Surface and curvature tensions of cold quark matter in the SU(3)f NJL model with vector interactions

We investigate the surface and curvature tensions of three-flavor cold quark matter in a state of electric charge neutrality and chemical equilibrium under weak interactions, employing the Nambu–Jona–Lasinio model with the inclusion of vector interactions. To account for finite-size effects we adopt the multiple-reflection expansion framework and present our results for various input parameters. Our results indicate that both surface and curvature tensions increase with heightened vector interactions and density. Furthermore, we note that the restoration of chiral symmetry in the strange quark sector leads to a modest reduction in curvature tension and a substantial increase in surface tension.     

Dark matter annihilation at cosmological redshifts: possible relic signal from annihilation of weakly interacting massive particles

We discuss the possibility of observing the products of the dark matter annihilation that was going on in the early Universe. Of all the particles that could be generated by this process, we consider only photons, as they are both uncharged and easily detectable. The younger the Universe was, the higher the dark matter concentration n and the annihilation rate (proportional to n ²) were. However, the emission from the very early Universe cannot reach us because of the opacity. The main part of the signal was generated at the moment the Universe had just become transparent for the photons produced by the annihilation. Thus, the dark matter annihilation in the early Universe should have created a sort of relic emission. We obtain its flux and the spectrum.
If weakly interacting massive particles (WIMPs) constitute dark matter, it is shown that we may expect an extragalactic gamma-ray signal in the energy range 0.5–20 MeV with a maximum near 8 MeV. We show that an experimentally observed excess in the gamma-ray background at 0.5–20 MeV could be created by the relic signal from the annihilation of WIMPs only if the dark matter structures in the Universe had appeared before the Universe became transparent for the annihilation products  ( z ≃ 300)  . We discuss in more detail physical conditions whereby this interpretation could be possible.     

Two-component galaxy models: the effect of density profile at large radii on the phase-space consistency

It is well known that the density and anisotropy profile in the inner regions of a stellar system with positive phase-space distribution function (DF) are not fully independent. Here, we study the interplay between density profile and orbital anisotropy at large radii in physically admissible (consistent) stellar systems. The analysis is carried out by using two-component  ( n - γ, γ₁)  spherical self-consistent galaxy models, in which one density distribution follows a generalized γ profile with external logarithmic slope n , and the other a standard  γ₁  profile (with external slope 4). The two density components have different 'core' radii, the orbital anisotropy is controlled with the Osipkov–Merritt recipe, and for simplicity we assume that the mass of the  γ₁  component dominates the total potential everywhere. The necessary and sufficient conditions for phase-space consistency are determined analytically, also in the presence of a dominant massive central black hole, and the analytical phase-space DF of (   n - γ  ,1) models, and of   n - γ  models with a central black hole, is derived for  γ= 0, 1, 2  . It is found that the density slope in the external regions of a stellar system can play an important role in determining the amount of admissible anisotropy: in particular, for fixed density slopes in the central regions, systems with a steeper external density profile can support more radial anisotropy than externally flatter models. This is quantified by an inequality formally identical to the 'cusp slope-central anisotropy' theorem by An & Evans, relating at all radii (and not just at the centre) the density logarithmic slope and the anisotropy indicator in all Osipkov–Merritt systems.     

GHASP: an Hα kinematic survey of spiral and irregular galaxies – V. Dark matter distribution in 36 nearby spiral galaxies

The results obtained from a study of the mass distribution of 36 spiral galaxies are presented. The galaxies were observed using Fabry–Perot interferometry as part of the GHASP survey. The main aim of obtaining high-resolution Hα 2D velocity fields is to define more accurately the rising part of the rotation curves which should allow to better constrain the parameters of the mass distribution. The Hα velocities were combined with low resolution H  i data from the literature, when available. Combining the kinematical data with photometric data, mass models were derived from these rotation curves using two different functional forms for the halo: an isothermal sphere (ISO) and a Navarro–Frenk–White (NFW) profile. For the galaxies already modelled by other authors, the results tend to agree. Our results point at the existence of a constant density core in the centre of the dark matter haloes rather than a cuspy core, whatever the type of the galaxy from Sab to Im. This extends to all types the result already obtained by other authors studying dwarf and low surface brightness galaxies but would necessitate a larger sample of galaxies to conclude more strongly. Whatever model is used (ISO or NFW), small core radius haloes have higher central densities, again for all morphological types. We confirm different halo scaling laws, such as the correlations between the core radius and the central density of the halo with the absolute magnitude of a galaxy: low-luminosity galaxies have small core radius and high central density. We find that the product of the central density with the core radius of the dark matter halo is nearly constant, whatever the model and whatever the absolute magnitude of the galaxy. This suggests that the halo surface density is independent from the galaxy type.