International Journal of Modern Physics D

Role of cosmological magnetic field and cosmological magnetic helicity for astrophysics is considered. We discuss possible mechanisms for cosmological magnetic field production in the early universe as well as upper observational estimate for such field. The general conclusion is that a substantial cosmological field with a non-vanishing magnetic helicity can be generated in the early universe and survive up to the epoch of galaxy formation.

A Bose–Einstein condensate of a neutral vector boson bearing an anomalous magnetic moment is suggested as a model for ferromagnetic origin of magnetic fields in neutron stars. The vector particles are assumed to arise from parallel spin-paired neutrons. A negative pressure perpendicular to the external field B is acting on this condensate, which for large densities, compress the system, and may produce a collapse. An upper bound of the magnetic fields observable in neutron stars is given. In the the non-relativistic limit, the analogy with the behavior of exploding Bose–Einstein condensates (BECs) for critical values of the magnetic field is briefly discussed.

We use a restricted sample of elliptical galaxies, whose kinematical parameters inside the semi-major axis were calculated correcting for the effect of the integration of the light along the line of sight, in order to analyze a possible relationship between the mass of a supermassive black hole (SMBH) and the kinetic energy of random motions in the host galaxy. We find M_BH ∝ (M_G σ²)^α with 0.87 ≤ α ≤ 1 depending on the different fitting methods and samples used. This result could be interpreted as a new fundamental relationship or as a new way to explain the old M_BH - σ law. In fact, the relations of the velocity dispersion both with the mass of the SMBH (M_BH ∝ σ^4.12) and with the mass of the host galaxy (M_G ∝ σ^2.16) induce us to infer an almost direct proportionality: M_BH ∝ M_Gσ². A similar relationship is found for the total kinetic energy involving the rotation velocity too.

We perform in this paper a statefinder diagnostic to a dark energy model with two scalar fields, called "quintom," where one of the scalar fields has a canonical kinetic energy term and the other has a negative one. Several kinds of potentials are discussed. Our results show that the statefinder diagnostic can differentiate quintom model with other dark energy models.

This paper is intended to investigate the luminosity due to the accretion of gas in supermassive black holes (SMBHs) in the center of quasars, using a brane-world scenario naturally endowed with extra dimensions, whereon theories formulated introduce corrections in the field equations at high energies. SMBHs possess the necessary highly energetic environment for the introduction of these corrections, which are shown to produce small deviations in all SMBH properties and, consequently, corrections in the accretion theory that supports quasars radiative processes. The radiative flux observed from quasars indicates these deviations, from which the magnitude of the AdS₅ bulk curvature radius, and consequently the extra dimension compactification radius is estimated.

We discuss a modified form of gravity implying that the action contains a power α of the scalar curvature. Coupling with the cosmic fluid is assumed. As equation of state for the fluid, we take the simplest version where the pressure is proportional to the density. Based upon a natural ansatz for the time variation of the scale factor, we show that the equations of motion are satisfied for a general α. Also the condition of conservation of energy and momentum is satisfied. Moreover, we investigate the case where the fluid is allowed to possess a bulk viscosity, and find the noteworthy fact that consistency of the formalism requires the bulk viscosity to be proportional to the power (2α-1) of the scalar expansion. In Einstein's gravity, where α = 1, this means that the bulk viscosity is proportional to the scalar expansion. This mathematical result is of physical interest; as discussed recently by the authors, there exists in principle a viscosity-driven transition of the fluid from the quintessence region into the phantom region, implying a future Big Rip singularity.

