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Black holes and their shadows in gravity
Shin'ichi Nojiri, S. D. Odintsov
We investigate the radii of the photon sphere and the black hole shadow in the framework of gravity. For this purpose, we derive the field equation for the corresponding the…
Black holes, photon sphere, and cosmology in ghost-free gravity
Shin'ichi Nojiri, S. D. Odintsov
The improved version of ghost-free gravity introduced in Phys.~Lett.~B \textbf{631} (2005), 1-6 is proposed and investigated. It is demonstrated that improved ghos…
Non-metricity approach to Jackiw-Teitelboim gravity
Shin'ichi Nojiri, S. D. Odintsov
We construct 2d Jackiw-Teitelboim (JT) gravity in the framework of symmetric teleparallel gravity based on a non-metricity tensor. In symmetric teleparallel gravity, we often use t…
gravity with Gauss-Bonnet corrections: from early-time inflation to late-time acceleration
Shin'ichi Nojiri, S. D. Odintsov
We show that in the gravity with a non-metricity scalar , the curvatures in Einstein's gravity, that is, the Riemann curvature constructed from the standard Levi-Civita c…
Well-defined Gravity, Reconstruction of FLRW Spacetime and Unification of Inflation with Dark Energy Epoch
Shin'ichi Nojiri, S. D. Odintsov
We formulate the convenient and mimetic gravities in terms of the metric and four scalar fields with the being the non-metricity scalar. As a result, it is shown that th…
Gravitational collapse, primordial black hole, and gravitational wave in Einstein--Gauss-Bonnet theory with two scalar fields
Shin'ichi Nojiri, G. G. L. Nashed
In this paper, we investigate the gravitational collapse to form the black hole in the acceleratingly expanding universe in the frame of Einstein--Gauss-Bonnet theory having two sc…
General geometry realized by four-scalar model and application to gravity
G. G. L. Nashed, Shin'ichi Nojiri
In this paper, we propose a model including four scalar fields coupled with general gravity theories, which is a generalization of the two-scalar model proposed in Phys. Rev. D \te…
Wormholes inside stars and black holes
Shin'ichi Nojiri, S. D. Odintsov, Vladimir Folomeev
We construct models of two exotic objects: (i) a wormhole whose throat is hidden by a stellar object like a neutron star; and (ii) a wormhole inside a black hole. We work within Ei…