Narrow Results

We develop a theoretical method of constructing the scalar (quintessence or phantom) potential directly from the dimensionless dark energy function X(z), the dark energy density in units of its present value. We apply our method to two parametrizations of the dark energy density, the quiessence-Lambda ansatz and the generalized Chaplygin gas model, and discuss some features of the constructed potentials.

Neutrino matter and the quintessence field interacting with a fermion field are added to a MSSM EW Lagrangian previously used to calculate the magnetic field created during the Electroweak Phase Transition (EWPT). Flavor neutrinos are linear combinations of neutrinos with a definite mass. We estimate the mass of neutrinos using the value of the quintessence field during the EWPT with a modification of parameters used in a previous work on Dark Matter–Dark Energy interactions for a weak neutrino interaction. The possibility that sterile neutrinos might be Dark Matter is briefly reviewed.

Recently literature is found to be enriched with studies related to anisotropic behaviors of different compact stars in the background of $f(T)$ gravity in different energy conditions. Quintessence field, as local impacts of cosmic acceleration upon the compact stars, is also very interesting in recent studies. In this paper, the quintessential field effects on the compact stars (mainly on the neutron stars with an wide range of mass distributions), repulsive gravitational effects inside the compact stars due to dark matter distribution in them, charge distribution inside them in strong energy condition, etc. are studied. All required equations of motion using anisotropic property and concept of Massachusetts Institute of Technology bag model are acquired. Black holes surrounded by quintessential matters which satisfy the additive and linearity conditions, with the form of energy tensors were proposed and the corresponding metric was derived by Kiselev.¹ The metric, described by Krori and Barua² with Reissner–Nordström metric³ are compared to find out the different numerical values of unknown parameters. The numerical values are derived and some important parameters like anisotropic stress, adiabatic constant, surface redshift, electric intensity, compactness factor, stability etc. are analyzed deeply to get a clear idea for further study on these types of stars and to understand their nature.

In this work, we investigate the Rastall–Maxwell theory around the strange quark matter (SQM) in the presence of a quintessence field and a quintessence dark energy having a characteristic parameter $w_q$ such that $-1<w_q<-1/3$. The SQM is governed by the simplified MIT bag model equation of state: $p_r=\frac{1}{3}(\rho -4B)$, with $B$ the bag constant, in the presence of a load distribution given by $q(r)=Q{(r/R)}^3=\alpha r^3$. We find some solutions by using the modified Tolman–Oppenheimer–Volkoff (TOV) equation in the framework of Rastall gravity. We investigate the energy condition, the mass–radius relation, modified TOV equation, redshift and the stability of the system is checked by exploring the adiabatic index, the compactification factor and the causality condition for verifying the physical consistency of our model. We notify that for physical values of Rastall parameter, the stellar system is more massive compared to its size. Hence, it is revealed that the alternative Rastall theory is appropriate to explain the behavior of massive stellar objects. The presence of dark energy motivates us to consider that the existing strange stars are a mixture of both ordinary matter and quintessence matter in different proportions. The incorporation of quintessence matter with the real one describes the well-known SQM.

In this paper, we study the quantum-corrected Schwarzschild AdS black hole surrounded by quintessence matter in two folds: its thermal quantities and shadows. For this purpose, first, we present a detailed analysis of the influences of the quintessence matter field on Hawking temperature, mass, Gibbs free energy, and specific heat functions. Then, we examine the shadows by following Carter’s approach. We find that the shadow radius value takes smaller values for greater quintessence state parameter values. On the other hand, we see that the shadow radius takes greater values for greater values of the normalization parameter. Finally, in a brief section, we discuss the energy emission rate and show that the Gaussian-type plots’ peak values are also affected by the quintessence matter field parameters.

This paper proposes a new framework to investigate the spherically symmetric of anisotropic stars with clouds of strings and quintessence field in Rastall gravity. We develop the field equations in a spherically symmetric space–time with a quintessence field and clouds of string. We utilize the mass and radius of Her X-1, Vela X-1, SMC X-1, SAX J1808 0.4-3658 and 4 U 1538-52, which are well mentioned in the literature. We applied the matching conditions by considering outer space calculated in Rastall gravity to evaluate the constants parameters. To check the stability and physical presence of compact models, we computed the most important features of quintessence stars in the presence of a cloud of strings. We explored characteristics including energy density, quintessence density, radial pressure, tangential pressure gradients, anisotropic factor, energy conditions, sound speeds, TOV forces, EoS components, mass function, compactification and redshift.

We propose a new model for studying the dark constituents of the universe by regarding the dark energy as a $q$-deformed scalar field interacting with the dark matter, in the framework of standard general relativity. Here we assume that the number of particles in each mode of the $q$-deformed scalar field varies in time by the particle creation and annihilation. We first describe the $q$-deformed scalar field dark energy quantum-field theoretically, then construct the action and the dynamical structure of these interacting dark sectors, in order to study the dynamics of the model. We perform the phase space analysis of the model to confirm and interpret our proposal by searching the stable attractor solutions implying the late-time accelerating phase of the universe. We then obtain the result that when interaction and equation-of-state parameter of the dark matter evolve from the present day values into a particular value, the dark energy turns out to be a $q$-deformed scalar field.

