Narrow Results

A breakthrough has been achieved in solving the Einstein field equations for a specific class of charged compact objects existing in higher dimensions with inhomogeneous matter distribution. The geometry of space-time is believed to be spheroid, encapsulated in $(n+2)$ dimensions of Euclidean space where $n=D-2$, $D$ be the space-time dimension. The internal physical $(n+1)$ space is elucidated by the Vaidya–Tikekar metric ansatz, which is defined by spheroidal and curvature parameters. The form of the equation of state in MIT bag model, $p=\frac{1}{3}(\rho -4B)$, where the constant $B$ is termed as bag constant, is implemented to investigate the relevant physical features of anisotropic strange quark stars containing a net amount of charge. The inclusion of higher dimensions effectively decreases the mass retained within a given radius of a compact object but increases its compactness. For a particular dimension, if one increases the value of $B$, the mass increases for a given value of radius. Determination of maximum radius and consequently, maximum mass have been obtained by equating the value of radial sound velocity as the extreme limit of causality $(=1)$ at the center of the star. Both the maximum mass and radius of a given compact object are found to increase when both charge and pressure anisotropy increase and decrease for an increment of surface density or bag constant $B$. The maximum mass attained in the model is $3.498M_{\odot }$. Prediction of the radius of some recently observed compact objects has also been done for different $D$, $B$, charge and pressure anisotropy parameters. Different energy conditions and stability criteria stand up throughout the compact object containing anisotropy in pressure and net charge. The tidal deformability of some compact objects has also been investigated using the present model.

In this paper, we calculate the Casimir energy for a massive fermionic field confined between two points in one spatial dimension, with the MIT bag model boundary condition. We compute the Casimir energy directly by summing over the allowed modes. The method that we use is based on the Boyer's method, and there will be no need to resort to any analytic continuation techniques. We explicitly show the graph of the Casimir energy as a function of the distance between the points and the mass of the fermionic field. We also present a rigorous derivation of the MIT bag model boundary condition.

In this paper, we analyze the fermionic Casimir effects associated with a massless quantum field in the context of Lorentz symmetry violation approach based on Horava–Lifshitz methodology. In order to obtain these observables, we impose the standard MIT bag boundary condition on the fields on two large and parallel plates. Our main objectives are to investigate how the Casimir energy and pressure depend on the parameter associated with the breaking of Lorentz symmetry.

This study is explored to discuss the anisotropic nature of charged strange compact stars by considering the MIT bag model in the context of our universe’s accelerated expansion scenario. For this purpose, we choose two models for spherically symmetric space–time components. In Model-I, we plug the embedded space–time to evaluate the Bardeen strange stellar structures. In Model-II, we choose the Krori–Barua space–time. We correlate the Bardeen geometry as an exterior solution with a spherically symmetric interior geometry to acquire unknown parameters involved in the study. We discuss the necessary properties of the strange stellar models with embedded space–time and Krori–Barua space–time via the MIT bag model. After witnessing the minor differences in our proposed models, Andreasson’s limit $\sqrt{M}\le \sqrt{R_{𝜖}}/3+\sqrt{R_{𝜖}/9+q^2/3R_{𝜖}}$ has been fulfilled as required by the charged stellar structures. Further, we conclude that all the acquired results show the stable and self-consistent behavior of charged anisotropic compact structures.

Quark matter is expected to exist in the interior of compact stellar objects as neutron stars or even the more exotic strange stars, based on the Bodmer–Witten conjecture. Bare strange quark stars and (normal) strange quark-matter stars, those possessing a baryon (electron-supported) crust, are hypothesized as good candidates to explain the properties of a set of peculiar stellar sources such as the enigmatic X-ray source RX J1856.5-3754, some pulsars such as PSR B1828-11 and PSR B1642-03, and the anomalous X-ray pulsars and soft γ-ray repeaters. In the MIT bag model, quarks are treated as a degenerate Fermi gas confined to a region of space having a vacuum energy density B_bag (the Bag constant). In this note, we modify the MIT bag model by including the electromagnetic interaction. We also show that this version of the MIT model implies the anisotropy of the bag pressure due to the presence of the magnetic field. The equations of state of the degenerate quarks gases are studied in the presence of ultra strong magnetic fields. The behavior of a system made up of quarks having (or not) anomalous magnetic moment is reviewed. A structural instability is found, which is related to the anisotropic nature of the pressures in this highly magnetized matter. The conditions for the collapse of this system are obtained and compared to a previous model of neutron stars that is built on a neutron gas having anomalous magnetic moment.

In this paper, we present a strange stellar model using Tolman $V$-type metric potential employing simplest form of the MIT bag equation of state (EOS) for the quark matter. We consider that the stellar system is spherically symmetric, compact and made of an anisotropic fluid. Choosing different values of $n$ we obtain exact solutions of the Einstein field equations and finally conclude that for a specific value of the parameter $n=1/2$, we find physically acceptable features of the stellar object. Further, we conduct different physical tests, viz., the energy condition, generalized Tolman–Oppeheimer–Volkoff (TOV) equation, Herrera’s cracking concept, etc., to confirm the physical validity of the presented model. Matching conditions provide expressions for different constants whereas maximization of the anisotropy parameter provides bag constant. By using the observed data of several compact stars, we derive exact values of some of the physical parameters and exhibit their features in tabular form. It is to note that our predicted value of the bag constant satisfies the report of CERN-SPS and RHIC.

