Results 71 to 80 of about 11,605 (193)

Novel Theorems on Spacetime Admitting Pseudo‐W2 Curvature Tensor

Journal of Mathematics, Volume 2026, Issue 1, 2026.
This paper investigates spacetime manifolds admitting a pseudo‐W2 curvature tensor. We show that a pseudo‐W2 flat spacetime is an Einstein manifold and therefore has constant curvature. Moreover, when the manifold satisfies the Einstein field equations (EFE), with a cosmological constant, the associated energy–momentum tensor is covariantly constant ...
B. B. Chaturvedi, Prabhawati Bhagat, Mohammad Nazrul Islam Khan, Ljubisa Kocinac   +3 more
wiley   +1 more source

Fermionic decay of a massive scalar in the early universe

European Physical Journal C: Particles and Fields, 2020
We derive a curved space generalization of a scalar to fermion decay rate with a Yukawa coupling in expanding Friedmann–Robertson–Walker universes. This is done using the full theory of quantum fields in curved spacetime and the added-up transition ...
Juho Lankinen, Joonas Malmi, Iiro Vilja
doaj   +1 more source

Cosmological Dynamics of Interacting Dark Energy and Dark Matter in f(Q)$f(Q)$ Gravity

Fortschritte der Physik, Volume 73, Issue 5, May 2025.
Abstract In this work, the behavior of interacting dark energy (DE) and dark matter (DM) within a model of f(Q)$f(Q)$ gravity is explored, employing the standard framework of dynamical system analysis. The power‐law f(Q)$f(Q)$ model is considered, incorporating two different forms of interacting DE and DM: 3αHρm$3\alpha H\rho _m$ and α3HρmρDE$\frac ...
Gaurav N. Gadbail, Simran Arora, Phongpichit Channuie, P. K. Sahoo   +3 more
wiley   +1 more source

Exact solutions to Elko spinors in spatially flat Friedmann-Robertson-Walker spacetimes

Journal of Cosmology and Astroparticle Physics, 2014
In this paper we present exact solutions to the so-called Elko spinors for three models of expanding universe, namely the de Sitter, linear and the radiation type evolution. The study was restrict to flat, homogeneous and isotropic Friedmann-Robertson-Walker backgrounds. Starting with an Elko spinor we present the solutions for these cases and compared
J. M. Hoff da Silva, S. H. Pereira
openaire   +3 more sources

Gravastar Model in Krori–Barua Metric Under f(Q)$f(\mathcal {Q})$ Gravity

Fortschritte der Physik, Volume 72, Issue 7-8, August 2024.
Abstract In this paper, the characteristics of a gravastar in f(Q)$f(\mathcal {Q})$ gravity, which is upheld by Krori–Barua (KB) metric are explored. The authors have used KB metric for the interior and shell regions of the gravastar. The field equations are deduced by using KB metric.
Debasmita Mohanty, Pradyumn K. Sahoo
wiley   +1 more source

Unified first law and some general prescription: a redefinition of surface gravity

European Physical Journal C: Particles and Fields, 2017
The paper contains an extensive study of the unified first law (UFL) in the Friedmann–Robertson–Walker spacetime model. By projecting the UFL along the Kodama vector the second Friedmann equation can be obtained.
Sourav Haldar, Sudipto Bhattacharjee, Subenoy Chakraborty   +2 more
doaj   +1 more source

Almost-homogeneity of the universe in higher-order gravity [PDF]

, 1995
In the $R+\alpha R^2$ gravity theory, we show that if freely propagating massless particles have an almost isotropic distribution, then the spacetime is almost Friedmann-Robertson-Walker (FRW).
David R. Taylor, G. F. R. Ellis, G. F. R. Ellis, J. D. Barrow, J. D. Barrow, J. D. Barrow, J. Ehlers, M. B. Mijić, M. Bruni, R. Maartens, Roy Maartens, W. R. Stoeger   +11 more
core   +2 more sources

The branch‐cut quantum gravity with a self‐coupling inflation scalar field: The wave function of the Universe

Astronomische Nachrichten, Volume 345, Issue 2-3, February-March 2024.
Abstract This paper focuses on the implications of a commutative formulation that integrates branch‐cutting cosmology, the Wheeler–DeWitt equation, and Hořava–Lifshitz quantum gravity. Building on a mini‐superspace structure, we explore the impact of an inflaton‐type scalar field on the wave function of the Universe.
Fridolin Weber, Peter O. Hess, Benno Bodmann, José de Freitas Pacheco, Dimiter Hadjimichef, Marcelo Netz‐Marzola, Geovane Naysinger, Moisés Razeira, César A. Zen Vasconcellos   +8 more
wiley   +1 more source

Einstein-Grisaru-Zanon gravity

Physics Letters B
The leading (α′)3-correction to the gravitational low-energy effective action of closed (type II) superstring theory in four-spacetime dimensions defines the Einstein-Grisaru-Zanon gravity action that is applied for a calculation of the leading ...
Ruben Campos Delgado, Sergei V. Ketov
doaj   +1 more source

Horizon thermodynamics and cosmological equations: a holographic-like connection between thermostatistical quantities on a cosmological horizon and in the bulk

European Physical Journal C: Particles and Fields, 2023
Horizon thermodynamics is expected to be related to the effective energy based on the energy density calculated from the Friedmann equation for a Friedmann–Robertson–Walker (FRW) universe.
Nobuyoshi Komatsu
doaj   +1 more source