Strong gravitational lensing of rotating regular black holes in non-minimally coupled Einstein-Yang-Mills theory

The strong gravitational lensing of a regular and rotating magnetic black hole in non-minimally coupled Einstein-Yang-Mills theory is studied. We find that, with the increase of any characteristic parameters of this black hole, such as the rotating parameter, magnetic charge and EYM parameter, the angular image position and relative magnification decrease while deflection angle and image separation increase. The results will degenerate to that of the Kerr case, R-N case with magnetic charge and Schwarzschild case when we take some specific values for the black hole parameters. The results also show that, due to the small influence of magnetic charge and Einstein-Yang-Mills parameters, it is difficult for current astronomical instruments to tell this black hole apart from a General Relativity one

Strong gravitational lensing for photons coupled to Weyl tensor in a regular phantom black hole

Abstract We study strong gravitational lensing for photons coupled to Weyl tensor in a regular phantom black hole spacetime. It is generally accepted that photons with different polarizations have different trajectories which yields a phenomenon of birefringence. As a result, there are two sets of relativistic images on each side of the object, this is quite different from the uncoupled case in which there is only one set of images. Nevertheless, we focus our attention on the relativistic images on one side of the object and investigate the difference between them by discussing how the coupling constant and phantom hair affect the difference of photon sphere radius, minimum impact parameter and deflection angle. After that, we find that the closer the light gets to the black hole, the larger the deflection angle will be. Then, we investigate the difference in angular image position and relative magnitudes of the first relativistic image between the two types of polarized photons, and find that the two images for different polarizations will separate further and be distinguished more easily in the cases that the phantom hair decreases or the absolute value of the coupling constant increases. Furthermore, the image is brighter when it seats closer to the optical axis

Phase Space Analysis of Barrow Agegraphic Dark Energy

Using the Barrow entropy and considering the timescale as IR cutoff, a new holographic dark energy model named Barrow agegraphic dark energy (BADE) was proposed. We use phase space analysis method to discuss the evolution of the universe in three different mode of BADE (Q=0; Q=3αH(ρm+ρD); Q=H(αρm+βρD)). We find the attractor which represents the dark energy-dominated era exists in all cases. In the case Q=0 and Q=H(αρm+βρD) with β=0, the attractor can behave as the cosmological constant, and these models can used to mimic the cosmological constant