Testing a possible way of geometrization of the strong interaction by a Kaluza–Klein star

Geometrization of the fundamental interactions has been extensively studied during the century. The idea of introducing compactified spatial dimensions originated by Kaluza and Klein. Following their approach, several model were built representing quantum numbers (e.g. charges) as compactified space-time dimensions. Such geometrized theoretical descriptions of the fundamental interactions might lead us to get closer to the unification of the principle theories. Here, we apply a [Formula: see text] dimensional theory, which contains one extra compactified spatial dimension [Formula: see text] in connection with the flavor quantum number in Quantum Chromodynamics. Within our model the size of the [Formula: see text] dimension is proportional to the inverse mass-difference of the first low-mass baryon states. We used this phenomena to apply in a compact star model — a natural laboratory for testing the theory of strong interaction and the gravitational theory in parallel. Our aim is to test the modification of the measurable macroscopical parameters of a compact Kaluza–Klein star by varying the size of the compactified extra dimension. Since larger the [Formula: see text] the smaller the mass difference between the first spokes of the Kaluza–Klein ladder resulting smaller-mass stars. Using the Tolman–Oppenheimer–Volkov equation, we investigate the [Formula: see text]-[Formula: see text] diagram and the dependence of the maximum mass of compact stars. Besides testing the validity of our model we compare our results to the existing observational data of pulsar properties for constraints.

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A new class of relativistic model of compact stars of embedding class I

International Journal of Modern Physics D ◽

10.1142/s0218271817500900 ◽

2017 ◽

Vol 26 (09) ◽

pp. 1750090 ◽

Cited By ~ 23

Author(s):

Piyali Bhar ◽

Ksh. Newton Singh ◽

Tuhina Manna

Keyword(s):

Compact Star ◽

Mass Function ◽

Static Stability ◽

Compact Stars ◽

Stable Region ◽

Energy Conditions ◽

Arbitrary Form ◽

Star Model ◽

Field Equations ◽

Anisotropic Matter

In the present paper, we have constructed a new relativistic anisotropic compact star model having a spherically symmetric metric of embedding class one. Here we have assumed an arbitrary form of metric function [Formula: see text] and solved the Einstein’s relativistic field equations with the help of Karmarkar condition for an anisotropic matter distribution. The physical properties of our model such as pressure, density, mass function, surface red-shift, gravitational redshift are investigated and the stability of the stellar configuration is discussed in details. Our model is free from central singularities and satisfies all energy conditions. The model we present here satisfy the static stability criterion, i.e. [Formula: see text] for [Formula: see text][Formula: see text]g/cm3(stable region) and for [Formula: see text][Formula: see text]g/cm3, the region is unstable i.e. [Formula: see text].

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Possible maximum mass of dark matter existing in compact stars based on the self-interacting fermionic model

International Journal of Modern Physics D ◽

10.1142/s0218271819501487 ◽

2019 ◽

Vol 28 (11) ◽

pp. 1950148

Author(s):

Xu Dong Wang ◽

Bin Qi ◽

Gao Le Yang ◽

Nai Bo Zhang ◽

Shou Yu Wang

Keyword(s):

Dark Matter ◽

Energy Density ◽

Strong Interaction ◽

Milky Way ◽

Compact Star ◽

Compact Stars ◽

Maximum Mass ◽

Obvious Effect ◽

Milky Way Galaxy ◽

Fermionic Model

The dark matter admixed neutron stars (DANSs) are studied using the two-fluid TOV equations separately, in which the normal matter (NM) and dark matter (DM) are simulated by the relativistic mean field theory and self-interacting fermionic model, respectively. A universal relationship [Formula: see text] is suggested, where [Formula: see text] is the maximum mass of DM existing in DANSs, [Formula: see text] is the particle mass of DM ranging from 5[Formula: see text]GeV to 1[Formula: see text]TeV, [Formula: see text] is the interaction mass scale with the value 300[Formula: see text]GeV (0.1[Formula: see text]GeV) for weak (strong) interaction DM model. This simple formula connects directly the microcosmic nature of DM particle with its macrocosmic mass existing in DANSs. Meanwhile, such a formula exhibits that the existence of NM has little effect on [Formula: see text]. It is found that the ratio of radius of DM in DANSs over [Formula: see text] is a constant with the value about 12[Formula: see text] (7[Formula: see text]) for weak (strong) interaction DM cases. According to the calculated results, only for the strong interaction DM cases with [Formula: see text] to [Formula: see text][Formula: see text]GeV and central energy density [Formula: see text][Formula: see text]MeV/fm3, DM has obvious effect on the mass of compact star. Compared with the energy density of DM in the Milky Way galaxy, [Formula: see text][Formula: see text]MeV/fm3, the existence of DM might hardly affect the mass of compact stars in the Milky Way galaxy.

