Mutually interacting tachyon dark energy with variable G and Λ

We consider a tachyonic scalar field as a model of dark energy with interaction between components in the case of variable G and Λ. We assume a flat Universe with a specific form of scale factor and study cosmological parameters numerically and graphically. Statefinder analysis is also performed. For a particular choice of interaction parameters we succeed in obtaining an analytical expression of densities. We find that our model will be stable at the late stage but there is an instability in the early Universe, so we propose this model as a realistic model of our Universe.     

Primordial nucleosynthesis and Ω B ∼1 cosmologies with interacting radiation and matter

The constraints on the present baryon density from primordial nucleosynthesis in universes with interacting radiation and matter are investigated. For illustration, a class of exact cosmological models is studied in which two separate, interacting fluids act as the source of the gravitational field, a radiative perfect fluid modelling the cosmic microwave background and a second perfect fluid modelling the observed material content of the Universe. Althought the two fluid models under consideration are found to predict primordial element abundances similar to those predicted in the standard model (and consequently in general accord with observed values), the upper limit on the present baryon density inferred from the observed abundances of the light elements is found to be greater than that in the standard model due to the different evolution of the baryon density in the models. From this result, and using the fact that the upper limit on _B (the ratio of the present value of the baryon density to the value of the critical density) is further weakened in inhomogeneous cosmological models, it is found that unlike the situation in the standard model, cosmologies with _B 1 are permitted without violating the constraints of nucleosynthesis, thereby allowing the possibility that the Universe could be closed by baryonic matter alone.     

Some rotating perfect fluid universes coupled with electromagnetic field interacting with gravitation

Some new interesting solutions, the dynamics, behaviour and phenomena of rotating charged perfect fluid models are investigated, and their physical and geometrical properties are studied in order to substantiate the possibility of the existence of such astrophysical bodies in this Universe. The nature and role of the metric rotation Ω(r,t) as well as that of the matter rotation ω(r,t) are studied for uniform and non-uniform motions. The reactions of the gravitational and charged fields with respect to the rotational motion are studied and possible results are explored for real astrophysical situations, and in some solutions we find the spatial restrictions on the models for realistic conditions. Rotating models which are expanding are obtained in which the rotational motions are decaying with time.     

On the various aspects of interacting Ricci dark energy and?tachyonic field

In this letter we considered an interaction between Ricci dark energy and tachyonic field. We investigated the equation of state parameters in presence of the interaction and revealed a quintessence like behavior. Also, we investigated the validity of the generalized second law of thermodynamics in presence of this interaction and observed that it is broken down under this interaction.     

Do morphological properties of interacting galaxies indicate that the latter are topological abelian higgs vorto-sources (vorto-sinks)?

We propose an Abelian Higgs model for spiral galaxies in which the latter are treated as topologically stable magneticvorto-sources (-sinks). The model is characterized by the minimum coupling between the electromagnetic vector potential and a scalar, complex-valued Higgs field that results - for an idealized cylindrically symmetric case - in a perpendicular to the galaxy's plane distribution of magnetic field strength whose total flux is a discrete-valued quantity - aninteger multiple of the elementary flux unit. Adopting the hypothesis that spiral arms trace the curves of a constant phase of the Higgs field we demonstrate that, for an almost-everywhere divergence-free vector potential, the arms acquire the observationally well-established form of logarithmic spirals whose woundness is here of an electromagnetic origin in the sense that it depends on the ratio between the specific volume-divergence of a galaxy and its total magnetic flux. The hypothesis further implies that the number of spiral arms is justtwice as that of magnetic flux quanta a galaxy possesses; the observed preponderance of two-armed spirals then simply reflects the fact that most galaxies carry single flux quantum which is energetically favourable for the vorto-sources (-sinks) whose disk-to-bulge radius ratio > 1. The latter property also leads to the process of galaxyfragmentation in the sense that a galaxy endowed withp magnetic flux quanta should fission into the topologically equivalent configuration consisting ofp singly-quantized galaxies.A unique possibility to test our model is provided by physically paired galaxies. Considering the simplest configuration consisting of spirals lying in the same plane and having equal in magnitude fluxes and volume-divergences we distinguish four topologically different distributions of the Higgs field phase which fairly well capture observed morphologies exhibited by double galaxies; we find, in particular, that of most frequent occurrence seem to be couples with anti-parallel orientation of magnetic field.Finally, we address the question of the periodicity in the distribution of galaxy redshifts and show that a discrete-valuedness of themass of spiral galaxies resulting from our model may serve as a starting point to solve this puzzling effect.     

Statistics of interacting galaxies at <Emphasis Type="Italic">z</Emphasis> ∼ 0.7

We present the results of our analysis of the frequencies of galaxies with tidal tails and M51-type galaxies in several deep fields of the Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS). In total, we have found about seven hundred interacting galaxies at redshifts z ≤ 1.5 in these fields. At z ≤ 0.7, the observed space densities of galaxies with tidal structures and M51-type galaxies have been found to increase as ∝(1 + z) ^m , where m ≈ 2.6. According to our estimates, over the last 6–7 Gyr, i.e., at z ≤ 0.7, about a third of the galaxies with M(B) ≤ −18 ^m must have undergone strong gravitational perturbations and mergers and ∼1/10−1/5 of the galaxies have swallowed relatively low-mass nearby satellites typical of M51-type galaxies. The possible decrease in the time scale on which a distant galaxy appears peculiar with growing z can increase considerably the estimated rate of mergers.     

Cosmic behavior, statefinder diagnostic and w?w′ analysis for?interacting new agegraphic dark energy model in non-flat universe

We investigate the interacting NADE model in non-flat universe. The effects of spatial curvature Ω _k , interaction coefficient α and the main parameter of NADE, n, on EoS parameter w _d and deceleration parameter q are studied. We obtain a minimum value for n in both early and present time, in order to that our DE model crosses the phantom divide. Also in a closed universe, changing the sign of q is strongly dependent on α. It has been shown that the quantities w _d and q have a different treatment for various spatial curvature. At last, we calculate the statefinder diagnostic and w−w ^′ analysis in non flat universe. In non flat universe, the statefinder trajectories are discriminated by both n and α.