Barotropic Matter Research Articles

Existence of static wormhole solutions in [formula omitted] gravity

This study explores wormhole solutions by analyzing energy conditions within the framework of f(R,A) modified theory of gravity, which is derived from the inverse of the Ricci tensor. For this purpose, we consider a linear model, defined as f(R,A)=R+αA, where R denotes the Ricci scalar, α is the coupling parameter, and A represents the anticurvature scalar. We further introduce a specific form of shape function to examine the characteristics of energy conditions for the distribution of anisotropic matter. Moreover, we examine the behavior of shape function and energy conditions for both isotropic and barotropic matter content as well. Through the selection of suitable parameter values, it has been shown that energy conditions are breached in some specified regions, indicating the existence of exotic matter. The thorough analysis confirms the presence of wormhole geometries in f(R,A) gravity.

Analysis of the boundary condition and equation of state in radiating stars

A model of a radiating star undergoing gravitational collapse is constructed by systematically studying both the boundary condition and equation of state for the first time. The resulting system of partial differential equations is analysed using Lie symmetries. The group analysis produces new classes of exact solutions with acceleration, expansion and shear in the presence of the cosmological constant. Known exact solutions are recovered as special cases of our solutions. In particular, we regain the Euclidean star model which is the relativistic version of the Newtonian star. The range of the equation of state parameters allows the solution to be interpreted as barotropic matter stars or dark energy stars. A particular case shows that the model is physically reasonable and the energy conditions are satisfied.

Universal relations for neutron star f -mode and g -mode oscillations

Among the various oscillation modes of neutron stars, $f$- and $g$- modes are the most likely to be ultimately observed in binary neutron star mergers due to their relatively large coupling and shared frequencies with tidal excitations. The $f$-mode frequency and damping time are known to correlate in normal neutron stars with their compactness, and previous fits to hadronic stars are extended and shown to be valid for an extremely broad sampling of equations of state using a piecewise polytropic parametrization scheme for hadrons and a constant sound-speed parametrization for quark matter. Separate fits applicable to quark (self-bound) stars are improved. Much more significant correlations exist with tidal deformability, and therefore with moment of inertia and quadrupole moment. It is conclusively demonstrated that these correlations are the same for all types of stars, whether hadronic, hybrid, or pure quark, and its accuracy is quantified. A novel 1-node branch of the $f$-mode that occurs in low-mass hybrid stars in a narrow mass range just beyond the critical mass necessary for a phase transition to appear is identified. This 1-node branch shows the largest, but still small, deviations from the universal correlation for any configuration. It is characterized by a nonmonotonic relation between neutron star mass and $f$-mode frequency, in contrast to the behavior otherwise observed in normal, quark and hybrid stars. The $g$-mode only exists in matter with a nonbarotropic equation of state involving temperature, chemical potential or composition (such as being out of beta equilibrium), or a phase transition in barotropic matter. The $g$-mode therefore could serve as a probe for studying phase transitions in hybrid stars. In contrast with the $f$-mode, $g$-mode frequencies do not correlate well with tidal deformability, but depend strongly on properties of the transition (the density and the magnitude of the discontinuity) at the transition. Imposing causality and maximum mass constraints, a fit involving neutron star and phase transition properties is found and the $g$-mode frequency is determined to have an upper bound of about 1.25 kHz. However, if the sound speed ${c}_{s}$ in the inner core at densities above the phase transition density is restricted to ${c}_{s}^{2}\ensuremath{\le}1/3$, $g$-mode frequencies can only reach about 0.8 kHz, which are significantly lower than $f$-mode frequencies (1.3--2.8 kHz). $g$-mode gravitational wave damping times are found to be extremely long, $>{10}^{4}\text{ }\text{ }\mathrm{s}$ (${10}^{2}\text{ }\text{ }\mathrm{s}$) in the inner core with ${c}_{s}^{2}\ensuremath{\le}1/3$ (1), in comparison with $f$-mode damping times (0.1--1 s).

