Narrow Results

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.

In this work, we calculate the moment of inertia of the pulsar of the binary system J0737-3039A in the framework of Einstein's gravitational theory combined with a relativistic field theoretical approach for nuclear matter in the slow rotating regime, taking into account that the star's frequency is much smaller than Kepler's frequency. In the description of the EoS for nuclear matter, we consider a generalized class of relativistic multi-baryon Lagrangian density mean field approach which contains adjustable nonlinear couplings of the meson fields with the baryon fields. Upon adjusting the model parameters to describe bulk static properties of ordinary nuclear matter, we determine the EoS of the pulsars. By analyzing the results, dynamical constraints for neutron star models are identified.

This work aims at using a semiclassical approach to explain how the universe was created out of nothing, i.e., with no input of initial energy nor mass. The inflationary phase with exponential expansion is accounted for, automatically, by our equation of state for the very early universe.

In this paper, a general formula of the symmetry energy for many-body interaction is proposed and the commonly used two-body interaction symmetry energy is recovered. Within Landau's theory (Lt), we generalize two equations of state (EoS) CCSδ3 and CCSδ5 to asymmetric nuclear matter. We assume that the density and density difference between protons and neutrons divided by their sum are order parameters. We use different EoS to study neutron stars by solving the TOV equations. We demonstrate that different EoS give different mass and radius relation for neutron stars even when they have exactly the same ground state (gs) properties (E/A, ρ₀, K, S, L and K_sym). Furthermore, for one EoS we change K_sym and fix all the other gs parameters. We find that for some K_sym the EoS becomes unstable at high density even for neutron matter. This suggests that a neutron star (NS) can exist below and above the instability region but in different states: a quark gluon plasma (QGP) at high density and baryonic matter at low density. If the star's central density is in the instability region, then we associate these conditions to the occurrence of supernovae (SN).

In the study of nuclear matter it is common to employ effective models, that in essence are relativistic mean-field theories based on the Yukawa formulation. In such models we consider the baryons interacting through scalar and vector mesons exchanges, without taking into account the presence of quarks and gluons. The intensity of the effective interaction carried on by mesons is regulated by effective coupling constants which must be selected so that the theory is able to reproduce the basic properties of nuclear matter. The present investigation is a first approach on the analysis and explicitness of the effects of the hyperon-meson coupling constants on the prediction of measurable quantities. The purpose is to use an effective generalized derivative-coupling model and parametrize the equation of state (EoS) as a function of the coupling constants. We show the stiffness dependence of the EoS on the couplings and the related phenomenological results for the mass radius ratio of neutron stars. From observations one may constrain validity regions for the hyperon couplings.