Results 21 to 30 of about 634,467 (244)

G\"{o}del-type universes in f(R) gravity

, 2009
The $f(R)$ gravity theories provide an alternative way to explain the current cosmic acceleration without a dark energy matter component. If gravity is governed by a $f(R)$ theory a number of issues should be reexamined in this framework, including the ...
A. J. Accioly, H. A. Buchdahl, J. Santos, M. J. Rebouças, W.-H. Huang   +4 more
core   +1 more source

Classical Euclidean wormhole solutions in Palatini $f(\tilde{R})$ cosmology

, 2012
We study the classical Euclidean wormholes in the context of extended theories of gravity. With no loss of generality, we use the dynamical equivalence between $f(\tilde{R})$ gravity and scalar-tensor theories to construct a point-like Lagrangian in the ...
A. G. Agnese, C. G. Boehmer, D. H. Coule, D. N. Page, F. Darabi, F. S. Accetta, F. S. N. Lobo, G. Allemandi, G. Allemandi, G. Allemandi, H. A. Buchdahl, H. Fukutaka, H. Fukutaka, I. Klebanov, J. Cheeger, J. J. Halliwell, J. O’Hanlon, K. K. Nandi, M. Roshan, M. Visser, O. Bertolami, P. F. González-Diaz, P. F. González-Diaz, S. Capoziello, S. Capoziello, S. Capozziello, S. Capozziello, S. Capozziello, S. Capozziello, S. Capozziello, S. Coleman, S. Coleman, S. Giddings, S. Mignemi, S. Nojiri, S. Nojiri, S. W. Hawking, T. P. Sotiriou, Y. Verbin   +38 more
core   +1 more source

Energy conditions in mimetic-$f(R)$ gravity

, 2017
The energy conditions of mimetic-$f(R)$ gravity theory is analyzed. We will obtain the parameter space of the theory in some special forms of $f(R)$ in which the self-acceleration is allowed.
Haghani, Zahra, Shahidi, Shahab, Shiravand, Maryam   +2 more
core   +1 more source

f(R) Gravity and scalar-tensor theory

, 2006
In the present paper we will investigate the relation between scalar-tensor theory and $f(R)$ theories of gravity. Such studies have been performed in the past for the metric formalism of $f(R)$ gravity; here we will consider mainly the Palatini ...
Amarzguioui M Elgaroy O Mota D F Multamaki T, Amendola L Polarski D Tsujikawa S, Birrell N D, Blaschke D Da̧browski M P, Brans C H, Buchbinder I L, Buchdahl H A, Capozziello S Carloni S Troisi A, Carroll S M, Carroll S M, Fabris J C Gonçalves S V B de Sá Ribeiro R, Faraoni V, Ferraris M Francaviglia M Volovich I, Fujii Y, Higgs P W, Hoyle F, Koivisto T, Misner C W, Narlikar J V, Nojiri S Odintsov S D, Olmo G J Komp W, Sotiriou T P, Sotiriou T P, Sotiriou T P Liberati S, Thomas P Sotiriou, Wands D, Will C M   +26 more
core   +3 more sources

Curvature scalar instability in f(R) gravity [PDF]

, 2006
An instability in the presence of matter in theories of gravity which include a 1/R correction in the gravitational action has been found by Dolgov and Kawasaki. In the present paper this instability is discussed for f(R) gravity in general.
Allemandi, Allemandi, Allemandi, Allemandi, Amendola, Amendola, Barrow, Brookfield, Buchbinder, Buchdahl, Capozziello, Capozziello, Capozziello, Capozziello, Carroll, Cembranos, Clifton, Dolgov, Easson, Erickcek, Faraoni, Faraoni, Ferraris, Ferraris, Flanagan, Hehl, Kunstatter, Maeda, Magnano, Navarro, Nojiri, Nojiri, Nojiri, Nojiri, Nojiri, Olmo, Papapetrou, Sotiriou, Sotiriou, Sotiriou, Sotiriou, Sotiriou, Sotiriou, Soussa, Spergel, Starobinsky, Stelle, Teyssandier, Thomas P. Sotiriou, Vollick, Wands, Whitt   +51 more
core   +4 more sources

$$f(\mathcal {R},\varphi ,\chi )$$ f(R,φ,χ) cosmology with Noether symmetry

European Physical Journal C: Particles and Fields, 2020
This paper is devoted to explore modified $$f(\mathcal {R})$$ f(R) theories of gravity using Noether symmetry approach. For this purpose, Friedmann–Robertson–Walker spacetime is chosen to investigate the cosmic evolution. The study is mainly divided into
M. Farasat Shamir
doaj   +1 more source

Hydrostatic equilibrium configurations of neutron stars in a non-minimal geometry-matter coupling theory of gravity

European Physical Journal C: Particles and Fields, 2020
In this work we analyze hydrostatic equilibrium configurations of neutron stars in a non-minimal geometry-matter coupling (GMC) theory of gravity. We begin with the derivation of the hydrostatic equilibrium equations for the f(R, L) gravity theory, where
G. A. Carvalho, P. H. R. S. Moraes, S. I. dos Santos, B. S. Gonçalves, M. Malheiro   +4 more
doaj   +1 more source

Effective actions for loop quantum cosmology in fourth-order gravity

European Physical Journal C: Particles and Fields, 2021
Loop quantum cosmology (LQC) is a theory which renders the Big Bang initial singularity into a quantum bounce, by means of short-range repulsive quantum effects at the Planck scale.
Marcello Miranda, Daniele Vernieri, Salvatore Capozziello, Francisco S. N. Lobo   +3 more
doaj   +1 more source

G\"{o}del-type universes in Palatini f(R) gravity

, 2010
We examine the question as to whether the Palatini f(R) gravity theories permit space-times in which the causality is violated. We show that every perfect-fluid G\"{o}del-type solution of Palatini f(R) gravity with density $\rho$ and pressure $p$ that ...
Oliveira, T. B. R. F., Reboucas, M. J., Santos, J.   +2 more
core   +1 more source

Exploring Dipolar Dynamics and Ionic Transport in Metal‐Organic Frameworks: Experimental and Theoretical Insights

Advanced Functional Materials, EarlyView.
In this study, the interplay of dipolar dynamics and ionic charge transport in MOF compounds is investigated. Synthesizing the novel structure CFA‐25 with integrated freely rotating dipolar groups, local and macroscopic effects, including interactions with Cs cations are explored.
Ralph Freund, Arthur Schulz, Peter Lunkenheimer, Maryana Kraft, Thomas Bergler, Harald Oberhofer, Dirk Volkmer   +6 more
wiley   +1 more source