Equation Of State Parameter Research Articles

Anisotropic effect on barrow holographic dark energy

In this paper, we investigate a non-interacting model considering a spatially anisotropic and homogeneous Bianchi type-[Formula: see text] Universe, filled with Barrow holographic dark energy (BHDE) and pressureless dark matter. We examine some important cosmological parameters for the evolutionary report and to witness adequate nature in BHDE model as including deceleration parameter, the jerk parameter, equation of state parameter and density parameter. To study more briefly, we diagnose statefinder parameters, [Formula: see text] analysis and explain that the model parameter significantly modifies the evolutionary trajectories in these planes.

Calculated Elasticity of Al-Bearing Phase D

Using first-principles calculations, this study evaluates the structure, equation of state, and elasticity of three compositions of phase D up to 75 GPa: (1) the magnesium endmember [MgSi2O4(OH)2], (2) the aluminum endmember [Al2SiO4(OH)2], and (3) phase D with 50% Al-substitution [AlMg0.5Si1.5O4(OH)2]. We find that the Mg-endmember undergoes hydrogen-bond symmetrization and that this symmetrization is linked to a 22% increase in the bulk modulus of phase D, in agreement with previous studies. Al2SiO4(OH)2 also undergoes hydrogen-bond symmetrization, but the concomitant increase in bulk modulus is only 13%—a significant departure from the 22% increase of the Mg-endmember. Additionally, Al-endmember phase D is denser (2%–6%), less compressible (6%–25%), and has faster compressional (6%–12%) and shear velocities (12%–15%) relative to its Mg-endmember counterpart. Finally, we investigated the properties of phase D with 50% Al-substitution [AlMg0.5Si1.5O4(OH)2], and found that the hydrogen-bond symmetrization, equation of state parameters, and elastic constants of this tie-line composition cannot be accurately modeled by interpolating the properties of the Mg- and Al-endmembers.

Constraining equation of state of nuclear matter by charge-changing cross section measurements of mirror nuclei

The nuclear symmetry energy plays a key role in determining the equation of state (EoS) of dense, neutron-rich matter, which connects the atomic nuclei with the hot and dense matter in universe, thus has been the subject of intense investigations in laboratory experiments, astronomy observations and theories. Various probes have been proposed to constrain the symmetry energy and its density dependence. Currently, the extensive data yield already a good and consistent constraint to the symmetry energy (Esym(ρ)) at saturation density, but do not yet give a consistent result of one critical EoS parameter, L, the density dependence of the symmetry energy. In this work, we report a new probe of L at saturation density. A good linear correlation is found between L and the charge changing cross section difference (Δσcc) of mirror nuclei 30Si-30S for both the Skyrme-Hartree-Fock theory (SHF) and covariant (relativistic) density functionals (CDF). We found that the pairing effect for this mirror pair is essential to get a consistent correlation between L and Δσcc in both the SHF and CDF. Here, the cross sections are calculated on the same target and at the same energy using the zero-range optical-limit Glauber model. The linearity is found to be in the same precision as those found between L and neutron skin thickness or proton radius difference.

The bouncing cosmic behavior with logarithmic law [formula omitted] model

In this paper, we study the bouncing behavior of our universe under f(G,T) theory, by taking Friedmann–Lemaître–Robertson–Walker metric, which is assumed to be coupled with an ideal fluid distribution. Here G is the Gauss–Bonnet scalar and T is the trace of stress energy tensor. The corresponding field equations are explored after assuming two specific forms of Hubble parameter in the presence of f(G,T)=G(log(ςG))+2λT correction terms. The energy bounds are examined analytically to provide necessary explanations for the theoretical phenomenon of cosmic bounce. The equation of state parameter, deceleration parameter, jerk and snap are also evaluated, accompanied by the associated dynamical parameters. With constraints-based model parameters, the modified geometrical action is configured to work for the removal of initial singularity.

Study of the effect of thermal radiation on singularities in presence of viscous holographic Ricci dark energy and modified Chaplygin gas

This work reports the effect of thermal radiation on singularities in the presence of holographic Ricci dark energy (HRDE) with generalized IR cut-off. The Eckart approach has been considered to initiate the study. The density of HRDE, which is a just particular cases of general Nojiri–Odintsov (NO) HDE [S. Nojiri and S. D. Odintsov, Unifying phantom inflation with late-time acceleration: Scalar phantom-non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38(8) (2006) 1285–1304], in non-interacting and non-viscous case has been reconstructed and it is found that with the passage of cosmic time t, it is decreasing. The Equation of State (EoS) parameter of HRDE in non-interacting and viscous scenario, the EoS parameter of modified Chaplygin gas (MCG) in a non-interacting and non-viscous scenario and the EoS parameter of MCG in an interacting and non-viscous scenario have been reconstructed and studied. There is a chance of Type I, Type II, Type III, Type IV and [Formula: see text]-singularities for the conditions we obtained. For the effect of thermal radiation of inhomogeneous viscous fluid in an interacting scenario, there is a scope of avoidance of Big-Rip Singularity.

