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In this paper, we determine the exact solutions of viscous ghost models in sign-changeable interaction scenarios for two choices of bouncing scale factor, assuming the existence of viscous interacting fluid across the flat Friedmann–Robertson–Walker universe in the form of ghost dark energy and pressure-less dark matter. The study demonstrates how the cosmological parameters evolve in viscous sign-changeable interacting scenarios to see the transition time frame. Next, a bounce inflation model is investigated, including the tensor-to-scalar ratio, scalar spectral index, and slow-roll parameters analytical results. Since inflation is usually associated with scalar fields, the study looked at a possible relationship between sign-changeable interacting ghost dark fluids and scalar field models. Lastly, the applicability of the generalized second law (GSL) of thermodynamics is examined for the scenarios that are being studied. [ABSTRACT FROM AUTHOR]

The present paper reports a study on neutron stars in the f (R) gravity framework for the Hu–Sawicki model, Starobinsky model, Tsujikawa model, and Exponential Gravity model. First, we have used the TOV equation for the f (R) gravity framework, where we obtained two higher order differential equations for λ and ψ , with both functions depending on the radial coordinate. Furthermore, we have considered the BD theory, which is an equivalent theory of f (R) gravity, and introduced a new scalar field ϕ 2 with the scalar potential V (ϕ 2) . We have observed an increase in the scalar potential with respect to R in each case. Furthermore, our proposed models, namely quadratic form, exponential form, and linear form and the other viable models show a similar type of evolution for the scalar potential V (ϕ 2) . [ABSTRACT FROM AUTHOR]

Motivated by the work of Paliathanasis et al. (A. Paliathanasis and G. Leon, "Cosmological solutions in Hořava–Lifshitz scalar field theory," ZnA, vol. 75, p. 523, 2020), this work reports the baryogenesis in Hořava–Lifshitz cosmology by taking the background evolution as modified Chaplygin gas and modified holographic dark energy. The Starobinsky potential has been selected to initiate the study. The scalar field and its potential have been reconstructed and found to be consistent with the universe's expansion. The quintessence behaviour of equation of state parameters has been observed for both cases. Finally, baryogenesis has been studied in both cases. The baryon entropy ratio attained the observed value. It is also well explained that either the model will achieve an equal number of baryon and antibaryon densities or will satisfy the Generalized Second Law of Thermodynamics. [ABSTRACT FROM AUTHOR]

In this work, we examine the cosmological characteristics of the Power Law Entropy Corrected Holographic Dark Energy (PLECHDE) model with infrared (IR) cut-off, which is determined by the curvature parameter k , the time derivative of H , and the average radius of the Ricci scalar curvature R , which varies with the Hubble parameter H squared. We obtain the deceleration parameter q and the Equation of State (EoS) parameter of Dark Energy (DE) ω D. Additionally, we derive the Hubble parameter H and the scale factor a expressions as functions of the cosmic time t. Additionally, we examine the limiting scenario that pertains to a flat Dark Dominated Universe. Furthermore, we establish a correspondence between the DE model considered and some scalar fields, in particular the Generalized Chaplygin Gas, the Modified Chaplygin Gas, the Modified Variable Chaplygin Gas, the New Modified Chaplygin Gas, the Viscous Generalized Chaplygin Gas, the Dirac–Born–Infeld, the Yang–Mills, and the Non Linear Electrodynamics scalar field models. • We have examined the cosmological characteristics of the Power Law Entropy Corrected HDE. • We obtained the deceleration parameter and the EoS parameter of Dark Energy. • We examined the limiting scenario that pertains to a flat Dark Dominated Universe. • We established a correspondence between the DE model considered and some scalar fields. [ABSTRACT FROM AUTHOR]

In this paper, we study the main cosmological properties of the classical Friedmann equations in the case of homogeneous and isotropic Friedmann–Robertson–Walker Universe and we also generalized the expression of the Friedmann equation in the case of Loop Quantum Cosmology (LQC). Considering the M 3 5 -model, we found the solutions of the equations considered for two particular cases, i.e.  Q = 0 (i.e. the de Sitter solution) and Q > 0. Moreover, we considered and studied two exact cosmological solutions of the M 3 5 -model, in particular the power-law and the exponential ones. Moreover, we also considered a third more complicated case and we derived the solution for an arbitrary function of the time f (t). A scalar field description of the model is presented by constructing its self-interacting potential. [ABSTRACT FROM AUTHOR]

