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The paper proposes a novel cosmological model based on a two-field scenario, where the two fields are independently coupled with a specific invariant, based on cubic contractions of the Riemann tensor. After obtaining the modified Friedmann equations and the specific Klein-Gordon relations, the investigation studies the corresponding physical features by adopting the linear stability theory in a quintom scenario case where the coupling functions and potential energies have an exponential behavior. The corresponding investigation revealed a high complexity of the phase space structure, with various stationary points which can explain different aspects in the evolution of our Universe, the matter dominated epoch, and the late time accelerated stage. The present model can represent a viable solution to the dark energy problem due to the high complexity of the phase space and the existence of the scaling solutions. Key words: modified gravity, dark energy, 1. Introduction In the present days the technological advances permit the study of the history and evolution of the Universe in a more profound manner, leading to a series of [...]

This work discusses the responsible quantities of the emergence inhomogeneity by taking locally anisotropic radiating fluid in f (G, T) theory, where T and G indicate the trace of stress energy tensor and Gauss-Bonnet terms. The temporal and radial change in mass function is observed with the help of a modified version of Einstein's field equations. To observe the dynamics of self-gravitating fluid, the dynamical equations and differential equations for conformal tensor are constructed, which help to understand the role of correction terms, Weyl curvature, and fluid parameter in the energy-density irregularity. Various forms of fluid are addressed to meet the desired results. Key words: f (G, T) gravity, radiating fluid, Weyl curvature, energy-density irregularity, 1. Introduction Dynamical relationships between space and time were discussed in Einstein's general theory of relativity (GR), in which Einstein assumed the universe to be static. His theory lightened up [...]

In the present article, we study the physical and geometric scenario of the inflection of the Friedmann-LemaitreRobertson-Walker (FLRW) and an axially symmetric perfect fluid Universe with thick domain walls in f(R, T) theory of gravitation (Harko et al. Phys. Rev. D, 84,024020 (2011)), where R and T represent Ricci scalar and trace of the stress-energy-momentum tensor, respectively, in the scenario of decelerating-accelerating transition phases. To ascertain the exact solution of the corresponding field equations, we use the concept of a time-subordinate deceleration parameter, which brings forth the scale factor a(t) = [sinh.sup.1/n]([alpha]t), where n and [alpha] are positive parameters. For n [member of] (0.27,1], a class of accelerating phase is ensured while for n > 1, the Universe attains a phase transition from positive (decelerating) to negative (accelerating), which is uniform with recent observations. The models have been tested for physical feasibility by using stability. Physical and geometric behavior of the models are also explored. Key words: Friedmann-Robertson-Walker, f(R, T) gravity, domain walls, axially symmetric, transition universe. Nous etudions ici le cadre physique et geometrique du point d'inflexion d'un univers de fluide parfait de FriedmannLemaitre-Robertson-Walker (FLRW) a symetrie axiale (SA) parfaite avec murs de domaine epais dans une theorie f(R, T) de la gravite (Harko et al. Phys. Rev. D, 84, 024020 (2011)), ou R est le scalaire de Ricci et T est la trace du tenseur energie-impulsion, dans un scenario de transition de phases deceleration-acceleration. Pour nous assurer d'une solution exacte des equations de champ correspondantes, nous utilisons le concept d'un parametre de deceleration (PD/DP) qui met en scene le facteur d'echelle a(t) = [sinh.sup.1/n]([alpha]t), ou n et a sont des parametres positifs. L'intervalle n [member of] (0.27,1], garantit une classe de phase d'acceleration, alors que pour n > 1, l'univers atteint une transition de phase de positive (deceleration) a negative (acceleration), conforme aux observations recentes. Les modeles ont ete testes pour leur validite physique en utilisant la stabilite. Nous analysons les comportements plus ou moins physiques et geometriques des modeles. [Traduit par la Redaction] Mots-cles : Friedmann-Lemaitre-Robertson-Walker, gravite f(R, T), murs du domaine, symetrie axiale, univers en transition., 1. Introduction The present acceleration of the expansion of the Universe is one of the most challenging problems in modern cosmology. Different cosmic observations [1-15] indicate that expansion of the [...]

