Quintessence compact stars satisfying Karmarkar condition

2019 ◽  
Vol 97 (4) ◽  
pp. 374-381 ◽  
Author(s):  
G. Abbas ◽  
Shahid Qaisar ◽  
Wajiha Javed ◽  
W. Ibrahim
Keyword(s):  
Radial Pressure ◽  
Compact Stars ◽  
Field Equations ◽  
Anisotropic Parameter ◽  
Proposed Model ◽  
Second Derivatives ◽  
Metric Functions ◽  
The Stability ◽  
Quintessence Field ◽  
Derivatives Of

In this research article, the authors have presented the modelling of quintessence compact stars, which satisfies the Karmarkar conditions. For this purpose, we have formulated the set of Einstein field equations with the static metric, anisotropic perfect fluid, and quintessence field. The equation of state pr= αρ and Karmarkar condition have been used to solve the set of field equations. The unknown constant in the metric functions (appearing due to the Karmarkar conditions) have been found by matching the interior metric with the Schwarzschild exterior metric. The observed value of mass and radius of some well-known classes of stars has been used. The fluid variables density, radial and transverse pressures, and anisotropic parameter have been plotted graphically. The first and second derivatives of density and radial pressure have been evaluated to discuss the regularity of the model. The speed of sound for the radial and transverse directions determines the stability of the proposed model. Moreover, the redshift for the proposed model of the star has been discussed.

scholarly journals An analytical anisotropic compact stellar model of embedding class I

2021 ◽  
Vol 36 (05) ◽  
pp. 2150028
Author(s):  
Lipi Baskey ◽  
Shyam Das ◽  
Farook Rahaman
Keyword(s):  
Radial Pressure ◽  
Stellar Model ◽  
Compact Objects ◽  
Compact Stars ◽  
Model Parameters ◽  
Field Equations ◽  
Principal Stresses ◽  
Schwarzschild Solution ◽  
Spherical Fluid ◽  
Physical Profile

A class of solutions of Einstein field equations satisfying Karmarkar embedding condition is presented which could describe static, spherical fluid configurations, and could serve as models for compact stars. The fluid under consideration has unequal principal stresses i.e. fluid is locally anisotropic. A certain physically motivated geometry of metric potential has been chosen and codependency of the metric potentials outlines the formation of the model. The exterior spacetime is assumed as described by the exterior Schwarzschild solution. The smooth matching of the interior to the exterior Schwarzschild spacetime metric across the boundary and the condition that radial pressure is zero across the boundary lead us to determine the model parameters. Physical requirements and stability analysis of the model demanded for a physically realistic star are satisfied. The developed model has been investigated graphically by exploring data from some of the known compact objects. The mass-radius (M-R) relationship that shows the maximum mass admissible for observed pulsars for a given surface density has also been investigated. Moreover, the physical profile of the moment of inertia (I) thus obtained from the solutions is confirmed by the Bejger–Haensel concept.

scholarly journals Advanced analysis in epidemiological modeling: Detection of wave

2021 ◽  
Author(s):  
Abdon Atangana ◽  
Seda IGRET ARAZ
Keyword(s):  
Simple Model ◽  
Reproductive Number ◽  
Second Derivative ◽  
Mathematical Concepts ◽  
Epidemiological Modeling ◽  
Derivative Analysis ◽  
Second Derivatives ◽  
Advanced Analysis ◽  
The Stability ◽  
Derivatives Of

Some mathematical concepts have been used in the last decades to predict the behavior of spread of infectious diseases. Among them, the reproductive number concept has been used in several published papers for study the stability of the spread. Some conditions were suggested to predict there would be either stability or instability. An analysis was also suggested to determine conditions under which infectious classes will increase or die out. Some authors pointed out limitations of the reproductive number, as they presented its inability to fairly help understand the spread patterns. The concept of strength number and analysis of second derivatives of the mathematical models were suggested as additional tools to help detect waves. In this paper, we aim at applying these additional analyses in a simple model to predict the future. Keywords: Strength number, second derivative analysis, waves, piecewise modeling.

scholarly journals A new class of analytical solutions describing anisotropic neutron stars in general relativity

2021 ◽  
pp. 2150091
Author(s):  
Jay Solanki ◽  
Bhashin Thakore
Keyword(s):  
General Relativity ◽  
Neutron Stars ◽  
Analytical Solutions ◽  
Radial Pressure ◽  
Compact Stars ◽  
Theory Of Relativity ◽  
Field Equations ◽  
Inherent Anisotropy ◽  
Anisotropic Matter ◽  
New Class

A new class of solutions describing analytical solutions for compact stellar structures has been developed within the tenets of General Relativity. Considering the inherent anisotropy in compact stars, a stable and causal model for realistic anisotropic neutron stars was obtained using the general theory of relativity. Assuming a physically acceptable nonsingular form of one metric potential and radial pressure containing the curvature parameter [Formula: see text], the constant [Formula: see text] and the radius [Formula: see text], analytical solutions to Einstein’s field equations for anisotropic matter distribution were obtained. Taking the value of [Formula: see text] as −0.44, it was found that the proposed model obeys all necessary physical conditions, and it is potentially stable and realistic. The model also exhibits a linear equation of state, which can be applied to describe compact stars.