The work presented in this paper reports a rigorous study of the reconstruction of the modified gravity in the framework of the scalar field models of dark energy and holographic Ricci dark energy, a generalized version of the holographic dark energy presented in S. Nojiri and S.D. Odintsov. Gen. Relativ. Gravitation, 38, 1285 (2006). The tachyon and quintessence scalar fields have been considered and the cosmology associated with the presence of bulk viscosity has been studied. In the first part of our study, we have demonstrated the behaviour of the bulk viscosity coefficient in the framework of the reconstructed tachyon scalar field model of dark energy. The scale factor is chosen in the form a(t) = a0tβ, where β > 0. Two scalar field models, namely, tachyon and quintessence, have been considered in the framework of the modified field equations through incorporation of the bulk viscous pressure. The reconstructed density and pressure of the scalar field models have been explored for the cosmological consequences in the presence of bulk viscosity. The behaviour of the effective equation of state parameters has been investigated. Finally, we have reconstructed f(T) gravity in the presence of holographic Ricci dark energy and a transition of the effective equation of state parameter from quintessence to phantom has been observed. [ABSTRACT FROM AUTHOR]

Work reported in this study demonstrates the reconstruction schemes for the f (G) gravity in the framework of bulk viscosity and holographic background evolution by considering the universe filled by the viscous fluid that is just special class of more general fluids as described in Nojiri and Odintsov [Inhomogeneous equation of state of the universe: Phantom era, future singularity, and crossing the phantom barrier, Phys. Rev. D72 (2005) 023003]. The bulk viscous pressure has been considered as Π = − 3 H ξ , with ξ = ξ 0 + ξ 1 H + ξ 2 (Ḣ + H 2). Considering the scale factor in power law form and taking holographic dark energy (HDE) with density ρ Λ = 3 c 3 M p 2 L − 2 and generalized extended holographic dark energy (EGHRDE) with density ρ Λ = 3 c 2 (α Ḣ + β H 2) , a specific case of Nojiri–Odintsov holographic DE ([Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit.38 (2006) 1285]) we have derived solutions for f (G) and the subsequent effective equation of state parameters have been found to behave like quintom irrespective of the choice of c 2 . Finally, considering f (G) as quintessence scalar field we have explored the possibility of quasi-exponential expansion and warm inflation. [ABSTRACT FROM AUTHOR]

The research presented in the current article explores the potential for inflation realization in a cosmic environment with bulk viscosity using a tachyon scalar field. The present study rewrites the entropy conservation equation to take bulk viscosity into account. The work's initial phase examined the behaviour of the equation of state parameter for logamediate, intermediate, and emergent scenarios within a framework of viscous cosmology having the viscosity coefficient in linear and polynomial forms. The study then focused on the relative dominance of the scalar field and potential for the tachyon scalar field in the presence of bulk viscosity for the different choices of scale factor and came to the conclusion that the prerequisite for the realization of inflation is met in the framework of bulk viscosity. • The study investigates the likelihood of inflation. • A cosmological background with bulk viscosity is taken into account. • The EoS parameter is investigated for various scale factor options. • Entropy conservation is rephrased with tachyon. • The inflation realization for viscous tachyon scalar field is examined. [ABSTRACT FROM AUTHOR]

The present paper reports a study on the f (T) gravity reconstruction scheme in the context of considering standard Chaplygin gas as tachyon scalar field model of dark energy. The solution for reconstructed f (T) gravity has been obtained from reconstructed potential and scalar field of tachyon based on the standard Chaplygin gas. It has been observed that the equation of state parameter due to the reconstructed torsion contribution to the density and pressure behaves like quintom and is consistent with the observational value of the equation of state parameter for the current universe. The reconstructed f (T) has then been tested for gravitational perturbation by deriving the frictional term, the effective mass and the sound speed parameter for the gravitational potential and it has been found to be stable against gravitational perturbations through positive value of the squared speed of sound. Finally, statefinder diagnostics has been carried out and the reconstructed f (T) gravity is found to interpolate between dust and Λ CDM phases of the universe. [ABSTRACT FROM AUTHOR]

This study proposes a method to reconstruct a generalized form of holographic dark energy and to analyse its cosmology, based on a logotropic equation of state. By assuming that the dark energy density is caused by holographic Ricci dark energy, one can calculate a scale factor for the universe's overall energy density, provided by baryons, dark matter, and dark energy density. For the situation where the internal energy is in logarithmic form, the equation of state parameter is similarly obtained. In the following stage, a generalized Chaplygin gas is investigated using a logotropic equation of state, considering the scenario of a logarithmic internal energy. Modified generalized Chaplygin gas is also examined in the situation of logarithmic internal energy with logotropic equation of state, and related reconstruction is carried out. The generalized second law of thermodynamics is subsequently validated for event, particle, and Hubble horizons after taking into account the phantom and quintessence models using a logotropic technique. • A generalized holographic dark energy is reconstructed using a logotropic equation of state. • The scale factor is rebuilt for HRDE with a logotropic equation of state. • The EoS parameter is obtained with internal energy in logarithmic form. • Using the logotropic EoS, GCG and MGCG are reconstructed for logarithmic internal energy. • A logotropic EoS is used to check GSL with various enveloping horizons for the phantom and quintessence models. [ABSTRACT FROM AUTHOR]