The energy, or mass scale M_SUSY, of the supersymmetry (SUSY) phase transition is, as yet, unknown. If it is very high (i.e. ≫10³GeV), terrestrial accelerators will not be able to measure it. We determine M_SUSY here by combining theory with the cosmic microwave background (CMB) data. Starobinsky suggested an inflationary cosmological scenario in which inflation is driven by quantum corrections to the vacuum Einstein's equation. The modified Starobinsky model (MSM) is a natural extension of this. In the MSM, the quantum corrections are the quantum fluctuations of the supersymmetric (SUSY) particles, whose particle content creates inflation and whose masses terminate it. Since the MSM is difficult to solve until the end of the inflation period, we assume here that an effective inflaton potential (EIP) that reproduces the time dependence of the cosmological scale factor of the MSM can be used to make predictions for the MSM. We predict the SUSY mass scale to be M_SUSY ≃ 10¹⁵GeV, thus satisfying the requirement that the predicted density fluctuations of the MSM is in agreement with the observed CMB data.

Here we study an anisotropic model of the universe with constant energy per particle. A decaying cosmological constant and particle production in an adiabatic process are considered as the sources for the entropy. The statefinder parameters {r, s} are defined and their behavior are analyzed graphically in some cases.

We consider a nonlinear sigma model coupled to the metric of a conic space. We obtain restrictions for a nonlinear sigma model to be a source of the conic space. We then study a nonlinear sigma model in the conic space background. We find coordinate transformations which reduce the chiral fields equations in the conic space background to field equations in Minkowski space–time. This enables us to apply the same methods for obtaining exact solutions in Minkowski space–time to the case of a conic space–time. In the case the solutions depend on two spatial coordinates we employ Ivanov's geometrical ansatz. We give a general analysis and also present classes of solutions in which there is dependence on three and four coordinates. We discuss with special attention the intermediate, instanton and meron solutions and their analogous in the conic space. We find differences in the total actions and topological charges of these solutions and discuss the role of the deficit angle.

We show that a previously proposed cosmological model based on the general relativity with non vanishing divergence for the energy–momentum tensor is consistent with the observed values for the nucleosynthesis of helium for some values of the arbitrary parameter α presented in this model. Furthermore values of α can be accommodated if we adopt the Randall–Sundrum single brane model.

We consider a five-dimensional Ricci flat bouncing cosmological model in which the four-dimensional induced matter contains two components at late times — the cold dark matter (CDM) + baryons and dark energy. We find that the arbitrary function f(z) contained in the solution plays a similar role as the potential V(ϕ) in quintessence and phantom dark energy models. To resolve the coincidence problem, it is generally believed that there is a scaling stage in the evolution of the universe. We analyze the condition for this stage and show that a hyperbolic form of the function f(z) can work well in this property. We find that during the scaling stage (before z ≈ 2), the dark energy behaves like (but not identical to) a cold dark matter with an adiabatic sound speed and p_x ≈ 0. After z ≈ 2, the pressure of the dark energy becomes negative. The transition from deceleration to acceleration happens at z_T ≈ 0.8 which, as well as other predictions of the 5D model, agrees with current observations.

Quark matter is expected to exist in the interior of compact stellar objects as neutron stars or even the more exotic strange stars, based on the Bodmer–Witten conjecture. Bare strange quark stars and (normal) strange quark-matter stars, those possessing a baryon (electron-supported) crust, are hypothesized as good candidates to explain the properties of a set of peculiar stellar sources such as the enigmatic X-ray source RX J1856.5-3754, some pulsars such as PSR B1828-11 and PSR B1642-03, and the anomalous X-ray pulsars and soft γ-ray repeaters. In the MIT bag model, quarks are treated as a degenerate Fermi gas confined to a region of space having a vacuum energy density B_bag (the Bag constant). In this note, we modify the MIT bag model by including the electromagnetic interaction. We also show that this version of the MIT model implies the anisotropy of the bag pressure due to the presence of the magnetic field. The equations of state of the degenerate quarks gases are studied in the presence of ultra strong magnetic fields. The behavior of a system made up of quarks having (or not) anomalous magnetic moment is reviewed. A structural instability is found, which is related to the anisotropic nature of the pressures in this highly magnetized matter. The conditions for the collapse of this system are obtained and compared to a previous model of neutron stars that is built on a neutron gas having anomalous magnetic moment.