Gravastars in energy–momentum squared gravity

This paper is devoted to studying the structure of gravitationally vacuum condensate stars under the influence of matter and geometry coupled gravity. This alternative to black hole comprises three domains, i.e. interior, exterior and thin-shell. We investigate such regions by considering particular equations of state for a specific model of energy–momentum squared gravity. The nonsingular solutions of field equations are obtained to describe the interior region of gravastar and the Schwarzschild spacetime represents the exterior region. The junction conditions are used to match interior and exterior domains while Lanczos equations provide the surface density and pressure at thin-shell. We investigate various attributes of gravastar such as the equation of state parameter, entropy, proper length as well as energy. The physical features of a gravitationally vacuum star indicate a linear relationship with the thickness of the shell and provide a viable structure similar to general relativity.

Toward the primordial black hole formation threshold in a time-dependent equation-of-state background

The study of the primordial black hole (PBH) gravitational collapse process requires the determination of a critical energy density perturbation threshold ${\ensuremath{\delta}}_{\mathrm{c}}$, which depends on the equation of state of the universe at the time of PBH formation. Up to now, the majority of analytical and numerical techniques calculate ${\ensuremath{\delta}}_{\mathrm{c}}$ by assuming a constant equation-of-state (EoS) parameter $w$ at the time of PBH formation. In this work, after generalizing the constant $w$ prescription of [T. Harada et al., Phys. Rev. D 88, 084051 (2013); T. Harada et al.Phys. Rev. D89, 029903(E) (2014).] for the computation of ${\ensuremath{\delta}}_{\mathrm{c}}$ and commenting its limitations we give a first estimate for the PBH threshold in the case of a time-dependent $w$ background. In particular, we apply our formalism in the case of the QCD phase transition, where the EoS parameter varies significantly with time and one expects an enhanced PBH production due to the abrupt softening of $w$. At the end, we compare our results with analytic and numerical approaches for the determination of ${\ensuremath{\delta}}_{\mathrm{c}}$ assuming a constant EoS parameter.

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.

Study of anisotropic compact stars with Krori–Barua spacetime in f(ℛ,𝒯2) gravity

The main objective of this paper is to examine the physical features and stability of anisotropic compact stellar objects in energy–momentum squared gravity. For this purpose, we apply Krori–Barua metric solutions and consider three different models of this modified theory to examine the physical characteristics of Her X-1, 4U 1538-52 and SAX J1808.4-3658 compact stars. We analyze the behavior of various physical quantities such as energy density, pressure components, energy conditions, equation of state parameter and anisotropic factor in the interior of these stars. We then use the estimated values of the sound speed and of the adiabatic index to explore the stability of these compact stars. It is found that all the required conditions are satisfied corresponding to all the selected models. We are therefore allowed to conclude that this modified theory provides viable and stable anisotropic compact stars.

Complete dark energy scenario in f(Q) gravity

In theoretical physics, the fundamental nature and evolution mechanism of dark energy is still an open question. In General Relativity Theory, the simplest explanation for dark energy is the cosmological constant $\Lambda$. However, the cosmological constant $\Lambda$ facing a sensitive problem called fine-tunning problem. In the present work, we follow a different approach where the gravitational sector is the responsible candidate for the evolution of dark energy instead of the matter source. The modified symmetric teleparallel gravity or $f(Q)$ gravity is a recently proposed theory of gravity where the gravitational interaction ruled by the non-metricity term $Q$. In this manuscript, we assume a $f(Q)$ model that contains a linear and a non-linear form of non-metricity scalar, particularly $f(Q)=\alpha Q + \beta Q^n$, where $\alpha$, $\beta$, and $n$ are free model parameters. Then we find the values of our model parameters that would be in agreement with the observed value of cosmographic parameters. We analyze the behavior of different cosmological parameters like deceleration parameter, density, and the equation of state parameter with the energy conditions for our cosmological model. We found that for higher positive values of $n$ specifically $n \geq 1$, dark energy fluid part evolving due to non-metricity behaves like quintessence type dark energy while for higher negative values of $n$ specifically $n \leq -1$ it follows phantom scenario. Further for $n=0$, our cosmological $f(Q)$ model behaves like $\Lambda$CDM model. Thus, we conclude that the geometrical generalization of GR can be a viable candidate for the description of origin of the dark energy.

