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PRAMIT REJ

Burdwan University, Mathematics, Faculty Member

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Presently, I'm working as an Assistant Professor in the Department of Mathematics at Sarat Centenary College, Dhaniakhali, Hooghly, West Bengal- 712302, India.My research interests include Atomic and Molecular physics (Specially focused on quantum scattering theory), Theoretical Astrophysics (Specially focused on compact star modelling in modified gravity, wormhole theory, gravastar modelling).

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University of Zagreb

Hernando S. SALAPARE III, Ph.D.

University of Nice

Masaryk University

Kansas State University

Sofia University "St. Kliment Ohridski"

Centro de Investigacion y Estudios Avanzados del IPN

Armando Marques-Guedes

UNL - New University of Lisbon

University of Leeds

Imperial College London

University of Illinois at Urbana-Champaign

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Papers by PRAMIT REJ

$Research paper thumbnail of Well behaved class of Heintzmann's solution within $f(R,\,T)$ framework$

Well behaved class of Heintzmann's solution within $f(R,\,T)$ framework

arXiv (Cornell University), Apr 21, 2024

The primary objective of this paper is to develop a well-behaved class of Heintzmann IIa [H. Hein... more The primary objective of this paper is to develop a well-behaved class of Heintzmann IIa [H. Heintzmann, Z. Physik 228, 489-493 (1969)] solution in the context of f (R, T ) gravity. In the f (R, T ) framework, the gravitational action includes both the Ricci scalar (R) and the trace of the energy-momentum tensor (T ). We chose a particular f (R, T ) model s.t. f (R, T ) = R + 2χT , where χ is known as the coupling parameter. This solution describes a novel isotropic compact fluid sphere with positively finite central pressure and density in this extended theory of gravity. The results obtained analytically are better described by graphical representations of the physical parameters for various values of the coupling parameter χ. The solution for a specific compact object, Vela X-1, with radius R = 9.56 +0.08 -0.08 km and mass M = 1.77 ± 0.08 M⊙ [M. L. Rawls et al. ApJ, 730, 25 (2011)], is shown here. We analyze the fundamental physical attributes of the star, which reveals the influence of the coupling parameter χ on the values of substance parameters. This helps us to make a fruitful comparison of this modified f (R, T ) gravity with the standard GR and notice that it holds good for stable compact objects. In this framework, the star under our consideration exhibits a stable structure consistent with the Heintzmann IIa ansatz. From all of our obtained graphical and numerical results, we can ultimately conclude that our reported model is physically admissible and satisfies all the physical criteria for an acceptable model.

Charged analog of anisotropic dark energy star in Rastall gravity

arXiv (Cornell University), Apr 21, 2024

Dark energy is one of the potential strategies for preventing compact objects from gravitationall... more Dark energy is one of the potential strategies for preventing compact objects from gravitationally collapsing into singularities. Because it is the cause of the accelerated expansion of our universe, it has the greatest impact on the cosmos. Thus, it is plausible that dark energy will interact with any stellar object that is compact in the universe [Phys. Rev. D 103, 084042 (2021)]. Our main goal in this work is to create a simplified model, in the Rastall gravitational framework, of a charged strange star coupled to anisotropic dark energy in Krori-Barua spacetime [J. Phys. A, Math. Gen. 8:508, 1975]. Here, we consider a specific strange star object, Her X-1, with observed values of mass = (0.85 ± 0.15)M⊙ and radius = 8.1 +0.41 -0.41 km., so that we can develop our model. In this context, we began by modeling dark energy using the equation of state (EoS), in which the dark energy density is proportional to the isotropic perfect fluid matter-energy density. The Darmois-Israel condition has been used to calculate the unknown constants that are present in the metric. We perform a detailed analysis of the model's physical properties, including the mass-radius relation, pressure, density, metric function, and dark energy parameters for different Rastall coupling parameter values. We also examine the stability and force equilibrium of our proposed stellar configuration. Following a comprehensive theoretical analysis, we discovered that our suggested model is both singularity-free and meets all stability requirements needed to be a stable, physically reasonable stellar model.

