We investigate the effects of background curvature, nontrivial topology and of a planar
boundary on the properties of the vacuum state for a charged scalar field. The
background geometry is locally dS with an arbitrary number of toroidally compact
dimensions. The planar boundary is perpendicular to one of infinite dimensions and on it
the charged scalar field obeys the Robin boundary...
Large scale B-mode patterns in CMB polarization, if detected, would constitute a “smoking gun” signature of primordial gravitational waves generated during an inflationary phase in the early universe. In this talk, I will discuss other sources of B-modes, such as primordial magnetic fields, axion-like fields and cosmic strings, and prospects of isolating their distinguishing features with...
We investigate the polarization of the vacuum for scalar, fermionic and electromagnetic fields induced by cosmic strings. Locally Minkowski, de Sitter and anti-de Sitter background geometries are considered. As local characteristics of the vacuum the expectation values of the field squared and of the energy-momentum tensor are considered. The contributions induced by the nontrivial topology of...
We investigate the vacuum expectation value (VEV) of the current density for charged quantum fields in background of locally AdS spacetime with an arbitrary number of toroidally compact dimensions and in the presence of a constant gauge field. Along compact dimensions the field operator obeys quasiperiodicity conditions with arbitrary phases. The VEVs for the charge density and the components...
All known solutions in GR describing rotating cylindrical wormholes lack asymptotic flatness in the radial directions and thus cannot describe wormhole entrances as local objects in our Universe. To overcome this difficulty, wormhole solutions are joined to flat asymptotic regions at some cylindrical surfaces on both sides of the throat. The whole configuration thus consists of three regions,...
Nowadays strong magnetic field has been observed or expected in compact stars or during
relativistic heavy-ion collisions. In particular, magnetars may have a huge magnetic field of
O(10 15 G) at the surface. We here consider the transport properties of Dirac particles in the
presence of a strong magnetic field. As a phenomenological implication, the heat conductivity is
interesting and...
I will demonstrate how the minimum main sequence mass of the low-mass stars is affected by the Palatini gravity: it turns out that such objects, whose the internal structure is known better in comparison to compact stars, can be used to test modified theories of gravity.
General introduction to cosmology of modified gravity is given. It is shown that different forms of modified gravity are possible: many of them being consistent with Solar system tests and cosmological bounds. Special attention is paid to F(R) gravity. It is shown that such theory may naturally describe the early-time inflation with late-time acceleration (dark energy epoch). Realistic...
In cold atoms and in the crust of neutron stars the pairing gap can reach values comparable with the Fermi energy. While in nuclei the neutron gap is smaller, it is still of the order of a few percent of the Fermi energy. The pairing mechanism in these systems is due to short range attractive interactions between fermions and the size of the Cooper pair is either comparable to the...
The high-density behavior of nuclear symmetry energy is the most uncertain part of the Equation
of State (EOS) of dense neutron-rich nucleonic matter [1]. It has significant ramifications in
understanding properties of nuclear reactions induced by rare isotopes, neutron stars and
gravitational waves from various sources. Using a new technique of inverting numerically...
The Compressed Baryonic Matter (CBM) experiment is of the major scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. In collisions between heavy nuclei at FAIR energies, it is expected that the matter in the reaction zone is compressed to more than five times saturation density, corresponding to the density in the core of a massive neutron star. This...
We consider the formation of structured and massless particles with spin 1 (vector boson), by using the Yang-Mills like stochastic equations system for the group symmetry $SU(2)\otimes U(1)$ without taking into account the nonlinear term characterizing self-action. We prove that, in the first phase of relaxation, as a result of multi-scale random fluctuations of quantum fields, massless...
We investigate the vacuum expectation value (VEV) of the surface energy-momentum tensor for a charged scalar field in a higher dimensional locally anti-de Sitter spacetime with two parallel branes and with a compact dimension (generalized Randall–Sundrum model). The presence of a constant background gauge field is assumed. The latter gives rise to Aharonov-Bohm type effect on the...
The change in mass of the protoquark stars during their cooling is studied. When a supernova explodes, its central part shrinks so quickly that the lepton charge due to weak processes does not have time to change. Therefore, the chemical equilibrium is established after the formation of the protoquark star with a temperature of 1012 K, when the star's matter is opaque to neutrinos. It is...
We evaluate the vacuum expectation values (VEVs) of the electric and magnetic fields squared and of the energy-momentum tensor for the electromagnetic field around a cosmic string on the background of (D+1)-dimensional locally de Sitter spacetime. It is assumed that the field is prepared in the Bunch-Davies vacuum state. The topological contributions in the VEVs are explicitly separated. It is...