Emergent universe from Energy–Momentum Squared Gravity

In order to bypass the big bang singularity, we develop an emergent universe scenario within a covariant extension of General Relativity known as “Energy–Momentum Squared Gravity”. The extra terms of the model emerge in the high energy regime. Considering dynamics in a Friedmann–Lemaître–Robertson–Walker background, critical points, representing stable Einstein static states of the phase space, result as solutions. It then turns out that as the equation of state parameter ω gradually declines from a constant value as t→−∞, eventually some of the static past eternal solutions find the chance to naturally enter into thermal history through a graceful exit mechanism. In this way, the successful realization of the emergent universe allows an expanding thermal history without the big bang singularity for the spatially flat universe free of cosmological constant.

Traversable wormhole solutions in the presence of scalar field

In the present work, exact solutions to Einstein’s field equations are obtained in the presence of a scalar field in three cases. In the first case, the equation of state constituting the matter of wormhole is considered as [Formula: see text], where [Formula: see text] is the equation of state parameter. In the second case, the pressures are assumed to follow the relation [Formula: see text], where [Formula: see text] is a nonzero constant. In the third case, the form of matter energy density is assumed as [Formula: see text], where [Formula: see text], [Formula: see text] is the scale radius and [Formula: see text] is the corresponding matter density. In every case, the shape function is derived and its necessary conditions such as throat condition, flare out condition and asymptotic conditions are examined. By using these shape functions, the wormhole solutions are obtained and energy conditions are tested.

Cosmic acceleration and energy conditions in symmetric teleparallel f(Q) gravity

In this paper, we study a spatially homogeneous and isotropic FLRW cosmological model in framework of the symmetric teleparallel f(Q) gravity proposed by Jimenez et al. (Physical Review D 98.4 (2018): 044048), where the non-metricity Q is responsible for the gravitational interaction. For the whole analysis we have considered a special form of f(Q) gravity function i.e. f(Q)=αQn+β (where α, β, and n are the dynamical model constant parameters) in the direction of t(z)=kt0bf(z), where, f(z)=W[bkeb−ln⁡(1+z)k] and W denotes the Lambert function. We have discussed two cases of the function: linear f(Q) model towards n=1 and quadratic for n=2. In both the model we had verified the validity of the models with the help of energy conditions along with some physical parameters like equation of state parameter, jerk parameter, statefinder parameters are also discussed in details and compared it with the observational data.

Stability analysis of anisotropic Bianchi type-I cosmological model in teleparallel gravity

In this work, we study a cosmological model of Bianchi type-I Universe in teleparallel gravity for a perfect fluid. To obtain the cosmological solution of the model, we assume that the deceleration parameter (DP) is a linear function of the Hubble parameter H i.e. q = −1 + βH (where β as a positive constant). Consequently, we get a model of our Universe, where it goes from the initial phase of deceleration to the current phase of acceleration. We have discussed some physical and geometric properties such as Hubble parameter, DP, energy density, pressure, and equation of state parameter and study their behavior graphically in terms of redshift and compare it with observational data such as Type Ia supernovae. We also discussed the behavior of other parameters such as the jerk parameter, statefinder parameters and we tested the validity of the model by studying the stability analysis and energy conditions.

Revisiting the Corresponding-States-Based Correlation for Pool Boiling Critical Heat Flux

A corresponding-states correlation for predicting the critical heat flux (CHF) in pool boiling conditions is proposed, and only requires knowledge of physical property constants of the fluid at any fluid temperature: molar mass, critical temperature, critical pressure, and the Pitzer acentric factor. If a fourth corresponding equation of state (EoS) parameter is added, a more accurate CHF correlation is obtained and matches Kutateladze–Zuber prediction within ±10% in the reduced temperature range of 0.55–0.95. This way, CHF can be easily predicted for any reduced temperature within the range of correlation’s validity by only knowing basic properties of the fluid. Additionally, two corresponding-states correlations for determining the capillary length are proposed and also do not rely on any temperature- and pressure-dependent fluid properties. A simpler correlation only using the Pitzer acentric factor is shown to be imprecise, and a more complex correlation also accounting for the fourth corresponding EoS parameter is recommended. These correlations are fundamental for further developments, which would allow for accurate prediction of CHF values on functionalized surfaces through further studies on the influence of interactions of fluid properties with other parameters, such as wetting and active nucleation site density.

Lagrangian formulation and implications of barotropic fluid cosmologies

In this paper, we investigate the behavior of cosmologies in homogeneous and isotropic background with a barotropic fluid. We solve the continuity equation and study several aspects of model including behavior of cosmological quantities like Hubble parameter, deceleration parameter, equation of state parameter along with statefinder diagnostic and validity of energy conditions. The [Formula: see text] plane is checked for identification of thawing and freezing regions. We derive the Lagrangian formulation with standard and non-standard kinetic terms for barotropic fluid model. It is demonstrated that the model possesses periodic potential in its Lagrangian description with standard kinetic terms. Using dynamical system analysis, we find the stability of solutions, too. We further explore the thermodynamic aspects at apparent horizon by investigating the validity of generalized second law of thermodynamics with equilibrium description. The model exhibits complete cosmological scenario for different values of model parameters and the inflationary scenario decays smoothly into radiation-dominated phase during its evolution. The model approaches to [Formula: see text] cold dark matter model during late times of its evolution.