Within the scope of Bianchi type-IX cosmological model we have studied the role of spinor field in the evolution of the Universe. It is found that unlike the diagonal Bianchi models in this case the components of energy-momentum tensor of spinor field along the principal axis are not the same (i.e., [T.sup.1.sub.1] [not equal to] [T.sup.2.sub.2] [not equal to] [T.sup.3.sub.3]), even in the absence of spinor field nonlinearity. The presence of nontrivial non-diagonal components of energy-momentum tensor of the spinor field imposes severe restrictions both on geometry of space-time and on the spinor field itself. As a result the space-time turns out to be either locally rotationally symmetric or isotropic. In this paper we considered the Bianchi type-IX space-time both for a trivial b, that corresponds to standard Bianchi type-IX and the one with a non-trivial b. It was found that a positive self-coupling constant [[lambda].sub.1] gives rise to an oscillatory mode of expansion, while a trivial [[lambda].sub.1] leads to rapid expansion at the early stage of evolution. Key words: spinor field, dark energy, anisotropic cosmological models, isotropization, oscillatory mode of expansion. Dans le cadre d'un espace-temps de type IX de Bianchi, nous etudions le role d'un champ de spineur dans revolution de l'univers. Nous trouvons que, contrairement aux modeles diagonaux de Bianchi, ici les composantes du tenseur d'energieimpulsion du champ de spineur le long des axes principaux ne sont pas les memes (i.e., [T.sup.1.sub.1] [not equal to] [T.sup.2.sub.2] [not equal to] [T.sup.3.sub.3]), meme en l'absence de non linearite du champ de spineur. La presence de composantes non triviales non diagonales du tenseur d'energie-impulsion du champ de spineur impose de severes restrictions a la fois a la geometrie de l'espace-temps et au champ de spineur lui- meme. Comme resultat, l'espace-temps se trouve etre soit localement symetrique sous rotation soit isotrope. Nous considerons ici un espace-temps de type IX de Bianchi, a la fois pour un b trivial, qui correspond a un type IX de Bianchistandard et un b non trivial. Nous trouvons qu'une valeur positive de [[lambda].sub.1] mene a un mode d'expansion oscillant, alors qu'un [[lambda].sub.1] trivial mene a une expansion rapide tot dans l'evolution de l'univers. Mots-cles: champ de spineur, energie sombre, modeles cosmologiques anisotropes, isotropisation, mode d'expansion oscillant., 1. Introduction Nonlinear spinor fields play a significant role in explaining the evolution of the Universe at different its stages. It was shown by a number of authors that the [...]

In this paper, we have obtained field equations of Saez-Ballester (Phys. Lett. A, 113, 467 (1986)) scalar-tensor theory in the presence of two minimally interacting fields; matter and holographic dark energy components in the space-time described by a spatially homogeneous and anisotropic Bianchi type V[I.sub.0] space-time. We have used the hybrid expansion law, proposed by Akarsu et al. (JCAP, 01, 022 (2014)), to obtain a determinate solution of the field equations. This solution represents a minimally interacting Bianchi type V[I.sub.0] Saez-Ballester universe. Physical and kinematical properties of the universe are also studied. Key words: Bianchi type V[I.sub.0] universe, holographic dark energy, scalar-tensor theory, Saez-Ballester theory, hybrid expansion law. Nous obtenons ici les equations de champ de la theorie scalaire-tenseur de Saez-Ballester (Phys. Lett. A, 113,497 (1987)) en presence de deux champs interagissant faiblement: un champ de matiere et un champ de composantes de l'energie sombre holographique, dans un espace-temps de Bianchi type VI spatialement homogene et anisotrope. Nous utilisons la loi d'expansion hybride proposee par Akarsu et al. (JCAP, 01, 022 (2014)) pour obtenir une solution determinee des equations de champ. Cette solution represente un espace-temps de Saez-Ballester Bianchi type VI en interaction minimale. Nous en analysons es proprietes physiques et cinematiques. [Traduit par la Redaction] Mots-cles : univers de Bianchi type VI, energie sombre holographique, theorie scalaire-tenseur, theorie de Saez-Ballester, loi d'expansion hybride., 1. Introduction Riess et al. [1], Perlmutter et al. [2], and Bennett et al. [3], through their cosmological observations, suggested that the universe is in a state of accelerated expansion. [...]

We assume here a slightly varying cosmological term which readily induces a permanent background field filling the physical vacuum. A precise form of the variable cosmological term is introduced containing an infinitesimal Killing vector which accounts for the space-time variation of this term. As a result the term can be added to the Einstein Lagrangian without affecting the varied action [delta]S. As a result, we showed in an earlier publications that the permanent background field filling the vaccum is excited in the vicinity of matter which precisely corresponds to its gravitational field classically described by a pseudo-tensor. With this preparation, the global energy-momentum tensor of matter and gravity field is no longer a pseudo-tensor and is formally conserved like the Einstein tensor. In the excited state, this antisymmetric tensor can be conveniently symmetrized by applying the Belinfante procedure which automatically self excludes far from matter since the background field tensor is naturally symmetric., Introduction The substance of this study is inspired by the following considerations. In the framework of the Theory of General Relativity (GR), the Einstein tensor exhibits a conceptually conserved property, [...]

The article presents a complete characterization of the different material parameters of the different three-dimensional pyramidal cloak. The study is shown to be extremely beneficial for the designing of 3D cloaks.

The characterization of the near-field spectral characteristics, images, and optical parameters of silver nanoparticles via the use of Green's tensor are reported. The findings for the optical efficiencies, scattering efficiencies, absorption, and extinction efficiencies of Ag nanoparticles are also reported.

A forward second-harmonic scattering method is described for determining the second-order susceptibility coefficients of ZnO nanorods. The results have shown that Kleinman's symmetry is destroyed at a near-resonant second-harmonic wavelength for the ZnO nanorods.