International Journal of Modern Physics D

Modern cosmological simulations predict that the first generation of stars formed with a mass scale around 100 M_⊙ about 300–400 million years after the Big Bang. When the first stars reached the end of their lives, many of them might have died as energetic supernovae (SNe) that could have significantly affected the early Universe via injecting large amounts of energy and metals into the primordial intergalactic medium. In this paper, we review the current models of the first SNe by discussing on the relevant background physics, computational methods and the latest results.

The generation of massive Gravitational Waves (GW) from metric f(R) theory of gravity is studied and the sensitivity of a spherical antenna detector towards such a wave is looked into. The energy sensitivity is maximum for the monopole mode of the sphere. Of the five quadrupole modes of a sphere, only three are triggered by a massive wave. Also, the sensitivity of a spherical antenna with mechanical resonators attached to it is studied. The Truncated Icosahedral Gravitational wave Antenna (TIGA), originally proposed for detecting the effect of massless GW on the quadrupole modes of a sphere, has been modified in this paper to get a Modified TIGA, in order to detect the sensitivity of monopole modes towards a massive wave.

Rather than tiling the black hole horizon by Planck area patches, we suggest that bits of information inhabit, universally and holographically, the entire black core interior, a bit per a light sheet unit interval of order Planck area difference. The number of distinguishable (tagged by a binary code) configurations, counted within the context of a discrete holographic shell model, is given by the Catalan series. The area entropy formula is recovered, including Cardy's universal logarithmic correction, and the equipartition of mass per degree of freedom is proven. The black hole information storage resembles, in the count procedure, the so-called stack data structure.

New solutions for (2 + 1)-dimensional Einstein–Maxwell spacetime are found for a static spherically symmetric charged fluid distribution with the additional condition of allowing conformal Killing vectors (CKV). We discuss physical properties of the fluid parameters. Moreover, it is shown that the model actually represents two structures, namely (i) Gravastar as an alternative of black hole and (ii) Electromagnetic Mass model depending on the nature of the equation of state of the fluid. Here the gravitational mass originates from electromagnetic field alone. The solutions are matched with the exterior region of the Bañados–Teitelboim–Zanelli (BTZ) type isotropic static charged black hole as a consequence of junction conditions. We have shown that the central charge density is dependent on the value of M₀, the conserved mass of the BTZ black hole. This, in turn, depends on the black hole event horizon which again is related to the Hawking radiation temperature of a BTZ black hole. Thus, one may have a clue that the central charge density is related with Hawking radiation temperature of the BTZ black hole on the exterior region of the static charged fluid sphere.

We consider a multiverse scenario made up of classically disconnected regions of the spacetime that are, nevertheless, in a quantum entangled state. The addition of a scalar field enriches the model and allows us to treat both the inflationary and the "oscillatory stage" of the universe on the same basis. Imposing suitable boundary conditions on the state of the multiverse, two different representations are constructed related by a Bogoliubov transformation. We compute the thermodynamic magnitudes of the entanglement, such as entropy and energy, explore the effects introduced by the presence of the scalar field and compare with previous results in the absence of scalar field.

It has been shown previously that an extremal Reissner–Nordström or an extremal Kerr black hole cannot be overcharged or overspun by a test particle, if radiative and self-force effects are neglected. In this paper, we consider extremal charged and rotating black holes with cosmological constants. By studying the motion of test particles, we find the following results: An extremal Reissner–Nordström anti-de Sitter (RN–AdS) black hole can be overcharged by a test particle but an extremal Reissner–Nordström de Sitter (RN–dS) black hole cannot be overcharged. We also show that both extremal Kerr–de Sitter (Kerr–dS) and Kerr–anti-de Sitter (Kerr–AdS) black holes can be overspun by a test particle, implying a possible breakdown of the cosmic censorship conjecture. For the Kerr–AdS case, the overspinning requires that the energy of the particle be negative, a reminiscent of the Penrose process. In contrast to the extremal RN and Kerr black holes, in which cases the cosmic censorship is upheld, our results suggest some subtle relations between the cosmological constants and the cosmic censorship. We also discuss the effect of radiation reaction for the Kerr–dS case and find that the magnitude of energy loss due to gravitational radiation may not be enough to prevent the violation of the cosmic censorship.

Two particles can collide inside a nonextremal black hole in such a way that the energy E_c.m. in their center-of-mass frame becomes as large as one likes. We show that this effect can be understood with the help of a simple analogy with particle collisions in flat spacetime. As the two-dimensional part of near-horizon geometry inside a black hole is described by the flat Milne metric, the results have a general character. Full classification of scenarios with unbound E_c.m. is suggested. Some scenarios of this kind require proximity of collision to the bifurcation point, but for some other ones this is not necessary.

We investigate a model based on a generalized version of the Fourier transform for curved spacetime manifolds. This model is possible if the metric has an asymptotic flat region which allows a duality to be implement between coordinates and momenta, hence, the model's name, trans-Planckian. The theory and the action are based on the postulate of the absolute egalitarian relation between coordinates x and momenta p. We show how to implement this construction in a cosmological setting, on a Friedman–Robertson–Walker (FRW) metric background, where the asymptotic time infinity plays the role of the required asymptotic flat region. We discuss the effect of gravity, and, in particular, of the Hubble expansion of the universe scale factor on the Fourier map. The dual-inflationary stage is responsible for making the dual-sector of the action inaccessible at ordinary low energies. We propose a scenario in which an effective positive cosmological constant is caused by how the dual-sector of the theory affects the equation of state for matter particles.