Analysis of compact stars in logarithmic-corrected R2 gravity

2019 ◽  
Vol 35 (02) ◽  
pp. 1950354 ◽  
Author(s):  
M. Farasat Shamir ◽  
Iffat Fayyaz
Keyword(s):  
Graphical Representation ◽  
Stellar Model ◽  
Compact Stars ◽  
Energy Conditions ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Logarithmic Corrections ◽  
Proposed Model ◽  
Physical Tests ◽  
Surface Redshift

We discuss the existence of compact stars in the context of [Formula: see text] gravity model, where additional logarithmic corrections are assumed. Here, [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are constant values. Further, the compact stars are considered to be anisotropic in nature, due to the spherical symmetry and high density. For this purpose, we derive the Einstein field equations by considering Krori–Barua spacetime. For our proposed model, the physical acceptability is verified by employing several physical tests like the energy conditions, Herrera cracking concept and stability condition. In addition to this, we also discuss some important properties such as mass–radius relation, surface redshift and the speed of sound are analyzed. Our results are compared with observational stellar mass data, namely, 4U 1820-30, Cen X-3, EXO 1785-248 and LMC X-4. The graphical representation of obtained solutions provide strong evidences for more realistic and viable stellar model.

scholarly journals Charged compact star in f(R, T) gravity in Tolman–Kuchowicz spacetime

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
Pramit Rej ◽  
Piyali Bhar ◽  
Megan Govender
Keyword(s):  
Modified Gravity ◽  
Line Element ◽  
Compact Star ◽  
Stellar System ◽  
Radial Pressure ◽  
Energy Conditions ◽  
Field Equations ◽  
Compactness Factor ◽  
Physical Validity ◽  
The Stability

AbstractIn this current study, our main focus is on modeling the specific charged compact star SAX J 1808.4-3658 (M = 0.88 $$M_{\odot }$$ M ⊙ ,  R = 8.9 km) within the framework of $$f(R,\,T)$$ f ( R , T ) modified gravity theory using the metric potentials proposed by Tolman–Kuchowicz (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) and the interior spacetime is matched to the exterior Reissner–Nordström line element at the surface of the star. Tolman–Kuchowicz metric potentials provide a singularity-free solution which satisfies the stability criteria. Here we have used the simplified phenomenological MIT bag model equation of state (EoS) to solve the Einstein–Maxwell field equations where the density profile ($$\rho $$ ρ ) is related to the radial pressure ($$p_{\mathrm{r}}$$ p r ) as $$p_{\mathrm{r}}(r) = (\rho - 4B_{\mathrm{g}})/3$$ p r ( r ) = ( ρ - 4 B g ) / 3 . Furthermore, to derive the values of the unknown constants $$a,\, b,\, B,\, C$$ a , b , B , C and the bag constant $$B_{\mathrm{g}}$$ B g , we match our interior spacetime to the exterior Reissner–Nordström line element at the surface of stellar system. In addition, to check the physical validity and stability of our suggested model we evaluate some important properties, such as effective energy density, effective pressures, radial and transverse sound velocities, relativistic adiabatic index, all energy conditions, compactness factor and surface redshift. It is depicted from our current study that all our derived results lie within the physically accepted regime which shows the viability of our present model in the context of $$f(R,\,T)$$ f ( R , T ) modified gravity.

Time-Dependent Ginzburg-Landau Equation in Car Following Model Considering the Traffic Interruption Probability

2012 ◽  
Vol 198-199 ◽  
pp. 843-847
Author(s):  
Yi Qiang Zhang ◽  
Rong Jun Cheng ◽  
Hong Xia Ge
Keyword(s):  
Landau Equation ◽  
Reductive Perturbation Method ◽  
Time Dependent ◽  
Ginzburg Landau ◽  
Car Following ◽  
Second Derivatives ◽  
Spinodal Line ◽  
Car Following Model ◽  
The Stability ◽  
Derivatives Of

This paper focuses on a car-following model which involves the effects of traffic interruption probability. The stability condition of the model is obtained through the linear stability analysis. The time-dependent Ginzburg-Landau (TDGL) equation is derived by the reductive perturbation method. In addition, the coexisting curve and the spinodal line are obtained by the first and second derivatives of the thermodynamic potential. The analytical results show that the traffic interruption probability indeed has an influence on driving behaviour.

