Article
Physics, Multidisciplinary
Andronikos Paliathanasis
Summary: This article investigates a cosmological model in a Friedmann-Lemaitre-Robertson-Walker background space, characterized by an ideal gas in Weyl Integrable gravity. A scalar field is introduced in a geometric way in the Weyl-Einstein gravity. The scalar field and the ideal gas interact in the gravitational Action Integral. Additionally, a potential term for the scalar field potential is introduced, and it is shown that the field equations can be described in a minisuperspace. The constraint of the potential function is analyzed using Noether's theorem, and corresponding conservation laws are established. Furthermore, a family of new analytic solutions in Weyl Integrable cosmology is derived by solving the Hamilton-Jacobi equation for the cosmological model, and closed-form expressions for the Hubble function are presented.
Article
Astronomy & Astrophysics
Damien A. Easson, Tucker Manton, Andrew Svesko
Summary: The Weyl double copy connects vacuum solutions in general relativity with Abelian gauge fields in Minkowski spacetime. In a previous work, the authors extended the Weyl double copy to handle external gravitational sources in line with the classical Kerr-Schild double copy. In this study, the authors provide a comprehensive double-copy analysis of electrovacuum Petrov type-D spacetimes, including the first analysis of the charged C metric and the introduction of the first double-copy prescription for the Ricci spinor.
Article
Multidisciplinary Sciences
Vincent Moncrief, Puskar Mondal
Summary: This article discusses a dynamical mechanism within the framework of the vacuum Einstein flow, suggesting that closed manifolds without homogeneous and isotropic metrics can evolve to be asymptotically compatible with the observed approximate homogeneity and isotropy of the physical universe, by including suitable matter sources.
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
(2022)
Article
Physics, Particles & Fields
Dmitry Chirkov, Alex Giacomini, Sergey A. Pavluchenko, Alexey Toporensky
Summary: The paper systematically investigates solutions with static compact extra dimensions and expanding three-dimensional subspace, providing a scheme for constructing solutions with stability analysis. It finds that solutions with negative spatial curvature of extra dimensions are always stable, while those with positive curvature are stable for a narrow range of parameters. Differences between positive and negative curvature cases, including the coexistence with maximally-symmetric solutions, are noted and discussed.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Jacob Oost, Shinji Mukohyama, Anzhong Wang
Summary: In Einstein-aether theory, spherically symmetric spacetimes are studied in different coordinate systems, yielding exact vacuum solutions characterized by parameters. These solutions satisfy observational constraints, but possess singularities leading to spacetime becoming singular.
Article
Astronomy & Astrophysics
Adriano Barros, Carlos Romero
Summary: In this paper, homogeneous cosmological solutions within the framework of Weyl geometrical scalar-tensor theory are investigated. An anisotropic Kasner type solution is first presented by exploiting similarities with the Brans-Dicke theory. An isotropic model with a flat spatial section sourced by a perfect fluid is then considered, where an analytical solution for the stiff matter case is obtained. For other cases, a complete qualitative analysis is performed to explore the general behavior of the solutions and propose potential scenarios. The absence of the cosmological constant and scalar field potential prevents the discovery of any solution describing the acceleration of the universe.
Article
Astronomy & Astrophysics
Andronikos Paliathanasis
Summary: The study investigates the cosmological evolution of physical parameters in Weyl integrable gravity in a universe with zero spatial curvature. It introduces a scalar field through a geometric approach and studies the stability properties of the stationary points of the field equations. The study also solves the inverse problem for an ideal gas, demonstrating that the gravitational field equations can be derived from the variation of a Lagrangian function, and applies variational symmetries for the construction of analytic and exact solutions.
