arXiv subjects

Panayiotis C. Stavrinos

Publications and source records attributed to Panayiotis C. Stavrinos.

6 recordsLinked to original sources

arXiv2025

Reissner-Nordström and Kerr-like solutions in Finsler-Randers Gravity

In a previous study we investigated the spherically symmetric Schwarzschild and Schwarzschild-de Sitter solutions within a Finsler-Randers-type geometry. In this work we extend our analysis to charged and rotating solutions, focusing on the Reissner-Nordström and Kerr-like metrics in the Finsler-Randers gravitational framework. In particular, we extract the modified gravitational field equations and we examine the geodesic equations, analyzing particle trajectories and quantifying the deviations from their standard counterparts. Moreover, we compare the results with the predictions of general relativity, and we discuss how potential deviations from Riemannian geometry could be reached observationally.

gr-qc↗

arXiv2019

Cosmology of Lorentz fiber-bundle induced scalar-tensor theories

We investigate the cosmological applications of scalar-tensor theories that arise effectively from the Lorentz fiber bundle of a Finsler-like geometry. We first show that the involved nonlinear connection induces a new scalar degree of freedom and eventually a scalar-tensor theory. Using both a holonomic and a nonholonomic basis, we show the appearance of an effective dark-energy sector, which additionally acquires an explicit interaction with the matter sector, arising purely from the internal structure of the theory. Applying the theory at late times we find that we can obtain the thermal history of the Universe, namely the sequence of matter and dark-energy epochs, and moreover the effective dark-energy equation-of-state parameter can be quintessencelike, phantomlike, or experience the phantom-divide crossing during cosmological evolution. Furthermore, applying the scenario at early times, we see that one can acquire an exponential de Sitter solution as well as obtain an inflationary realization with the desired scale-factor evolution. These features arise purely from the intrinsic geometrical structure of Finsler-like geometry and reveal the capabilities of the construction.

gr-qc↗

arXiv2019

Bounce cosmology in generalized modified gravities

We investigate the bounce realization in the framework of generalized modified gravities arising from Finsler and Finsler-like geometries. In particular, the richer intrinsic geometrical structure is reflected in the appearance of extra degrees of freedom in the Friedmann equations that can drive the bounce. We examine various Finsler and Finsler-like constructions. In the cases of general very special relativity as well as of Finsler-like gravity on the tangent bundle we show that a bounce cannot be easily obtained. However, in the Finsler-Randers space the induced scalar anisotropy can fulfill the bounce conditions and bouncing solutions are easily obtained. Finally, for the general class of theories that include a nonlinear connection a new scalar field is induced, leading to a scalar-tensor structure that can easily drive a bounce. These features reveal the capabilities of Finsler and Finsler-like geometries.

gr-qc↗

arXiv2017

Raychaudhuri equation in the Finsler-Randers spacetime and Generalized scalar-tensor theories

In this work, we obtain the Raychaudhuri equations for various types of Finsler spaces as the Finsler-Randers (FR) space-time and in a more general geometrical structure of the space-time manifold which contains two fibres that are two scalars which represent inflaton fields $ϕ^{(1)}, ϕ^{(2)}.$In addition, the energy-conditions are studied in a FR cosmology and are correlated with FRW model. Finally an application of Raychaudhuri equation for the model $M \times \{ ϕ^{(1)} \} \times \{ ϕ^{(2)} \}$ with M a FRW space is given.

gr-qc↗

arXiv2013

Cyclic and Ekpyrotic Universes in Modified Finsler Osculating Gravity on Tangent Lorentz Bundles

We consider models of accelerating Universe elaborated for Finsler like gravity theories constructed on tangent bundles to Lorentz manifolds. In the osculating approximation, certain locally anisotropic configurations are similar to those for f(R) gravity. This allows us to generalize a proposal (by Nojiri, Odintsov and Saez-Gomez, arXiv: 1108.0767) in order to reconstruct and compare two classes of Einstein-Finsler gravity, EFG, and f(R) gravity theories using modern cosmological data and realistic physical scenarios. We conclude that EFG provides inflation, acceleration and little rip evolution scenarios with realistic alternatives to standard Lambda CDM cosmology. The approach is based on a proof that there is a general decoupling property of gravitational field equations in EFG and modified theories which allows us to generate off-diagonal cosmological solutions.

astro-ph.CO↗

arXiv2006

A locally anisotropic geometrical model of space-time based on CMBR

We study a locally anisotropic model of General Relativity in the framework of a more general geometrical structure than the Riemannian one. In this model the observable anisotropy of the CMBR (WMAP) is represented by a tensor of anisotropy and it is included in the metric structure of space-time. As well, some interesting special cases of spaces are considered.

gr-qc↗