In this work, we have discussed the anisotropic compact stars in the framework of modified Gauss–Bonnet gravity, named by f(G) theory of gravity. We have found the equations of motion of stars with respect to spherically symmetric metric, describing interior geometry of the compact stellar object, anisotropic mode of the matter distribution in the presence of electromagnetic field and quintessence field. We have taken the metric coefficients in the form $\mu ={\mathrm{\text{Br}}}^{\alpha }+{\mathrm{\text{Cr}}}^{\beta }$ and $\lambda ={\mathrm{\text{Ar}}}^{\gamma }$ as well as a particular form of $f(G)=G^2$, where the powers and coefficients of r are constants. The unknown constants are evaluated by matching between interior and exterior Reissner–Nordström–de Sitter metric. We have analyzed some physical aspects like energy density, radial and tangential pressures, anisotropic parameter of matter distribution, energy conditions, mass-radius relation, compactness factor, surface redshift, and stability of our resulting solutions through graphical behavior by comparing to the observational data of different types of compact stars like 4U1820-30, Vela X-1 and SAXJ1808.4-3658. We conclude that all physical attributes maintain their experimental ranges which deliver our anisotropic compact star models are viable and also stable upto certain region in $f(G)$ gravity theory.

Recent research works have shown the existence of super-massive neutron stars (NSs) with mass about $2.2M_{\odot }$ or even more. The query about those super-massive NSs inspires the researchers to analyze their features and structures immensely. Here, we have inspected the behavior and properties of some of those super-massive NSs in $f(T)$ modified gravity with $T=T+\alpha T^2$, where $T$ is the torsional scalar and $\alpha$ is a regulatory parameter. In this framework of teleparallel formalism of modified gravity, we obtain the equations of motion by considering quintessence field, modified Chaplygin gas (MCG) and electromagnetic field. For our model, we use matching conditions under spherical symmetry, in order to find out the numerical values of different unknown constants of our model. This helps us to acquire various physical quantities thoroughly and to understand about the nature of those super-massive NSs deeply and quite clearly. Moreover, from our work, we can also explain the role of quintessence field and MCG in case of massive compact stars. The mass–radius relationship curve of this model can effectively describe the mass of the heaviest NS (about $2.6M_{\odot }$) ever detected via gravitational wave detection. Again, we overall investigate the anisotropic behavior, density profile, pressure profile, core repulsive force, stability, equilibrium and energy conditions of those massive compact objects. We further analyze different important parameters like anisotropic stress, surface redshift, adiabatic behavior, compactness factor, sound speed, etc. in case of super-massive NSs for better realization and future study.

In this work, we study the phase transition of the charged-AdS black hole surrounded by quintessence via an alternative extended phase space defined by the charge square $Q^2$ and her conjugate $\mathrm{\Psi }$, a quantity proportional to the inverse of horizon radius, while the cosmological constant is kept fixed. The equation of state is derived under the form $Q^2=Q^2(T,\mathrm{\Psi })$ and the critical behavior of such black hole analyzed. In addition, we examine the role of the quintessence parameter and its effects on phase transitions. Besides that, we explore the connection between the microscopic structure and Ruppeiner geothermodynamics. We also find that, at certain points of the phase space, the Ruppeiner curvature is characterised by the presence of singularities that are interpreted as a signal of the occurrence of the phase transitions.

Immediate local impacts of cosmic acceleration upon a rapidly rotating black hole are very interesting in recent studies. In this paper, the stability of a rapidly rotating black hole and the minimum value of the ratio between the black hole’s angular momentum to it’s mass which ensures the stability, are investigated simultaneously. Also, two modern forms of uncertainty relations are proposed by enhancing the usual Heisenberg algebra with superior terms, in order to supervise on thermodynamic properties of the rotating black hole. An asymptotically flat Kiselev black hole solution, cultivated by quintessence field is chosen for this purpose. The local shifts in spacetime geometry next to the rotating black hole can be resolved from a modified metric, occupying the surrounding spacetime of the black hole. The angular momentum of a rotating black hole depends on the rate of change in acquiring mass by it. On the other hand, at the same time, due to the effect of the quintessence field, there exists repulsive gravitational force inside the black hole. So, there is an uncertainty in the position of innermost stable circular orbit as well as radius of the rotating black hole. This uncertainty is also investigated in our work. Relying on two new forms of uncertainty principle, the modified thermodynamic variables like black hole’s Hawking temperature, heat-capacity, entropy at the black hole’s event horizon, etc. are computed under rotation. Quantum corrections of black hole’s Hawking temperature, entropy, free-energy, etc. are also explored. Further, quantum corrected heat capacity of the rotating black hole is studied and also thermal stability is inquired. The existence of transitions of phase in case of a rapidly rotating black hole are also found out. Again, quantum corrected entropy of black hole contains logarithmic terms and their effects on thermal stability of the rotating black hole are also discussed. Modifications in the mass-temperature, specific heat, etc. of a rotating black hole are also presented according to the modified extension parameters.

This paper proposes a new model for anisotropic compact stars with quintessence in Rastall teleparallel gravity via embedding approach. In the gravity, the acquired field equations encompassing the anisotropic matter source as well as the quintessence field are studied using the specific character of the scalar torsion $T$ for the observed stars candidates PSRJ1416–2230, 4U1608–52, CenX–3, EXO 1785–248 and SMCX–1. All of the stellar structures under consideration are said to be advantageously independent of any central singularity and are stable. A thorough graphical analysis reveals that numerous physical properties critical for forming stellar structures are satisfied.