Thin-shell wormholes constructed via polytropic surgery

Chinese Journal of Physics, Nov 30, 2023

Polytropic stellar structure in 5<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e771" altimg="si7.svg"><mml:mi mathvariant="script">D</mml:mi></mml:math> Einstein–Gauss–Bonnet gravity

Chinese journal of physics/Zhōngguó wùlǐ xuékān, May 1, 2024

Celestial attributes of hybrid star in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e830" altimg="si6.svg"><mml:mrow><mml:mn>5</mml:mn><mml:mi mathvariant="script">D</mml:mi></mml:mrow></mml:math> Einstein-Gauss–Bonnet gravity

Chinese Journal of Physics, Jan 31, 2024

Hybrid star is the term given to a neutron star with a quark core. Due to a lot of uncertainties ... more Hybrid star is the term given to a neutron star with a quark core. Due to a lot of uncertainties in the calculations and compositions of such a high-density system, it is of great interest and a preferred scenario for particle physicists and astrophysicists. To explore some novel aspects within the framework of the 5D Einstein-Gauss-Bonnet(EGB) gravity, our current study presents a hybrid star model that includes strange quark matter in addition to regular baryonic matter. In hybrid stellar objects, a hadronic outer component surrounds a quark inner component, which prompts the consideration of the most basic MIT bag model equation of state to correlate the density and pressure of strange quark matter within the stellar interior, while radial pressure and matter density due to baryonic matter are connected by a linear equation of state. The model is constructed within the specifications of the Krori and Barua (KB) ansatz (Krori and Barua, J. Phys. A: Math. Gen. 8, 508, 1975). Here we present the solution for a particular compact object 4U 1538-52 with mass M = 0.87 ± 0.07 M⊙ and radius R = 7.866 +0.21 −0.21 km. We examine the fundamental physical characteristics of the star, which highlights how the values of matter variables are affected by the Gauss-Bonnet coupling parameter α. Finally, as it meets all the physical requirements for a realistic model, we have come to realize that our present model is realistic.

$Research paper thumbnail of Polytropic stellar structure in 5$\mathcal{D}$ Einstein-Gauss-Bonnet gravity$

Polytropic stellar structure in 5$\mathcal{D}$ Einstein-Gauss-Bonnet gravity

arXiv (Cornell University), Mar 5, 2024

Polytropic stars are useful tools for learning about stellar structure without the complexity of ... more Polytropic stars are useful tools for learning about stellar structure without the complexity of comprehensive stellar models. These models rely on a certain power-law correlation between the star's pressure and density. This paper proposes a polytropic star model to investigate some new features in the context of 5D Einstein-Gauss-Bonnet (EGB) gravity using the Finch-Skea ansatz [M. R. Finch and J. E. Skea, Classical and Quantum Gravity 6, 467 (1989)]. Analytical results are better described by graphical representations of the physical parameters for various values of the Gauss-Bonnet coupling constant α. The solution for a specific compact object, EXO 1785-248, with radius R = 8.849 +0.04 −0.04 km and mass M = 1.3 ± 0.02 M⊙, is shown here. We analyze the essential physical attributes of the star, which reveal the influence of the coupling parameter α on the values of the parameters. Ultimately, we conclude that our current model is realistic because it satisfies all the physical criteria for an acceptable model.

Isotropic Durgapal IV fluid sphere in bigravity

Canadian Journal of Physics

We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV... more We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV metric (M.C. Durgapal, J. Phys. A: Math. Gen. 15, 2637 (1982)). In this work, we investigate the effects of the scale parameter k on the local matter distribution. Here, we have chosen the compact star candidate SMC X-1 with observed values of mass = (1.29 ± 0.05) M⊙ and radius [Formula: see text] km, respectively, to analyze our results analytically as well as graphically. For smaller values of k, we get the stiff (or hard) equation of state (EoS). Here, we solve the modified Einstein field equations in the presence of the background metric γμν. Due to this constant curvature background, the density and pressure terms are modified by adding an extra term, which affects the EoS. For r ≪ k, the background de Sitter space–time reduces into Minkowski form, and the coupling vanishes. We discuss certain physical quantities of our obtained solution, such as density, isotropic pressure, sound ...