In the work reported in the present paper, we have considered the inflationary dynamics inspired by holographic Ricci dark energy (HRDE) with the energy density ρ Λ = 3 β 2 (Ḣ + 2 H 2) in the framework of f (T) gravity. We have considered a f (T) -gravity model in linear form, which is sourced by a canonical scalar field due to the HRDE. We have investigated an inflationary Universe in this framework through slow-roll formalism. We also studied the scalar spectral index (n s) and tensor-to-scalar ratio (r) , which have come out to be in agreement with WMAP + BAO + H 0 and Planck 2015 data. [ABSTRACT FROM AUTHOR]

In this work, we investigate the cosmological application of modified Chaplygin gas (MCG) interacting with pressureless dark matter (DM) in the modified gravity framework, where is the torsion scalar in teleparallelism. The interaction term has been chosen proportional to the MCG density with positive coupling constant. In the Einstein general relativity (GR) framework, the interacting MCG has been found to have equation of state (EoS) parameter behaving like quintessence. However, the gravity reconstructed via the interacting MCG has been found to have EoS crossing the phantom boundary of . Thus, one can generate a quintom-like EoS from an interacting MCG model in flat universe in the modified gravity cosmology framework. The reconstructed model has been found to interpolate between dust and CDM. Stability of the reconstructed has been investigated and it has been observed that the model is stable against gravitational perturbation. Cosmological evolution of primordial perturbations has also been investigated and the self-interacting potential has been found to increase with cosmic time and the squared speed of sound has been found to be non-negative. [ABSTRACT FROM AUTHOR]

The present paper reports a study on accreting tachyon, Dirac-Born-Infeld essence and h-essence scalar field models of dark energy onto Morris-Thorne wormhole. Using three different parameterisation schemes and taking , we have derived the mass of the wormhole for all of the three parameterisation schemes that are able to get hold of both quintessence and phantom behaviour. With suitable choice of parameters, we observed that accreting scalar field dark energy models are increasing the mass of the wormhole in the phantom phase and the mass is decreasing in the quintessence phase. Finally, we have considered accretion with power law form of scale factor and without any parameterisation scheme for the equation of state parameter and observed the fact that phantom-type dark energy supports the existence of wormholes. [ABSTRACT FROM AUTHOR]

In this paper, we studied the cosmological application of the interacting Ricci Dark Energy (RDE) model in the framework of the scalar Gauss-Bonnet modified gravity model. We studied the properties of the reconstructed potential $V\left (t \right )$, the Strong Energy Condition (SEC), the Weak Energy Condition (WEC) and the deceleration parameter q for three different models of scale factor, i.e. the emergent, the intermediate and the logamediate one. We obtained that $V\left (t \right )$, for the emergent scenario, has a decreasing behavior, while, for the logamediate scenario, the potential start with an increasing behavior then, for later times, it shows a slowly decreasing behavior. Finally, for the intermediate scenario, the potential has an initial increasing behavior, then for a time of t≈1.2, it starts to decrease. We also found that both SEC and WEC are violated for all the three scale factors considered. Finally, studying the plots of q, we derived that an accelerated universe can be achieved for the three models of scale factor considered. [ABSTRACT FROM AUTHOR]

In this work, we study the New Agegraphic Dark Energy (NADE) model (which contains the conformal time η as infrared cut-off) in the framework of Brans-Dicke cosmology with chameleon scalar field which is non-minimally coupled to the matter field. Considering interacting Dark Energy and Dark Matter (DM), we calculate some relevant cosmological parameters, i.e. the equation of state (EoS) parameter, the deceleration parameter q and the evolution of the energy density parameter $\varOmega_{D}'$ for different forms of scale factors, i.e. the power-law, the emergent, the intermediate and the logamediate ones, which leads to different expressions of η. [ABSTRACT FROM AUTHOR]

The present work reports a Holographic reconstruction of Dirac–Born–Infeld (DBI)-essence Dark Energy (DE) in a flat FRW universe. The scale factor a( t) is chosen in power law form. We have reconstructed the scalar field and potential and subsequently the equation of state (EoS) parameter ω of the DBI-essence DE. The corresponding plots show increasing scalar field, decaying tension and decaying potential. The reconstructed EoS parameter stays below −1, showing a phantom-like behavior. The stability of the reconstructed DBI-essence DE is investigated through squared speed of sound $v_{s}^{2}$ : its negative sign reveals that the holographically reconstructed DBI-essence is classically unstable. [ABSTRACT FROM AUTHOR]

