MIT Bag Model Research Articles

Self-gravitating electrically charged anisotropic strange star model

The main focus of this paper is devoted to exploring the physical aspects of compact stars with the presence of electric charge under an embedded Class I approach in the arena of Bardeen geometry. We derive the embedded Class I solutions by taking spherically symmetric static spacetime with an anisotropic source of matter. We also look at the equation of state (EoS) for strange quark matter (SQM), which inspired the phenomenological MIT-Bag model as a free Fermi gas of quarks. The unknown constants are evaluated through the boundary conditions along with the Bardeen model to portray as an exterior space–time. Bardeen’s model becomes very interesting in an entertaining and unique way with great precision as it could be interpreted as the analytical solutions of some appropriate nonlinear electrodynamics associated with the gravitational field. In this concern, we thoroughly explored the dependence of several physical parameters, such as the metric potentials, energy density, pressure constituents, anisotropy, and electric charge, etc., on the chosen varied values of n. Finally, we discuss the physical viability and stability of the stellar model through various physical tests. It is important to mention here that the obtained stellar configuration is in agreement with the physical viability and stability criteria under the effect of the electric charge and anisotropic fluid source of matter.

Variable hadronic bag pressure effect in colorless deconfining phase transition: Thermodynamic lower bounds for hadronic bag pressure and hadronic bag surface tension

The Quantum Chromo Dynamics (QCD), with its two main properties of confinement and asymptotic freedom, is considered as the fundamental theory of the strong interaction from which the phenomenology of string model and hadronic bag models can be derived as particular cases. In QCD, besides quark masses, there is only one parameter, the renormalization scale parameter [Formula: see text], which comes into play. In nonperturbative models, like string model and bag models, the string constant [Formula: see text], the hadronic bag surface tension [Formula: see text] and the concept of the hadronic bag pressure [Formula: see text] emerge naturally. Since these parameters characterize the same color confining force, this explains the existence of simple mathematical relationships that connect them. Although in most applications of the MIT bag model, considering [Formula: see text] with its phenomenologically determined value as a constant does not generate any inconsistency, however, there are some indications that [Formula: see text] is not a universal constant. The concept of hadronic bag pressure [Formula: see text] as a parameter was introduced long before, and we plan in this work to extrapolate the concept of [Formula: see text] to become a full-fledged thermodynamic variable and to explore the consequences of its variability in the context of our colorless MIT bag model. To achieve this, we carry out a detailed thermodynamic study based on the three variables [Formula: see text] using an improved [Formula: see text]-method and considering the hadronic bag pressure [Formula: see text] as a thermodynamic variable like the temperature [Formula: see text] and volume [Formula: see text]. The findings in the small [Formula: see text] region, in themselves, are very unexpected and exciting that essentially concern the abnormal behavior of the order parameter [Formula: see text]. This shows that, from an experimental point of view, a low value of the hadronic bag pressure [Formula: see text] would have dramatic consequences. Thus, it is argued that the abnormal behavior observed in the order parameter [Formula: see text] well reflects the appearance of the mixed state at low temperature before the deconfining process. We also indicate how this result might be avoided by imposing a lower bound on the hadronic bag pressure: [Formula: see text]. A detailed study of the global properties of the order parameter [Formula: see text] as function on the three variables is given, and as an illustration of our ideas we construct three different criteria from which we extract the lower bound of the hadronic bag pressure [Formula: see text]. We succeeded to show that the physically genuine colorless deconfining phase transition is feasible only if the thermodynamic lower bound is taken as [Formula: see text][Formula: see text]MeV. As a consequence, the corresponding lower bound of the hadronic bag surface tension is [Formula: see text][Formula: see text]MeV. Our results are consistent with each other, and seem to corroborate the results obtained by other approaches, such as the thermodynamic model of chromo-magnetism. We focus not only on certain technical details, but also on physical understanding and interpretation. The results are relevant for the parton phenomenology of stars and for URHIC experiments. We review some of the underlying physics and discuss outstanding questions regarding this variability.