Impact of charge on gravastars in f(ℜ,𝒯2) gravity

This paper studies the influence of charge on a compact stellar structure also regarded as vacuum condensate star in the background of [Formula: see text] gravity. This object is considered the alternate of black hole whose structure involves three distinct regions, i.e. interior, exterior and thin-shell. We analyze these domains of a gravastar for a particular model of this modified theory. In the inner region of a gravastar, the considered equation of state defines that energy density is equal to negative pressure which is the cause of repulsive force on the spherical shell. In the intermediate shell, pressure and energy density are equal and contain ultra-relativistic fluid. The inward-directed gravitational pull of thin-shell counterbalances the force exerted by the inner region of a gravastar allowing the formation of a singularity-free object. The Reissner–Nordström metric presents the outer vacuum spherical domain. Moreover, we discuss the impact of the charge on physical attributes of a gravastar such as the equation of state parameter, entropy, proper length and energy. We conclude that singularity-free solutions of charged gravastar are physically consistent in this modified theory.

P-V-T equation of state of α-ScOOH.

ABSTRACT In this study, an in situ X-ray diffraction study of α-ScOOH, scandium oxyhydroxide with a diaspore-type structure, was conducted at a pressure and temperature of up to 4.12 GPa and 700 K, respectively, to determine the pressure-volume-temperature (P-V-T) equation of state (EoS). Using a least-squares fit of the second-order Birch–Murnaghan EoS to the P-V-T data, the EoS parameters of α-ScOOH were determined as bulk modulus KT 0 = 101(1) GPa, (∂KT /∂T) P = −0.009(5) GPa K−1, and thermal expansion coefficient at zero pressure α = 3.12(6) 10−5 K−1. α-ScOOH exhibits anisotropic compression and thermal expansion behaviors, which are consistent with those of previous studies on diaspore-type oxyhydroxides. α-ScOOH is more compressible than other diaspore-type oxyhydroxides, and the product of the bulk modulus and volume is approximately constant among diaspore-type M3 + OOH (M = Al, Sc, and Fe).

Ultraviolet dimensional reduction of spacetime with zero-point length

Among the many disparate approaches towards quantum gravity, the reduction of spacetime dimension in the ultraviolet regime is expected to be a common thread. The spectral dimension of spacetime is defined in the context of diffusion processes on a manifold. We show that a spacetime with zero-point length has spectral dimension 3.5 when the characteristic diffusion time has the size of the zero-point length. The spectral dimension (negatively) diverges for an even shorter diffusion time, thus preventing reliable physical interpretation in the deep ultraviolet regime. The thermodynamic dimension is defined by realizing that the free energy F(beta ) of a free field or ideal gas at finite temperature (beta ^{-1}) in D dimensions scales as Fsim beta ^{-D}. Using Schwinger’s proper time formalism, we show that for spacetime incorporating a zero-point length, the thermodynamic dimension reduces to 1.5 near the Planck scale and then to 1 in the deep ultraviolet regime. This signifies a “phase-transition” in which a (massless) bosonic ideal gas in four dimensions essentially behaves like radiation (w=1/3) at low energies, whereas near the Planck scale, it behaves equivalently to having an equation of state parameter w=2. Furthermore, dimension can be deduced from the potential V_D(r) of interaction between two point-like sources separated at a distance r as its scaling depends on D. Comparing with the scaling behavior of conventional Yukawa-like potentials at short distances, we show that the ultraviolet dimension appears to be either 2 or 3 depending on the use of massive or massless force carriers as probes.

Gravastars with Karmarkar condition in f(ℜ,𝒯2) gravity

This paper examines the structure of gravastar (gravitationally vacuum star) in the background of [Formula: see text] theory. The gravastar can be regarded as a substitute for a black hole comprising of three regions (i) the interior domain, (ii) the intrinsic shell and (iii) the exterior domain. We investigate these domains by employing Karmarkar’s condition by assuming a specific [Formula: see text] model. The field equations are solved to evaluate nonsingular solutions of both the interior and intermediate regions. Inner as well as outer spacetimes are matched together using Israel formalism to obtain density and pressure at the joining surface. Different attributes of gravastar like the equation of state parameter, proper length, entropy and energy are analyzed through graphical behavior. It is found that the gravastar model is a viable alternative to the black hole in the context of this gravity.