Influence of the weakly interacting light U boson on the properties of massive protoneutron stars

Considering the octet baryons in relativistic mean field theory and selecting entropy per baryon S=l,we calculate and discuss the influence of U bosons on the equation of state,mass-radius,moment of inertia and gravitational redshift of massive protoneutron stars(PNSs).The effective coupling constant gu of U bosons and nucleons is selected from 0 to 70 GeV~(-2).The results indicate that U bosons will stiffen the equation of state(EOS).The influence of U bosons on the pressure is more obvious at low density than high density,while the influence of U bosons on the energy density is more obvious at high density than low density.The U bosons play a significant role in increasing the maximum mass and radius of PNS.When the value of gu changes from 0 to 70 GeV~(-2),the maximum mass of a massive PNS increases from 2.11M_⊙ to 2.58M_⊙,and the radius of a PNS corresponding to PSR J0348+0432 increases from 13.71 km to 24.35 km.The U bosons will increase the moment of inertia and decrease the gravitational redshift of a PNS.For the PNS of the massive PSR J0348+0432,the radius and moment of inertia vary directly with gu,and the gravitational redshift varies approximately inversely with gu.     

A Class of Super Dense Stars Models Using Charged Analogues of Hajj-Boutros Type Relativistic Fluid Solutions

We present a spherically symmetric solution of the general relativistic field equations in isotropic coordinates for perfect charged fluid, compatible with a super dense star modeling. The solution is well behaved for all the values of Schwarzschild parameter u lying in the range 0 < u < 0.1727 for the maximum value of charge parameter K = 0.08163. The maximum mass of the fluid distribution is calculated by using stellar surface density as ρ _b = 4.6888×10¹⁴g cm^?3. Corresponding to K = 0.08 and u _max = 0.1732, the resulting well behaved solution has a maximum mass M = 0.9324M _⊙ and radius R = 8.00 and by assuming ρ _b = 2×10¹⁴g cm^?3 the solution results a stellar configuration with maximum mass M = 1.43M _⊙ and radius R _b = 12.25 km. The maximum mass is found increasing with increasing K up to 0.08. The well behaved class of relativistic stellar models obtained in this work might has astrophysical significance in the study of internal structure of compact star such as neutron star or self-bound strange quark star like Her X-1.     

Stars of strange matter?

We investigate suggestions that quark matter with strangeness per baryon of order unity may be stable. We model this matter at nuclear matter densities as a gas of close packed Λ-particles. From the known mass of the Λ-particle we obtain an estimate of the energy and chemical potential of strange matter at nuclear densities. These are sufficiently high to preclude any phase transition from neutron matter to strange matter in the region near nucleon matter density. Including effects from gluon exchange phenomenologically, we investigate higher densities, consistently making approximations which underestimate the density of transition. In this way we find a transition density ρ_tr≳7ρ₀, where ρ₀ is nuclear matter density is not far from the maximum density in the center of the most massive neutron stars that can be constructed. Since we have underestimated ρ_tr and still find it to be ∼7ρ₀, we do not believe that the transition from neutron to quark matter is likely in neutron stars. Moreover, measured masses of observed neutron stars are ≅1.4 M_⊙, where M_⊙ is the solar mass. For such masses, the central (maximum) density is ρ_c<5ρ₀. Transition to quark matter is certainly excluded for these densities.     

Total energy of the neutrino burst from the supernova 1987A and the mass of the neutron star just born

From the data of the neutrino burst detected by the Kamiokande-II and IMB groups we calculated the total neutrino energy carefully taking into account the efficiency of their water Čerenkov counters. By using this result, we discussed the neutron star mass which was formed by this supernova explosion. We conjectured that the mass is 1.0–1.7M_⊙ and a black hole was not formed, assuming that the distance to the supernova is 50 kpc. If the distance is 56 kpc, the mass range turns into 1.0–1.8M_⊙ and the possibility of black hole formation is also ruled out.     