$Research paper thumbnail of Charged quark stars represented by the MIT bag approach in $$5\mathcal {D}$$ Einstein–Maxwell–Gauss–Bonnet formalism$

Charged quark stars represented by the MIT bag approach in $$5\mathcal {D}$$ Einstein–Maxwell–Gauss–Bonnet formalism

The European Physical Journal Plus

Relativistic isotropic stellar model in f(R,T) gravity with Durgapal- IV metric

New Astronomy

Charged strange star coupled to anisotropic dark energy in Tolman–Kuchowicz spacetime

The European Physical Journal C

The concept of dark energy can be used as a possible option to prevent the gravitational collapse... more The concept of dark energy can be used as a possible option to prevent the gravitational collapse of compact objects into singularities. It affects the universe on the largest scale, as it is responsible for our universe’s accelerated expansion. As a consequence, it seems possible that dark energy will interact with any compact astrophysical stellar object [Phys. Rev. D 103, 084042 (2021)]. In this work, our prime focus is to develop a simplified model of a charged strange star coupled to anisotropic dark energy in Tolman–Kuchowicz spacetime (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) within the context of general relativity. To develop our model, here we consider a particular strange star object, Her X-1 with observed values of mass $$=(0.85 \pm 0.15)M_{\odot }$$ = ( 0.85 ± 0.15 ) M ⊙ and radius $$= 8.1_{-0.41}^{+0.41}$$ = 8 . 1 - 0.41 + 0.41 km. respectively. In this context, we initially started with the equation of state (EoS) to model the dark ene...

$Research paper thumbnail of Isotropic Buchdahl's relativistic fluid sphere within $f(R,\,T)$ gravity$

Isotropic Buchdahl's relativistic fluid sphere within $f(R,\,T)$ gravity

arXiv (Cornell University), Dec 15, 2022

The aim of the research is to look into a new solution for isotropic compact stars in the context... more The aim of the research is to look into a new solution for isotropic compact stars in the context of the f (R, T) theory of gravity. We used the Buchdahl [H.A. Buchdahl, Phys. Rev. 116 (1959) 1027] metric potentials as input to deal with the field equations in the f (R, T) framework. For different values of the coupling parameter χ, graphical representation of the model parameters have been shown to canvass the analytical results more clearly. Interestingly, we have proven that for χ = 0, the standard General Relativity (GR) results can be recovered. A comparison of our obtained solutions with the GR results is also discussed. To study the effect of the coupling parameter χ, the numerical values of the different physical variables have been tabulated for the values of the coupling parameter χ = 0, 0.25, 0.5, 0.75, 1, 1.25. We used the compact stars candidate LMC X-4 with mass= (1.04 ± 0.09)M⊙; Radius = 8.301 +0.2 −0.2 km. respectively, for graphical analysis. To determine the physical acceptability of the model, we looked into the necessary physical properties such as energy conditions, causality, hydrostatic equilibrium, and pressure-density ratio etc. and found that our system satisfies all of these criteria, indicating that the model is physically reasonable.

Isotropic Buchdahl’s relativistic fluid sphere within f(R,T) gravity

New Astronomy

Asymptotic cross section and scaling law: positronium formation in Rydberg states in positron–hydrogen collisions

Indian Journal of Physics, 2015

Positronium formation in Rydberg states from the ground state of the hydrogen atom by positron im... more Positronium formation in Rydberg states from the ground state of the hydrogen atom by positron impact has been studied within the framework of a distorted wave theory which includes static dipole polarization potential. The distorted wave scattering amplitude has been obtained in a closed form. A detailed investigation has been made on the differential and total cross sections in the energy range 25-300 eV of incident positron. It has been found that asymptotic cross sections for the positronium formation into different angular momentum states obey a simple law.

