Article
Physics, Multidisciplinary
Joaquin Estevez-Delgado, Joel Arturo Rodriguez Ceballos, Jorge Mauricio Paulin-Fuentes, Jose Vega Cabrera, Antonio Rendon Romero
Summary: This report generalizes the solution to Einstein's equations with perfect fluid to the case of Einstein-Maxwell with perfect fluid. The effect of the charge is determined by a parameter ν, which is constrained by the positivity condition from the pressure inside the star. It is shown that the solution is stable according to the Zeldovich criteria and the adiabatic index criteria. The presence of charge increases the compactness of the model, allowing it to represent stars with high compactness.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2023)
Article
Mathematics, Applied
Hyunjin Ahn, Seung-Yeal Ha, Myeongju Kang, Woojoo Shim
Summary: The study presents a relativistic counterpart of the Cucker-Smale model on Riemannian manifolds and examines its collective behavior. By replacing usual time derivatives with appropriate geometric quantities, the model is extended from Euclidean space to connected, complete, and smooth Riemannian manifolds. Concrete examples on the unit sphere and hyperbolic space show the emergence of weak velocity alignment in compact manifolds.
PHYSICA D-NONLINEAR PHENOMENA
(2021)
Article
Physics, Multidisciplinary
Bin Hong, Xue-Ling Mu
Summary: This study examines the effects of relativistic parameter sets established at saturation density on the tidal deformabilities and f-mode oscillations of neutron stars. The findings indicate that the isovector saturation parameters have a greater impact than the isoscalar saturation parameters. The study also observes a linear correlation between f-mode frequencies and saturation properties.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2022)
Article
Astronomy & Astrophysics
Thomas Madler, Emanuel Gallo
Summary: Using a quasispherical approximation and affine-null coordinates, this paper presents high order approximations of the metric functions for a slowly rotating stationary and axisymmetric vacuum spacetime. It verifies the equivalence of the metric with the Kerr metric in the slowly rotating approximation and shows that the additional integration constants can be absorbed into the overall Komar mass and Komar angular momentum of a slowly rotating black hole.
Article
Astronomy & Astrophysics
Raj Kishor Joshi, Indranil Chattopadhyay, Dongsu Ryu, Lallan Yadav
Summary: This study focuses on the evolution of one-dimensional relativistic jets using the exact solution of the Riemann problem for relativistic flows. The composition of the jet and ambient medium significantly affects the jet solution, with jet propagation speed depending on the composition and being maximum for a pair-dominated jet. The propagation direction of the reverse-shock may also strongly depend on the composition of the jet.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Tuna Demircik, Christian Ecker, Matti Jarvinen
Summary: The study focuses on rapidly spinning compact stars with a first-order phase transition between strongly coupled nuclear matter and deconfined quark matter. Models allow for purely hadronic uniformly rotating stars with masses up to approximately 2.9 solar masses, and the maximal mass is determined by the phase transition in cases with the largest values.
ASTROPHYSICAL JOURNAL LETTERS
(2021)
Article
Mechanics
Maximilian Krause, Tarkes Dora Pallicity, Thomas Boehlke
Summary: This paper derives analytical equations for the second moments of local fields in particulate composites with isotropic phases. Using the Mori-Tanaka approach, the Hashin-Shtrikman bounds, and the singular approximation, explicit expressions are provided. The results are compared to full-field simulations, showing that the Hashin-Shtrikman covariance is not suitable for predicting behavior under deviatoric loadings, while the singular approximation and Mori-Tanaka methods yield sensible approximations for the second moment of matrix strain.
EUROPEAN JOURNAL OF MECHANICS A-SOLIDS
(2023)
Article
Astronomy & Astrophysics
F. Cipolletta, J. Kalinani, E. Giangrandi, B. Giacomazzo, R. Ciolfi, L. Sala, B. Giudici
Summary: This article introduces a new version of the GRMHD code Spritz, with an added neutrino leakage scheme and a series of tests to verify its correct implementation. It also discusses the implementation of high-order methods in the Spritz code.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Alexandre Toubiana, Stanislav Babak, Enrico Barausse, Luis Lehner
Summary: Exotic compact objects can be difficult to distinguish from black holes in the inspiral phase of binaries observed by gravitational-wave detectors, but significant differences may be present in the merger and post-merger signal. A toy model capturing the key features of binaries of exotic compact objects with low compactness was introduced to assess their detectability and distinguishability from black hole binaries. The study showed that current detectors like LISA could potentially observe exotic binaries and differentiate them from black hole binaries.