Crust-core properties of neutron stars in the Nambu–Jona-Lasinio model

We adopt the Nambu–Jona-Lasinio(NJL) model to study the crust-core transition properties in neutron stars(NSs). For a given momentum cutoff and symmetry energy of saturation density in the NJL model, decreasing the slope of the symmetry energy gives rise to an increase in the crust-core transition density and transition pressure.Given the slope of the symmetry energy at saturation density, the transition density and corresponding transition pressure increase with increasing symmetry energy. The increasing trend between the fraction of the crustal moment of inertia and the slope of symmetry energy at saturation density indicates that a relatively large momentum cutoff of the NJL model is preferred. For a momentum cutoff of 500 Me V, the fraction of the crustal moment of inertia clearly increases with the slope of symmetry energy at saturation density. Thus, at the required fraction(7%) of the crustal moment of inertia, the NJL model with momentum cutoff of 500 Me V and a large slope of the symmetry energy of saturation density can give the upper limit of the mass of the Vela pulsar to be above 1.40 M_⊙.     

Calculations of mass and moment of inertia for neutron stars

Masses and moments of inertia for slowly-rotating neutron stars are calculated from the Tolman-Oppenheimer-Volkoff equations and various equations of state for neutron-star matter. We have also obtained pressure and density as a function of the distance from the centre of the star. Generally, two different equations of state are applied for particle densities n > 0.47 fm^?3 and n < 0.47 fm^?3.The maximum mass is, in our calculations for all equations of state except for the unrealistic non-relativistic ideal Fermi gas, given by 1.50 M_⊙ < M < 1.82 M_⊙, which agrees very well with “experimental results”. Corresponding results for the maximum moment of inertia are 9.5 × 10⁴⁴ g · cm² < I < 1.58 × 10⁴⁵ g · cm², which also seem to agree very well with “experimental results”. The radius of the star corresponding to maximum mass and maximum moment of inertia is given by 8.2 km < R < 10.0 km, but a smaller central density ρ_c will give a larger radius.     

Dynamical properties of superconducting cosmic strings: (II). Heavy closed strings in magnetic field

We discuss a circular static superconducting cosmic string in a homogeneous magnetic field and show that the mass is independent of the radius provided we choose a GUT scale as well as a reasonable value for the intergalactic magnetic field. A conservative estimate gives a mass of order 10¹⁶ M_⊙. We also discuss various gravitational effects related to this string. The most striking effect is the gravitational lens effect that can produce four images.     

Dark Matter annihilation in small-scale clumps in the Galactic halo

The enhancement of the annihilation signal due to Dark Matter (DM) clumpiness in the Galactic halo, valid for arbitrary DM particles, is described. The mass spectrum of small-scale DM clumps with M≤10³ M _⊙ is calculated with tidal destruction of the clumps taken into account within the hierarchical model of clump structure. The mass distribution of the clumps has a cutoff at M _min due to diffusion of DM particles out of a fluctuation and free streaming. In the case of neutralino (considered as a pure bino) being a DM particle, M _min～10⁸ M _⊙. The evolution of the density profile in a DM clump does not result in singularity, because of formation of the core under the influence of tidal interaction. The number density of clumps as a function of their mass, radius, and distance to the Galactic center is presented.     

Symmetry energy impact in simulations of core-collapse supernovae

In this work we study the effect of the symmetry energy on several properties of neutron stars. First, we discuss its effect on the density, proton fraction and pressure of the neutron star crust-core transition. We show that whereas the first two quantities present a clear correlation with the slope parameter L of the symmetry energy, no satisfactory correlation is seen between the transition pressure and L . However, a linear combination of the slope and curvature parameters at ρ = 0.1 fm^?3 is well correlated with the transition pressure. In the second part we analyze the effect of the symmetry energy on the pasta phase. It is shown that the size of the pasta clusters, number of nucleons and the cluster proton fraction depend on the density dependence of the symmetry energy: a small L gives rise to larger clusters. The influence of the equation of state at subsaturation densities on the extension of the inner crust of the neutron star is also discussed. Finally, the effect of the density dependence of the symmetry energy on the strangeness content of neutron stars is studied in the last part of the work. It is found that charged (neutral) hyperons appear at smaller (larger) densities for smaller values of the slope parameter L. A linear correlation between the radius and the strangeness content of a star with a fixed mass is also found.     

