Magnetic fields, if present in the plasma prior to last scattering, would induce baryon inhomogeneities and speed up the recombination process. As a consequence, the sound horizon at last scattering would be smaller, which would help relieve the Hubble tension. Intriguingly, the strength of the magnetic field required to alleviate the Hubble tension happens to be of the right order to also...
In this talk I will present recent results about cross-correlation techniques between gravitational waves and galaxy catalogues. I will report on the possibility of combined near-future gravitational wave detectors and galaxy surveys constraining the origin of binary black holes, as well as the cosmic propagation law of gravitational waves. The former might shed light on whether the observed...
We derive the gravitational energy momentum tensor for a general Lagrangian of any order and prove that this tensor, in general, is not covariant but only affine, then it is a pseudo-tensor. Furthermore, the pseudo-tensor is calculated in the weak field limit up to a first non-vanishing term of second order in the metric perturbations. The average value of the pseudo-tensor over a suitable...
The vacuum expectation values (VEVs) of the field squared and energy-momentum tensor for a massive scalar field with general curvature coupling parameter are investigated inside and outside a spherical shell in background of de Sitter (dS) spacetime. It is assumed that the field is prepared in the hyperbolic vacuum state. The latter differs from the maximally symmetric Bunch-Davies vacuum...
New observations of a transient neutron star in a low mass X-ray binary HETE J1900.1–2455 were carried out in 2018. Despite detecting only six net photons, it was still possible to infer the effective surface temperature of the star. It turned out to be quite low, ≈30 – 39 eV (for an observer at infinity) depending on the assumed mass, radius and distance to the star. Taking into account the...
We apply path-integral Monte Carlo simulations to calculate the energy of crystallized one-component plasma: the system of atomic nuclei and a uniform incompressible background (electrons). We consider full range of conditions, which are typical for core of white dwarfs and envelope of neutron stars. The results are approximated by analytic formulae, which allow us to obtain various...
Recently, author theoretically proved the possibility of the existence of a massless spin 1 particle within
the framework of the stochastic extension of Yang-Mills theory within the framework of the gauge
symmetry group SU(2) x U(1) [1]. We have shown that these particles (vector bosons called hions),
entangling in pairs, form Bose particles with spin-0, which in turn form a Bose-Einstein...
In simulations of compact stars, binary mergers and core-collapse
supernovae an equation of state (EoS) is needed to close the system of
combined Einstein and hydrodynamics equations. I will discuss
requirements for such an equation of state. Then I will present the
data base Compose, part of the PHAROS project, which contains EoS and
related data ready for use in simulations. I will show...
Precise and reliable measurements of neutron star radii are essential to our understanding of cold, catalyzed matter beyond nuclear saturation density. Recently, NASA’s Neutron Star Interior Compo- sition Explorer (NICER) satellite has provided high-quality data sets that have yielded measurements of the mass (M=1.44+-0.15 Msun) and radius (R=13+1.2-1.0 km) of the 206 Hz pulsar PSR J0030+0451,...
First 1S0 nn and pp pairings in baryon matter will be discussed. Then focus will be made on the study of phases of the complex neutral and charged vector boson coupled with magnetic field by the Zeeman coupling. I will discuss presence of nonmagnetic and ferromagnetic superfluid phases. It will be shown that in a strong magnetic field spin-triplet pairing and ferromagnetic superfluidity...
Ferromagnetic spin ordering can take place in neutron stars. This phase transition
alters the neutron star equation of state. Here, applying the scalar-tensor theories of gravity, we investigate the structure of neutron stars which are in the ferromagnetic phase. Considering the equation of state of ferromagnetic neutron matter with Skyrme-type interactions at zero temperature and using the...
In this work, we develop an analytic treatment that would allow us to model the magnetic deformation of neutron stars in the quasi-Newtonian framework. We analyze the problem with taking density profiles from various analytic approaches. The first density profile is the n=1 solution of the Lane-Emden equation, the second one is a parabolic ansatz for density and the last density distribution...
Analytical expressions for the components of the tensors of thermal conductivity, diffusion, thermal diffusion and the diffusional thermal effect are obtained from the solution of the Boltzmann equation by the Chapman-Enskog method, taking into account electron-electron collisions for the case of non-degenerate electrons in a magnetic field. For strongly degenerate electrons, asymptotically...