Article
Physics, Particles & Fields
R. Chan, M. F. A. da Silva, V. H. Satheeshkumar
Summary: The text analyzes all possible spherically symmetric exterior vacuum solutions allowed by the Einstein-Aether theory with static aether. Three classes of solutions are identified based on different values of a combination of free parameters, with explicit analytical solutions provided for specific cases. There are singularities present in some solutions while others are asymptotically flat spacetimes without horizons. This characteristic is different from general relativity. Additionally, the thermodynamics for the case where a horizon exists is briefly discussed.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Mathematics
Marie-Claude Arnaud, Maxime Zavidovique
Summary: For exact symplectic twist maps of the annulus, a choice of weak K.A.M. solutions dependent on the cohomology class c is established in a Lipschitz-continuous way. This bridges the gap between Fathi's weak K.A.M. theory, Bangert's Aubry-Mather theory for semi-orbits, and the existence of backward invariant pseudo-foliations observed by Katnelson & Ornstein. Various precise descriptions and interesting results regarding the pseudographs of weak K.A.M. solutions are deduced.
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
A. Bonanno, S. Silveravalle, A. Zuccotti
Summary: A new type of asymptotically flat wormhole, characterized by a Newtonian potential with a Yukawa correction in its outer spacetime and possessing a singularity at r = ??? in its internal spacetime, has been studied. Geodesics reaching this singularity exhibit a divergence in the expansion scalar in a finite amount of proper time, resembling the future singularity of the big rip cosmological scenario. These wormholes fill a large region of the parameter space of physical solutions.
Article
Astronomy & Astrophysics
Christopher S. Gallagher, Timothy Clifton, Chris Clarkson
Summary: Two-parameter perturbation theory is a framework designed to study the relativistic gravitational effects of small-scale nonlinear structures on the large-scale properties of the Universe. The approach in this paper uses Newtonian perturbation theory to model the gravitational fields of quasi-nonlinear structures and then applies them as source terms for large-scale cosmological perturbations. This work represents a first step towards deploying a formalism that can simultaneously model the weak gravitational fields of both linear and nonlinear structures in a realistic model of the Universe.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
History & Philosophy Of Science
Benat Monfort-Urkizu, Jaume Navarro
Summary: The development and evolution of the ae-theory reveals the re-emergence of the word "ether" in the field of cosmology. However, it remains uncertain whether this AE ether is a continuation of previous ethers or a completely new entity. This paper aims to understand the nature of this new ether by exploring its historical context and the attempts to revive the concept over the last century, with a focus on the ae-theory. The article emphasizes the complexity of establishing a consistent historical narrative for scientific objects like the ether, without advocating for or against its new usage.
EUROPEAN PHYSICAL JOURNAL H
(2023)
Article
Physics, Multidisciplinary
Mrinnoy M. Gohain, Kalyan Bhuyan
Summary: In this paper, exact solutions to the Raychaudhuri equation in the presence of a bulk viscous fluid in f(R, T) modified gravity were derived. The obtained solutions for two cases, general relativity (GR) and non-GR, can describe a non-singular inflationary Universe, known as the Emergent Universe (EU). It was found that the Einstein static (ES) radius of the EU depends on viscosity parameters and the parameter associated with the f(R, T) model. Furthermore, the inflationary evolution of the model was studied in relation to the Equation of State (EoS) parameter and found to be consistent with the BICEP2-Keck-Planck (BKP) data.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Astronomy & Astrophysics
Javlon Rayimbaev, Ahmadjon Abdujabbarov, Mubasher Jamil, Wen-Biao Han, Malika Khudoyberdieva
Summary: This paper discusses the motion of various types of charged, magnetized, and neutral test particles near static and spherically symmetric electrically charged black holes in the Einstein-/Ether gravitational theory. The effects of the free parameters in the theory on particle motion in curved spacetime are analyzed, focusing on the stability of circular and radially varying orbits for different types of particles. The behavior of charged particle motion around black holes with a uniform magnetic field is investigated, and values of the parameters c13 and c14 are proposed to model astrophysical black holes based on the spin of Kerr black holes.
MODERN PHYSICS LETTERS A
(2022)
Article
Mathematics, Interdisciplinary Applications
Esteban Gonzalez, Genly Leon, Guillermo Fernandez-Anaya
Summary: This paper investigates exact solutions of cosmological interest in fractional cosmology. Given mu and w, specific exact power-law solutions are presented. The general solution of the Riccati Equation is discussed and the free parameters are estimated using cosmological data. Best-fit values for the free parameters are obtained through analyses with type Ia supernova data and observational Hubble parameter data. The results suggest that the parameter region with mu > 2 is not ruled out by observations, indicating the potential of fractional cosmology in providing accelerated solutions without matter.