Article
Physics, Multidisciplinary
C. Las Heras, P. Leon
Summary: The study focuses on a particular case of extended geometric deformation involving consecutive deformations of metric's temporal and spatial components, presenting two inequivalent ways of performing this two-step GD. By using different seed solutions, two different physical solutions with anisotropy in pressures were obtained in Schwarzschild-like coordinates. In the isotropic sector, four solutions with anisotropy in pressures satisfying physical acceptability conditions were derived using a specific seed solution.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Physics, Nuclear
H. Nazar, M. Azam, G. Abbas, Riaz Ahmed, R. Naeem
Summary: In this paper, new solutions to the Einstein-Maxwell field equations incorporating anisotropic matter distributions were introduced using the framework of general relativity. Various models of generalized polytropes were constructed with different values of the polytropic index, and their physical characteristics were studied through graphical analysis, showing compliance with essential conditions for astrophysical compact objects. The outcomes of charged anisotropic compact star models could be replicated in different cases, including linear, quadratic, and polytropic equations of state.
Article
Astronomy & Astrophysics
Zhong-Hao Tu, Shan-Gui Zhou
Summary: The effects of the phi meson on hyperon stars are systematically studied in a density-dependent relativistic mean field model. It is found that the phi meson can shift the hyperon threshold and affect the equation of state and maximum mass of hyperon stars. Only a few effective interactions survive under the constraints from astrophysical observations. The possibility of the secondary object of GW190814 being a rapidly rotating hyperon star is discussed.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Han Rui Fu, Jia Jie Li, Armen Sedrakian, Fridolin Weber
Summary: A set of hyperonic equations of state (EoS) are constructed by assuming SU(3) symmetry and using a covariant density functional theory approach. The EoS is constrained by terrestrial experiments at low density and modeled by varying the nuclear matter skewness coefficient and symmetry energy slope at high density. The results show that the model can support a range of static and rotating stellar masses under certain conditions.
Article
Astronomy & Astrophysics
Ismael Delgado Gaspar, Thomas Buchert, Jan J. Ostrowski
Summary: We have developed a new nonlinear method to model structure formation in general relativity, based on a generalization of the relativistic Lagrangian perturbation schemes controlled by Szekeres and LTB exact solutions. This approach can be seen as the evolution of a deformation field on an inhomogeneous reference model, following locally Friedmann-like equations. In the special case of locally one-dimensional deformations, the model includes the entire Szekeres family of exact solutions. This formulation is similar to the Newtonian and relativistic Zel'dovich approximations, making it highly applicable in contexts where relativistic degrees of freedom are relevant. Numerical simulations have been performed to demonstrate the capabilities and accuracy of the model.
Article
Astronomy & Astrophysics
J. Kumar, H. D. Singh, A. K. Prasad
Summary: This paper investigates the stellar structure using the f(R, T) gravity theory, specifically considering the function f(R, T) = R + 2 sigma T. A stellar model is developed to explain the isotropic matter distribution within compact objects filled with perfect fluid, and its stability is demonstrated through various physical and stability conditions. The theory is shown to be acceptable by accurately collecting data for compact stars like PSR-B0943+10, CEN X-3, SMC X-4, Her X-1, and 4U1538-52.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Physics, Multidisciplinary
Neeraj Pant, Satyanarayana Gedela, Ravindra K. Bisht
Summary: The paper aims to find an anisotropic and charged version of the Heintzmann interior solution in a space-time using the minimal geometric deformation approach to gravitational decoupling. Through various physical tests, the obtained model of neutron star 4U1608-52 proves to be a well-behaved physical solution to Einstein-Maxwell's field equations.
CHINESE JOURNAL OF PHYSICS
(2021)
Article
Astronomy & Astrophysics
Satyanarayana Gedela, Neeraj Pant, Jaya Upreti, R. P. Pant
Summary: This paper presents a new parametric class of solutions to study the relativistic structure of compact stars via embedding class I condition. The interior of the star is delineated by Karmarkar condition and matched with Bardeen and Reissner-Nordstrom exterior spacetimes. By solving Maxwell field equations, all thermodynamic properties are verified and compared.
MODERN PHYSICS LETTERS A
(2021)
Article
Physics, Multidisciplinary
Satyanarayana Gedela, Neeraj Pant, Megandhren Govender
Summary: In this paper, a new exact anisotropic charged version of Pant's interior solution is presented, integrating coupled Einstein-Maxwell field equations to generate a family of new charged anisotropic solutions. Rigorous tests were conducted to validate the physical viability of the model, showing the intrinsic connection between the deformation parameter and key features.
BRAZILIAN JOURNAL OF PHYSICS
(2021)
Article
Astronomy & Astrophysics
Saibal Ray, Prasenjit Paul, Rikpratik Sengupta, Neeraj Pant, Riju Nag
Summary: This paper investigates anisotropic universes with Modified Chaplygin gas in the context of the Randall Sundrum-2 braneworld model. Solutions for Kantowski-Sachs and Bianchi-I universes with MCG are obtained, showing modifications from GR solutions due to the braneworld correction term. The possibility of future singularities is considered, with the model overcoming some drawbacks of the relativistic framework.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2021)
Article
Astronomy & Astrophysics
Satyanarayana Gedela, Ravindra K. Bisht, Neeraj Pant, Jaya Upreti, R. P. Pant
Summary: In this paper, two new exact and analytic solutions are presented for compact anisotropic charged stars in the background of Bardeen black hole geometry satisfying the Karmarkar condition. The models consist of inner region described by class I Karmarkar space-time and exterior characterized by both Bardeen and Reissner-Nordstrom spacetimes. Analysis shows that the models are well-behaved in terms of matter and thermodynamic variables.
