scholarly journals Scalar mode propagation in modified gravity with a scalar field

2009 ◽  
Vol 80 (8) ◽  
Author(s):  
Antonio De Felice ◽  
Teruaki Suyama
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Mode Propagation ◽  
Scalar Mode

scholarly journals Anti-screening of the Galileon force around a disk center hole

2019 ◽  
Vol 34 (02) ◽  
pp. 1950013 ◽  
Author(s):  
Hiromu Ogawa ◽  
Takashi Hiramatsu ◽  
Tsutomu Kobayashi
Keyword(s):  
Field Equation ◽  
Scalar Field ◽  
Modified Gravity ◽  
Disk Center ◽  
Academic Interest ◽  
Screening Effect ◽  
Matter Source ◽  
Fifth Force ◽  
Scalar Field Equation

The Vainshtein mechanism is known as an efficient way of screening the fifth force around a matter source in modified gravity. This has been verified mainly in highly symmetric matter configurations. To study how the Vainshtein mechanism works in a less symmetric setup, we numerically solve the scalar field equation around a disk with a hole at its center in the cubic Galileon theory. We find, surprisingly, that the Galileon force is enhanced, rather than suppressed, in the vicinity of the hole. This anti-screening effect is larger for a thinner, less massive disk with a smaller hole. At this stage, our setup is only of academic interest and its astrophysical consequences are unclear, but this result implies that the Vainshtein screening mechanism around less symmetric matter configurations are quite nontrivial.

scholarly journals General Slow-Roll Inflation in f(R) Gravity under the Palatini Approach

Symmetry ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 1958
Author(s):  
Sabit Bekov ◽  
Kairat Myrzakulov ◽  
Ratbay Myrzakulov ◽  
Diego Sáez-Chillón Gómez
Keyword(s):  
Scalar Field ◽  
Simple Model ◽  
Spectral Index ◽  
Effective Potential ◽  
Modified Gravity ◽  
Palatini Formalism ◽  
Slow Roll ◽  
Slow Roll Inflation

Slow-roll inflation is analyzed in the context of modified gravity within the Palatini formalism. As shown in the literature, inflation in this framework requires the presence of non-traceless matter; otherwise, it does not occur just as a consequence of the nonlinear gravitational terms of the action. Nevertheless, by including a single scalar field that plays the role of the inflaton, slow-roll inflation can be performed in these theories, where the equations lead to an effective potential that modifies the dynamics. We obtain the general slow-roll parameters and analyze a simple model to illustrate the differences introduced by the gravitational terms under the Palatini approach, and the modifications on the spectral index and the tensor to scalar ratio predicted by the model.

scholarly journals Accelerating cosmology in modified gravity with scalar field

2005 ◽  
Vol 37 (5) ◽  
pp. 953-958 ◽  
Author(s):  
Yulia A. Shaido ◽  
Akio Sugamoto
Keyword(s):  
Scalar Field ◽  
Modified Gravity

scholarly journals Quintessential Inflation with Dynamical Higgs Generation as an Affine Gravity

2020 ◽  
Author(s):  
David Benisty ◽  
Eduardo Guendelman ◽  
Emil Nissimov ◽  
Svetlana Pacheva
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Riemannian Metric ◽  
Explicit Representation ◽  
Inflationary Universe ◽  
Inflationary Model ◽  
Scale Invariant ◽  
Inflationary Scenario ◽  
Higgs Effect ◽  
Affine Gravity

First, we propose a scale-invariant modified gravity interacting with a neutral scalar inflaton and a Higgs-like SU(2)xU(1) iso-doublet scalar field based on the formalism of non-Riemannian (metric-independent) spacetime volume-elements. This model describes in the physical Einstein frame a quintessential inflationary scenario driven by the "inflaton" together with gravity-inflaton assisted dynamical spontaneous SU(2)xU(1) symmetry breaking in the post-inflationary universe, whereas SU(2)xU(1) symmetry remains intact in the inflationary epoch. Next, we find the explicit representation of the latter quintessential inflationary model with a dynamical Higgs effect as an Eddington-type purely affine gravity.