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Constraining values of bag constant for strange star candidates

International Journal of Modern Physics D ◽

10.1142/s0218271819410062 ◽

2019 ◽

Vol 28 (13) ◽

pp. 1941006 ◽

Cited By ~ 10

Author(s):

Abdul Aziz ◽

Saibal Ray ◽

Farook Rahaman ◽

M. Khlopov ◽

B. K. Guha

Keyword(s):

Compact Star ◽

A Priori ◽

Stellar System ◽

Mass Function ◽

Strange Star ◽

Compact Stars ◽

Stellar Structure ◽

Star Model ◽

Field Equations ◽

Bag Constant

We provide a strange star model under the framework of general relativity by using a general linear equation of state (EOS). The solution set thus obtained is employed on altogether 20 compact star candidates to constraint values of MIT bag model. No specific value of the bag constant ([Formula: see text]) a priori is assumed, rather possible range of values for bag constant is determined from observational data of the said set of compact stars. To do so, the Tolman–Oppenheimer–Volkoff (TOV) equation is solved by homotopy perturbation method (HPM) and hence we get a mass function for the stellar system. The solution to the Einstein field equations represents a nonsingular, causal and stable stellar structure which can be related to strange stars. Eventually, we get an interesting result on the range of the bag constant as [Formula: see text]. We have found the maximum surface redshift [Formula: see text] and shown that the central redshift ([Formula: see text]) cannot have value larger than [Formula: see text], where [Formula: see text]. Also, we provide a possible value of bag constant for neutron star with quark core using hadronic as well as quark EOS.

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Topology change, emergent symmetries and compact star matter

AAPPS Bulletin ◽

10.1007/s43673-021-00016-1 ◽

2021 ◽

Vol 31 (1) ◽

Author(s):

Yong-Liang Ma ◽

Mannque Rho

Keyword(s):

Nuclear Matter ◽

Compact Star ◽

Momentum Tensor ◽

Effective Field ◽

Compact Stars ◽

Strongly Correlated ◽

Topology Change ◽

Dense Nuclear Matter ◽

Skyrmion Matter ◽

Energy Constants

AbstractTopology effects have being extensively studied and confirmed in strongly correlated condensed matter physics. In the limit of large number of colors, baryons can be regarded as topological objects—skyrmions—and the baryonic matter can be regarded as a skyrmion matter. We review in this paper the generalized effective field theory for dense compact-star matter constructed with the robust inputs obtained from the skyrmion approach to dense nuclear matter, relying on possible “emergent” scale and local flavor symmetries at high density. All nuclear matter properties from the saturation density n0 up to several times n0 can be fairly well described. A uniquely novel—and unorthdox—feature of this theory is the precocious appearance of the pseudo-conformal sound velocity $v^{2}_{s}/c^{2} \approx 1/3$ v s 2 / c 2 ≈ 1 / 3 , with the non-vanishing trace of the energy momentum tensor of the system. The topology change encoded in the density scaling of low energy constants is interpreted as the quark-hadron continuity in the sense of Cheshire Cat Principle (CCP) at density $\gtrsim 2n_{0}$ ≳ 2 n 0 in accessing massive compact stars. We confront the approach with the data from GW170817 and GW190425.