Over the past few years, we have enjoyed a wide variety of gravitational-wave detections of compact binary coalescences. However, the wait continues for the first observation of a rotating neutron star via gravitational waves and, so far, only upper limits on the size of the involved deformations have been obtained. For these reasons, the maximum quadrupole deformation (or mountain) that a...
Since 1997 the attempts to build the relativistic generalization of the Newtonian r-modes - predominantly toroidal oscillations, inherent to rotating neutron stars, - have lead to contradictory results concerning the properties of their frequency spectrum. While numerical calculations predict the discrete oscillation spectrum, theoretical studies in the slow-rotation approximation relying on...
Recently discovered high-mass X-ray binary (HMXB) in the supernova remnant MCSNR J0513-6724 (Maitra et al., 2019) is a puzzle for the standard magneto-rotational evolution of neutron stars. If the observed period of 4.4 s corresponds to the critical period of Proppeller-Accretor transition, the magnetic field should be about 3×1011 G. With such a magnetic field, the duration of the Ejector and...
Recent constraints from neutron star measurements and nuclear experiments have narrowed the allowed physical regions for the compact stars equation of state (EoS) resulting in some of the well established models being less probable than before. These new constraints include the NICER mass-radius measurement of the object PSR J0740+6620, whereas laboratory experiments like Spectral Pion Ratio...
Over the last few decades, there are enormous interest in massive neutron stars and white dwarfs with their indirect/direct evidences. Here I will touch upon their possible formation channels and possible direct detection. They have many consequences including possible second standard candle.
We investigate the properties of anisotropic, spherically symmetric compact stars, especially neutron stars and strange quark stars, made of strongly magnetized matter. The neutron stars are described by SLy equation of state, the strange quark stars by an equation of state based on the MIT Bag model. The stellar models are based on an a priori assumed density dependence of the magnetic field...
I will describe the recent progress in the studies of hyperonization and onset of delta-resonances in compact stars, their effect on the integral parameters of compact stars. I will then focus on the recent extension of zero-temperature equations of state to finite temperatures in a manner suitable for implementation in the numerical studies of proto-neutron stars and binary neutron star...
The deep crustal heating, associated with exothermal nuclear reactions, is believed to be a key parameter for describing the thermal evolution of accreting neutron stars. In this talk, we present the first thermodynamically consistent calculations of the crustal heating for realistic compositions of thermonuclear ashes. In contrast to previous studies based on the traditional approach, we...
We show that the diffusion of various particle species in superconducting neutron star cores can be extremely powerful dissipative mechanism. In particular, it can be much more efficient than the shear and bulk viscosities. This result has important implications for the damping times of NS oscillations, development and saturation of dynamical instabilities in NSs, and for the excitation and...
A new "2SC"+"dd" phase containing 1S0 "ud" and 3P2 "dd" condensates is proposed [1]. Semi superfluid vortices carrying color magnetic fluxes together with fractionally quantized superfluid circulations appear in this phase [2].
1.Y.Fujimoto.Nucl. Phys.1005,2021,121757.
2.Y.Fujimoto,M.Nitta,Phys.Rev.D103,2021,114003.
In this work, we extend our previous study of the bulk viscosity of hot and dense 𝑛𝑝𝑒 matter induced by the Urca process in the neutrino trapped regime to 𝑛𝑝𝑒𝜇 matter by adding the muonic Urca processes as well as the purely leptonic electroweak processes involving electron-muon transition.
The nuclear matter is modeled in a relativistic density functional approach with two different...
The existence of quark matter inside the cores of massive neutron stars is supported by many recent studies. We model hybrid stars using the extended linear sigma model $-$ which reproduces vacuum quantities and finite tempreture behaviour accurately $-$ to describe quark matter, together with various hadronic models. We show that crossover phase transitions between the hadronic and quark...
The thermodynamic characteristics of hot β -equilibrium electrically neutral three-flavor quark matter at neutrino confinement are investigated. For the thermodynamic description of such a quark-lepton system, the local SU(3) Nambu-Jona-Lasinio (NJL) model is used, in which also takes into account the 't Hooft interaction, leading to the quark flavor mixing effect. The energy density ε and...
We develop a new equation of state (EoS) table involving thermal (anti)kaons, Bose-Einstein condensate of $K^{-}$ mesons and $\Lambda$-hyperons for core-collapse supernova and neutron star merger simulations. This EoS table is based on a finite temperature density-dependent relativistic hadron field theory where baryon-baryon interaction is mediated by scalar $\sigma$, vector $\omega$...