Impact of minimal matter-geometry coupling on anisotropic quark stars

This paper inspects the impact of minimal matter-geometry coupling present in [Formula: see text] model of [Formula: see text] theory on the physical attributes of anisotropic quark stars. The geometry of considered stellar candidates is modeled via spherically symmetric static spacetime whose metric functions are influenced by Heintzmann solutions. The inner matter distribution of the stellar system is assumed as anisotropic with the phenomenological MIT bag model equation of state. The expressions of unknown parameters that appear in Heintzmann solution are evaluated in terms of mass and radius by the continuity of interior and exterior geometries. Further, insertion of masses and radii of some particular observed stellar models will yield their numerical values. In order to discuss the physical acceptability as well as stability of the quarks stars based on the considered solutions, we have checked the physical behavior of matter variables, mass and related quantities, energy conditions, equilibrium of forces, adiabatic index and Herrera’s cracking concept. The energy conditions are fulfilled ensuring the compatibility of assumed matter and geometry of quark stars. It is also found that all compact star candidates exhibit stable structures corresponding to the proposed values of the model parameters. Hence, the considered [Formula: see text] model shows consistency with all the physical conditions and presents a viable study to the nature of anisotropic massive stellar system.

Gravitational wave echoes from compact stars in f(R,T) gravity

We have calculated the static and spherically symmetric solutions for compact stars in the $f(\mathcal{R},T)$ gravity metric formalism. To describe the matter of compact stars, we have used the MIT Bag model equation of state (EoS) and the color-flavor-locked (CFL) EoS. Solving the hydrostatic equilibrium equations i.e., the modified TOV equations in $f(\mathcal{R},T)$ gravity, we have obtained different stellar models. The mass-radius profiles for such stars are eventually discussed. The stability of these configurations are then analysed using different parameters. From the obtained solutions of TOV equations for mass and radius, we have checked the compactness of such objects. It is found that similar to the unrealistic EoS, like the stiffer form of the MIT Bag model, under some considerations the realistic interacting quark matter CFL EoS can give stellar structures which are compact enough to possess a photon sphere outside the stellar boundary and hence can echo GWs. The obtained echo frequencies are found to lie in the range of 39-55 kHz. Also we have shown that for different parametrizations of the gravity theory, the structure of stars and also the echo frequencies differ significantly. Moreover, we have constrained the pairing constant value $\beta$ from the perspective of emission of echo frequencies. For the stiffer MIT Bag model $\beta\geq-2.474$ and for the CFL phase with massless quark condition $\beta\geq-0.873$, whereas for the massive case $\beta\geq-0.813$.

Decoupled quark stars relativistic models in the regime of self-interacting Brans–Dicke gravity

In this work, we generate two static anisotropic solutions for a sphere containing quark matter in the framework of self-interacting Brans–Dicke theory. For this purpose, we add an anisotropic source in the seed distribution and decouple the field equations through deformation in the radial metric function. As a result of this transformation, the field equations are disintegrated into two systems which separately include the effects of isotropic and anisotropic sources. The system related to the additional source is solved via the MIT bag model equation of state. We consider Tolman V spacetime and Karmarkar condition to formulate two solutions for the isotropic sector which are extended to the anisotropic domain via decoupling technique. The junction conditions at the boundary determine the unknown parameters in terms of mass and radius of the spherical object. We investigate the viability and stability of the constructed strange star models in the presence of massive scalar field corresponding to three strange star candidates: Her X-1, PSR J1614-2230 and 4U 1608-52. It is concluded that the anisotropic models are well-behaved as they fulfill the necessary requirements for lower as well as higher values of the decoupling parameter. • We generate two anisotropic spherical solutions with quark matter in self-interacting Brans–Dicke theory. • Viability and stability of the constructed strange star models are checked for three strange star candidates. • Anisotropic models are well-behaved for lower as well as higher values of the decoupling parameter.

Eigenvalue Curves for Generalized MIT Bag Models

We study spectral properties of Dirac operators on bounded domains $\Omega \subset \mathbb{R}^3$ with boundary conditions of electrostatic and Lorentz scalar type and which depend on a parameter $\tau\in\mathbb{R}$; the case $\tau = 0$ corresponds to the MIT bag model. We show that the eigenvalues are parametrized as increasing functions of $\tau$, and we exploit this monotonicity to study the limits as $\tau \to \pm \infty$. We prove that if $\Omega$ is not a ball then the first positive eigenvalue is greater than the one of a ball with the same volume for all $\tau$ large enough. Moreover, we show that the first positive eigenvalue converges to the mass of the particle as $\tau \downarrow -\infty$, and we also analyze its first order asymptotics.