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ANISOTROPIC COMPACT STARS WITH VARIABLE COSMOLOGICAL CONSTANT

International Journal of Modern Physics D ◽

10.1142/s0218271812500885 ◽

2012 ◽

Vol 21 (13) ◽

pp. 1250088 ◽

Cited By ~ 74

Author(s):

SK. MONOWAR HOSSEIN ◽

FAROOK RAHAMAN ◽

JAYANTA NASKAR ◽

MEHEDI KALAM ◽

SAIBAL RAY

Keyword(s):

Dark Energy ◽

Cosmological Constant ◽

Compact Star ◽

Compact Stars ◽

Radial Dependence ◽

Regularity Conditions ◽

Variable Cosmological Constant ◽

Expansion Of The Universe ◽

The Universe ◽

Surface Redshift

Recently, the small value of the cosmological constant and its ability to accelerate the expansion of the universe is of great interest. We discuss the possibility of forming of anisotropic compact stars from this cosmological constant as one of the competent candidates of dark energy. For this purpose, we consider the analytical solution of Krori and Barua metric. We take the radial dependence of cosmological constant and check all the regularity conditions, TOV equations, stability and surface redshift of the compact stars. It has been shown as conclusion that this model is valid for any compact star and we have cited 4U 1820-30 as a specific example of that kind of star.

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Self-gravitating anisotropic star using gravitational decoupling

Physica Scripta ◽

10.1088/1402-4896/ac41ee ◽

2021 ◽

Author(s):

Baiju Dayanandan ◽

T. T. Smitha ◽

Sunil Maurya

Keyword(s):

Compact Star ◽

Radial Component ◽

Energy Conditions ◽

Regularity Conditions ◽

Star Model ◽

Anisotropic Solution ◽

Seed System ◽

The Stability ◽

Metric Function ◽

Anisotropic Star

Abstract This paper addresses a new gravitationally decoupled anisotropic solution for the compact star model via the minimal geometric deformation (MGD) approach. We consider a non-singular well-behaved gravitational potential corresponding to the radial component of the seed spacetime and embedding class I condition that determines the temporal metric function to solve the seed system completely. However, two different well-known mimic approaches such as pr = Θ1 1 and ρ = Θ0 0 have been employed to determine the deformation function which gives the solution of the second system corresponding to the extra source. In order to test the physical viability of the solution, we have checked several conditions such as regularity conditions, energy conditions, causality conditions, hydrostatic equilibrium, etc. Moreover, the stability of the solutions has been also discussed by the adiabatic index and its critical value. We find that the solutions set seems viable as far as observational data are concerned.

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Compact stars in f(ℛ,𝒢,𝒯 ) gravity

International Journal of Modern Physics A ◽

10.1142/s0217751x21501657 ◽

2021 ◽

Vol 36 (24) ◽

pp. 2150165

Author(s):

M. Ilyas

Keyword(s):

Test Particle ◽

Gravitational Theory ◽

Momentum Tensor ◽

Conservation Equation ◽

Compact Objects ◽

Compact Stars ◽

Energy Conditions ◽

Field Equations ◽

Physical Features ◽

The Impact

This work is to introduce a new kind of modified gravitational theory, named as [Formula: see text] (also [Formula: see text]) gravity, where [Formula: see text] is the Ricci scalar, [Formula: see text] is Gauss–Bonnet invariant and [Formula: see text] is the trace of the energy–momentum tensor. With the help of different models in this gravity, we investigate some physical features of different relativistic compact stars. For this purpose, we develop the effectively modified field equations, conservation equation, and the equation of motion for test particle. Then, we check the impact of additional force (massive test particle followed by a nongeodesic line of geometry) on compact objects. Furthermore, we took three notable stars named as [Formula: see text], [Formula: see text] and [Formula: see text]. The physical behavior of the energy density, anisotropic pressures, different energy conditions, stability, anisotropy, and the equilibrium scenario of these strange compact stars are analyzed through various plots. Finally, we conclude that the energy conditions hold, and the core of these stars is so dense.

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Color-flavor locked compact stars: An exact solution approach

International Journal of Modern Physics A ◽

10.1142/s0217751x2150192x ◽

2021 ◽

Author(s):

Ksh. Newton Singh ◽

Shyam Das ◽

Piyali Bhar ◽

Monsur Rahaman ◽

Farook Rahaman

Keyword(s):

