Considering the finite IR behavior of quantum chromodynamics (QCD) running coupling constant in some experiments, we intend to investigate different models presenting running coupling with finite values in the IR region. Using analytic and background
perturbation theories, we obtain some equation of states (EoSs) of strange quark matter which satisfy necessary conditions of suitable EoSs. Then we evaluate the properties of strange quark stars in general relativity. Our results for maximum gravitational mass is comparable with the recent LIGO data for the compact binary merger, GW190425.
In this work, based on the cluster expansion of the energy functional, we have extracted a formalism for calculation of the thermodynamic properties of fluids with non-spherical molecules. The salient feature of the extracted formalism is that it has
no restrictions on the type of interaction. In fact our formalism can be employed for all types of realistic inter-particle interactions. Here, for the interaction of two anisotropic molecules, we have applied the Gay-Berne potential. Finally, we have applied this formalism to calculate some thermodynamic properties of fluid H_2 which shows some expected results.
Motivated by importance of the cosmological constant on structure of the hybrid neutron star. In other words, we want to investigate the structure of neutron stars by considering both the effects of the cosmological constant and the existence of quar
k matter for neutron stars in Einstein gravity. For this purpose, we use of a suitable equation of state (EoS) which includes a layer of hadronic matter, a mixed phase of quarks and hadrons, and, a quark matter in core. In order to investigate the effect of the cosmological constant on the structure of hybrid neutron stars, we utilize of modified TOV equation in Einstein-$Lambda $ gravity. Then we plot the mass-radius diagram for different value of the cosmological constant. Our results show that for small values of the cosmological constant ($Lambda $), especially for the cosmological constant from the cosmological perspective $(Lambda=10^{-52}$ $m^{-2})$, $Lambda $ has no significant effect on structure of hybrid neutron star. But for bigger values, for example, by considering $Lambda>10^{-14}$ $m^{-2}$, this quantity affects on the maximum mass and radius of these stars. The maximum mass and radius of these stars decrease by increasing the cosmological constant $Lambda$. Also by determining and analyzing radius, compactness, Kretschmann scalar and gravitational redshift of a hybrid neutron star with $M=1.4M_{,odot }$ in the presence of the cosmological constant, we find that, by increasing $Lambda$, this star is contracted. Also, our results about dynamical stability show that these stars satisfy this stability.
Regarding the strong magnetic field of neutron stars and high energy regime scenario which is based on high curvature region near the compact objects, one is motivated to study magnetic neutron stars in an energy dependent spacetime. In this paper, w
e show that such strong magnetic field and energy dependency of spacetime have considerable effects on the properties of neutron stars. We examine the variations of maximum mass and related radius, Schwarzschild radius, average density, gravitational redshift, Kretschmann scalar and Buchdahl theorem due to magnetic field and also energy dependency of metric. First, it will be shown that the maximum mass and radius of neutron stars are increasing function of magnetic field while average density, redshift, the strength of gravity and Kretschmann scalar are decreasing functions of it. These results are due to a repulsive-like force behavior for the magnetic field. Next, the effects of the gravitys rainbow will be studied and it will be shown that by increasing the rainbow function, the neutron stars could enjoy an expansion in their structures. Then, we obtain a new relation for the upper mass limit of a static spherical neutron star with uniform density in gravitys rainbow (Buchdahl limit) in which such upper limit is modified as $M_{eff}<frac{4c^{2}R}{9G}$. In addition, stability and energy conditions for the equation of state of neutron star matter are also investigated and a comparison with empirical results is done. It is notable that the numerical study in this paper is conducted by using the lowest order constrained variational (LOCV) approach in the presence of magnetic field employing AV18 potential.