Stable and self consistent charged gravastar model within the framework of f(R, T) gravity

In this work, we discuss the configuration of a gravastar (gravitational vacuum stars) in the con... more In this work, we discuss the configuration of a gravastar (gravitational vacuum stars) in the context of f(R, T ) gravity by employing the Mazur-Mottola conjecture [P. Mazur and E. Mottola, Report No. LA-UR-01-5067; P. Mazur and E. Mottola, Proc. Natl. Acad. Sci. USA 101, 9545 (2004)]. Gravastar is conceptually a substitute for a black hole theory as available in literature and it has three regions with different equation of states. By assuming that the gravastar geometry admits conformal killing vector, the Einstein-Maxwell field equations have been solved in different regions of gravastar by taking a specific equation of state as proposed by Mazur and Mottola. We match our interior spacetime to the exterior spherical region which is completely vacuum and described by Reissner-Nordström geometry. For a particular choice of f(R, T) as f(R, T )=R+2γ T, here we analyze various physical properties of the thin shell and also presented our results graphically for these properties. The st...

Charged strange star in f(R,T) gravity with linear equation of state

Our present study involves the strange stars model in the framework of f(R,T) theory of gravitati... more Our present study involves the strange stars model in the framework of f(R,T) theory of gravitation. We have taken a linear function of the Ricci scalar R and the trace T of the stress-energy tensor T_μν for the expression of f(R,T), i.e., f(R,T)=R+ 2 γ T to obtain the proposed model, where γ is a coupling constant. Moreover, to solve the hydrostatic equilibrium equations, we consider a linear equation of state between the radial pressure p_r and matter density ρ as p_r=αρ-β, where α and β are some positive constants, Both α, β depend on coupling constant γ which have been also depicted in this paper. By employing the Krori-Barua ansatz already reported in the literature [J. Phys. A, Math. Gen. 8:508, 1975] we have found the solutions of the field equations in f (R, T ) gravity. The effect of coupling constant γ have been studied on the model parameters like density, pressures, anisotropic factor, compactness, surface redshift, etc. both numerically and graphically. A suitable range...

Charged gravastar model in f(T) gravity admitting conformal motion

In this paper, model of charged gravastar under f(T) modified gravity is obtained. The model has ... more In this paper, model of charged gravastar under f(T) modified gravity is obtained. The model has been explored by taking the diagonal tetrad field of static spacetime together with electric charge. To solve the Einstein-Maxwell field equations, along with f(T) gravity, we assume the existence of a conformal Killing vector which relates between geometry and matter through the Einstein-Maxwell field equations by an inheritance symmetry. We study several cases of interest to explore physically valid features of the solutions. Some physical properties of the model are discussed and we match our interior spacetime to the exterior Reissner-Nordstrom spacetime in presence of thin shell.

Electron transfer in proton-hydrogen collisions in nonideal classical plasmas

Contributions to Plasma Physics

Excited-state positronium formation in positron–hydrogen collisions under weakly coupled plasmas

Journal of Physics B: Atomic, Molecular and Optical Physics

Positron scattering from hydrogen atom in dense quantum plasmas: Positronium formation in Rydberg states

Physics of Plasmas

Effects of dense quantum plasmas on positronium (Ps) formation in an arbitrary nlm–state in the s... more Effects of dense quantum plasmas on positronium (Ps) formation in an arbitrary nlm–state in the scattering of positrons from the ground state of hydrogen atoms have been investigated within the framework of a distorted wave theory that incorporates the effect of screened dipole polarization potential. The interaction of charged particles in plasmas has been modeled by a modified Debye-Huckel potential. Effects of plasma screening on the structures of differential and total cross sections have been explored for various incident positron energies in the range 20–300 eV. For the free atomic case, our results are in conformity with the existing results available in the literature. It has been found that for small screening effects, the cross section presents the oscillatory behaviour. To the best of our knowledge, this is the first attempt to estimate the screening effects on the differential and total cross sections for Ps formation in Rydberg states in dense quantum plasmas.

Positron impact excitations of hydrogen atom embedded in weakly coupled plasmas: Formation of Rydberg atoms

Physics of Plasmas, 2014

ABSTRACT Formation of Rydberg atoms due to 1s!nlmexcitations of hydrogen, for arbitraryn, l, m,by... more ABSTRACT Formation of Rydberg atoms due to 1s!nlmexcitations of hydrogen, for arbitraryn, l, m,by positron impact in weakly coupled plasma has been investigated using a distorted-wave theory in the momentum space. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. Making use of a simple variationally determined wave function for the hydrogen atom, it has been possible to obtain the distorted-wave scattering amplitude in a closed analytical form. A detailed study has been made on the effects of plasma screening on the differential and total cross sections in the energy range 20–300 eV of incident positron. For the unscreened case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for 1s!nlminelastic positron-hydrogen collisions for arbitrary n, l, min weakly coupled plasmas is the first reported in the literature.

