Zobrazeno 1 - 10
of 869
pro vyhledávání: '"Nojiri, Shin'ichi"'
We give a short review of the recent developments of entropic cosmology based on two thermodynamic laws of the apparent horizon, namely the first and the second laws of thermodynamics. The first law essentially provides the change of the entropy of t
Externí odkaz:
http://arxiv.org/abs/2409.01090
We investigate compact stars in the noninteger power (NIP) model of $f(R)$ gravity theory, which includes the higher-curvature correction to the Einstein-Hilbert action. The mass-radius relation of the compact stars in the NIP model predicts large de
Externí odkaz:
http://arxiv.org/abs/2408.12301
Autor:
Nojiri, Shin'ichi, Odintsov, Sergei D.
It is not easy to treat the spacetime with horizon(s) in the standard mimetic gravity. The solution to this problem has been presented in Phys.~Lett.~B 830 (2022), 137140, where it was suggested to modify the Lagrange multiplier constraint. In this p
Externí odkaz:
http://arxiv.org/abs/2408.05668
We investigate future singularities originating from the anisotropy in the Universe. We formulate a new class of singularities in the homogeneous and anisotropic universe, comparing them with the known singularities in the homogeneous and isotropic u
Externí odkaz:
http://arxiv.org/abs/2406.18368
This work investigates Early Dark Energy (EDE) scenarios as a potential precombination solution to the Hubble tension problem in the $F(R)$ gravity theory. We first develop a dimensionless quantity to visualize the density ratio between the EDE field
Externí odkaz:
http://arxiv.org/abs/2406.16503
Autor:
Nojiri, Shin'ichi, Odintsov, S. D.
We show that in the $f(Q)$ gravity with a non-metricity scalar $Q$, the curvatures in Einstein's gravity, that is, the Riemann curvature constructed from the standard Levi-Civita connection, could not be excluded or naturally appear. The first observ
Externí odkaz:
http://arxiv.org/abs/2406.12558
Autor:
Nojiri, Shin'ichi, Nashed, G. G. L.
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 scalar fields and we study the propagation of the gravitational wave (GW
Externí odkaz:
http://arxiv.org/abs/2405.00936
Autor:
Nojiri, Shin'ichi, Odintsov, S. D.
We formulate the convenient and mimetic $f(Q)$ gravities in terms of the metric and four scalar fields with the $Q$ being the non-metricity scalar. As a result, it is shown that the obtained field equations are well-defined. By using the field equati
Externí odkaz:
http://arxiv.org/abs/2404.18427
Autor:
Nashed, G. G. L., Nojiri, Shin'ichi
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 \textbf{103} (2021) no.4, 044055, where it has been shown that any given
Externí odkaz:
http://arxiv.org/abs/2402.12860
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 Einstein's gravity coupled to two scalar fields with a specific choice o
Externí odkaz:
http://arxiv.org/abs/2401.15868