FRACTAL AND FRACTIONAL
(2023)
Article
Engineering, Multidisciplinary
Andronikos Paliathanasis, Genly Leon, P. G. L. Leach
Summary: This study applies the Painleve test to the Benney and Benney-Gjevik equations, which are used to describe waves in falling liquids. The research proves that these two nonlinear 1 + 1 evolution equations pass the singularity test for the traveling-wave solutions. Algebraic solutions based on Laurent expansions are presented.
INTERNATIONAL JOURNAL OF NONLINEAR SCIENCES AND NUMERICAL SIMULATION
(2023)
Article
Engineering, Multidisciplinary
Andronikos Paliathanasis
Summary: We apply Lie theory to determine the infinitesimal generators of point transformations that leave the 3 + 1 Kudryashov-Sinelshchikov equation invariant. We classify the one-dimensional optimal system and derive all possible independent Lie invariants. The existence of travel-wave solutions is proven using the results, and singularity analysis shows that the equation possesses the Painleve property and solutions can be written using a Laurent expansion.
INTERNATIONAL JOURNAL OF NONLINEAR SCIENCES AND NUMERICAL SIMULATION
(2023)
Article
Mathematics
Andronikos Paliathanasis
Summary: In this study, we analyze the group properties of a recently proposed 2+1 extended Boiti-Leon-Manna-Pempinelli equation using the theory of Lie symmetries. We find that the equation possesses an infinite number of Lie symmetries, leading to an infinite number of solutions. By applying Lie invariants, we obtain D'Alembert-type wave solutions and identify new periodic solutions.
QUAESTIONES MATHEMATICAE
(2023)
Article
Engineering, Multidisciplinary
Andronikos Paliathanasis
Summary: This paper presents a symmetry classification study of the hyperbolic system of partial differential equations describing a drift-flux two-phase flow in a one-dimensional pipe. The results show that the fluid equations are invariant under the elements of a three-dimensional Lie algebra for general polytropic indices, but additional Lie point symmetries occur for specific values of the polytropic indices. The one-dimensional systems are investigated in each case, with similarity transformations used to reduce the fluid equations into a system of ordinary differential equations. Exact solutions are derived and the reduced systems are studied numerically.
INTERNATIONAL JOURNAL OF NONLINEAR SCIENCES AND NUMERICAL SIMULATION
(2023)
Article
Mathematics, Applied
Andronikos Paliathanasis, Genly Leon
Summary: We investigate exact solutions and the asymptotic dynamics for the Friedmann-Lemaitre-Robertson-Walker universe with nonzero spatial curvature in the fourth-order modified teleparallel gravitational theory known as f(T,B) theory. The field equations can be described in minisuperspace and can reproduce any exact form of the scale factor. Equilibrium points are calculated and their stability is analyzed. Milne and Milne-like solutions are supported, and the existence of a de Sitter universe is shown. Poincare variables are used to investigate the dynamics at infinity in order to complete the analysis.
MATHEMATICAL METHODS IN THE APPLIED SCIENCES
(2023)
Article
Multidisciplinary Sciences
Andronikos Paliathanasis
Summary: We conducted a detailed study on the potential classification of the Klein-Gordon equation in anisotropic Riemannian manifolds. Specifically, we focused on the Klein-Gordon equations in four-dimensional anisotropic and homogeneous spacetimes of Bianchi I, Bianchi III, and Bianchi V. By deriving closed-form expressions for the potential function, we were able to find the Lie and Noether symmetries of the equations. Applying previous results connecting the Lie symmetries with the collineations of the Riemannian space, we systematically solved the classification problem.
Article
Mathematics
Genly Leon, Alfredo D. Millano, Andronikos Paliathanasis
Summary: In this study, we investigate the phase space of a scalar field theory obtained through minisuperspace deformation. We consider quintessence or phantom scalar fields in the action derived from minisuperspace deformation on the Einstein-Hilbert action. Our analysis utilizes a modified Poisson algebra with alpha-deformed Poisson brackets that are linked to the Moyal-Weyl star product. We discuss both early- and late-time attractors and reconstruct the cosmological evolution. Additionally, we demonstrate that the model can exhibit the lambda CDM model as a future attractor if we start with a massless scalar field without a cosmological constant term.
