Phantom Phase Research Articles

Traces of Quantum Gravity Effects at Late-time Cosmological Dynamics via Distance Measures

Inspired by the entropy–area relation of black hole thermodynamics, we study the thermodynamics of the cosmological apparent horizon in a spatially flat Friedmann–Robertson–Walker universe in the framework of an extended uncertainty principle (EUP). The adopted EUP naturally admits a minimal measurable momentum (equivalently a maximal measurable length), as an infrared cutoff in the theory. We derive the modified Friedmann equations in this setup and explore some predictions of these equations for the late-time universe via distance measures. We show that in this framework it is possible to realize the late-time cosmic speedup and transition to the phantom phase of the equation-of-state parameter of the effective cosmic fluid without recourse to any dark energy component or modified gravity. Inspection of various distance measures in this framework shows that an EUP with a negative deformation parameter suffices for the interpretation of the late-time asymptotically de Sitter universe with standard nonrelativistic matter.

Probing the universe's expansion dynamics: The linear correction scenario perspective on dark energy

In this study, we investigate the cosmological evolution of the universe, focusing on the KMMS models in a model-independent approach, particularly the scenario involving linear correction, given by E2(z)=A(z)+β(1+γB(z)), where A(z)=Ωm0(1+z)3 and B(z)=z. By analyzing recent Cosmic Chronometers (CC) and the Pantheon+ samples, we determine the best-fit values of model parameters using a Markov chain Monte Carlo analysis. Our models exhibit unique dynamics, transitioning from super-exponential to exponential expansion, with a significant shift at redshift zt=0.83−0.10+0.11 and present deceleration parameter q0=−0.69−0.17+0.17. The jerk parameter exceeds 1, indicating a faster change in acceleration than predicted by ΛCDM. The energy density parameter is consistent with Planck observations, and the dark sector evolution follows the expected thermal history. The EoS parameter approaches ωde=−1 over time, with a current value of ωde0=−1.06±0.12, aligning with the phantom phase. Our model presents a new dark energy alternative, emphasizing the importance of considering models like KMMS in understanding cosmic evolution.

Generalized ghost dark energy in [formula omitted] gravity

In this manuscript, we use the correspondence principle to construct the generalized ghost dark energy f(Q) model, where Q is the non-metricity. For this purpose, we use the Friedman–Robertson–Walker universe model with power-law scale factor. The energy density in this model linearly depends on the Hubble parameter, with a sub-leading term of H2, resulting in an energy density ρD=ξH+ζH2, where ξ and ζ are arbitrary constants. We reconstruct interacting fluid scenario of this dark energy with dark matter. The reformulated f(Q) gravity model shows how different epochs of the cosmic history can be reproduced by this modified gravity model. The physical characteristics of the model are discussed through the equation of state parameter with the planes of ωD−ωD′ and r−s. We also explore the stability criteria for the interacting model using the squared speed of sound. The equation of state parameter indicates phantom phase of the universe and the squared speed of sound represents stability of the interacting model. The (ωD−ωD′)-plane indicates freezing region, while the (r−s)-plane corresponds to the Chaplygin gas. We conclude that our findings coincide with the latest observational data.

FLRW universe in f(Q,T) gravity

A cosmological model is described in this study using [Formula: see text] gravity, and the parameters are restricted using cosmological data sets. We start out by using a well-motivated form of [Formula: see text] as [Formula: see text], where [Formula: see text] and [Formula: see text] are model parameters. To solve the field equations, we use the relation that the deceleration parameter is inversely related to the Hubble parameter. In this case, we find that by parametrizing the cosmological parameters the transition redshift between early deceleration and late time acceleration occurs at [Formula: see text] The positive slope of the Om [Formula: see text] diagnostic analysis indicates that the model is in a phantom phase. Based on the current study, it seems that [Formula: see text] gravity might offer a substitute for dark energy in order to address the current cosmic acceleration.