Strange stars confronting with the observations: Non‐Newtonian gravity effects, or the existence of a dark‐matter core

AbstractWe find that the existence of strange stars is ruled out by the dimensionless tidal deformability of a star of GW170817 and the mass of PSR J0740 + 6620, both for the standard MIT bag model and for the density‐dependent quark mass model. However, if non‐Newtonian gravity effects are considered, strange stars can exist for certain ranges of the values of the non‐Newtonian gravity parameter. An alternative explanation to these observations is to suppose that strange stars in GW170817 have a dark‐matter core.

Strange Quark Star (SQS) in Tolman IV potential with density dependent B-parameter and charge

In this paper, the solutions of Einstein–Maxwell Field Equations for relativistic strange quark star in Tolman-IV potential considering MIT bag model EoS p=frac{1}{3}(rho -4B) of interior matter in presence of charge in higher dimensions is presented, where B is bag parameter. Here we consider density dependent B as it has more practical application. We note some interesting results. It is observed that interior of a strange quark star may contain bulk stable quarks as a whole having energy per baryon E_B<930.4 MeV/fm^3 or stable quark matter core enclosed by a thin metastable quark matter layer enveloped by unstable quark matter. It is also found that interior composition depends on the value of space-time dimension (D) and net charge (Q). The model presented in this paper satisfies all the necessary stability and energy conditions for a viable stellar configuration. We also note the maximum mass of stable strange quark star is 1.773 M_{odot } for density dependent B and 1.684 M_{odot } for constant B.

Maximum mass of anisotropic charged strange quark stars in a higher dimensional approach (D ≥ 4)

In this article, a new class of solutions of Einstein-Maxwell field equations of relativistic strange quark stars obtained in dimensions , is shown. We assume that the geometry of space-time is pseudo-spheroid, embedded in Euclidean space of dimensions. The MIT bag model equation of state is employed to study the relevant properties of strange quark stars. For the causal and non-negative nature of the square of the radial sound velocity , we observe that some restrictions exist on the reduced radius , where R is a parameter related to the curvature of the space-time, and b is the radius of the star. The spheroidal parameter λ used here defines the metric potential of the component, which is pseudo-spheroidal in nature. We note that the pressure anisotropy and charge have some effects on λ. The maximum mass for a given surface density () or bag constant assumes a maximum value in dimension and decreases for other values of D. The generalized Buchdahl limit for a higher dimensional charged star is also obeyed in this model. We observe that in this model, we can predict the mass of a strange quark star using a suitable value of the electric charge (Q) and bag constant (B). Energy and stability conditions are also satisfied in this model. Stability is also studied considering the dependence of the Lagrangian perturbation of radial pressure () on the frequency of normal modes of oscillations. The tidal Love number and tidal de-formability are also evaluated.

Detailed analysis of the special points on M−R solutions of hybrid/twin stars

Hadron-quark phase transition in neutron star cores is achieved in the present work with the help of Maxwell construction. For the purpose we employ six different and well-known hadronic models for the pure hadronic phase. The quark phase is described with the MIT Bag model in which the density dependence of the bag pressure $B(\rho)$ is invoked for different asymptotic values ($B_{as}$) of $B(\rho)$. The resulting hybrid star (HS) configurations exhibit twin star characteristics and distinct special points (SPs) on the mass-radius diagram of the HSs irrespective of the transition densities and the value of $B_{as}$. We find that for any particular value of $B_{as}$, the mass corresponding to SP ($M_{SP}$) and the maximum mass ($M_{max}$) of the HSs, obtained with different hadronic models, follow a nearly linear (fitted) relationship where the slope is independent of the value of $B_{as}$. The $M_{SP}-M_{max}$ dependence of the HSs is found to be consistent with any hadronic equation of state (EoS) chosen to obtain the hybrid EoS and thus such relations can be considered as universal relations in the context of formation of SPs. A change in the value of $B_{as}$ shifts the position of the fitted line in the $M_{SP}-M_{max}$ plane, with the linearity, however, retained.