We revisit the Polyakov Loop coupled Nambu-Jona-Lasinio model that maintains the Polyakov loop dynamics at zero temperature, which is the most interesting for astrophysical applications. For this purpose we re-examine potential for the deconfinement order parameter at finite baryonic densities. Secondly, and the most important, we explicitly demonstrate that naive modification of this...
A class of hybrid compact star equations of state is investigated that joins by a Maxwell construction a low-density phase of hadronic matter, modeled by a relativistic meanfield approach with excluded nucleon volume, with a high-density phase of color superconducting two-flavor quark matter, described within a nonlocal covariant chiral quark model. We find the conditions on the vector meson...
The 3C315 galaxy and its surroundings were examined. According to galaxies and quasars, there is a lack of galaxies and quasars in that domain. Only 4 of these 35 domains have a lack of quasars and galaxies. The deficit of galaxies and quasars is the reason why there is empty space around the 3C315 galaxie.
This work discovers few extraordinary features of an anisotropic dark energy cosmological model in a two fluid situation such as the usual dark energy and the electromagnetic fluid. We have assumed the dark energy pressure to be anisotropic in spatial directions in terms of skewness parameters and have been studied their behavior through cosmic evolution. In order to yield a healthy...
The properties of dense QCD matter are delineated through the construction of equations of state which should be consistent with QCD calculations in the low and high density limits, nuclear laboratory experiments, and the neutron star observations. These constraints, together with the causality condition of the sound velocity, are used to develop the picture of hadron-quark continuity in which...
Newly discovered binary neutron star and black hole-neutron star mergers via gravitational waves can offer interesting constraints on the properties of dense matter. There are also important implications for the structure and composition of neutron stars. In the case of black hole-neutron star mergers, it is shown how to infer information about the components from GCN announcements, long...
We investigate the hydrostatic equilibrium of stellar structure by taking into account the modified Lane'-Emden equation coming from Extended Theories of Gravity. Such an equation is obtained in metric approach by considering the Newtonian limit of Extended Gravity, which gives rise to a modified Poisson equation, and then introducing a relation between pressure and density with polytropic...
In this talk I briefly review material properties of the neutron star crust and the plasma screening effects on the nuclear reaction rates. I start from elastic properties. In particular, I demonstrate that for pure Coulomb crystals the elasticity tensor has additional symmetry, which do not depend on the actual crystalline structure and composition. As a particular result of this symmetry,...
Fast radio bursts (FRBs) are short (duration ~ ms) but intense (flux ~ Jy) flashes, generally believed to be of extragalactic origin due to their high dispersion measures, which appear in the GHz-band. Currently, there are two sources which are known to repeat, thereby suggesting that there may be at least a subclass of FRBs resulting from transient outbursts of a young, compact object. We...
The effect of pasta phases on the quark-hadron phase transition is investigated for a set of
relativistic mean-field equations of state for both hadron and quark matter. The results of the full
numerical solution with pasta phases are compared with those of an interpolating construction used
in previous works, for which we demonstrate an adequate description of the numerical results....
Measurements of the low masses for the pulsar PSR J0737-3039B, for the companion of PSR J1756-2251 and for the companion of PSR J0453+1559 on the one hand and of the high masses for the pulsars PSR J1614-2230 and PSR J0348-0432 on the other demonstrate the existence of compact stars with masses in a broad range from 1.2 to 2 Msun. We show that for realistic stellar matter EoS it is possible to...
The effect of magnetic fields in the equations of state (EoS) of compact objects is the splitting of the pressure in two components, one parallel and the other perpendicular to the magnetic field. This anisotropy suggests the necessity of using structure equations considering the axial symmetry of the magnetized system. In this work, we consider an axially symmetric metric in spherical...
An effective, multi-polytope equation of state (EoS) model is used to study the so-called “mass twins” scenario, where two compact stars have approximately the same mass but (significant for observation) quite different radii. Stellar mass twin configurations are obtained if a strong first-order phase transition occurs in the interior of a compact star. In the mass-radius diagram of compact...
We study the properties of compact stars by taking into account the hadron-quark phase transition, as a result of which a quark matter core is formed in the central part of the star. In order to describe the quark matter, the local version of three-flavor Nambu-Jona-Lasinio (NJL) model is used. The thermodynamic characteristics of the hadronic matter are calculated within the framework of the...