Big Rip in Swiss-cheese brane-worlds with cosmic transit

We study the Big Rip scenario in Swiss-cheese brane-worlds. The results obtained have been found to be independent of the value of the cosmological constant Λ whether it is positive, negative, or zero. Negative tension branes are not allowed in the current model. There is a sign flipping in cosmic pressure corresponding to the sign flipping in the deceleration parameter from positive to negative. The evolution of the equation of state parameter shows the presence of three phases: the matter-dominant decelerating era, the accelerated-Quitessence phase, and the phantom phase. The evolution of the potential and kinetic term also shows a change of sign. The energy conditions and cosmographic parameters have also been investigated.

Phantom Cosmological Model with Observational Constraints in f(Q)$f(Q)$ Gravity

AbstractIn this paper, the cosmological model of the Universe has been presented in gravity and the parameters are constrained from the cosmological data sets. At the beginning, a well motivated form of has been employed, where α, β, and n are model parameters. The Hubble parameter is obtained in redshift with some algebraic manipulation from the considered form of . Then it is parameterized with the recent data and data using Markov chain Monte Carlo analysis. The obtained model parameter values are validated with the baryon acoustic oscillation data set. A parametrization of the cosmographic parameters shows the early deceleration and late time acceleration with the transition at . The diagnostics gives positive slope which shows that the model is in the phantom phase. Also the current age of the Universe has been obtained as, . Based on the present analysis, it indicates that the gravity may provide an alternative to dark energy for addressing the current cosmic acceleration.

Generic Modification of Gravity, Late Time Acceleration and Hubble Tension

We consider a scenario of large-scale modification of gravity that does not invoke extra degrees of freedom, but includes coupling between baryonic matter and dark matter in the Einstein frame. The total matter energy density follows the standard conservation, and evolution has the character of deceleration in this frame. The model exhibits interesting features in the Jordan frame realised by virtue of a disformal transformation where individual matter components adhere to standard conservation but gravity is modified. A generic parametrization of disformal transformation leaves thermal history intact and gives rise to late time acceleration in the Jordan frame, which necessarily includes phantom crossing, which, in the standard framework, can be realised using at least two scalar fields. This scenario is embodied by two distinguished features, namely, acceleration in the Jordan frame and deceleration in the Einstein frame, and the possibility of resolution of the Hubble tension thanks to the emergence of the phantom phase at late times.

Analysis of cosmic aspects through string-inspired teleparallel gravity models

We consider a generic string inspired gravitational theory in the framework of teleparallel gravity whose stringy action based on a particular function which depends on the scalar field, its kinetic energy, the boundary and torsion terms as well as the Gauss-Bonnet terms We examine some cosmographic parameters like the equation of state parameter (ω tot), plane behavior and their stability with the help of squared speed of sound parameter (v2 s ). Under the choice of some specific values of model parameters, the equation of state parameter ω tot indicates the range of cosmological constant and quintessence region of the evolving universe for the past, present and near future times while phantom phase in the far future times. The phase plane expresses the super accelerated phase (the freezing region) whereas gives the stability of each underlying model in the realm of accelerated universe.

Barrow holographic dark energy in deformed Hořava–Lifshitz gravity

We discuss the cosmological implications of the interacting Barrow holographic dark energy model in the context of flat deformed Hořava–Lifshitz gravity by assuming the interaction ([Formula: see text]) between dark energy and pressureless dark matter. To understand the mechanism of recent accelerated expansion of the universe, we consider Hubble and event horizons as infrared cutoff. We investigate the evolutionary history of cosmological parameters especially the equation of state, Hubble, deceleration, squared speed of sound and find results that favor observational data of Planck 2018. It is found that the Hubble parameter lies in the range [Formula: see text] (for event horizon) and [Formula: see text] (for Hubble horizon). The equation of state parameter provides the phantom phase of the universe, while the deceleration parameter illustrates the accelerated phase of the universe. On the other hand, we plot the squared speed of sound and find the positive behavior which ensures the stability of underlying model. Moreover, we examine the generalized second law of thermodynamics of this cosmological system with barrow entropy as horizon entropy and observe that this law holds for both horizons.

