Decision-Theoretic Consequentialism and the Desire-Luck Problem

Jackson (1991) proposes an interpretation of consequentialism, namely, the Decision Theoretic Consequentialism (DTC), which provides a middle ground between internal and external criteria of rightness inspired by decision theory. According to DTC, a right decision either leads to the best outcomes (external element) or springs from right motivations (internal element). He raises an objection to fully external interpretations, like objective consequentialism (OC), which he claims that DTC can resolve. He argues that those interpretations are either too objective, which prevents them from giving guidance for action, or their guidance leads to wrong and blameworthy actions or decisions. I discuss how the emphasis on blameworthiness in DTC constraints its domain to merely the justification of decisions that relies on rationality to provide a justification criterion for moral decisions. I provide examples that support the possibility of rational but immoral decisions that are at odds with DTC’s prescription for right decisions. Moreover, I argue what I call the desire-luck problem for the external element of justification criterion leads to the same objection for DTC that Jackson raised for OC. Therefore, DTC, although successful in response to some objections, fails to provide a prescription for the right decision

Shadows and photon rings of a spherically accreting Kehagias-Sfetsos black hole

By considering Kehagias-Sfetsos black hole in the framework of the Ho\v{r}ava-Lifshitz gravity, we study the optical appearance of such black holes surrounded by spherical accretion flow. For the static/infalling spherical accretion flow, we compute the observed specific intensity as a function of impact parameter. We also investigate the effect of the Ho\v{r}ava parameter and accreting matter on the luminosity of shadows and photon rings. It is found that an increase in the Ho\v{r}ava parameter decreases the shadow size, while the shadows and photon rings luminosities increase. Moreover, we constrain the Ho\v{r}ava parameter from the observational data reported by the Event Horizon Telescope for M87* and Sgr A*.Comment: 12pages, 6figure

Thin accretion disk luminosity and its image around rotating black holes in perfect fluid dark matter

Motivated by the fact that the universe is dominated by dark matter and dark energy, we consider rotating black holes surrounded by perfect fluid dark matter and study the accretion process in thin disk around such black holes. Here, we are interested in how the presence of dark matter affects the properties of the electromagnetic radiation emitted from a thin accretion disk. For this purpose, we use the Novikov-Thorn model and obtain the electromagnetic spectrum of an accretion disk around a rotating black hole in perfect fluid dark matter and compare with the general relativistic case. The results indicate that for small values of dark matter parameter we considered here, the size of the innermost stable circular orbits would decrease and thus the electromagnetic spectrum of the accretion disk increases. Therefore, disks in the presence of perfect fluid dark matter are hotter and more luminous than in general relativity. Finally, we construct thin accretion disk images around these black holes using the numerical ray-tracing technique. We show that the inclinaion angle has a remarkable effect on the images, while the effect of dark matter parameter is small.Comment: 16 pages, 10 figure

Bending of light in novel 4DD Gauss-Bonnet-de Sitter black holes by Rindler-Ishak method

We study the bending of light in the space-time of black holes in four-dimensional Einstein-Gauss-Bonnet theory of gravity, recently proposed by Glavan and Lin \cite{Glavan}. Using Rindler-Ishak method, the effect of Gauss-Bonnet coupling on the bending angle is studied. We show that a positive Gauss-Bonnet coupling gives a negative contribution to the Schwarzschild-de Sitter deflection angle, as one would expect.Comment: 10 pages, 1 figure. To appear in EP

Thin accretion disks around rotating black holes in 4D4D Einstein-Gauss-Bonnet gravity

Recently, Kumar and Ghosh have derived Kerr-like rotating black hole solutions in the framework of four-dimensional Einstein-Gauss-Bonnet theory of gravity and investigated the black hole shadow. Using the steady-state Novikov-Thorne model, we study thin accretion disk processes for such rotating black holes including the energy flux, temperature distribution, emission spectrum, energy conversion efficiency as well as the radius of the innermost stable circular orbit. We also study the effects of the Gauss-Bonnet coupling parameter $\alpha$ on these quantities. The results are compared to slowly rotating relativistic Kerr black holes which show that for a positive Gauss-Bonnet coupling, thin accretion disks around rotating black holes in four-dimensional Einstein-Gauss-Bonnet gravity are hotter and more efficient than that for Kerr black holes with the same rotation parameter $a$, while for a negative coupling they are cooler and less efficient. Thus the accretion disk processes may be considered as tools for testing Einstein-Gauss-Bonnet gravity using astrophysical observations.Comment: 18 pages, 8 figures, to appear in EPJ