THE TDGL EQUATION FOR CAR-FOLLOWING MODEL WITH CONSIDERATION OF THE TRAFFIC INTERRUPTION PROBABILITY

2012 ◽  
Vol 23 (07) ◽  
pp. 1250053 ◽  
Author(s):  
HONG-XIA GE ◽  
YI-QIANG ZHANG ◽  
HUA KUANG ◽  
SIU-MING LO
Keyword(s):  
Traffic Flow ◽  
Reductive Perturbation Method ◽  
Ginzburg Landau ◽  
Car Following ◽  
Second Derivatives ◽  
Spinodal Line ◽  
Car Following Model ◽  
Tdgl Equation ◽  
The Stability ◽  
Derivatives Of

A car-following model which involves the effects of traffic interruption probability is further investigated. The stability condition of the model is obtained through the linear stability analysis. The reductive perturbation method is taken to derive the time-dependent Ginzburg–Landau (TDGL) equation to describe the traffic flow near the critical point. Moreover, the coexisting curve and the spinodal line are obtained by the first and second derivatives of the thermodynamic potential, respectively. The analytical results show that considering the interruption effects could further stabilize traffic flow.

scholarly journals Pair production and gravity as the weakest force

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Eduardo Gonzalo ◽  
Luis E. Ibáñez
Keyword(s):  
Pair Production ◽  
Relative Strength ◽  
Alternative Formulation ◽  
Long Distance ◽  
Pair Annihilation ◽  
Second Derivatives ◽  
The Stability ◽  
Bps States ◽  
Derivatives Of ◽  
Extremal Black Holes

Abstract The Weak Gravity Conjecture (WGC) is usually formulated in terms of the stability of extremal black-holes or in terms of long distance Coulomb/Newton potentials. However one can think of other physical processes to compare the relative strength of gravity versus other forces. We argue for an alternative formulation in terms of particle pair production at threshold or, equivalently, pair annihilation at rest. Imposing that the production rate by any force mediator (photon or scalar) of pairs of charged particles be larger or equal to graviton production, we recover known conditions for the U(1) WGC and its extensions. Unlike other formulations though, threshold pair production is sensitive to short range couplings present in scalar interactions and gives rise to a Scalar WGC. Application to moduli scalars gives rise to specific conditions on the trilinear and quartic couplings which involve first and second derivatives of the WGC particle mass with respect to the moduli. Some solutions saturating equations correspond to massive states behaving like BPS, KK and winding states which feature duality invariance and are in agreement with the Swampland distance conjecture. Conditions for N = 2 BPS states saturate our bounds and we discuss specific examples of BPS states which become massless at large Kahler moduli in Type IIA N=2, D=4 CY and orbifold compactifications. We study possible implications for potentials depending on moduli only through WGC massive states. For some simple classes of potentials one recovers constraints somewhat similar but not equivalent to a Swampland dS conjecture.

Quintessence compact stars with Vaidya–Tikekar type grr for anisotropic fluid

2020 ◽  
Vol 98 (9) ◽  
pp. 869-876
Author(s):  
G. Abbas ◽  
M.R. Shahzad
Keyword(s):  
Killing Vector ◽  
Graphical Analysis ◽  
Compact Stars ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Conformal Killing ◽  
Field Equations ◽  
Anisotropic Matter ◽  
Quintessence Field ◽  
Analytical Expressions

The present study provides a new solution to the Einstein field equations for anisotropic matter configuration in static and spherically symmetric space–time. By taking benefit from the conformal Killing vector (CKV) technique and quintessence field specified by a parameter ωq as –1 < ωq < –1/3, we generate an exact solution to the field equations. For this investigation, we have used a specific form of metric potential taken fromVaidya–Tikekar (J. Astrophys. Astron. 3, 325 (1982)) geometry. To canvass the physical plausibility of the presented solution, we explored some analytical expressions such as energy conditions, the TOV equation, stability analysis, and equation of state parameters. We present graphical analysis of the necessary analytical expressions that revealed that our solution satisfies the necessary physical conditions.

Analysis of physically realizable stellar models in embedded class one spacetime manifold

2019 ◽  
Vol 35 (04) ◽  
pp. 2050001 ◽  
Author(s):  
Ritu Tamta ◽  
Pratibha Fuloria
Keyword(s):  
Transverse Velocity ◽  
Compact Star ◽  
Graphical Analysis ◽  
Compact Stars ◽  
Field Equations ◽  
Star Models ◽  
New Exact Solutions ◽  
Spacetime Manifold ◽  
Stellar Models ◽  
The Stability

In this paper, we searched two new exact solutions of Einstein’s field equations for modeling of compact cold stars using embedded class one spacetime continuum. We find out the expressions for pressure, density, anisotropy, redshift, metric potentials and other physical variables in terms of algebraic and trigonometric expressions and observe that all variables show well-behaved trends inside the compact stellar configurations. The causality condition is well maintained by our stellar models, i.e. the radial velocity and transverse velocity are less than l. The stability of our models is assessed via different stability criteria. The Buchdahl condition holds good for our solution. Herrera’s cracking method is applied to check the stability of stellar models. We generate anisotropic compact star models, whose masses and radii are in close agreement with the observed values for compact stars 4U 1538-52, LMCX-4, PSRJ1614-2230. A comparative analysis of the proposed models is carried out based on two different solutions reported in the paper. The appropriate graphical analysis is provided to authenticate the viability of the models.

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