A study of bouncing cosmology in framework of f(T,𝒯 ) gravity with probing of cosmographic parameters

This paper is devoted to explore bouncing cosmology in [Formula: see text] modified gravity. In the background of [Formula: see text] modified theory with [Formula: see text] being Torsion scalar and [Formula: see text] being the trace of energy–momentum tensor, the Hubble parameter is considered for the isotropic, flat, and homogenous universe. The standard bouncing scale factor has employed the exponential term to unify bounce with late-time acceleration. Phase portrait analysis reveals us that Minkowskian origin transfers to de Sitter origin in [Formula: see text]-plane and as past infinite time [Formula: see text][Formula: see text][Formula: see text] and [Formula: see text] constant which corresponds to some physical cosmological scenarios. Since field equations of [Formula: see text] gravity are of second order, a one-dimensional autonomous system has been extracted. Finally, outcomes have been plotted graphically, and any type of singular behavior has not been experienced. The study of the equation of state parameter against cosmic time reveals that phantom phase is quite significant for both models. The inertial force in terms of Hubble parameter and cosmic time gives rise to pseudo Rip. The study of cosmographic parameters tells us that the present model corresponds to [Formula: see text]CDM at a large value of cosmic time.

Cosmic and growth matter analysis of deformed Hořava–Lifshitz gravity

Hořava–Lifshitz gravity is a very fascinating proposal of modified gravity for explaining the current acceleration and other cosmic issues. In continuation to this discussion, we explore the consequences of Tsallis dark energy with Hubble and particle horizons in the framework of deformed Hořava–Lifshitz gravity for flat FRW universe. The interaction between Tsallis holographic dark energy and dark matter is also taken into account to discuss the underlying scenario. It is found that fractional dark energy density ([Formula: see text]) approaches to [Formula: see text] as redshift goes to zero (present epoch) for both cases of horizons. The cosmic parameter ([Formula: see text]) shows phantom crossing behavior in both models, i.e. it evolutes the universe from quintessence phase to phantom phase by crossing the vacuum horizon. In both cases of horizons, the deceleration supports the cosmic acceleration by exhibiting the negative values. The perturbation sound speed also favors the viability of our models through positive behavior. The coincidence parameter supports the exchange of dark matter to dark energy phenomenon through positivity. We also discuss the behavior of growth rate and growth index in the growth of matter density perturbations for both horizons. These parameters mimic the [Formula: see text]CDM behavior of the universe.

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.

Bouncing universe models in an extended gravity theory

Some bouncing models are investigated in the framework of an extended theory of gravity. The extended gravity model is a simple extension of the General Relativity where an additional matter geometry coupling is introduced to account for the late time cosmic speed up phenomena. The dynamics of the models are discussed in the background of a flat FRW universe. Some viable models are reconstructed for specifically assumed bouncing scale factors. The behavior of the models are found to be decided mostly by the parameters of the respective models. The extended gravity based minimal matter-geometry coupling parameter has a role to remove the omega singularity occurring at the bouncing epoch. It is noted that the constructed models violate the energy conditions, however, in some cases this violation leads to the evolution of the models in phantom phase. The stability of the models are analyzed under linear homogeneous perturbations and it is found that, near the bounce, the models show instability but the perturbations decay out smoothly to provide stable models at late times.

Interacting Tsallis holographic dark energy in higher dimensional cosmology

We discuss Tsallis holographic dark energy (THDE) model in higher dimension. An interacting dark energy model is proposed with Generalized Chaplygin Gas (GCG) in the framework of Compact Kaluza-Klein gravity. It is shown that a stable configuration can be found in the present epoch which is also compatible with the observed value of the density parameter. It is noted that dark energy (DE) might have evolved from a phantom phase in the past. Nature of dark energy is found to depend on the coupling parameter of the interaction. Classical stability consideration is also found to put an upper bound on the model parameter.

Mixed fluid cosmological model in f(R, T) gravity

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

An FLRW interacting dark energy model of the Universe

In this paper, we have presented an FLRW universe containing two-fluids (baryonic and dark energy), by assuming the deceleration parameter as a linear function of the Hubble function. This results in a time-dependent deceleration parameter (DP) having a transition from past decelerating to the present accelerating universe. In this model, dark energy (DE) interacts with dust to produce a new law for the density. As per our model, our universe is at present in a phantom phase after passing through a quintessence phase in the past. The physical importance of the two-fluid scenario is described in various aspects. The model is shown to satisfy current observational constraints such as recent Planck results. Various cosmological parameters relating to the history of the universe have been investigated.