Dark matter and dark energy from a Kaluza–Klein inspired Brans–Dicke gravity with barotropic fluid

We study the Kaluza–Klein inspired Brans–Dicke model with barotropic matter. Following from our previous work, the traditional Kaluza–Klein gravity action is introduced with an additional scalar field and 2 gauge fields. The compactification process results in a Brans–Dicke model with a dilaton coupled to the tower of scalar fields whereas a gauge field from 5-dimensional metric forms a set of mutually orthogonal vectors with 2 additional gauge fields. The barotropic matter is then introduced to complete a realistic set up. To demonstrate the analytical solutions of the model, we consider the case in which only 2 lowest modes becoming relevant for physics at low scale. After derivation, equations of motion and Einstein field equations form a set of autonomous system. The dynamical system is analysed to obtain various critical points. Interestingly, by only inclusion of barotropic matter, the model provides us the critical points which capable of determining the presences of dark matter, dark energy and phantom dark energy.

Radiating composite stars with electromagnetic fields

We derive the junction conditions for a general spherically symmetric radiating star with an electromagnetic field across a comoving surface. The interior consists of a charged composite field containing barotropic matter, a null dust and a null string fluid. The exterior atmosphere is described by the generalised Vaidya spacetime. We generate the boundary condition at the stellar surface showing that the pressure is determined by the interior heat flux, anisotropy, null density, charge distribution and the exterior null string density. A new physical feature that arises in our analysis is that the surface pressure depends on the internal charge distribution for generalised Vaidya spacetimes. It is only in the special case of charged Vaidya spacetimes that the matching interior charge distribution is equal to the exterior charge at the surface as measured by an external observer. Previous treatments, for neutral matter and charged matter, arise as special cases in our treatment of composite matter.

Junction conditions for composite matter in higher dimensions

We derive the junction conditions for a general higher dimensional spherically symmetric radiating star across a comoving surface with an electromagnetic field. The charged composite interior consists of barotropic matter, a null dust and a null string fluid. The higher dimensional generalised Vaidya geometry describes the exterior radiating atmosphere of the charged composite star. We show at the stellar surface that the pressure is determined by the interior heat flux, anisotropy, null string density, charge distribution and the exterior null string density. The charge distribution affects the stellar pressure in general; the higher dimensional charged Vaidya spacetime is special and does not exhibit this feature. The number of dimensions appears explicitly in the surface pressure showing that the dimensions affect the gravitational dynamics. All previous treatments, for matter which is neutral or charged, emerge as special cases in our treatment.

Radiating stars with composite matter distributions

In this paper we study the junction conditions for a generalised matter distribution in a radiating star. The internal matter distribution is a composite distribution consisting of barotropic matter, null dust and a null string fluid in a shear-free spherical spacetime. The external matter distribution is a combination of a radiation field and a null string fluid. We find the boundary condition for the composite matter distribution at the stellar surface which reduces to the familiar Santos result with barotropic matter. Our result is extended to higher dimensions. We also find the boundary condition for the general spherical geometry in the presence of shear and anisotropy for a generalised matter distribution.

Probing kinematics and fate of Bianchi type V Universe

In this paper, we have constrained the cosmological parameters of Bianchi type V universe by bounding the model under consideration with recent observational [Formula: see text] and Pantheon data. It is assumed that the energy conservation law holds separately for barotropic fluid and dark energy fluid i.e. dark energy component does not interact with barotropic matter. We obtain the present value of deceleration parameter and age of universe as [Formula: see text] and 13.329 Gyrs respectively. The analysis of [Formula: see text] and jerk parameters concur that the derived model approaches [Formula: see text]CDM universe at late time. We find that estimated values of Hubble’s constant and energy density parameters have pretty consistency with their corresponding values, obtained by recent observations of WMAP and PLANCK collaborations. It is also observed that the universe shows signature flipping from decelerating to accelerating phase for transitional red-shift value [Formula: see text] in past.

Stable contraction in Brans-Dicke cosmology

Contracting Universe (including bouncing models) solution generally depends on the initial conditions and hence possesses an extreme fine-tuning problem. In order to probe the stability of those solutions, in this work, we consider the Brans-Dicke theory with the power law potential in the presence of an additional barotropic matter in the homogeneous and isotropic background. We study the phase space and obtain critical points. We find that the quadratic potential is a special case where one of the solutions always gives rise to de-Sitter solution in all conformally connected frame. We generalize the condition for arbitrary power law potential and find that contracting Universe solution can indeed lead to an attractor solution. In doing so, we also provide an example of a matter contracting Universe that leads to near scale-invariant spectra and study the behavior near the fixed point. In the vicinity of this point, the system behaves as the Universe contains three different types of matter. Amongst them, with time, energy densities of two effective fluids decay down and only the leading order solution survives. Therefore, the non-minimal coupling can address and solve the problem of fine-tuning of the contraction models and may open a different outlook.