Nuclear matter properties and relativistic mean-field theory

Nuclear matter properties are calculated in the relativistic mean-field theory by using a number of different parameter sets. The result shows that the volume energy a₁ and the symmetry energy J are around the acceptable values 16MeV and 30MeV, respectively; the incompressibility K₀ is unacceptably high in the linear model, but assumes reasonable value if nonlinear terms are included; the density symmetry L is around 100MeV for most parameter sets, and the symmetry incompressibility K _s has positive sign which is opposite to expectations based on the nonrelativistic model. In almost all parameter sets there exists a critical point (,), where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero, falling into ranges 0.014fm^-3 < < 0.039fm^-3 and 0.74 < ≤0.95; for a few parameter sets there is no critical point and the pure neutron matter is predicted to be bound. The maximum mass M _NS of neutron stars is predicted in the range 2.45M ?M _NS? 3.26M , the corresponding neutron star radius R _NS is in the range 12.2km ?R _NS? 15.1km. Received: 5 May 2000 / Accepted: 28 November 2000     

An Exact Family of Einstein–Maxwell Wyman–Adler Solution in General Relativity

This paper presents a family of two-parametric interior solutions of Einstein–Maxwell field equations in general relativity for a static spherically symmetric distribution of a charged perfect fluid with particular choice of charge distribution and the metric component g ₀₀. This family gives us wide range of parameters, n and K, for which the solutions are regular and acceptable on physical grounds and hence suitable for modeling of charged compact star. The maximum allowable mass and corresponding radius, for this family of solutions with the particular form of charge distribution, is determined to be 2.48M _⊙ and 10.56 km respectively by assuming the stellar “surface” density equal to strange (quark) matter density at zero pressure. It is hoped that our investigation may be of some importance in connection with the study of internal structure of electrically charged strange (quark) star.     

Search for strong gravitational lensing effect in the current GRB data of BATSE

Because gamma-ray bursts(GRBs)trace the high-z universe,there is an appreciable probability for a GRB to be gravitational lensed by galaxies in the universe.Herein we consider the gravitational lensing effect of GRBs contributed by the dark matter halos in galaxies.Assuming that all halos have the singular isothermal sphere(SIS)mass profile in the mass range 1010h?1M?M2×1013h?1M?and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample,we calculated the gravitational lensing probability in BATSE,Swift/BAT and Fermi/GBM GRBs,respectively.With an derived probability result in BATSE GRBs,we searched for lensed GRB pairs in the BATSE5B GRB Spectral catalog.The search did not find any convincing gravitationally lensed events.We discuss our result and future observations for GRB lensing observation.     

Effects of Fock term,tensor coupling and baryon structure variation on a neutron star

The equation of state for neutron matter is calculated within relativistic Hartree–Fock approximation. The tensor couplings of vector mesons to baryons are included, and the change of baryon internal structure in matter is also considered using the quark–meson coupling model. We obtain the maximum neutron-star mass of ∼2.0M_⊙$\sim 2.0M_{\odot }$, which is consistent with the recently observed, precise mass, 1.97±0.04M_⊙$1.97\pm 0.04M_{\odot }$. The Fock contribution is very important and, in particular, the inclusion of tensor coupling is vital to obtain such large mass. The baryon structure variation in matter also enhances the mass of a neutron star.     

