Narrow Results

We study the absorption and scattering of massless scalar waves propagating in spherically symmetric spacetimes with dynamical cosmological constant both in low-energy and high-energy zones. In the former low-energy regime, we solve analytically the Regge–Wheeler wave equation and obtain an analytic absorption probability expression which varies with , where M is the central mass and Λ is cosmological constant. The low-energy absorption probability, which is in the range of [0, 0.986701], increases monotonically with increase in Λ. In the latter high-energy regime, the scalar particles adopt their geometric optics limit value. The trajectory equation with effective potential emerges and the analytic high-energy greybody factor, which is relevant with the area of classically accessible regime, also increases monotonically with increase in Λ, as long Λ is less than or of the order of 10⁴. In this high-energy case, the null cosmological constant result reduces to the Schwarzschild value .

Semiclassical black holes emit radiation called Hawking radiation. Such radiation, as seen by an asymptotic observer far outside the black hole, differs from the original radiation near the horizon of the black hole by a redshift factor and the so-called "greybody factor." In this paper, we concentrate on the greybody factor; various bounds for the greybody factors of non-rotaging black holes are obtained, concentrating primarily on charged Reissner–Nordström (RN) and RN–de Sitter black holes. These bounds can be derived using a 2 × 2 transfer matrix formalism. It is found that the charges of black holes act as efficient barriers. Furthermore, adding extra dimensions to spacetime can shield Hawking radiation. Finally, it is also found that the cosmological constant can increase the emission rate of Hawking radiation.

In this paper, we study the sparsity of Hawking radiation from nonrotating singularity-free black holes in conformal gravity. We give a rigorous bound on the greybody factor for massless scalar field and calculate the sparsity of Hawking radiation from the black hole. Besides, we investigate the dependence of the bound of the greybody factor and the sparsity of Hawking radiation on the conformal parameters, respectively. Our study shows that when the conformal parameters are large, the increase of conformal parameters will lead to a more sparse Hawking radiation, while to a less sparse Hawking radiation if the conformal parameters are small.

This paper deals with formulation of analytic solution for greybody factor taking a rotating black hole (BH) in the vicinity of perfect fluid dark matter. To this end, the Klein–Gordon equation is transformed into the standard Schrödinger equation in order to portray the behavior of effective potential. We compute the asymptotic solutions in two different regimes, namely, BH and far field horizons under the influence of perfect fluid dark matter. The derived solutions are smoothly matched in an intermediate region for the sake of their viability. It is observed that a large amount of radiations approach infinity by decreasing intensity of dark matter in the surrounding of BH and hence the greybody factor increases. We also analyze the impact of thermal fluctuations on the considered gravitational background. In this context, the corrected entropy near the equilibrium state is computed which further modifies other thermodynamic potentials. We conclude that the larger BHs become more stable taking positive ranges of specific heat in the vicinity of quantum corrections.