m}_{\ensuremath{\nu}}(z)=\mathrm{const}$. We obtain a larger bound on the neutrino mass at low redshifts coinciding with the onset of dark energy domination, $\ensuremath{\sum}{m}_{\ensuremath{\nu}}(z=0)&lt;1.46\text{ }\text{ }\mathrm{eV}$ (95% CL). This result can be explained either by the well-known degeneracy between $\ensuremath{\sum}{m}_{\ensuremath{\nu}}$ and ${\mathrm{\ensuremath{\Omega}}}_{\mathrm{\ensuremath{\Lambda}}}$ at low redshifts, or by models in which neutrino masses are generated very late in the Universe. We finally convert our results into cosmological limits for models with nonrelativistic neutrino decay and find $\ensuremath{\sum}{m}_{\ensuremath{\nu}}&lt;0.21\text{ }\text{ }\mathrm{eV}$ (95% CL), which would be out of reach for the KATRIN experiment.

A stringy perspective on the coincidence problem

We argue that, for string compactifications broadly consistent with swampland constraints, dark energy is likely to signal the beginning of the end of our universe as we know it, perhaps even through decompactification, with possible implications for the cosmological coincidence problem. Thanks to the scarcity (absence?) of stable de Sitter vacua, dark energy in string theory is assumed to take the form of a quintessence field in slow roll. As it rolls, a tower of heavy states will generically descend, triggering an apocalyptic phase transition in the low energy cosmological dynamics after at most a few hundred Hubble times. As a result, dark energy domination cannot continue indefinitely and there is at least a percentage chance that we find ourselves in the first Hubble epoch. We use a toy model of quintessence coupled to a tower of heavy states to explicitly demonstrate the breakdown in the cosmological dynamics as the tower becomes light. This occurs through a large number of corresponding particles being produced after a certain time, overwhelming quintessence. We also discuss some implications for early universe inflation.

Constraining a bulk viscous Bianchi type I dark energy dominated universe with recent observational data

In this paper, we have investigated a bulk viscous universe with dominance of dark energy in Bianchi type I space-time and constrained its parameter with observational $H(z)$ data (OHD) and joint OHD and Pantheon compilation of SN Ia data. We constrain Hubble's constant ${H}_{0}=69.3{8}_{\ensuremath{-}1.54}^{+1.57}$ and ${H}_{0}=70.01{7}_{\ensuremath{-}1.60}^{+1.62}\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ by bounding this model with OHD and joint OHD and Pantheon compilation of SN Ia data respectively. These estimated values of ${H}_{0}$ have $1.27\ensuremath{\sigma}$ and $1.69\ensuremath{\sigma}$ tension with its corresponding Planck collaboration value. We have constrained the best fit value of model parameter $\ensuremath{\zeta}$ as $\ensuremath{\zeta}=0.00002{7}_{\ensuremath{-}0.00052}^{+0.00052}$ and $\ensuremath{\zeta}=0.00003{3}_{\ensuremath{-}0.00296}^{+0.00296}$ respectively for the above observational datasets. We also have obtained a kinematic expression for deceleration parameter and constrained its present value ${q}_{0}=\ensuremath{-}0.58{2}_{\ensuremath{-}0.023}^{+0.021}$ and transition redshift ${z}_{t}=0.72{3}_{\ensuremath{-}0.16}^{+0.34}$. Furthermore, we observe that the derived model exhibits the properties of transitioning the universe and its present age is ${t}_{0}=14.0{4}_{\ensuremath{-}0.32}^{+0.33}\text{ }\text{ }\mathrm{Gyrs}$. The kinematics of the Om(z) parameter and the jerk parameter are also discussed and the analysis of these parameters shows a marginal departure of the derived model from the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model of the universe.

