International Journal of Modern Physics D

We investigate the attractor solution in the coupled Yang–Mills field dark energy models with the general interaction term, and obtain the constraint equations for the interaction if the attractor solution exists. The research also shows that, if the attractor solution exists, the equation of state of dark energy must evolve from w_y > 0 to w_y ≤ -1, which is slightly suggested by the observation. At the same time, the total equation of state in the attractor solution is w_tot = -1, the universe is a de Sitter expansion, and the cosmic big rip is naturally avoided. These features are all independent of the interacting forms.

The vacuum inflation with a boundary condition specified at a short distance scale in a generally primeval nonflat universe, and implications of the correspondingly modified primordial power spectrum via the WMAP data are investigated. We obtain a general form of the modified primordial power spectrum including the effects of both the possibly new physics scale and the spatial curvature. The modulation of the primordial power spectrum due to new physics is of the order H/Λ, where H is the Hubble parameter during inflation and Λ is the new physics scale which is key to inflation, while the modulation from the curvature effect is of the order K/k², where K is the spatial curvature before inflation and k is the comoving wave number. We also find that a closed universe before inflation is favored by WMAP five-year data.

The Starobinsky model is a natural inflationary scenario in which inflation arises due to quantum effects of the massless matter fields. A modified version of the Starobinsky (MSt) model takes the masses of matter fields and the cosmological constant, Λ, into account. The equations of motion become much more complicated; however, approximate analytic and numeric solutions are possible. In the MSt model, inflation starts due to the supersymmetric (SUSY) particle content of the underlying theory, and the transition to the radiation-dominated epoch occurs due to the relatively heavy s-particles decoupling. For Λ = 0 the inflationary solution is stable until the last stage, just before decoupling. In the present paper we generalize this result for Λ ≠ 0, since Λ should be nonvanishing at the SUSY scale. We also take into account the radiative corrections to Λ. The main result is that the inflationary solution of the MSt model remains robust and stable.

All galaxies beyond the Magellanic clouds with detected H₂O maser emission so far are investigated and their X-ray observations are collected in detail to probe the X-ray properties of this special kind of galaxies. The soft excess and the strong iron emission line are commonly presented in their X-ray spectrum. Similar to the spectra of normal Seyfert 2 galaxies, the X-ray soft components are usually explained well by two alternative models or their combination: the absorbed power law model and the thermal emission model. The hard X-ray continua are usually flat, which should be caused by the increase of the reflection component, with the increase of the absorbing material density. Modeling their X-ray spectra shows that high absorbing column density is prevalent in our H₂O megamaser host AGNs. Further, we investigate a possible relation between the iron line emission and the nuclear X-ray emission. It shows no significant correlation between the equivalent width (EW) of the neutral FeK_α emission line (~ 6.4 keV) and the intrinsic nuclear X-ray luminosity. However, one trend appears clearly — the EW of the iron line decreases with the increase of the observed X-ray luminosity for our H₂O maser galaxies. We also estimate the accretion rate of H₂O maser host AGNs and the results show that maser galaxies may have a higher accretion rate than nonmaser Seyfert galaxies. In addition, possible relations between the EW of the iron line with the accretion rate and the central black hole mass are investigated and no significant trend of correlation can be found between them.

Constraints on a parametrized deceleration parameter, q(a) = q₀ + q₁(1 - a), are investigated using cosmological observations of type Ia supernovae (SN Ia), baryon acoustic oscillations (BAOs) and cosmic microwave background (CMB) and observational Hubble data (OHD) which correspond to the cosmological distance measure. When a high redshift dataset of CMB is added in the SN + BAO + OHD case, a stronger constraint is obtained than for the lower redshift case, SN + BAO + OHD. The evolutions of the deceleration and Hubble parameters with respect to redshift z are reconstructed from cosmic observations. With cosmic observations as constraints, it is found that a smaller current deceleration parameter and a larger transition redshift are obtained in the SN + BAO + OHD case than in the SN + BAO + OHD + CMB case. In the SN + BAO + OHD + CMB case, slightly larger Hubble parameter values will be obtained than in the SN + BAO + OHD case.

We analyze the generation of seed magnetic fields during de Sitter inflation considering a noninvariant conformal term in the electromagnetic Lagrangian of the form , where I(ϕ) is a pseudoscalar function of a nontrivial background field ϕ. In particular, we consider a toy model that could be realized owing to the coupling between the photon and either a (tachyonic) massive pseudoscalar field or a massless pseudoscalar field nonminimally coupled to gravity, where I follows a simple power law behavior I(k,η) = g/(-kη)^β during inflation, while it is negligibly small subsequently. Here, g is a positive dimensionless constant, k the wave number, η the conformal time, and β a real positive number. We find that only when β = 1 and 0.1 ≲ g ≲ 2 can astrophysically interesting fields be produced as excitation of the vacuum, and that they are maximally helical.

We provide a new electromagnetic mass model admitting the Chaplygin gas equation of state. We investigate three specializations, the first characterized by a vanishing effective pressure, the second provided with a constant effective density and the third described by a constant effective pressure p₀. For these specializations we will discuss the models assuming that , where σ, σ₀, λ and s represent the charge density of the spherical distribution, the charge density at the center of the system, the metric potential and a constant, respectively. In addition, for specialization I, we have found the isotropic coordinate as well as the Kretschmann scalar for a particular case, and for specialization III two special scenarios have been studied.

We exactly calculate the quasinormal frequencies of the electromagnetic and Klein–Gordon perturbations propagating in a five-dimensional dilatonic black hole. Furthermore, we exactly find the quasinormal frequencies of the massive Dirac field. Using these results we study the linear stability of this black hole. We compare our results for the quasinormal frequencies and for the linear stability of the five-dimensional black hole with those already published.

A family of models of counterrotating and rotating relativistic thin disks of infinite extension based on a charged and magnetized Kerr–NUT metric are constructed using the well-known "displace, cut and reflect" method extended to solutions to vacuum Einstein–Maxwell equations. The metric considered has as limiting cases a charged and magnetized Taub–NUT solution and the well-known Kerr–Newman solutions. We show that for Kerr–Newman fields the eigenvalues of the energy–momentum tensor of the disk are for all the values of the parameters' real quantities so that these disks do not present heat flow in any case, whereas for charged and magnetized Kerr–NUT and Taub–NUT fields we always find regions with heat flow. We also find a general constraint on the counterrotating tangential velocities needed to cast the surface energy–momentum tensor of the disk as the superposition of two counterrotating charged dust fluids. We show that, in general, it is not possible to take the two counterrotating fluids as circulating along electrogeodesics or take the two counterrotating tangential velocities as equal and opposite.