$Research paper thumbnail of Well behaved class of Heintzmann's solution within $f(R,\,T)$ framework$

Well behaved class of Heintzmann's solution within $f(R,\,T)$ framework

arXiv (Cornell University), Apr 21, 2024

The primary objective of this paper is to develop a well-behaved class of Heintzmann IIa [H. Hein... more The primary objective of this paper is to develop a well-behaved class of Heintzmann IIa [H. Heintzmann, Z. Physik 228, 489-493 (1969)] solution in the context of f (R, T ) gravity. In the f (R, T ) framework, the gravitational action includes both the Ricci scalar (R) and the trace of the energy-momentum tensor (T ). We chose a particular f (R, T ) model s.t. f (R, T ) = R + 2χT , where χ is known as the coupling parameter. This solution describes a novel isotropic compact fluid sphere with positively finite central pressure and density in this extended theory of gravity. The results obtained analytically are better described by graphical representations of the physical parameters for various values of the coupling parameter χ. The solution for a specific compact object, Vela X-1, with radius R = 9.56 +0.08 -0.08 km and mass M = 1.77 ± 0.08 M⊙ [M. L. Rawls et al. ApJ, 730, 25 (2011)], is shown here. We analyze the fundamental physical attributes of the star, which reveals the influence of the coupling parameter χ on the values of substance parameters. This helps us to make a fruitful comparison of this modified f (R, T ) gravity with the standard GR and notice that it holds good for stable compact objects. In this framework, the star under our consideration exhibits a stable structure consistent with the Heintzmann IIa ansatz. From all of our obtained graphical and numerical results, we can ultimately conclude that our reported model is physically admissible and satisfies all the physical criteria for an acceptable model.

Charged analog of anisotropic dark energy star in Rastall gravity

arXiv (Cornell University), Apr 21, 2024

Dark energy is one of the potential strategies for preventing compact objects from gravitationall... more Dark energy is one of the potential strategies for preventing compact objects from gravitationally collapsing into singularities. Because it is the cause of the accelerated expansion of our universe, it has the greatest impact on the cosmos. Thus, it is plausible that dark energy will interact with any stellar object that is compact in the universe [Phys. Rev. D 103, 084042 (2021)]. Our main goal in this work is to create a simplified model, in the Rastall gravitational framework, of a charged strange star coupled to anisotropic dark energy in Krori-Barua spacetime [J. Phys. A, Math. Gen. 8:508, 1975]. Here, we consider a specific strange star object, Her X-1, with observed values of mass = (0.85 ± 0.15)M⊙ and radius = 8.1 +0.41 -0.41 km., so that we can develop our model. In this context, we began by modeling dark energy using the equation of state (EoS), in which the dark energy density is proportional to the isotropic perfect fluid matter-energy density. The Darmois-Israel condition has been used to calculate the unknown constants that are present in the metric. We perform a detailed analysis of the model's physical properties, including the mass-radius relation, pressure, density, metric function, and dark energy parameters for different Rastall coupling parameter values. We also examine the stability and force equilibrium of our proposed stellar configuration. Following a comprehensive theoretical analysis, we discovered that our suggested model is both singularity-free and meets all stability requirements needed to be a stable, physically reasonable stellar model.