Exploring physical properties of minimally deformed strange star model and constraints on maximum mass limit in f(\U0001d4ac) gravity

Our current investigation is inherently linked to the observations of gravitational waves from the GW190814 event which suggests that the source of the signals can be ascribed to a compact binary coalescence of a 22.2 to 24.3M ⊙ black hole and a compact object endowed with a mass of 2.50 to 2.67M ⊙. In the current exposition, we are concerned with modeling of the lower mass component of the coalescence pair. We utilize the f(\U0001d4ac) gravity together with the Minimal Geometric Deformation (MGD) technique to obtain compact stellar objects with masses aligned with the GW190814 event. Starting off with the Tolman IV ansatz for one of the metric functions, together with an MIT Bag model equation of state we are able to reduce the problem of fully describing the gravitational behavior of the seed solution to a quadrature. Through the MGD technique, we introduce anisotropy by deforming the radial part of the gravitational potential. This enables us to obtain two new classes of solutions which depend on the metricity parameter, \U0001d4ac and the deformation constant, β. We show that these two parameters play a crucial role in determining the thermodynamical behavior and stability of our models. In particular, we show that the interplay between the metricity parameter and the deformation constant predicts the mass of the progenitor articulating as the secondary component of GW190814.

Anisotropic Strange Star Model Beyond Standard Maximum Mass Limit by Gravitational Decoupling in f(Q)$f(Q)$ Gravity

AbstractThe current theoretical development identified as the gravitational decoupling via Complete Geometric Deformation (CGD) method that has been introduced to explore the nonmetricity Q effects in relativistic astrophysics. In the present work, we have investigated the gravitationally decoupled anisotropic solutions for the strange stars in the framework of gravity by utilizing the CGD technique. To do this, we started with Tolman metric ansatz along with the MIT Bag model equation of state related to the hadronic matter. The solutions of the governing equations of motions are obtained by using two approaches, namely the mimicking of the θ sector to the seed radial pressure and energy density of the fluid model. The obtained models describe the self‐gravitating static, compact objects whose exterior solution can be given by the vacuum Schwarzschild Anti‐de Sitter spacetime. In particular, we modeled five stellar candidates, viz., LMC X‐4, PSR J1614‐2230, PSR J0740+6620, GW190814, and GW 170817 by using observational data. The rigorous viability tests of the solutions have been performed through regularity and stability conditions. We observed that the nonmetricity parameter and decoupling constant show a significant effect on stabilizing to ensure the physically realizable stellar models. The innovative feature of this work is to present the stable compact objects with masses beyond the without engaging of exotic matter. Therefore, the present study shows a new perception and physical significance about the exploration of ultra‐compact astrophysical objects.

Vector dark boson mediated feeble interaction between fermionic dark matter and strange quark matter in quark stars

Abstract We study the structural properties like the gravitational mass, radius, and tidal deformability of dark matter (DM) admixed strange quark stars (SQSs). For the purpose we consider the vector MIT Bag model to describe the strange quark matter (SQM) and investigate the possible presence of accreted DM in the SQSs consequently forming DM admixed SQSs. We introduce feeble interaction between SQM and the accreted fermionic DM via a vector dark boson mediator. Considering the present literature, in the context of possible presence of DM in SQSs, this work is the first to consider interaction between DM and SQM in the DM admixed SQSs. The mass of the DM fermion (mχ) and the vector mediator (mξ) and the coupling (yξ) between them are determined in accordance with the constraint from Bullet cluster and the present day relic abundance, respectively. We find that the presence of DM reduces both the mass and radius of the star compared to the no-DM case. The massive the DM fermion, the lower the values of maximum mass and radius of the DM admixed SQSs. For the chosen values of mχ and corresponding values of mξ and yξ, the computed structural properties of the DM admixed SQSs satisfy all the various present day astrophysical constraints. We obtain massive DM admixed SQSs configurations consistent with the GW190814 observational data. Hence the secondary compact object associated with this event may be a DM admixed SQS.

Compact star coupled with dark energy in the background of Tolman–Kuchowicz spacetime

This paper provides a simplified description for simulating the coupling of dark energy with baryonic matter by considering a super-dense pulsar PSRJ1614-2230 as the model star. The starting equation of state for modeling the dark energy is motivated by the MIT Bag model for spherically confined hadrons and the observational evidences of its repulsive nature. Einstein field equations are solved in the stellar interior using the generalized framework of Tolman–Kuchowicz spacetime metric. The solutions are then analyzed for various physical parameters such as metric potential, pressure, density, energy conditions, etc. The physical analysis of multiple parameters indicates stable star formation. The proposed stellar model is free from all singularities and also meets the requisite stability criteria. The numerical results obtained for relativistic adiabatic index indicate that the model star is stiff and stable against radially induced adiabatic perturbations.