Exact Solution ◽

Compact Star ◽

Density Perturbation ◽

Compact Stars ◽

Stable Configuration ◽

Physical Parameters ◽

Superconducting Gap ◽

Field Equations ◽

Critical Limit ◽

Solution Approach

We present an exact solution that could describe compact star composed of color-flavor locked (CFL) phase. Einstein’s field equations were solved through CFL equation of state (EoS) along with a specific form of [Formula: see text] metric potential. Further, to explore a generalized solution we have also included pressure anisotropy. The solution is then analyzed by varying the color superconducting gap [Formula: see text] and its effects on the physical parameters. The stability of the solution through various criteria is also analyzed. To show the physical validity of the obtained solution we have generated the [Formula: see text] curve and fitted three well-known compact stars. This work shows that the anisotropy of the pressure at the interior increases with the color superconducting gap leading to decrease in adiabatic index closer to the critical limit. Further, the fluctuating range of mass due to the density perturbation is larger for lower color superconducting gap leading to more stable configuration.

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Study of charged compact stars with class 1 metric under general relativity

Canadian Journal of Physics ◽

10.1139/cjp-2018-0560 ◽

2019 ◽

Vol 97 (12) ◽

pp. 1323-1331 ◽

Cited By ~ 1

Author(s):

S.K. Maurya ◽

S. Roy Chowdhury ◽

Saibal Ray ◽

B. Dayanandan

Keyword(s):

General Relativity ◽

Compact Star ◽

Space Time ◽

Electron Cloud ◽

Compact Stars ◽

Stellar Structure ◽

Spherically Symmetric ◽

Class 1 ◽

Maxwell Space ◽

Physical Tests

In the present paper we study compact stars under the background of Einstein–Maxwell space–time, where the 4-dimensional spherically symmetric space–time of class 1 along with the Karmarkar condition has been adopted. The investigations, via the set of exact solutions, show several important results, such as (i) the value of density on the surface is finite; (ii) due to the presence of the electric field, the outer surface or the crust region can be considered to be made of electron cloud; (iii) the charge increases rapidly after crossing a certain cutoff region (r/R ≈ 0.3); and (iv) the avalanche of charge has a possible interaction with the particles that are away from the center. As the stellar structure supports all the physical tests performed on it, therefore the overall observation is that the model provides a physically viable and stable compact star.

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Physically Acceptable Embedded Class-I Compact Stars in Modified Gravity with Karmarkar Condition

Symmetry ◽

10.3390/sym12060962 ◽

2020 ◽

Vol 12 (6) ◽

pp. 962 ◽

Cited By ~ 1

Author(s):

Saira Waheed ◽

Ghulam Mustafa ◽

Muhammad Zubair ◽

Asifa Ashraf

Keyword(s):

Compact Star ◽

Graphical Analysis ◽

Specific Model ◽

Compact Stars ◽

Fluid Distribution ◽

Anisotropic Fluid ◽

Strong Impact ◽

Metric Tensor ◽

Physical Conditions ◽

New Family

The present study is devoted to explore the existence of a new family of compact star solutions by adopting the Karmarkar as well as Pandey–Sharma condition in the background of f ( R , T ) modified gravitational framework. For this purpose, we consider static spherically symmetric spacetime with anisotropic fluid distribution in absence of electric charge. In respect of Karmarkar condition, we assume a specific model of g r r metric potential representing a new family of solutions which is also compatible with the Pandey–Sharma condition. This assumed model permits us to calculate the g t t component of metric tensor by making the use of Karmarkar condition. Further, we investigate the interior solutions for V e l a X − 1 model of compact star by utilizing this new family of solutions for different values of parameter λ . We have tuned the solution for V e l a X − 1 so that the solutions matches the observed mass and radius. For the same star we have extensively discussed the behavior of the solutions. It is found that these solutions fulfill all the necessary conditions under the observational radii and mass attribute data for small values of parameter λ and hence physically well-behaved and promising. Through graphical analysis, it is observed that our obtained analytical solutions are physically acceptable with a best degree of accuracy for n ∈ [ 1.8 , 7 ) − { 2 , 4 , 6 } , where parameter n is involved in the discussed model. It is also noticed the causality condition is violated for all n ≥ 7 and the tangential sound velocity v t is observed as complex valued for all 0 < n < 1.8 . Likewise, we explore these properties by considering large parameter λ values. It is seen that the presented model violates all the physical conditions for n ∈ { 2 , 4 , 6 } , while some of these for large values of λ . Consequently, it can be concluded that the parameters n and λ have a strong impact on the obtained solutions.

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