Thin-shell wormholes constructed via polytropic surgery

Chinese Journal of Physics, Nov 30, 2023

Polytropic stellar structure in 5<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e771" altimg="si7.svg"><mml:mi mathvariant="script">D</mml:mi></mml:math> Einstein–Gauss–Bonnet gravity

Chinese journal of physics/Zhōngguó wùlǐ xuékān, May 1, 2024

Celestial attributes of hybrid star in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e830" altimg="si6.svg"><mml:mrow><mml:mn>5</mml:mn><mml:mi mathvariant="script">D</mml:mi></mml:mrow></mml:math> Einstein-Gauss–Bonnet gravity

Chinese Journal of Physics, Jan 31, 2024

Hybrid star is the term given to a neutron star with a quark core. Due to a lot of uncertainties ... more Hybrid star is the term given to a neutron star with a quark core. Due to a lot of uncertainties in the calculations and compositions of such a high-density system, it is of great interest and a preferred scenario for particle physicists and astrophysicists. To explore some novel aspects within the framework of the 5D Einstein-Gauss-Bonnet(EGB) gravity, our current study presents a hybrid star model that includes strange quark matter in addition to regular baryonic matter. In hybrid stellar objects, a hadronic outer component surrounds a quark inner component, which prompts the consideration of the most basic MIT bag model equation of state to correlate the density and pressure of strange quark matter within the stellar interior, while radial pressure and matter density due to baryonic matter are connected by a linear equation of state. The model is constructed within the specifications of the Krori and Barua (KB) ansatz (Krori and Barua, J. Phys. A: Math. Gen. 8, 508, 1975). Here we present the solution for a particular compact object 4U 1538-52 with mass M = 0.87 ± 0.07 M⊙ and radius R = 7.866 +0.21 −0.21 km. We examine the fundamental physical characteristics of the star, which highlights how the values of matter variables are affected by the Gauss-Bonnet coupling parameter α. Finally, as it meets all the physical requirements for a realistic model, we have come to realize that our present model is realistic.

$Research paper thumbnail of Polytropic stellar structure in 5$\mathcal{D}$ Einstein-Gauss-Bonnet gravity$

Polytropic stellar structure in 5$\mathcal{D}$ Einstein-Gauss-Bonnet gravity

arXiv (Cornell University), Mar 5, 2024

Polytropic stars are useful tools for learning about stellar structure without the complexity of ... more Polytropic stars are useful tools for learning about stellar structure without the complexity of comprehensive stellar models. These models rely on a certain power-law correlation between the star's pressure and density. This paper proposes a polytropic star model to investigate some new features in the context of 5D Einstein-Gauss-Bonnet (EGB) gravity using the Finch-Skea ansatz [M. R. Finch and J. E. Skea, Classical and Quantum Gravity 6, 467 (1989)]. Analytical results are better described by graphical representations of the physical parameters for various values of the Gauss-Bonnet coupling constant α. The solution for a specific compact object, EXO 1785-248, with radius R = 8.849 +0.04 −0.04 km and mass M = 1.3 ± 0.02 M⊙, is shown here. We analyze the essential physical attributes of the star, which reveal the influence of the coupling parameter α on the values of the parameters. Ultimately, we conclude that our current model is realistic because it satisfies all the physical criteria for an acceptable model.

Isotropic Durgapal IV fluid sphere in bigravity

Canadian Journal of Physics

We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV... more We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV metric (M.C. Durgapal, J. Phys. A: Math. Gen. 15, 2637 (1982)). In this work, we investigate the effects of the scale parameter k on the local matter distribution. Here, we have chosen the compact star candidate SMC X-1 with observed values of mass = (1.29 ± 0.05) M⊙ and radius [Formula: see text] km, respectively, to analyze our results analytically as well as graphically. For smaller values of k, we get the stiff (or hard) equation of state (EoS). Here, we solve the modified Einstein field equations in the presence of the background metric γμν. Due to this constant curvature background, the density and pressure terms are modified by adding an extra term, which affects the EoS. For r ≪ k, the background de Sitter space–time reduces into Minkowski form, and the coupling vanishes. We discuss certain physical quantities of our obtained solution, such as density, isotropic pressure, sound ...

