In this contribution we consider hybrid compact stars located in the third branch of the corresponding mass-radius diagram. We introduce a set of equations of state whose symmetry energy parameters vary. These are described by multi-polytropes and by a RMF model with several isovector mesons, fulfilling laboratory constraints. We find correlations between tidal deformabilities, stellar radii...
We study the properties of hybrid stars containing a color superconducting quark matter phase in their cores, which is described by the chirally symmetric formulation of the confining relativistic density functional approach. It is shown that depending on the dimensionless vector and diquark couplings of quark matter, the characteristics of the deconfinement phase transition are varied,...
Determining the equation of state (EoS) of superdense matter from neutron star (NS) observations is an important problem of modern physics. In the literature one can find several hundreds of EoS models (nucleonic, hyperonic, hybrid), based on different approaches to the NS microphysics. In spite of the differences, for a wide set of such models, the relation between pressure $P$ and density...
In the last 10-15 years, observations of neutron stars have revolutionized our understanding of cold, catalyzed matter beyond nuclear saturation density. These observations include the discovery of high-mass neutron stars, limits on tidal deformability from gravitational wave observations, and measurements using NICER data of the radii of two neutron stars. These observations, combined with...
In the most equation of state the electron chemical potential in the neutron star (NS) matter reaches the value of the free pion mass already at rather moderate baryon densities. That would lead to pionization of the NS matter when negative pions replace electrons. The repulsive s-wave pi- -neutron interaction could prevent it. We apply the effective chiral Lagrangian at the second chiral...
We compute the anisotropic electrical conductivity tensor of the inner crust of a compact star at non-zero temperature by extending a previous work on the conductivity of the outer crust. The physical scenarios, where such crust is formed, involve proto-neutron stars born in supernova explosions, binary neutron star mergers and accreting neutron stars. The temperature-density range studied...
In our study, we analyzed how neutrino oscillations impact the thermodynamic properties of three-flavor hot electrically neutral beta-stable quark matter that cannot be penetrated by neutrinos. Through the use of the local SU(3) Nambu-Jona-Lasinio (NJL) model, we were able to determine the thermodynamic characteristics of quark matter for two different temperatures, specifically at T = 60 and...
The gravitational wave (GW) events offer new insights into compact stars. The binary merger GW170817 and its electromagnetic counterpart have led to new constraints on the maximum mass of neutron stars (NSs). Based on GW170817, the upper bound of MTOV for NSs is predicted as (2.3-2.4)M⊙. However, there are other observations of pulsars and binary mergers consisting of components or remnants...
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It is expected that the density at the center of neutron stars will be high enough that hyperons or quark matter may be present. In this paper, we investigate the presence of hyperons ($\Lambda$, $\Sigma^{-}$) along with Leptons (Muons, Electrons) and nucleons in the neutron star. For this purpose, we used a relativistic model called the Sigma-omega-rho model. In this method, the coupling...
We discuss a model of quark-hadron duality to explain soft-to-stiff evolution of stiffness in neutron star equations of state. To explain rapid stiffening, the quark substructure of a baryon plays essential roles, already at density as low as a few times nuclear saturation density. We present an analytic model of the duality as a representative model of quarkyonic matter. We also argue the...
Since the last several years, there are enormous interest in the understanding of the possible formation of massive compact objects: white dwarfs and neutron stars (also intermediate-mass black holes). This stems from many direct and indirect observations related to pulsars, type Ia supernovae, gravitational waves, and even quasi-periodic oscillations. The question also arises, if a massive...
We investigate the thermodynamic properties of the hot β-equilibrated hadronic matter, which consists of neutrons(n), protons(p), electrons(e), electron neutrinos(ν_e), muons(μ), and muon neutrinos(ν_e). To describe such matter, we use an improved version of the relativistic mean field theory (RMF) at a finite temperature, where, in addition to the effective fields of σ-, ω-, and ρ-mesons, the...
The study of matter at extreme densities has been a major focus in theoretical physics in the last half-century. The wide spectrum of the information provides an insight into the world around us. The models and concepts put forward by the study of nuclear matter help to solve mystery of the interaction in the universe. Through the study of neutron stars we are able to investigate the process...