Cosmic evolution of ghost dark energy models in f(G,T) gravity

The aim of this paper is to study the reconstruction paradigm for both ghost as well as generalized ghost dark energy models in the context of [Formula: see text] gravity. To accomplish this, we use correspondence scenario for pressureless flat FRW universe with power-law scale factor. The cosmological behavior of reconstructed models is analyzed through graphical analysis of deceleration, equation of state, squared speed of sound parameters and phase planes. It is found that the deceleration parameter represents accelerated epoch for both models whereas equation of state parameter indicates phantom era of the universe for ghost dark energy model and quintessence for its generalized version. The phase planes [Formula: see text] and [Formula: see text] indicate the freezing region with phantom phase for both reconstructed dark energy models. We conclude that the squared speed of sound parameter leads to the stability of generalized ghost dark energy model only.

Cosmic accelerated expansion of the Universe with phantom fluid

The phantom behavior of the Universe is discussed in an extended version of Gauss–Bonnet gravity. Following the method proposed by the author (Int. J. Mod. Phys. D, 27, 1850078. 2018. doi: 10.1142/S0218271818500785 ), we obtain a viable cosmological model for the phantom phase of the Universe. We find a condition for m in the model ∼Gm, which shows phantom expansion of the Universe. On the other hand, using a phantom source term ∼T2n in the model we observe that the term ∼Gn, with n > 3/4, gives a phantomic space–time expansion. This form (Gn + T2n) obtained for the phantom phase of the Universe exhibits a similar form to Einstein’s gravity theory (R + Lm). However, we addressed the cosmic coincidence problem for the model.

LRS Bianchi type-I cosmological models with accelerated expansion in f(R, T) gravity in the presence of $\Lambda$(T)

This paper examines the physical behaviour of the transition of the LRS Bianchi type-I perfect-fluid cosmological models from early decelerating to the current accelerating phase within the framework of the f(R,T) theory of gravity. To determine the solution of the field equations, the concept of a time-dependent deceleration parameter is used. This yields scale factors for which the universe attains a phase transition scenario, and is consistent with recent cosmological observations. Two cases are considered, firstly $a(t) = \sinh^{1/n} (\alpha t)$ , where n and $\alpha$ are positive constants. For $0 < n\leq 1$ , this generates a class of accelerating models, while for $n > 1$ , the universe attains a phase transition from an early decelerating to the present accelerating phase. This model 1 starts from quintessence ( $\omega > - 1$ ) initially and ended up with phantom phase $(\omega < - 1)$ when $t \rightarrow \infty$ . The second case is $a(t) = (t^{k} e^{t})^{1/n}$ , where n and k are positive constants. It is observed that for $n \geq 2$ and $k = 1$ , a class of transit models of the universe are obtained. The model 2 belongs to the scenario of phantom energy ( $ \omega > - 1$ ). We have observed the existence of type-III singularity in our model 2. Some physical and geometric properties of the models are found and discussed.

New agegraphic dark energy in f(G, T) gravity

This paper is devoted to the reconstruction paradigm for new agegraphic dark energy model in the context of f(G, T) gravity (G and T denote the Gauss–Bonnet invariant and trace of the energy-momentum tensor). To accomplish this, we choose the correspondence scenario for pressureless perfect fluid configuration in the framework of flat FRW universe. The cosmic behavior of reconstructed models is analyzed through cosmic diagnostic parameters and phase planes. It is found that the deceleration parameter indicates accelerated regime while the equation of state parameter gives the phantom phase for non-conserved and quintessence universe for conserved energy-momentum tensor. The squared speed of sound parameter represents the stability of the conserved model for late-time cosmic evolutionary paradigm whereas instability for the non-conserved regime. The trajectories of ωeff−ωeff′ plane correspond to thawing as well as freezing region for the non-conserved and conserved scenario, respectively. The r−s plane gives phantom as well as the non-phantom regime for conserved and Chaplygin gas model for the non-conserved paradigm. We conclude that the resulting models exhibit self-consistent quintessence as well as the phantom-like universe for appropriate choice of free parameters.