$Research paper thumbnail of Charged quark stars represented by the MIT bag approach in $$5\mathcal {D}$$ Einstein–Maxwell–Gauss–Bonnet formalism$

Charged quark stars represented by the MIT bag approach in $$5\mathcal {D}$$ Einstein–Maxwell–Gauss–Bonnet formalism

The European Physical Journal Plus

Relativistic isotropic stellar model in f(R,T) gravity with Durgapal- IV metric

New Astronomy

Charged strange star coupled to anisotropic dark energy in Tolman–Kuchowicz spacetime

The European Physical Journal C

The concept of dark energy can be used as a possible option to prevent the gravitational collapse... more The concept of dark energy can be used as a possible option to prevent the gravitational collapse of compact objects into singularities. It affects the universe on the largest scale, as it is responsible for our universe’s accelerated expansion. As a consequence, it seems possible that dark energy will interact with any compact astrophysical stellar object [Phys. Rev. D 103, 084042 (2021)]. In this work, our prime focus is to develop a simplified model of a charged strange star coupled to anisotropic dark energy in Tolman–Kuchowicz spacetime (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) within the context of general relativity. To develop our model, here we consider a particular strange star object, Her X-1 with observed values of mass $$=(0.85 \pm 0.15)M_{\odot }$$ = ( 0.85 ± 0.15 ) M ⊙ and radius $$= 8.1_{-0.41}^{+0.41}$$ = 8 . 1 - 0.41 + 0.41 km. respectively. In this context, we initially started with the equation of state (EoS) to model the dark ene...

$Research paper thumbnail of Isotropic Buchdahl's relativistic fluid sphere within $f(R,\,T)$ gravity$

Isotropic Buchdahl's relativistic fluid sphere within $f(R,\,T)$ gravity

arXiv (Cornell University), Dec 15, 2022

The aim of the research is to look into a new solution for isotropic compact stars in the context... more The aim of the research is to look into a new solution for isotropic compact stars in the context of the f (R, T) theory of gravity. We used the Buchdahl [H.A. Buchdahl, Phys. Rev. 116 (1959) 1027] metric potentials as input to deal with the field equations in the f (R, T) framework. For different values of the coupling parameter χ, graphical representation of the model parameters have been shown to canvass the analytical results more clearly. Interestingly, we have proven that for χ = 0, the standard General Relativity (GR) results can be recovered. A comparison of our obtained solutions with the GR results is also discussed. To study the effect of the coupling parameter χ, the numerical values of the different physical variables have been tabulated for the values of the coupling parameter χ = 0, 0.25, 0.5, 0.75, 1, 1.25. We used the compact stars candidate LMC X-4 with mass= (1.04 ± 0.09)M⊙; Radius = 8.301 +0.2 −0.2 km. respectively, for graphical analysis. To determine the physical acceptability of the model, we looked into the necessary physical properties such as energy conditions, causality, hydrostatic equilibrium, and pressure-density ratio etc. and found that our system satisfies all of these criteria, indicating that the model is physically reasonable.

Isotropic Buchdahl’s relativistic fluid sphere within f(R,T) gravity

New Astronomy

Asymptotic cross section and scaling law: positronium formation in Rydberg states in positron–hydrogen collisions

Indian Journal of Physics, 2015

Positronium formation in Rydberg states from the ground state of the hydrogen atom by positron im... more Positronium formation in Rydberg states from the ground state of the hydrogen atom by positron impact has been studied within the framework of a distorted wave theory which includes static dipole polarization potential. The distorted wave scattering amplitude has been obtained in a closed form. A detailed investigation has been made on the differential and total cross sections in the energy range 25-300 eV of incident positron. It has been found that asymptotic cross sections for the positronium formation into different angular momentum states obey a simple law.

Stable and self consistent charged gravastar model within the framework of f(R, T) gravity

In this work, we discuss the configuration of a gravastar (gravitational vacuum stars) in the con... more In this work, we discuss the configuration of a gravastar (gravitational vacuum stars) in the context of f(R, T ) gravity by employing the Mazur-Mottola conjecture [P. Mazur and E. Mottola, Report No. LA-UR-01-5067; P. Mazur and E. Mottola, Proc. Natl. Acad. Sci. USA 101, 9545 (2004)]. Gravastar is conceptually a substitute for a black hole theory as available in literature and it has three regions with different equation of states. By assuming that the gravastar geometry admits conformal killing vector, the Einstein-Maxwell field equations have been solved in different regions of gravastar by taking a specific equation of state as proposed by Mazur and Mottola. We match our interior spacetime to the exterior spherical region which is completely vacuum and described by Reissner-Nordström geometry. For a particular choice of f(R, T) as f(R, T )=R+2γ T, here we analyze various physical properties of the thin shell and also presented our results graphically for these properties. The st...