The Hadamard function and the vacuum expectation values (VEVs) of the field squared and energy-momentum tensor are evaluated for a massless conformally coupled scalar field in de Sitter (dS) spacetime with general number of spatial dimensions, described by coordinates with negative constant spatial curvature. It is assumed that the field is prepared in the hyperbolic vacuum state. An integral...
The dynamical system analysis of the cosmological models in f(T,T) gravity, where T and T respectively represents the torsion scalar and trace of the energy-momentum tensor has been investigated. It demonstrates how first-order autonomous systems can be treated as cosmological equations and analyzed using standard dynamical system theory techniques. Two forms of the function f(T,T) are...
We discuss an extended model of FRW cosmology with additional chiral
tensor particles. We discuss the influence of these particles on the
expansion rate of the Universe, their cosmological place and derive
cosmological constraints on their interaction strength.
The origin and formation of the Universe is always one of the most discussed and researched topics of all time. It is relevant and several theories have been developed to explain the evolution of the Universe, such as the standard, De Sitter , Alven-Klein and other models. The Big Bang was immediately followed by an inflationary phase lasting 10-34 second, as confirmed by experimentally...
Neutron stars possess very strong magnetic fields of order 10^11~10^12 G. Such strong magnetic fields
modify properties of Neutron star matter. We investigate the effect of this strong magnetic field on EOS
(Equation of State) of neutron stars. So far, various models and EOS for neutron stars have been
proposed and properties of neutron stars are calculated and compared with observations....
It is thought that the H0 tension problem can be an indicator of new physics. It seems to be an easy task to solve. However, this is not the case and strongly depends on the assumptions used to craft a theoretical model. In this talk, we will discuss some of our results on searching for a solution to the problem using some Machine Learning tools.
Shortly after the postulation of quarks by Zweig and Gell-Mann in 1964 and the experimental confirmation of these subnucleon formations [1,2] in 1969, Feynman, Ravndal and Kislinger (FRK) in 1971 proposed a relativistic three-quark model of nucleons [3] to study the internal structure and state of these dynamical systems and explain a number of thier important properties. The idea of this...
In this work, we present singular bounce scenario
in the framework of the generalised Brans-Dicke (GBD)theory where an evolving BD parameter along with a self-interacting potential is considered. The GBD field equations are derived for an anisotropic space time to provide a more general approach to the cosmic expansion. The evolutionary behaviour of the Brans-Dicke scalar field, dynamical...
Static traversable wormhole solutions within extended gravity theories have been obtained by exploring the Casimir energy. The shape function and the associated energy conditions are obtained. Also, the concept of minimal length leading to the generalized uncertainty principle (GUP) is used to assess the effect of GUP correction on the wormhole geometry and the exotic matter content of the...
The detections of gravitational waves (GWs) have significantly influenced physics and astrophysics since the analysis and interpretation of data from merger events constrain the equation of state (EoS) of the neutron stars.
In this work, we explore gravitational waveforms of magnetized rotating neutron stars. For this aim, we use realistic EoS for rotating magnetized neutron stars and...
Recently, within the framework of the stochastic Yang-Mills equations for the gauge symmetry group SU(2)xU(1), the possibility of the evidenc of massless Bose particles with spin-1-Hions has been proved [1]. Theoretically, the formation of a vector field from Hions in the form of a spin glass and, accordingly, a scalar field as a result of Bose condensation of entangled pairs of Hions with a...
Quark hadron continuity with two- flavor quarks connects hadronic matter with neutron 3P2 superfluidity and two-flavor dense quark matter. This two- flavor dense quark phase consists of the coexistence of the 2SC diquark condensate of ud - quarks and P –wave diquark condensate of d –quarks , which gives rise to color superconductivity as well as superfluidity. The stable vortices are...
The vacuum expectation value of the current density for a charged scalar field with general curvature coupling is investigated in locally de Sitter spacetime with toroidally compactified spatial dimensions and in the presence of boundaries. In addition, the presence of a classical constant gauge field is assumed. General quasiperiodic boundary condition are imposed along compact dimensions and...
In this study, we consider different features induced by the presence of dark matter (DM) in a new type of compact object so-called DM admixed neutron star (NS), in light of the latest observational data of NICER X-ray telescope and LIGO/Virgo Gravitational-Wave (GW) detectors. We investigate self-repulsive sub-GeV bosonic DM which can be distributed as a core inside the NS or as an extended...