Discovery of eight lensing clusters of galaxies

Clusters of galaxies have a huge mass which can act as gravitational lenses.Galaxies behind clusters can be distorted by the lenses to form arcs in images.Herein a search was done for giant lensed arcs using the SDSS data.By visually inspecting SDSS images of newly identified clusters in the SDSS DR8 and Stripe 82 data,we discover 8 strong lensing clusters together with additional 3probable and 6 possible cases.The lensed arcs show bluer colors than the member galaxies of clusters.The masses and optical luminosities of galaxy clusters interior to the arcs are calculated.The mass-to-light ratios are found to be in the range of a few tens of M⊙/L⊙,consistent with the distribution of previously known lensing clusters.     

Hyperonic neutron stars: reconciliation between nuclear properties and NICER and LIGO/VIRGO results

Using an extended version of quantum hadrodynamics,I propose a new microscopic equation of state(EoS)that is able to correctly reproduce the main properties of symmetric nuclear matter at the saturation density,as well as produce massive neutron stars and satisfactory results for the radius and the tidal parameter.I show that this EoS can reproduce at least a 2.00 solar mass neutron star,even when hyperons are present.The constraints about the radius of a 2.00 M_⊙ and the minimum mass that enables a direct Urea effect are also checked.     

Detactability of Dark Matter Subhalos by Means of the GAMMA-400 Telescope

The potential of the planned GAMMA-400 gamma-ray telescope for detecting subhalos of mass between 10⁶M_⊙ and 10⁹M_⊙ in the Milky Way Galaxy that consist of annihilating dark matter in the form of weakly interacting massive particles (WIMPs) is studied. The inner structure of dark matter subhalos and their distribution in the Milky Way Galaxy are obtained on the basis of respective theoretical models. Our present analysis shows that the expected gamma-ray flux from subhalos depends strongly on the WIMP mass and on the subhalo concentration, but that it depends less strongly on the subhalo mass. Optimistically, a flux of 10 to 100 ph per year in the energy range above 100 MeV can be expected from the closest and most massive subhalos, which can therefore be thought to be detectable sources for GAMMA-400. Because of the smallness of fluxes, however, only via a joint analysis of future GAMMA-400 data and data from other telescopes would it become possible to resolve the inner structure of the subhalos. Also, the recent subhalo candidates 3FGL J2212.5+0703 and J1924.8–1034 are considered within our model. Our conclusion is that these sources hardly belong to the subhalo population.     

Neutrinos from supernova 1987A

The neutrino detection associated with the recent supernova SN1987A is reexamined in terms of a newtonian cooling model, and the results confronted with the so far fragmentary theoretical simulations of post-explosion cooling. We find a binding energy for the compact remnant of (2.0 ± 0.50) × 10⁵³ erg, a mass 1.1–1.7 M_⊙, and an initial cooling temperature of 5.0 ± 0.6 MeV. T extraction of a neutrino mass limit is considered in this framework and found, in agreement with some previous work, to give a slightly superior limit to present terrestrial experiments.     

Phenomenology of dynamical symmetry breaking in QCD

A consistent treatment of the QCD quark propagator and quark-antiquark bound state equations is presented which follows the Nambu and Jona-Lasinio approach to the discussion of chiral symmetry breaking. An expression is obtained for the dynamical, momentum dependent, mass. In the approximation used here the dynamical mass is determined byM ₀, its value at zero momentum, and by the strong coupling constant α _s and bare quark massm ₀. In the limiting case of no explicit chiral symmetry breaking. i.e.,m ₀=0, this expression coincides in form with the one obtained by Chang and Chang in their renormalization-group analysis. In this limit chiral symmetry remains broken and we show the explicit appearance of a Nambu-Goldstone pion. A consistent calculation of the pseudoscalar, scalar and vector meson masses gives values ofm ₀, α _s andM ₀ well in step with other estimates. This makes possible a calculation off _π, the pion decay constant, in reasonable agreement with experiment.     

Low-energy dilation

We study consequences of scale symmetry breaking in the QCD effective SU(2)×SU(2) chiral model. The mass of a pseudo-Goldstone boson dilation is estimated to be M_σ≅1 GeV and the upper bound to its lifetime τ_σ⩽4×10⁻²⁸ s. We also show that the dilation gives a considerable contribution to the pion scalar radius.