Strange stars in f(ℛ) gravity palatini formalism and gravitational wave echoes from them

The compact stars are promising candidates associated with the generation ofgravitational waves (GWs). In this work, we study a special type of compactstars known as strange stars in the f(ℛ) gravity Palatiniformalism. Here we consider three promising f(ℛ) gravity modelsviz., Starobinsky, Hu-Sawicki and Gogoi-Goswami models in the domain of MITBag model and linear equations of state (EoSs). We compute the stellarstructures numerically and constrained the f(ℛ) model parameterswith a set of probable strange star candidates. The study shows that theconsideration of stiffer MIT Bag model and linear EoSs within a favourableset of f(ℛ) gravity model parameters may result in strange starswith sufficient compactness to produce echoes of GWs. Thus, we have computedthe GWs echo frequencies and characteristic echo times for such stars. It isfound that in compliance with the experimentally obtained possible strange starcandidates, the obtained GW echo frequencies for all the models are in therange of 65 - 85 kHz.

Charged quark stars in metric f(R) gravity

We provide the modified TOV equations for the hydrostatic equilibrium of charged compact stars within the metric f(R) gravitational background. We adopt the MIT bag model EoS for the dense matter and assume a charge distribution where the electric charge density ρ ch is proportional to the standard energy density ρ. Using the Starobinsky model, we explore the role of the αR 2 term, where α is a free constant and R the Ricci scalar, on the global properties of charged stars such as radius, mass and total charge. We present the dependence of the structure of the star for several values of α and for different values of the constant parameter β ≡ ρ ch/ρ. Remarkably, we find that the radius decreases with respect to its GR value for low central densities, while the opposite occurs in the high-central-density region. The mass measured at the surface always decreases and the maximum-total charge undergoes a substantial increase as the parameter α increases. We also illustrate the variations of the asymptotic mass as a consequence of the electric charge and the extra quadratic term.

Semiclassical Effects in Color Flavor Locked Strange Stars

Strange stars in the color flavor locked phase, as described by a generalization of the phenomenological MIT bag model proposed in the context of color superconductivity, are studied through a model motivated by the semiclassical solutions for hydrostatic equilibrium. Results show that within this framework it is possible to find ultracompact configurations situated between regular compact stars and black holes.

Dependence of maximum mass of strange star on finite strange quark mass (m s ≠ 0)

In this article we analyze a class of compact object in spheroidal geometry described by Vaidya–Tikekar model and MIT bag model equation of state considering the finite mass of strange quark (m s). The maximum mass and radius is found by maximizing the square of radial sound velocity at the centre. For monotonically decreasing nature of the sound velocity we note that an upper limit of the spheroidal parameter (λ) exists. Therefore for the calculation of maximum mass arbitrary choice of λ is not possible. The effect of strange quark mass on the maximum mass is found to satisfy previously obtained result (Li et al 2021 Eur. Phys. J. C 81 921). To apply the present model we consider the compact stars 4U 1608-52 and 4U 1820-30. The stability of strange quark matter inside these compact objects is explored by taking different values of the bag constant B. It is found that 4U 1608-52 may be categorized as strange star with wider stability window for three-flavor quark matter whereas 4U 1820-30 only shows metastability. The model is found to be stable against small radial perturbation. One possible drawback of the present model is the prediction of maximum mass from mass-radius plot. For this reason we have predicted the maximum mass from alternative approach.

Thermal relaxation and cooling of quark stars with a strangelet crust

Context. In this article we explore the cooling of isolated quark stars. These objects are structured from a homogeneous quark matter core and crusted by ordinary matter or by strangelets. Aims. Our main purpose is to quantify the effects of a strangelet crust on the cooling and relaxation times of these strange stars. Methods. We adopt two kinds of crust: (i) a crust made of purely nuclear matter following the Baym-Pethick-Sutherland equation of state (EOS) and (ii) a crust made of nuggets of strange quark matter (strangelets). Both models have the same quark matter core, described by the MIT bag model EOS. Our study also includes the possible effects of color superconductivity in the quark core. Results. We have found that objects with a strangelet crust have a significantly different thermal relaxation time.

Charged Anisotropic Stellar Models with the MIT Bag Model Equation of State

In this paper we present a new classes of solutions for the Einstein-Maxwell system of field equations in a spherically symmetric spacetime under the influence of an electric field considering the MIT bag model equation of state with a particular form the metric potential that depends on an adjustable parameter. The obtained solutions can be written in terms of elementary functions, namely polynomials and algebraic functions. The obtained models satisfy all physical properties expected in a realistic star. The results of this research can be useful in the development and description of new models of compact structures.