Article
Physics, Multidisciplinary
Andronikos Paliathanasis
Summary: A detailed analysis is presented on the phase-space for the field equations in scalar field cosmology with a chameleon cosmology. Four different sets of potential and coupling function are considered. The H-normalization approach and dimensionless variables are used to analyze the field equations. The asymptotic solutions describe the main eras of cosmological history and the existence of acceleration solutions. The Chameleon dark energy model is concluded to be a unified model for the dark sector of the universe.
FORTSCHRITTE DER PHYSIK-PROGRESS OF PHYSICS
(2023)
Article
Mathematics
Alfredo D. Millano, Genly Leon, Andronikos Paliathanasis
Summary: We perform a detailed study of the phase-space of the field equations of an Einstein-Gauss-Bonnet scalar field cosmology for a spatially flat Friedmann-Lemaitre-Robertson-Walker spacetime. We consider the exponential function for the scalar field potential and assume two cases for the coupling function of the scalar field with the Gauss-Bonnet term: the exponential function and the power-law function. By writing the field equations in dimensionless variables and studying the equilibrium points using normalized and compactified variables, we recover previous results and discover new asymptotic solutions. These couplings provide a rich cosmological phenomenology.
Article
Mathematics, Interdisciplinary Applications
Bayron Micolta-Riascos, Alfredo D. Millano, Genly Leon, Cristian Erices, Andronikos Paliathanasis
Summary: Recently, researchers have been using fractional calculus to address cosmological problems by altering the gravitational action integral, comparing the resulting theory with observational data. By studying the phase spaces for different fractional order derivatives and matter contents, equilibrium points can be classified, providing a range for investigating cosmological history and obtaining an accelerating power-law solution for the scale factor. This paper discusses the physical interpretation of these cosmological solutions and emphasizes the influence of fractional derivatives in a theory of gravity with a scalar field.
FRACTAL AND FRACTIONAL
(2023)
Article
Astronomy & Astrophysics
Andronikos Paliathanasis
Summary: This study analyzes the phase-space of an alternate scalar field cosmology that combines the concepts of dark energy and the dark sector. The findings indicate that a de Sitter universe can only be achieved when the potential function is constant. The presence of a de Sitter universe depends on the functional form of the potential function, with a finite regime for a constant potential and an infinite regime for an exponential potential. The cosmological viability of the theory is discussed.
Article
Physics, Particles & Fields
K. Dialektopoulos, G. Leon, A. Paliathanasis
Summary: The Noether symmetry analysis is used to investigate a multiscalar field cosmological model in teleparallel gravity. Specifically, the study focuses on two scalar fields interacting in scalar-torsion theory. The field equations are described in a minisuperspace framework, and the evolution of physical variables depends on the potential function governing the dynamics of the scalar fields. By requiring the field equations to possess non-trivial Noether point symmetries and utilizing the first theorem of Noether, restrictions are imposed on the functional forms of the potential. Finally, symmetry vectors and corresponding conservation laws are employed to determine exact and analytic solutions in multiscalar-torsion cosmology.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
H. B. Benaoum, Genly Leon, A. Ovgun, H. Quevedo
Summary: This study investigates inflation driven by a nonlinear electromagnetic field based on an NLED lagrangian density. The study formulates an f-NLED cosmological model with a general function f (F) and explores two interesting examples of the function f (F). The study also analyzes the implications of NLED by studying inflationary parameters and compares the results with observational data.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Alfredo D. Millano, Genly Leon, Andronikos Paliathanasis
Summary: In this study, we investigate the dynamics of the field equations in a four-dimensional isotropic and homogeneous spatially flat Friedmann-Lemaitre-Robertson-Walker geometry, using the Einstein-Gauss-Bonnet theory. We consider a matter source and a scalar field coupled to the Gauss-Bonnet scalar. The theory can explain the acceleration phases of the Universe and may be used as a model for studying inflation or as a candidate for dark energy.
