arXiv subjects

Panayiotis Stavrinos

Publications and source records attributed to Panayiotis Stavrinos.

11 recordsLinked to original sources

arXiv2025

The Anholonomic Frame and Connection Deformation Method for constructing off-diagonal solutions in (modified) Einstein gravity and nonassociative geometric flows and Finsler-Lagrange-Hamilton theories

This article is a status report on the Anholonomic Frame and Connection Deformation Method, AFCDM, for constructing generic off-diagonal exact and parametric solutions in general relativity, GR, relativistic geometric flows, and modified gravity theories, MGTs. Such models can be generalized to nonassociative and noncommutative star products on phase spaces and modelled equivalently as nonassociative Finsler-Lagrange-Hamilton geometries. Our approach involves a nonholonomic geometric reformulation of classical models of gravitational and matter fields described by Lagrange and Hamilton densities on relativistic phase spaces. Using nonholonomic dyadic variables, the Einstein equations in GR and MGTs can be formulated as systems of nonlinear partial differential equations(PDEs), which can be decoupled and integrated in some general off-diagonal forms. In this approach, the Lagrange and Hamilton dynamics and related models of classical and quantum evolution are equivalently described in terms of generalized Finsler-like or canonical metrics and (nonlinear) connection structures on deformed phase spaces defined by solutions of modified Einstein equations. New classes of exact and parametric solutions in (nonassociative) MGTs are formulated in terms of generating and integration functions and generating effective/ matter sources. The physical interpretation of respective classes of solutions depends on the type of (non) linear symmetries, prescribed boundary/ asymptotic conditions, or posed Cauchy problems.

gr-qc↗

arXiv2023

Anisotropic Conformal Dark Gravity on the Lorentz Tangent Bundle Spacetime

In this work we investigate the anisotropic conformal structure of the gravitational field incorporating dark gravity in a generalized Lagrange geometric framework on the Lorentz tangent bundle and we present two applications; the anisotropic conformal Minkowski spacetime and the anisotropic conformal FLRW cosmology. In the first application, the conformal factor induces an anisotropic conformal de-Sitter-like space with extra curvature which causes extra gravity and allows for Sasaki-type Finsler-like structures which could potentially describe certain gravitational phenomena in a more extended form. The cosmological properties of the model are also studied using a FLRW metric structure for the underlying base manifold in the second application, where we derive generalized Friedmann-like equations for the horizontal subspace of the Lorentz tangent bundle spacetime that reduce under certain conditions to those given by A. Triantafyllopoulos and P. C. Stavrinos (2018) [Class. Quantum Grav. 35 085011] as well as those of general relativity.

gr-qc↗

arXiv2021

Broken Scale Invariance, Gravity Mass, and Dark Energy in Modified Einstein Gravity with Two Measure Finsler Like Variables

We study new classes of generic off-diagonal and diagonal cosmological solutions for effective Einstein equations in modified gravity theories, MGTs, with modified dispersion relations, MDRs, encoding possible violations of (local) Lorentz invariance, LIVs. Such MGTs are constructed for Lagrange densities with two non-Riemannian volume forms (two-measure theories, TMTs) and associated bimetric/ biconnection geometric structures. For conventional 2+2 splitting, we can describe such models in Finsler like variables, which is important for elaborating geometric methods of constructing exact and parametric solutions. Such formulations of general relativity, GR, and MGTs are considered for Lorentz manifolds and their (co) tangent bundles, in brief, FTMT. Off-diagonal metrics solving gravitational field equations in FTMTs are determined by generating functions, effective sources and integration constants and characterized by nonholonomic frame torsion effects. Restricting the class of integration functions, we can extract torsionless and diagonal configurations and model emergent cosmological theories with square scalar curvature, $R^2$, when the global Weyl-scale symmetry is broken via nonlinear dynamical interactions with nonholonomic constraints. In the physical Einstein-Finsler frame, the constructions involve (i) nonlinear re-parametrization symmetries of the generating functions and effective sources; (ii) effective potentials for the scalar field with possible two flat regions which allows a unified description of locally anisotropic and/or isotropic early universe inflation related to acceleration cosmology and dark energy; (iii) there are "emergent universes" described by (off-) diagonal solutions for certain nonholonomic phases and parametric cosmological evolution resulting in various inflationary phases; (iv) we can reproduce in two-measure theories massive gravity effects.

physics.gen-ph↗

arXiv2021

Dark Gravitational Field on Riemannian and Sasaki Spacetime

The aim of this paper is to provide the geometrical structure of a gravitational field that includes the addition of dark matter in the framework of a Riemannian and a Riemann--Sasaki spacetime. By means of the classical Riemannian geometric methods we arrive at modified geodesic equations, tidal forces, and Einstein and Raychaudhuri equations to account for extra dark gravity. We further examine an application of this approach in cosmology. Moreover, a possible extension of this model on the tangent bundle is studied in order to examine the behavior of dark matter in a unified geometric model of gravity with more degrees of freedom. Particular emphasis shall be laid on the problem of the geodesic motion under the influence of dark matter.

gr-qc↗

arXiv2020

Gravitational Field on the Lorentz Tangent Bundle: Generalized Paths and Field Equations

We investigate the dynamics of gravitational field and particles in a generalized framework of a Lorentz tangent bundle. By variating an appropriate action for each case, we obtain generalized forms of paths and generalized field equations for a Sasaki type metric. We show that Stokes theorem is modified with respect to general relativity due to local anisotropy and the presence of a nonlinear connection which induces an adapted basis in our space.