Article
Astronomy & Astrophysics
Ravindra K. Bisht, Satyanarayana Gedela, Neeraj Pant, Neeraj Tewari
Summary: This work presents a novel solution for neutron stars with different layers of matter and equations of state, showing continuous and feasible trends in physical and geometrical parameters. The model meets various stability conditions, providing a more realistic and accurate modeling of stellar objects.
RESEARCH IN ASTRONOMY AND ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Neeraj Pant, Megandhren Govender, Satyanarayana Gedela
Summary: This work presents a theoretical framework within Einstein's classical general relativity to model stellar compact objects, with the assumption of a class I spacetime for the interior structure and the adoption of a robust gravitational potential form. The model satisfies all the requirements for physically realistic stellar structures.
RESEARCH IN ASTRONOMY AND ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Neeraj Pant, Satyanarayana Gedela, Saibal Ray, Kumar Gaurav Sagar
Summary: This paper explores a solution to the Einstein-Maxwell field equations in four-dimensional spacetime by using the Karmarkar conditions and the minimal geometric decoupling technique. The obtained solution is shown to be physically viable for neutron stars.
MODERN PHYSICS LETTERS A
(2022)
Article
Astronomy & Astrophysics
Kumar Gaurav Sagar, Brajesh Pandey, Neeraj Pant
Summary: The paper proposes a hybrid stellar model consisting of gravitating baryonic matter and a linearly coupled repulsive dark energy field by using Einstein field equations. The physical viability of the solutions is analyzed, revealing that dark energy can provide stability against gravitational collapse.
ASTROPHYSICS AND SPACE SCIENCE
(2022)
Article
Astronomy & Astrophysics
Shweta Saklany, Neeraj Pant, Brajesh Pandey
Summary: The main aim of this study is to investigate the influence of background dark energy on a gravitationally compact star, PSRJ0740 + 6620. The Einstein field equations are used in an anisotropic regime to model the space-time fabric and associated gravity. The spatial metric potential of Vaidya-Tikekar type is utilized to obtain the temporal metric potential using Karmarkar's connecting relation and the unknown constants are calculated using Darmois-Israel conditions. Through rigorous theoretical analysis, it is found that the model star satisfies all the necessary and sufficient conditions to form a viable stellar configuration. The key findings suggest that the background repulsive scalar field of dark energy can aid in the formation of dense and stable stellar structures at masses beyond the TOV limit.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Shweta Saklany, Neeraj Pant, Brajesh Pandey
Summary: A singularity free and smoothly connected complete solution for a three-layered compact star is presented, including a deconfined quark matter core, a coherent quantum fluid, and a repulsive neutron-Coulomb fluid envelope. Insights into the pressure-density distribution and thermodynamic properties are obtained, shedding light on the structural stability and mass-radius relation.
Article
Astronomy & Astrophysics
Shweta Saklany, Brajesh Pandey, Neeraj Pant
Summary: This study provides a simulation of the coupling of dark energy and baryonic matter using a super-dense pulsar as the model star. The analysis of various physical parameters indicates stable star formation. The proposed stellar model is free from singularities and meets the requisite stability criteria.
MODERN PHYSICS LETTERS A
(2022)
Article
Physics, Multidisciplinary
K. N. Singh, F. Rahaman, N. Pant
Summary: This paper proposes a three-layered hybrid compact star model, with a quark matter core, neutron liquid intermediate layer, and matter envelope satisfying a quadratic EoS. By tuning free parameters, physical parameters are continuous across regions, but stability is not defined at interfaces. Calculations verify a smooth transition density between different regions.
INDIAN JOURNAL OF PHYSICS
(2022)
Article
Physics, Multidisciplinary
S. Gedela, R. K. Bisht, N. Pant
Summary: This paper introduces a new class of exact solutions that satisfy Einstein's field and modified TOV equations, using the Karmarkar condition. The solutions meet various stability criteria and energy conditions, and a complete graphical analysis of neutron stars in the Karmarkar space-time is performed.
INDIAN JOURNAL OF PHYSICS
(2021)
Article
Physics, Multidisciplinary
K. N. Singh, F. Rahaman, N. Pradhan, N. Pant
Summary: The study presents an anisotropic charged analogue solution which can be used to model various types of compact stars, such as quark stars and neutron stars. By adjusting parameters, specific models for super-dense quark stars and neutron stars are obtained, showing that the increase in charge and anisotropy can enhance the stability of configurations.
INDIAN JOURNAL OF PHYSICS
(2021)