We study the Ashtekar formulation of linear gravity starting from the Arnowitt–Deser–Misner (ADM) first-order action of the exact theory, linearizing it, and performing a canonical transformation that coordinatizes the phase-space in terms of the already linearized Ashtekar variables. A quantum geometrical representation, based on the realization of the transverse-traceless part of the linear canonical variables, is presented, and its relationship with previous attempts is discussed. A related geometric representation that realizes directly the observables of the Fierz–Pauli theory, without resorting to deal with the linearized Ashtekar variables, is also discussed.

We investigate the physical properties of conformally Schwarzschild black holes (BHs) in a background of accelerating universe. We discuss the effect of the cosmic expansion on the principal quantities of the BH such as mass, temperature, entropy and horizon radius. In particular, we investigate the quasi-static thermodynamics of the BH by considering the fact that the cosmic expansion is very slow on local time scales. We show that, by imposing a condition on Ricci scalar, one can describe time-dependent, spherically symmetric solutions of Einstein gravity in an accelerating universe background in a unified way. A generalization of cosmological horizon, its temperature and other properties of conformally Schwarzschild BHs in a background of accelerating universe is addressed.

We study spherically symmetric perturbations determined by alternative theories of gravity to the gravitational field of a central mass in General Relativity (GR). In particular, we focus on perturbations in the form of power laws and calculate their effect on the secular variations of the orbital elements of a Keplerian orbit. We show that, to lowest approximation order, only the argument of pericenter and mean anomaly undergo secular variations; furthermore, we calculate the variation of the orbital period. We give analytic expressions for these variations which can be used to constrain the impact of alternative theories of gravity.

The existence of the black hole (BH)–torus system has been given a considerable attention to explain the variability of X-ray and Gamma-ray (γ-ray) data. The perturbation of this system by a Bondi–Hoyle accretion leads to an instability which might be used to understand the dynamics of X-ray binaries and γ-ray burst (GRB). The instability is of a Papaloizou–Pringle type and the fastest growing mode of this instability corresponds to m = 1. In this paper, we put forward a scenario in which the stable BH–torus system is perturbed by a matter which is coming from red giants due to the stellar winds. We model the perturbed BH–torus system to find out how the dynamics of the system changes depending on the rest-mass density of the initial perturbation and to estimate the maximum rest-mass density of the perturbation, ρ_p, which creates a quasi-periodic oscillation without having a shock cone around the BH for fixed ρ_c (ρ_c is the maximum rest-mass density of the initial stable torus). We have found that the perturbation with a rest-mass density, ρ_p < 100ρ_atm (ρ_atm is the rest-mass density of the atmosphere), for any Mach number is the best model for the formation of the oscillating torus around the BH. Otherwise, the shock cone appears in the downstream region of the accreted domain. It is also found that the instability is observed while ρ_p < 100ρ_atm.

In this paper, we study the cosmological constraints from the measurements of Hubble parameters — H(z) data. Here, we consider two kinds of H(z) data: the direct H₀ probe from the Hubble Space Telescope (HST) observations of Cepheid variables with H₀ = 73.8 ± 2.4 km s^-1 Mpc^-1 and several measurements on the Hubble parameter at high redshifts H(z). Employing Markov Chain Monte Carlo (MCMC) method, we also combine the WMAP nine-year data (WMAP9), the baryon acoustic oscillations (BAO) and type Ia supernovae (SNIa) Union2.1 compilation to determine the cosmological parameters, such as the equation of state (EoS) of dark energy w, the curvature of the universe Ω_k, the total neutrino mass ∑m_ν, the effective number of neutrinos N_eff and the parameters associated with the power spectrum of primordial fluctuations. These H(z) data provide extra information on the accelerate rate of our universe at high redshifts. Therefore, adding these H(z) data significantly improves the constraints on cosmological parameters, such as the number of relativistic species. Moreover, we find that direct prior on H₀ from HST can also give good constraints on some parameters, due to the degeneracies between these parameters and H₀.

We provide the quantum treatment of the relational quadrilateral. The underlying reduced configuration spaces are ℂℙ² and the cone over this. We consider exact free and isotropic HO potential cases and perturbations about these. Moreover, our purely relational kinematical quantization is distinct from the usual one for ℂℙ², which turns out to carry absolutist connotations instead. Thus, this paper is the first to note absolute-versus-relational motion distinctions at the kinematical rather than dynamical level. It is also an example of value to the discussion of kinematical quantization along the lines of Isham, 1984. The relational quadrilateral is the simplest RPM whose mathematics is not standard in atomic physics (the triangle and four particles on a line are both based on 𝕊² and ℝ³ mathematics). It is far more typical of the general quantum relational N-a-gon than the previously studied case of the relational triangle. We consider useful integrals as regards perturbation theory and the peaking interpretation of quantum cosmology. We subsequently consider problem of time (PoT) applications of this: quantum Kuchař beables, the Machian version of the semiclassical approach and the timeless naïve Schrödinger interpretation. These go toward extending the combined Machian semiclassical-Histories-Timeless Approach of [Int. J. Mod. Phys. D23 (2014) 1450014] to the case of the quadrilateral, which will be treated in subsequent papers.