The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The anisotropy of the pressures is discussed. The mass-radius relation for such stars is also studied.

The aim of this paper is to study the charged anisotropic strange stars in the Rastall framework. Basic formulation of field equations in this framework is presented in the presence of charged anisotropic source. To obtain the solutions of the Rastall field equations in spherically symmetric Karori and Barua (KB) type space-time, we have considered a linear equation of state of strange matter, using the MIT bag model. The constraints on the Rastall dimensionless parameter $\gamma$ are also discussed to obtain the physically reasonable solution. We explore some physical features of the presented model like energy conditions, stability and hydrostatic equilibrium, which are necessary to check the physical viability of the model. We also sought for the influence of the Rastall dimensionless parameter on the behavior of the physical features of obtained solution. We plot the graphs of matter variables for different chosen values of the parameter $\gamma$ to inspect more details of analytical investigations and predict the numerical values of these variables exhibited in the tabular form. For this analysis, we choose four different arbitrary models of strange stars with compactness $u(=\frac{M}{R})$ 0.25, 0.30, 0.35 and 0.40. We observed that all the necessary physical conditions are satisfied and the presented model is quite reasonable to study the strange stars.

The strange quark matter (SQM) for which the distribution is governed by the equation of state of the simplified MIT bag model such as: $p_r=\frac{1}{3}(\rho -4B)$, with $B$ the bag constant, in the presence of a load distribution given by $q(r)=Q{(r/R)}^3=\alpha r^3$ has been the subject of a series of investigations within the framework of Rastall–Maxwell theory. We used the Modified Tolman–Oppenheimer–Volkoff (TOV) equation in Rastall gravity to generate the solutions by make using the conformal Killing vector. In order to check the physical acceptability of our solutions from conformal Killing vector method, we investigated around the Energy conditions, the Mass–Radius relation, Modified TOV equation, redshift and the stability of the system through Adiabatic Index, the Compactification factor and Causality condition. For physical values of Rastall parameters, we noticed that the stellar systems become more massive in proportion to their size. Then, this leads them into less dense compact objects which reveals that the alternative theory of Rastall is appropriate to better explain the behavior of massive stellar objects.

By constructing models of quark stars (QSs), we use the MIT bag model as a strange quark matter equation of state (EoS). According to the strange matter hypothesis, the MIT bag model is the most successful phenomenological models of quarks confined to hadrons. This paper aims to explore the internal structure and the physical properties of QSs in the context of four-dimensional (4D) Einstein–Gauss–Bonnet (EGB) theory of gravity. The main feature of 4D EGB theory is that there is a nontrivial contribution to the gravitational dynamics in 4D spacetime. We present the essential features of QSs concerning the mass-radius relation depending on the interplay of matter parameters and the GB coupling constant. Our results show that all studied cases are found to be consistent with observations and physically relevant.

In this paper, we have developed a class of new solutions for relativistic compact stars in higher-dimensional $(D\ge 4)$ space-time assuming pseudo-spheroidal geometry of the $g_{rr}$ metric component. To study the physical properties, we consider equation of state of interior strange matter $p=\frac{1}{3}(\rho -4B)$, as proposed in MIT bag model in the presence of a density-dependent $B$ parameter. The interior matter of a quark star may consist of three flavor quarks. We observe some interesting results. The parameter $B$ depends on the anisotropy $(\alpha )$ in the interior, and at the stellar surface, $B$ attains a constant value independent of $\alpha$. At the interior, $B$ increases with the increase of $\alpha$. We also note that the value of B approaches a constant value with increasing spheroidal parameter $\lambda$. $B(\rho )$ also depends on space-time dimensions and it is interesting to note that $B(\rho )$ picks up negative values near core region which limits the number of space-time dimensions available for a stellar model. All the stability criterion and energy conditions hold good for a physically realistic stellar configuration. It is observed that strange quark matter may be stable or metastable or unstable depending upon the value of energy per baryon $(E_B)$. Strange quark matter will be stable if energy per baryon $E_B<930.4{\mathrm{\text{MeV/fm}}}^3$. It is noted that the maximum mass obtainable in this model is $1.99M_{\odot }$ considering stable strange quark matter when dimension $D=4$. In addition, we observe that the dimensions have some effect on the gross properties of strange stars (SS).

Equation of state of strange quark matter (SQM) in a nonuniform magnetic field is studied within the phenomenological MIT bag model under the charge neutrality and beta equilibrium conditions, relevant to the interior of strange quark stars. The spatial dependence of the magnetic field strength is modeled by the dependence on the baryon chemical potential. The total energy density, longitudinal and transverse pressures in magnetized SQM are found as functions of the baryon chemical potential. It is clarified that the central magnetic field strength in a strange quark star is bound from above by the value at which the derivative of the longitudinal pressure with respect to the baryon chemical potential vanishes first somewhere in the interior of a star under varying the central field. Above this upper bound, the instability along the magnetic field is developed in magnetized SQM.

We investigate the rigidly rotating quantum thermal distribution of fermions in flat space-time. We find that thermal states diverge on the speed of light surface. We remove the divergences by enclosing the system inside a cylindrical boundary and investigate thermal expectation values and the Casimir effect for two sets of boundary conditions.