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M. Bigdeli

Publications and source records attributed to M. Bigdeli.

16 recordsLinked to original sources
arXiv2023

Structure of $3D$ gravastars in the context of massive gravity

In this paper, we investigate a new model of $(2+1)-$dimensional ($3D$) gravitational vacuum stars (gravastars) with an isotropic matter distribution anti-de Sitter (AdS) spacetime in the context of massive gravity. For this purpose, we explore free singularity models with a specific equation of state. Using Mazur-Mottola's approach, we predict $3D$ gravastars as alternatives to BTZ black holes in massive gravity. We find analytical solutions to the interior of gravastars free of singularities and event horizons. For a thin shell containing an ultra-relativistic stiff fluid, we discuss length, energy, and entropy. In conclusion, the parameter of massive gravity plays a significant role in predicting the proper length, energy contents and entropyand parameters of gravastars.

gr-qc↗
arXiv2023

Stable three-dimensional (un)charged AdS gravastars in gravity's rainbow

In this work, we study the three-dimensional AdS gravitational vacuum stars (gravastars) in the context of gravity's rainbow theory. Then we extend it by adding the Maxwell electromagnetic field. We compute the physical features of gravastars, such as proper length, energy, entropy, and junction conditions. Our results show that the physical parameters for charged and uncharged states depend significantly on rainbow functions. Besides from charged state, they also depend on the electric field. Finally, we explore the stability of thin shell of three-dimensional (un)charged AdS gravastars in gravity's rainbow. We show that the structure of thin shell of these gravastars may be stable and is independent of the type of matter.

gr-qc↗
arXiv2021

Binary neutron star mergers within kaon condensation: GW170817

The equation of state (EoS) of neutron star (NS) matter is investigated considering kaon condensation. Moreover, the tidal parameters related to the components of binary neutron star mergers are determined and compared to the constraints of GW170817 imposed on these quantities. In this study, we employ the lowest-order constrained variational (LOCV) approach and utilize {AV6$'$, AV8$'$, and AV18 potentials} accompanied by the three nucleon interaction (TNI) {in order to consider the nucleon-nucleon interaction}. It is known that the existence of kaons in the core of NSs softens the EoS {and thus} lowers the value of maximum mass which is expected to be greater than 2 M$_\odot$. Our results demonstrate that considering kaon condensation with a strangeness value, a$_{3}$m$_s$=-134 MeV satisfies the maximum mass constraint except for AV8$'$+TNI potential. However, the calculation of dimensionless tidal deformability shows that with the decrease of strangeness value, the neutron star gets less deformed.

astro-ph.HE↗
arXiv2021

Studying VLOCV twin compact stars with binary mergers

GW170817 has provided valuable constraints on the equations of state of merging binary neutron stars, which can be considered as the most probable candidate for the source of gravitational waves. On the other hand, these natural laboratories of extreme temperature and density may lead to the estimation of some exotic matter like {deconfined quark matter in their cores}. In this paper, we investigate the neutron star matter equation of state (EoS) with the lowest order constrained variational (LOCV) method considering the excluded volume effect (VLOCV) for nucleons {to} compute the tidal deformability of binary neutron star mergers (BNSMs). Within this approach, the size of nucleons makes the EoS {so} stiff that requires a phase transition in order to avoid causality violation. Therefore, this phase transition {may lead} to the appearance of the third family of compact stars {including} ``twin star'' configurations. {Our EoS models are confronted with observations from GW170817, GW190814, GW190425, and also NICER. We find out that regarding all these constraints, the EoS models having the {transition} pressure$\approx$30-100 MeV/fm$^{3}$ and the energy density discontinuity $Δ\varepsilon$$\lesssim$300 MeV/fm$^{3}$ are preferable.

astro-ph.HE↗
arXiv2020

Semi-regular sequences and other random systems of equations

The security of multivariate cryptosystems and digital signature schemes relies on the hardness of solving a system of polynomial equations over a finite field. Polynomial system solving is also currently a bottleneck of index-calculus algorithms to solve the elliptic and hyperelliptic curve discrete logarithm problem. The complexity of solving a system of polynomial equations is closely related to the cost of computing Groebner bases, since computing the solutions of a polynomial system can be reduced to finding a lexicographic Groebner basis for the ideal generated by the equations. Several algorithms for computing such bases exist: We consider those based on repeated Gaussian elimination of Macaulay matrices. In this paper, we analyze the case of random systems, where random systems means either semi-regular systems, or quadratic systems in n variables which contain a regular sequence of n polynomials. We provide explicit formulae for bounds on the solving degree of semi-regular systems with m > n equations in n variables, for equations of arbitrary degrees for m = n+1, and for any m for systems of quadratic or cubic polynomials. In the appendix, we provide a table of bounds for the solving degree of semi-regular systems of m = n + k quadratic equations in n variables for 2 <= k; n <= 100 and online we provide the values of the bounds for 2 <= k; n <= 500. For quadratic systems which contain a regular sequence of n polynomials, we argue that the Eisenbud-Green-Harris Conjecture, if true, provides a sharp bound for their solving degree, which we compute explicitly.

cs.CR↗
arXiv2018

Eigenspectra and Statistical Properties of the Klein-Gordon Equation with Cornell Potential: Unequal Mixings of Scalar and Time-Like Vector Potentials