Charged strange star in f(R,T) gravity with linear equation of state

Our present study involves the strange stars model in the framework of f(R,T) theory of gravitati... more Our present study involves the strange stars model in the framework of f(R,T) theory of gravitation. We have taken a linear function of the Ricci scalar R and the trace T of the stress-energy tensor T_μν for the expression of f(R,T), i.e., f(R,T)=R+ 2 γ T to obtain the proposed model, where γ is a coupling constant. Moreover, to solve the hydrostatic equilibrium equations, we consider a linear equation of state between the radial pressure p_r and matter density ρ as p_r=αρ-β, where α and β are some positive constants, Both α, β depend on coupling constant γ which have been also depicted in this paper. By employing the Krori-Barua ansatz already reported in the literature [J. Phys. A, Math. Gen. 8:508, 1975] we have found the solutions of the field equations in f (R, T ) gravity. The effect of coupling constant γ have been studied on the model parameters like density, pressures, anisotropic factor, compactness, surface redshift, etc. both numerically and graphically. A suitable range...

Charged gravastar model in f(T) gravity admitting conformal motion

In this paper, model of charged gravastar under f(T) modified gravity is obtained. The model has ... more In this paper, model of charged gravastar under f(T) modified gravity is obtained. The model has been explored by taking the diagonal tetrad field of static spacetime together with electric charge. To solve the Einstein-Maxwell field equations, along with f(T) gravity, we assume the existence of a conformal Killing vector which relates between geometry and matter through the Einstein-Maxwell field equations by an inheritance symmetry. We study several cases of interest to explore physically valid features of the solutions. Some physical properties of the model are discussed and we match our interior spacetime to the exterior Reissner-Nordstrom spacetime in presence of thin shell.

Electron transfer in proton-hydrogen collisions in nonideal classical plasmas

Contributions to Plasma Physics

Excited-state positronium formation in positron–hydrogen collisions under weakly coupled plasmas

Journal of Physics B: Atomic, Molecular and Optical Physics

Positron scattering from hydrogen atom in dense quantum plasmas: Positronium formation in Rydberg states

Physics of Plasmas

Effects of dense quantum plasmas on positronium (Ps) formation in an arbitrary nlm–state in the s... more Effects of dense quantum plasmas on positronium (Ps) formation in an arbitrary nlm–state in the scattering of positrons from the ground state of hydrogen atoms have been investigated within the framework of a distorted wave theory that incorporates the effect of screened dipole polarization potential. The interaction of charged particles in plasmas has been modeled by a modified Debye-Huckel potential. Effects of plasma screening on the structures of differential and total cross sections have been explored for various incident positron energies in the range 20–300 eV. For the free atomic case, our results are in conformity with the existing results available in the literature. It has been found that for small screening effects, the cross section presents the oscillatory behaviour. To the best of our knowledge, this is the first attempt to estimate the screening effects on the differential and total cross sections for Ps formation in Rydberg states in dense quantum plasmas.

Positron impact excitations of hydrogen atom embedded in weakly coupled plasmas: Formation of Rydberg atoms

Physics of Plasmas, 2014

ABSTRACT Formation of Rydberg atoms due to 1s!nlmexcitations of hydrogen, for arbitraryn, l, m,by... more ABSTRACT Formation of Rydberg atoms due to 1s!nlmexcitations of hydrogen, for arbitraryn, l, m,by positron impact in weakly coupled plasma has been investigated using a distorted-wave theory in the momentum space. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. Making use of a simple variationally determined wave function for the hydrogen atom, it has been possible to obtain the distorted-wave scattering amplitude in a closed analytical form. A detailed study has been made on the effects of plasma screening on the differential and total cross sections in the energy range 20–300 eV of incident positron. For the unscreened case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for 1s!nlminelastic positron-hydrogen collisions for arbitrary n, l, min weakly coupled plasmas is the first reported in the literature.