We study an impact of asymmetric fermionic and bosonic dark matter on general properties and tidal deformabilities of neutron stars and their ability to reach the two solar masses limit. It allows us to present a new range of masses of dark matter particles and their fractions inside the star. Our analysis is based on the observational fact of the existence of two pulsars reaching this limit...
A principal element of strongly interacting matter phenomenology is the quark confinement at low baryonic densities. We develop an approach based on the relativistic density functional motivated by the string-flip model, which provides the low density suppresion of quarks due to rise of their self-energy already at the mean-field level. Dynamical restoration of chiral symmetry is ensured by...
The discovery of gravitational waves from a binary neutron star merger event GW170817 has allowed for the study of the neutron stars’ interior, particularly the matter at nuclear densities [1]. This detection has also resulted in the improvement of our insight into the maximum mass of neutron stars and their tidal deformability. Moreover, the new knowledge of matter at extreme densities and...
The Magnificent Seven is a unique group of seven nearby thermally emitting isolated neutron stars. They are visible mostly in a soft X-ray band, their spectrum is close to a blackbody one, and their lightcurves show pulsations (up to 25%) in detected radiaton. These pulsations tell us, that temperature distributions in such neutron stars may be highly non-uniform due to the effect of their...
Nuclear mass measurements and neutron matter theory tightly constrain the parameters SV and L of the nuclear symmetry energy. Corroboration can be found from measurements of the neutron skin thicknesses and dipole polarizabilities of neutron-rich nuclei, as well as astrophysical measurements of the neutron star radius.
We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius diagram. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the constant-sound-speed (CSS) equation of state (EoS) and the nuclear matter phase around saturation density is varied...
I overview the current status of the stripping model for short gamma-ray bursts. After the historical joint detection of the gravitational wave event GW170817 and the accompanying gamma-ray burst GRB170817A, the relation between short gamma-ray bursts and neutron star mergers has been reliably confirmed. Many properties of GRB170817A, which turned out to be peculiar in comparison with other...
Machine Learning opens a new era in Physics, Cosmology, and Astrophysics. In the last couple of years, indeed, the effort of applying Machine Learning to tackle various problems seems to be very promising. The growing number of research papers and the nature of solved problems is a bright example of this.
One of the widely used Machine Learning techniques is Gaussian Processes. This...
The dynamical aspects of some accelerating models are investigated in the framework of an extension of symmetric teleparallel gravity dubbed as f (Q, T) gravity. In this gravity theory, the usual Ricci tensor in the geometrical action is replaced by a functional f (Q, T) where Q is the non-metricity and T is the trace of the energy-momentum tensor. Two different functional forms are considered...
Vacuum currents near horizon of a cylindrical black hole V. Kh. Kotanjyan, A. A. Saharian, M. R. Setare We investigate the vacuum expectation value (VEV) of the current density for a charged massive scalar field with general curvature coupling parameter near a cylindrical black hole in background of (D+1)-dimensional spacetime. It is shown that, to the leading order, the near-horizon geometry...
In this talk, we will propose the big rip and pseudo rip cosmological models in an extended theory of gravity. The matter field is considered to be that of perfect fluid. The geometrical parameters are adjusted in such a manner that it matches the prescriptions given by cosmological observations, to be specific to the H0 range. The models favour phantom behaviour. The violation of strong...
We construct some Rip cosmological models in the framework of Brans-Dicke theory where the Brans-Dicke parameter is considered to be a function of the scalar field. We obtained the time evolution of the scalar field, the Brans-Dicke paramete and the Newtonian Gravitational constant for the rip cosmological models. The cosmic dynamics of the model have been discussed.
I argue how the concept of the quark-hadron continuity leads to stiffening of matter just above the nuclear saturation density. The relation to the McLerran-Reddy model of quarkyonic matter is also discussed.
The GW170817 event answered one of the important questions regarding a
potential site of heavy element synthesis in the cosmos. The observations of the
gravitational waves (VIRGO and LIGO) along with signatures from 70
electromagnetic transients indicated that heavy element synthesis was indeed
going on up to the rare-earth region of the chart of nuclides. These series of
connected...
We discuss the vacuum expectation values (VEV) of the field squared and energy-momentum tensor for quantum fields in background of anti-de Sitter (AdS) spacetime in the presence of branes. The boundary conditions imposed on the fields modify the spectrum of vacuum fluctuations and give rise to contributions in the VEVs depending on the geometry of the branes and on the specific boundary...