The D-dimensional Klein-Gordon (KG) wave equation with unequal scalar and time-like vector Cornell interactions is solved by the Laplace transform method. In fact, we obtained the bound state energy eigenvalues of the spinless relativistic heavy quarkonium systems under such potentials. Further, the stationary states are calculated due to the good behavior of wave functions at the origin and at infinity. The statistical properties of this model are also investigated. Our results are found to be of great importance in particle physics.

quant-ph↗
arXiv2018

LOCV calculation of the equation of state and properties of rapidly rotating neutron stars

In this paper, we have investigated the structural properties of rotating neutron stars using the numerical RNS code and the equation of states which have been calculated within the lowest order constrained variational approach. In order to calculate the equation of state of nuclear matter, we have used UV$_{14}$ $+$TNI and AV$_{18}$ potentials. Here, we have computed the maximum mass of the neutron star and the corresponding equatorial radius at different angular velocity. We have also computed the structural properties of Keplerian rotating neutron star for maximum mass configuration, $M_{K}$, $R_{K}$, $f_{K}$ and $j_{max}$.

nucl-th↗
arXiv2015

Influence of spin polarizability on liquid gas phase transition in the nuclear matter

In this paper, we investigate the liquid gas phase transition for the spin polarized nuclear matter. Applying the lowest order constrained variational (LOCV) method, and using two microscopic potentials, $AV_{18}$ and $UV_{14}$+TNI, we calculate the free energy, equation of state, order parameter, entropy, heat capacity and compressibility to derive the critical properties of spin polarized nuclear matter. Our results indicate that for the spin polarized nuclear matter, the second order phase transition takes place at lower temperatures with respect to the unpolarized one. It is also shown that the critical temperature of our spin polarized nuclear matter with a specific value of spin polarization parameter is in good agreement with the experimental result.

nucl-th↗
arXiv2010

Finite temperature calculations for the spin polarized asymmetric nuclear matter with the LOCV method

The lowest order constrained variational (LOCV) technique has been used to investigate some of the thermodynamic properties of spin polarized hot asymmetric nuclear matter, such as the free energy, symmetry energy, susceptibility and equation of state. We have shown that the symmetry energy of the nuclear matter is substantially sensitive to the value of spin polarization. Our calculations show that the equation of state of the polarized hot asymmetric nuclear matter is stiffer for the higher values of the polarization as well as the isospin asymmetry parameter. Our results for the free energy and susceptibility show that the spontaneous ferromagnetic phase transition cannot occur for hot asymmetric matter.

nucl-th↗
arXiv2009

Temperature dependence of magnetic susceptibility of nuclear matter: lowest order constrained variational calculations

In this paper we study the magnetic susceptibility and other thermodynamic properties of the polarized nuclear matter at finite temperature using the lowest order constrained variational (LOCV) method employing the $AV_{18}$ potential. Our results show a monotonic behavior for the magnetic susceptibility which indicates that the spontaneous transition to the ferromagnetic phase does not occur for this system.

nucl-th↗
arXiv2008

Spin Polarized Asymmetric Nuclear Matter and Neutron Star Matter Within the Lowest Order Constrained Variational Method

In this paper, we calculate properties of the spin polarized asymmetrical nuclear matter and neutron star matter, using the lowest order constrained variational (LOCV) method with the $AV_{18}$, $Reid93$, $UV_{14}$ and $AV_{14}$ potentials. According to our results, the spontaneous phase transition to a ferromagnetic state in the asymmetrical nuclear matter as well as neutron star matter do not occur.

nucl-th↗
arXiv2008

Spin polarized liquid 3He

We have employed the constrained variational method to study the influence of spin polarization on the ground state properties of liquid $^3{\rm He}$. The spin polarized phase, we have found, has stronger correlation with respect to the unpolarized phase. It is shown that the internal energy of liquid $^3{\rm He}$ increases by increasing polarization with no crossing point between polarized and unpolarized energy curves over the liquid density range. The obtained internal energy curves show a bound state, even in the case of fully spin polarized matter. We have also investigated the validity of using a parabolic formula for calculating the energy of spin polarized liquid $^3{\rm He}$. Finally, we have compared our results with other calculations.

cond-mat.stat-mech↗
arXiv2008

Lowest order constrained variational calculation of polarized neutron matter at finite temperature

Some properties of the polarized neutron matter at finite temperature has been studied using the lowest order constrained variational (LOCV) method with the $AV_{18}$ potential. Our results indicate that spontaneous transition to the ferromagnetic phase does not occur. Effective mass, free energy, magnetic susceptibility, entropy and the equation of state of the polarized neutron matter at finite temperature are also calculated. A comparison is also made between our results and those of other many-body techniques.

nucl-th↗
arXiv2008

Structure of Neutron Star with a Quark Core

The equation of state of de-confined quark matter within the MIT bag model is calculated. This equation of state is used to compute the structure of a neutron star with quark core. It is found that the limiting mass of the neutron star is affected considerably by this modification of the equation of state. Calculations are carried out for different choices of the bag constant.

astro-ph↗
arXiv2008

Polarized Neutron Matter: A Lowest Order Constrained Variational Approach

In this paper, we calculate some of the polarized neutron matter properties, using the lowest order constrained variational method with the $AV_{18}$ potential and employing a microscopic point of view. A comparison is also made between our results and those of other many-body techniques.

nucl-th↗