Existence of static wormholes in f(𝒢,T) gravity

This paper investigates static spherically symmetric traversable wormhole (WH) solutions in [Formula: see text] gravity ([Formula: see text] and [Formula: see text] represent the Gauss–Bonnet invariant and trace of the energy–momentum tensor, respectively). We construct explicit expressions for ordinary matter by taking specific form of redshift function and [Formula: see text] model. To analyze the possible existence of wormholes, we consider anisotropic, isotropic, as well as barotropic matter distributions. The graphical analysis shows the violation of null energy condition for the effective energy–momentum tensor throughout the evolution while ordinary matter meets energy constraints in certain regions for each case of matter distribution. It is concluded that traversable WH solutions are physically acceptable in this theory.

String gravitational equations with Hermitian structure

We consider a string model at one-loop related to a [Formula: see text]-model whose antisymmetric tensor field is constructed as complex structure on the background manifold, especially on a manifold [Formula: see text] where [Formula: see text] is a complex manifold. As an example, we consider a homogeneous anisotropic [Formula: see text]-dimensional [Formula: see text]-model where space part of the background is a four-dimensional complex manifold. By solving the related one-loop [Formula: see text]-functions, we obtain a static solution so that by reduction of this solution to [Formula: see text]-dimension, we obtain a static solution of Einstein equation where the matter sector is effectively interpreted as an inhomogeneous, anisotropic and barotropic matter satisfying all the energy conditions. Finally, the [Formula: see text]-dual background of the solution is investigated and it is shown that the duality transformation and reduction processes commute with each other.

Non-minimal derivative coupling gravity in cosmology

We give a brief review of the non-minimal derivative coupling (NMDC) scalar field theory in which there is non-minimal coupling between the scalar field derivative term and the Einstein tensor. We assume that the expansion is of power-law type or super-acceleration type for small redshift. The Lagrangian includes the NMDC term, a free kinetic term, a cosmological constant term and a barotropic matter term. For a value of the coupling constant that is compatible with inflation, we use the combined WMAP9 (WMAP9+eCMB+BAO+ $H_0$) dataset, the PLANCK+WP dataset, and the PLANCK $TT,TE,EE$+lowP+Lensing+ext datasets to find the value of the cosmological constant in the model. Modeling the expansion with power-law gives a negative cosmological constants while the phantom power-law (super-acceleration) expansion gives positive cosmological constant with large error bar. The value obtained is of the same order as in the $\Lambda$CDM model, since at late times the NMDC effect is tiny due to small curvature.

Non-Minimally Conformally Coupling Cosmology with Multiple Vacua Potential with Cubic-Quintic-Septic Duffing Oscillator Properties

Abstract The dynamics of a flat Friedmann–Robertson–Walker (FRW) cosmological model with a barotropic matter is studied, which is dominated by an oscillating scalar field conformally coupled to the gravity with a scalar potential characterised by multiple vacua. Several motivating consequences are observed and discussed accordingly.

Dynamical complexity of the Brans-Dicke cosmology

The dynamics of the Brans-Dicke theory with a quadratic scalar field potential function and barotropic matter is investigated. The dynamical system methods are used to reveal complexity of dynamical evolution in homogeneous and isotropic cosmological models. The structure of phase space crucially depends on the parameter of the theory ωBD as well as barotropic matter index wm. In our analysis these parameters are treated as bifurcation parameters. We found sets of values of these parameters which lead to generic evolutional scenarios. We show that in isotropic and homogeneous models in the Brans-Dicke theory with a quadratic potential function the de Sitter state appears naturally. Stability conditions of this state are fully investigated. It is shown that these models can explain accelerated expansion of the Universe without the assumption of the substantial form of dark matter and dark energy. The Poincare construction of compactified phase space with a circle at infinity is used to show that phase space trajectories in a physical region can be equipped with a structure of a vector field on nontrivial topological closed space. For ωBD < −3/2 we show new types of early and late time evolution leading from the anti-de Sitter to the de Sitter state through an asymmetric bounce. In the theory without a ghost we find bouncing solutions and the coexistence of the bounces and the singularity. Following the Peixoto theorem some conclusions about structural stability are drawn.