In this work, we considered an effective scalar field theory described by a Lagrangian with a noncanonical kinetic term, which leads to accelerated expansion in the present Universe and is known as k-essence in the framework of the fractional action cosmology recently introduced by El-Nabulsi. We have chosen a particular ansatz for the scale factor and the scalar field, in which both are described as a power-law of the time, t. We have studied the behavior of some cosmological quantities in other models to obtain some useful information about the model considered. We observed that the equation of state parameter, w, has decreasing behavior and it never crosses the phantom divide line (i.e., w = -1). Studying the statefinder pair { r, s} and { w, w′}, we observed that the model considered is able to obtain the ΛCDM phase of the Universe. [ABSTRACT FROM AUTHOR]

In this paper, we have considered the generalized Ricci dark energy (GRDE) and generalized holographic dark energy in the scenario of an emergent universe. Fractional energy density and deceleration parameters for GRDE were derived in an emergent universe scenario. Also, the role of GRDE on the chameleon field in the emergent universe scenario has been examined. Finally, the behaviours of the chameleon scalar field, , corresponding potential, V, and associated function, f, were investigated in the presence of GRDE. [ABSTRACT FROM AUTHOR]

In the present work, we consider the tachyonic field, the phantom field, and the scalar field in both interacting and non-interacting situations and investigate the validity of the generalized second law of thermodynamics in a flat FRW universe. We find that in all cases, except for the phantom field dominated universe, the derivative of the entropy remains at negative level and increases with the decrease in redshift. [ABSTRACT FROM AUTHOR]

The present work considers interaction between DBI-essence and other candidates of dark energies like modified Chaplygin gas, hessence, tachyonic field, and new agegraphic dark energy. The potentials of the fields have been reconstructed under interaction and their evolutions have been viewed against cosmic time t and scalar field φ. Equation of state parameters have also been obtained. The nature of potentials and the equation of state parameters of the dark energies have been found graphically in presence of interaction (both small and large interaction). [ABSTRACT FROM AUTHOR]

In this letter, we have considered that the universe is filled with normal matter and variable modified Chaplygin gas. Also we have considered the interaction between normal matter and variable modified Chaplygin gas in FRW universe. Then we have considered a correspondence between the holographic dark energy density and interacting variable modified Chaplygin gas energy density. Then we have reconstructed the potential of the scalar field which describes the variable modified Chaplygin cosmology. [ABSTRACT FROM AUTHOR]

The present study reports a reconstruction scheme for f (R) gravity with the scale factor a (t) ∝ (t * − t) 2 c 2 describing the pre-bounce ekpyrotic contraction, where t * is the big crunch time. The reconstructed f (R) is used to derive expressions for density and pressure contributions, and the equation of state parameter resulting from this reconstruction is found to behave like "quintom". It has also been observed that the reconstructed f (R) has satisfied a sufficient condition for a realistic model. In the subsequent phase, the reconstructed f (R) is applied to the model of the chameleon scalar field, and the scalar field ϕ and the potential V (ϕ) are tested for quasi-exponential expansion. It has been observed that although the reconstructed f (R) satisfies one of the sufficient conditions for realistic model, the quasi-exponential expansion is not available due to this reconstruction. Finally, the consequences of pre-bounce ekpyrotic inflation in f (R) gravity are compared to the background solution for f (R) matter bounce. [ABSTRACT FROM AUTHOR]

From the hydrodynamic viewpoint, the inclusion of viscosity in the theory of cosmic fluid may appear as an abstraction. Using modern observational results for the Hubble parameter and standard Friedmann formalism, we may have a description of the universe up to the inflationary era, or we may be able to analyse the probable ultimate fate of the universe. Inspired by this bulk viscosity formalism reviewed in Brevik et al., (2017) in this work, we report a study of the DBI essence scalar field model of dark energy (DE) interacting with pressureless dark matter (DM) in the presence of bulk viscous pressure of the form ξ = ξ 0 + ξ 1 H + ξ 2 (H ̇ + H 2). We choose the scale factor in three forms: emergent, logamediate, and intermediate. We choose the interaction term Q in the form Q = 3 H δ ρ Λ , where ρ Λ denotes the density of the scalar field model of DE. We present a detailed cosmology of the interacting DE and observe a quintom behaviour of the equation of state (EoS). We conduct a statefinder analysis to attain Λ CDM fixed point by the interacting DE. Subsequently, we report a reconstruction scheme for f (T) gravity. Finally, we conduct thermodynamic analysis where we consider entropy's logarithmic and power-law corrections. • DBI essence scalar field model interacting with pressureless dark matter is considered in viscous scenario. • A detailed cosmology of the interacting DE with quintom behaviour of the equation of state (EoS) choosing different scale factors. • A statefinder analysis is carried out to check attainment of Λ CDM fixed point. • A reconstruction scheme for f (T) gravity is presented and its cosmology is demonstrated. • Thermodynamic analysis is carried out with logarithmic and power-law corrections. [ABSTRACT FROM AUTHOR]