The influence of a spherical boundary on the vacuum fluctuations of a massive scalar field is investigated in background of $\left( D+1\right) $-dimensional Milne universe, assuming that the field obeys Robin boundary condition on the sphere. The normalized mode functions are derived for the regions inside and outside the sphere. For the interior region, the boundary-induced contribution is...
We discuss a time-dependent generalization of the stationary Ginzburg-Landau theory for interacting neutron superfluid and proton superconducting condensates and its modification in the presence of rotation.
We study bulk viscosity arising from weak current Urca processes in
dense baryonic matter at and beyond nuclear saturation density. We
consider the temperature regime where neutrinos are trapped and
therefore have non-zero chemical potential. We model the nuclear
matter in a relativistic density functional approach, taking into
account the trapped neutrino component. We find...
We perform a Bayesian analysis for selecting the most probable equation of state under a set of constraints from compact star physics, which now include the tidal deformability from GW170817. It was considered a two-parameter family of hybrid equations of state, which produces a third family of hybrid stars in the mass-radius diagram. We present the corresponding results for compact star...
I will discuss the features pertaining to the new family of compact stars that are denser than the hybrid stars and arises if multiple phase transitions take place in the dense quark matter. The mass, radius, deformability and internal structure of these new objects will be discussed and confronted with the constraints from astrophysics.
We construct some cosmological models in an extended gravity theory. The gravitational action of the extended gravity theory contains a term proportional to the trace of the energy momentum tensor in addition to the usual Ricci scalar. Keeping in view the cosmic transit behavior from a decelerated universe to an accelerated one, we have employed a hybrid scale factor (HSF) to study the cosmic...
We construct some cosmological models in an extended gravity theory. The gravitational action of the extended gravity theory contains a term proportional to the trace of the energy momentum tensor in addition to the usual Ricci scalar. Keeping in view the cosmic transit behavior from a decelerated universe to an accelerated one, we have employed a hybrid scale factor (HSF) to study the cosmic...
The cosmological models of the universe with an anisotropic variable parameter has been constructed. The field equations for Bianchi type I space-time have been derived in $f(R,T)$ gravity for the functional relationship $f(R,T)=R+2f(T)$, where $R$ is the Ricci scalar and $T$ is the trace of the energy momentum tensor. Two different models are constructed with respect to the scale factors,...
In this paper, we have investigated the extended gravity particularly the f(R,T) gravity in Bianchi 〖VI〗_(h=-1) space time filled with magnetized anisotropic matter contents. We have explored the field equations and obtain the solution with power law function. The kinematical and geometrical parameters are derived and analyzed in detail. The effect of energy conditions is also studied. It is...
Since the mechanisms of compact objects’ formation in the framework of alternative new theory of cosmology (called as “Non-Inflationary Cosmology” (NIC), to distinguish from the Inflation theory of Modern Cosmology (MoC)) is essentially correlated with the galaxies’ generation scenario, this thesis is designed in the form of compressed review on the new cosmological and astrophysical scenarios...
We investigate the thermodynamic properties of strange quark matter under the strong magnetic field in the framework of the MIT bag model with the density-dependent bag constant. We consider two cases of the magnetic field, the uniform magnetic fields, and the density-dependent magnetic field to calculate the equation of state of strange quark matter. For the density-dependent magnetic field...
The structural properties of neutron stars, namely, maximum mass is a subject that theoretical astrophysicists have desired to study. Theoretically, investigation of structure for neutron stars necessities obtaining the perfect hydrostatic equilibrium equations. Up to now, different models and metrics have been used to calculate these equations. It is expected higher order energy-momentum...
In this work, we review the formalism which would allow us to model magnetically deformed neutron stars. We study the effect of different magnetic field configurations on the equation of state (EoS) and structure of such stars. In this study, the EoS of magnetars is acquired by using the lowest order constraint variational (LOCV) method and the upper limit of the magnetic field is derived...
Interior structures of stellar objects might have small pressure anisotropy due to several reasons, including rotation and the presence of magnetic fields. Here, retaining the approximation of spherical symmetry, we study the possible role of small anisotropy in stellar interiors in theories of modified gravity, that are known to alter the hydrostatic equilibrium condition inside stars. We...
In this work we use the dynamical system approach to study the stability of a normal DGP model in which we assume that a tachyon scalar field plays the role of dark energy. We consider an exponential potential ($V_0e^{\alpha\phi}$) for the tachyon field. We write the main equations of the model. Then, with attention to these equations, we introduce a set of new dimensionless dynamical...