Wormhole solutions with scalar field and electric charge in modified gravity

2020 ◽  
Vol 96 (1) ◽  
pp. 015303
Author(s):  
Nisha Godani ◽  
Gauranga C Samanta
Keyword(s):  
Scalar Field ◽  
Electric Charge ◽  
Modified Gravity

scholarly journals Dark energy and modified gravity in degenerate higher-order scalar–tensor (DHOST) theories: A review

2019 ◽  
Vol 28 (05) ◽  
pp. 1942006 ◽  
Author(s):  
David Langlois
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Higher Order ◽  
Second Order ◽  
Compact Objects ◽  
Degree Of Freedom ◽  
Scalar Mode

This paper reviews scalar–tensor theories characterized by a Lagrangian that, despite the presence of second-order derivatives, contains a single scalar degree of freedom. These theories, known as Degenerate Higher-Order Scalar–Tensor (DHOST) theories, include Horndeski and Beyond Horndeski theories. They propagate a single scalar mode as a consequence of the degeneracy of their Lagrangian and, therefore, are not plagued by an Ostrogradsky instability. They have been fully classified up to cubic order in second-order derivatives. The study of their phenomenological consequences restricts the subclass of DHOST theories that are compatible with observations. In cosmology, these theories can be described in the language of the unified effective approach to dark energy and modified gravity. Compact objects in the context of DHOST theories are also discussed.

scholarly journals Cosmological reconstruction of f(T, 𝒯) gravity

2014 ◽  
Vol 11 (08) ◽  
pp. 1450077 ◽  
Author(s):  
Davood Momeni ◽  
Ratbay Myrzakulov
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Two Fluids ◽  
Consistent Model ◽  
The Universe

Motivated by the newly proposal for gravity as the effect of the torsion scalar T and trace of the energy momentum tensor 𝒯, we investigate the cosmological reconstruction of different models of the Universe. Our aim here is to show that how this modified gravity model, f(T, 𝒯) is able to reproduce different epochs of the cosmological history. We explicitly show that f(T, 𝒯) can be reconstructed for ΛCDM as the most popular and consistent model. Also we study the mathematical reconstruction of f(T, 𝒯) for a flat cosmological background filled by two fluids mixture. Such model describes phantom–non-phantom era as well as the purely phantom cosmology. We extend our investigation to more cosmological models like perfect fluid, Chaplygin gas and massless scalar field. In each case we obtain some specific forms of f(T, 𝒯). These families of f(T, 𝒯) contain arbitrary function of torsion and trace of the energy momentum.

scholarly journals 1D Supergravity FLRW Model of Starobinsky

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 449
Author(s):  
Nephtalí E. Martínez-Pérez ◽  
Cupatitzio Ramírez-Romero ◽  
Víctor M. Vázquez-Báez
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Energy State ◽  
Hamiltonian Formulation ◽  
Low Energy ◽  
The Other ◽  
Classical Dynamics ◽  
Massive Scalar ◽  
Massive Scalar Field ◽  
Cosmic Inflation

We study two homogeneous supersymmetric extensions for the f(R) modified gravity model of Starobinsky with the FLRW metric. The actions are defined in terms of a superfield R that contains the FLRW scalar curvature. One model has N = 1 local supersymmetry, and its bosonic sector is the Starobinsky action; the other action has N = 2, its bosonic sector contains, in additional to Starobinsky, a massive scalar field without self-interaction. As expected, the bosonic sectors of these models are consistent with cosmic inflation, as we show by solving numerically the classical dynamics. Inflation is driven by the R2 term during the large curvature regime. In the N = 2 case, the additional scalar field remains in a low energy state during inflation. Further, by means of an additional superfield, we write equivalent tensor-scalar-like actions from which we can give the Hamiltonian formulation.

scholarly journals Jointly modelling Cosmic Inflation and Dark Energy

2021 ◽  
Vol 2105 (1) ◽  
pp. 012001
Author(s):  
Konstantinos Dimopoulos
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Modified Gravity ◽  
Cosmic Inflation

Abstract Quintessential inflation utilises a single scalar field to account for the observations of both cosmic inflation and dark energy. The requirements for modelling quintessential inflation are described and two explicit successful models are presented in the context of α-attractors and Palatini modified gravity.

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