Growth rate and configurational entropy in Tsallis holographic dark energy

In this work, we analyzed the effect of different prescriptions of the IR cutoffs, namely the Hubble horizon cutoff, particle horizon cutoff, Granda and Oliveros horizon cut off, and the Ricci horizon cutoff on the growth rate of clustering for the Tsallis holographic dark energy (THDE) model in an FRW universe devoid of any interactions between the dark Universe. Furthermore, we used the concept of configurational entropy to derive constraints (qualitatively) on the model parameters for the THDE model in each IR cutoff prescription from the fact that the rate of change of configurational entropy hits a minimum at a particular scale factor a_{DE} which indicate precisely the epoch of dark energy domination predicted by the relevant cosmological model as a function of the model parameter(s). By using the current observational constraints on the redshift of transition from a decelerated to an accelerated Universe, we derived constraints on the model parameters appearing in each IR cutoff definition and on the non-additivity parameter delta characterizing the THDE model and report the existence of simple linear dependency between delta and a_{DE} in each IR cutoff setup.

Possible Explanation of the Dynamics of the Universe Expansion without Dark Energy and without New Gravitational Degrees of Freedom

The commonly accepted view is that the Universe is currently in the dark energy dominance era (estimated to start about 5 billion years ago)—the era where yet unknown dark energy dominates over the gravitation and is responsible for the observed acceleration of the Universe expansion. In the present paper, we consider a “gas” of a large number of gravitating neutral nonrelativistic particles having a practically infinite lifetime and zero or very little interaction with the rest of the matter (neutrinos could be an example). One of the central points is the application of Dirac’s Generalized Hamiltonian Dynamics to pairs of these particles. Another central point is the application of the virial theorem to pairs of zero total energy. We demonstrate that as a result, the gravitational interaction within the entire system effectively decreases. Together with the observational fact of the Universe rotation (according to Shamir’s study of 2020), this model provides a possible explanation of the entire history of the Universe expansion: both the era of the decelerating expansion and the current era of the accelerated expansion.

Thermodynamics in the Evolution of the Dark Universe

We present a model of the universe based on the theory that space consists of energy quanta. We use the thermodynamics of an ideal gas to elucidate the composition, accelerated expansion, and the nature of dark energy and dark matter without an Inflation stage. From wave-particle duality, the space quanta can be treated as an ideal gas. The universe started from an atomic size volume at very high temperature and pressure. Upon expansion and cooling, phase transitions occurred to form fundamental particles, and matter. These nucleate and grew into stars, galaxies, and clusters due to gravity. From cooling data, a thermodynamic phase diagram of cosmic composition was constructed which yielded a correlation between dark energy and the energy of space. Using Friedmann’s equations, our model fits well the Williamson Microwave Anisotropy Platform (WMAP) data on cosmic composition with an equation of state parameter, w = -0.7. The dominance of dark energy started at 7.25 × 109 years, in good agreement with Baryon Oscillation Spectroscopic Survey (BOSS) measurements. The expansion of space can be attributed to a scalar space field. Dark Matter is identified as a plasma form of matter similar to that which existed before recombination and during the reionization epoch. The expansion of the universe was adiabatic and decelerating during the first 7 billion years after the Big Bang; it accelerated thereafter. A negative pressure for Dark Energy is required to sustain it; this is consistent with the theory of General Relativity and energy conservation. We propose a mechanism for the acceleration as due to the consolidation of matter to form Black Holes and other massive compact objects. The resulting reduction in gravitational potential energy feeds back energy for the acceleration. It is not due to a repulsive form of gravity. Our Quantum Space model fits well the observed behavior of the universe and resolves the outstanding questions in Inflationary Big Bang Theory.

Reconstruction Method in &amp;lt;i&amp;gt;F(G)&amp;lt;/i&amp;gt; Gravity: Stability Study and Inflationary Survey

The present paper is devoted to reconstruction and cosmological study in modified F(G) theory of gravity. Our reconstruction scheme is based on Friedmann metric induced equations in modified F(G) theory by supposing a power law form for the scale factor of Friedmann metric. Firstly, we deal with the stability study, the obtained model. This survey reveals that for appropriated choice of the reconstructed model parameter, this model is stable under two cosmological evolutions namely the de Sitter and the power law evolutions symbolized by the appropriated scale factor. Secondly, we investigate the inflationary survey by fitting the model with the inflation observables. These observables are determined and their comparison with Planck’s results leads to a special inflationary F(G) model. We prove that this model especially obtained for radiation domination evolution develops an instability, so can fall to ordinary matter domination era or dark energy domination era. This is the key of graceful exit from inflation.