Brans-Dicke theory and the emergence ofΛCDMmodel

The dynamics of the Brans-Dicke theory with a scalar field potential function is investigated. We show that the system with a barotropic matter content can be reduced to an autonomous three-dimensional dynamical system. For an arbitrary potential function we found the values of the Brans-Dicke parameter for which a global attractor in the phase space representing de Sitter state exists. Using linearized solutions in the vicinity of this critical point we show that the evolution of the Universe mimics the $\Lambda$CDM model. From the recent Planck satellite data, we obtain constraints on the variability of the effective gravitational coupling constant as well as the lower limit of the mass of the Brans-Dicke scalar field at the de Sitter state.

Magnetohydrodynamic equilibria in barotropic stars

AbstractAlthough barotropic matter does not constitute a realistic model for magnetic stars on short timescales, it would be interesting to confirm a recent conjecture that states that magnetized stars with a barotropic equation of state would be dynamically unstable (Reisenegger 2009). In this work we construct a set of barotropic equilibria, which can eventually be tested using a stability criterion. A general description of the ideal MHD equations governing these equilibria is summarized, allowing for both poloidal and toroidal magnetic field components. A new finite-difference numerical code is developed in order to solve the so-called Grad-Shafranov equation describing the equilibrium of these configurations, and some properties of the equilibria obtained are briefly discussed.

On coincidence problem in ELKO dark energy model

We study the critical points of a universe dominated by Eigenspinoren des Ladungskonjugationsoperatorsin (ELKO) spinor field dark energy and a barotropic matter without considering a specific potential or interaction. The coincidence problem and attractor solutions are discussed at late time, and it is shown that the coincidence problem can not be solved in this model.

Twister quintessence scenario

We study generic solutions in a non-minimally coupled to gravity scalar field cosmology. It is shown that dynamics for both canonical and phantoms scalar fields with the potential can be reduced to the dynamical system from which the exact forms for an equation of the state parameter can be derived. We have found the stationary solutions of the system and discussed their stability. Within the large class of admissible solutions we have found a non-degenerate critical points and we pointed out multiple attractor type of trajectory travelling in neighborhood of three critical points at which we have the radiation dominating universe, the barotropic matter dominating state and finally the de Sitter attractor. We have demonstrated the stability of this trajectory which we call the twister solution. Discovered evolutional path is only realized if there exist the non-minimal coupling constant. We have found simple duality relations between twister solutions in phantom and canonical scalar fields in the radiation domination phase. For the twister trajectory we have found an oscillating regime of approaching the de Sitter attractor.

Three steps to accelerated expansion

We study the dynamics of a non-minimally coupled scalar field cosmology with a potential function. We use the framework of dynamical systems theory to investigate all evolutional paths admissible for all initial conditions. Additionally, we assume the presence of barotropic matter and show that the dynamics can be formulated in terms of an autonomous dynamical system. We have found fixed points corresponding to three main stages of the evolution of the universe, namely, radiation, matter and quintessence domination epochs. Using the linearization of the dynamical systems in the vicinity of the critical points we explicitly obtain formulas determining the effective equation of state parameter for the universe at different epochs. In our approach the form of $w(z)$ parametrisation is derived directly from the dynamical equations rather than postulated {\it a priori}.

Three steps to accelerated expansion

AbstractWe study the dynamics of a non‐minimally coupled scalar field cosmology with a potential function. We use the framework of dynamical systems theory to investigate all evolutional paths admissible for all initial conditions. Additionally, we assume the presence of barotropic matter and show that the dynamics can be formulated in terms of an autonomous dynamical system. We have found fixed points corresponding to three main stages of the evolution of the universe, namely, radiation, matter and quintessence domination epochs. Using the linearization of the dynamical systems in the vicinity of the critical points we explicitly obtain formulas determining the effective equation of state parameter for the universe at different epochs. In our approach the form of w(z) parametrisation is derived directly from the dynamical equations rather than postulated a priori.