gr-qc↗

arXiv2014

Modified Einstein and Finsler Like Theories on Tangent Lorentz Bundles

We study modifications of general relativity, GR, with nonlinear dispersion relations which can be geometrized on tangent Lorentz bundles. Such modified gravity theories, MGTs, can be modeled by gravitational Lagrange density functionals $f(\mathbf{R},\mathbf{T},F)$ with generalized/ modified scalar curvature $\mathbf{R}$, trace of matter field tensors $\mathbf{T}$ and modified Finsler like generating function $F$. In particular, there are defined extensions of GR with extra dimensional "velocity/ momentum" coordinates. For four dimensional models, we prove that it is possible to decouple and integrate in very general forms the gravitational fields for $f(\mathbf{R},\mathbf{T},F)$-modified gravity using nonholonomic 2+2 splitting and nonholonomic Finsler like variables $F$. We study the modified motion and Newtonian limits of massive test particles on nonlinear geodesics approximated with effective extra forces orthogonal to the four--velocity. We compute the constraints on the magnitude of extra-accelerations and analyze perihelion effects and possible cosmological implications of such theories. We also derive the extended Raychaudhuri equation in the framework of a tangent Lorentz bundle. Finally, we speculate on effective modelling of modified theories by generic off-diagonal configurations in Einstein and/or MGTs and Finsler gravity. We provide some examples for modified stationary (black) ellipsoid configurations and locally anisotropic solitonic backgrounds.

physics.gen-ph↗

arXiv2013

Resembling dark energy and modified gravity with Finsler-Randers cosmology

In this article we present the cosmological equivalence between the relativistic Finsler-Randers cosmology, with dark energy and modified gravity constructions, at the background level. Starting from a small deviation from the quadraticity of the Riemannian geometry, through which the local structure of General Relativity is modified and the curvature theory is extended, we extract the modified Friedmann equation. The corresponding extended Finsler-Randers cosmology is very interesting, and it can mimic dark-energy and modified gravity, describing a large class of scale-factor evolutions, from inflation to late-time acceleration, including the phantom regime. In this respect, the non-trivial universe evolution is not attributed to a new scalar field, or to gravitational modification, but it arises from the modification of the geometry itself.

gr-qc↗

arXiv2013

Cosmological equivalence between the Finsler-Randers space-time and the DGP gravity model

We perform a detailed comparison between the Finsler-Randers cosmological model and the Dvali, Gabadadze and Porrati braneworld model. If we assume that the spatial curvature is strictly equal to zero then we prove the following interesting proposition: {\it despite the fact that the current cosmological models have a completely different geometrical origin they share exactly the same Hubble expansion}. This implies that the Finsler-Randers model is cosmologically equivalent with that of the DGP model as far as the cosmic expansion is concerned. At the perturbative level we find that the Finsler-Randers growth index of matter perturbations is $γ_{FR} \simeq 9/14$ which is somewhat lower than that of DGP gravity ($γ_{DGP} \simeq 11/16$) implying that the growth factor of the Finsler-Randers model is slightly different ($\sim 0.1-2%$) from the one provided by the DGP gravity model.

gr-qc↗

arXiv2002

Anholonomic Triads and New Classes of (2+1)-Dimensional Black Hole solutions

We apply the method of moving anholonomic frames in order to construct new classes of solutions of the Einstein equations on (2+1)-dimensional pseudo-Riemannian spaces. There are investigated black holes with deformed horizons and renormalized locally anisotropic constants. We speculate on properties of such anisotropic black holes with characteristics defined by anholonomic frames and anisotropic interactions of matter and gravity. The thermodynamics of locally anisotropic black holes is discussed in connection with a possible statistical mechanics background based on locally anisotropic variants of Chern-Simons theories.

gr-qc↗

arXiv2002

Anholonomic Frames and Thermodynamic Geometry of 3D Black Holes

We study new classes three dimensional black hole solutions of Einstein equations written in two holonomic and one anholonomic variables with respect to anholonomic frames Thermodynamic properties of such (2+1)-black holes with generic local anisotropy (having elliptitic horizons) are studied by applying geometric methods. The corresponding thermodynamic systems are three dimensional with entropy S being a hypersurface function on mass M, anisotropy angle $θ$ and eccentricity of elliptic deformations $ε>.$ Two-dimensional curved thermodynamic geometries for locally anistropic deformed black holes are constructed after integration on anisotropic parameter $θ$. Two approaches, the first one based on two-dimensional hypersurface parametric geometry and the second one developed in a Ruppeiner-Mrugala-Janyszek fashion, are analyzed. The thermodynamic curvatures are computed and the critical points of curvature vanishing are defined.

gr-qc↗

arXiv2002

Spinors and Space-Time Anisotropy

This is the first monograph on the geometry of anisotropic spinor spaces and its applications in modern physics. The main subjects are the theory of gravity and matter fields in spaces provided with off--diagonal metrics and associated anholonomic frames and nonlinear connection structures, the algebra and geometry of distinguished anisotropic Clifford and spinor spaces, their extension to spaces of higher order anisotropy and the geometry of gravity and gauge theories with anisotropic spinor variables. The book summarizes the authors' results and can be also considered as a pedagogical survey on the mentioned subjects.

gr-qc↗