scholarly journals Generalized Galileon scenario inspires chaotic inflation

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Matías López ◽  
Jorge Maggiolo ◽  
Nelson Videla ◽  
Pablo González ◽  
Grigoris Panotopoulos

Abstract We study chaotic inflation with a Galileon-like self-interaction $$G(\phi ,X)\Box \phi $$G(ϕ,X)□ϕ, where $$G(\phi ,X)\propto X^{n}$$G(ϕ,X)∝Xn. General conditions required for successful inflation are deduced and discussed from the background and cosmological perturbations under slow-roll approximation. Interestingly, it is found that in the regime where the Galileon term dominates over the standard kinetic term, the tensor-to-scalar ratio becomes significantly suppressed in comparison to the standard expression in General Relativity (GR). Particularly, we find the allowed range in the space of parameters characterizing the chaotic quadratic and quartic inflation models by considering the current observational data of Planck from the $$n_{\mathcal {S}}-r$$nS-r plane. Finally, we discuss about the issue if the Galileon term is dominant by the end of inflation, this can affect the field oscillation during reheating.

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Kh. Saaidi ◽  
A. Mohammadi ◽  
T. Golanbari

Slow-roll inflationary scenario is considered in noncanonical scalar field model supposing a power-law function for kinetic term and using two formalisms. In the first approach, the potential is picked out as a power-law function, that is, the most common approach in studying inflation. Hamilton-Jacobi approach is selected as the second formalism, so that the Hubble parameter is introduced as a function of scalar field instead of the potential. Employing the last observational data, the free parameters of the model are constrained, and the predicted form of the potential and attractor behavior of the model are studied in detail.


2018 ◽  
Vol 15 (08) ◽  
pp. 1850129 ◽  
Author(s):  
G. P. Singh ◽  
Nikhil Hulke ◽  
Ashutosh Singh

In this paper, a cosmological model with linear equation of state in the framework of General relativity is studied. We explore the thermodynamical aspects of the cosmological model with equilibrium description. In particular, we discuss the validity of generalized second law of thermodynamics for resulting cosmologies. General conditions for this model to satisfy the slow roll conditions for inflation are discussed.


2015 ◽  
Vol 24 (07) ◽  
pp. 1550053 ◽  
Author(s):  
Amare Abebe

One of the exact solutions of f(R) theories of gravity in the presence of different forms of matter exactly mimics the ΛCDM solution of general relativity (GR) at the background level. In this work we study the evolution of scalar cosmological perturbations in the covariant and gauge-invariant formalism and show that although the background in such a model is indistinguishable from the standard ΛCDM cosmology, this degeneracy is broken at the level of first-order perturbations. This is done by predicting different rates of structure formation in ΛCDM and the f(R) model both in the complete and quasi-static regimes.


2014 ◽  
Vol 2014 (06) ◽  
pp. 033-033 ◽  
Author(s):  
Yves Dirian ◽  
Stefano Foffa ◽  
Nima Khosravi ◽  
Martin Kunz ◽  
Michele Maggiore

Author(s):  
JE-AN GU

We discuss the stability of the general-relativity (GR) limit in modified theories of gravity, particularly the f(R) theory. The problem of approximating the higher-order differential equations in modified gravity with the Einstein equations (2nd-order differential equations) in GR is elaborated. We demonstrate this problem with a heuristic example involving a simple ordinary differential equation. With this example we further present the iteration method that may serve as a better approximation for solving the equation, meanwhile providing a criterion for assessing the validity of the approximation. We then discuss our previous numerical analyses of the early-time evolution of the cosmological perturbations in f(R) gravity, following the similar ideas demonstrated by the heuristic example. The results of the analyses indicated the possible instability of the GR limit that might make the GR approximation inaccurate in describing the evolution of the cosmological perturbations in the long run.


2019 ◽  
Vol 34 (35) ◽  
pp. 1975002
Author(s):  
A. Stepanian

It is shown that the concept of “negative mass” introduced by Farnes [Astron. Astrophys. 620, A92 (2018)] to describe the dark sector within a unifying theory with the negative cosmological constant contradicts both the essence of the General Relativity (GR) and the available observational data. A viable model with modified weak-field GR is mentioned.


1968 ◽  
Vol 64 (4) ◽  
pp. 1071-1079 ◽  
Author(s):  
J. V. Narlikar

AbstractIt is well known that classical electrodynamics can be described both as a field theory and as a theory of direct interparticle action. In the present paper it is shown that, provided certain general conditions are satisfied, fields of arbitrary spin have their counterparts in ‘direct particle fields’. This correspondence between the two formalisms is established in the Riemannian space-time used for general relativity.


2018 ◽  
Vol 33 (10) ◽  
pp. 1850058 ◽  
Author(s):  
H. Es-sobbahi ◽  
M. Nach

In the framework of the braneworld Randall–Sundrum type II model, we investigate an inflationary scalar model in the high-energy regime. In this regime, the slow-roll parameters and the perturbation spectrum of the model are derived. The corresponding results are dealt with according to the known observational data. Then the solutions to the equations of motion on the brane are given.


2010 ◽  
Vol 81 (10) ◽  
Author(s):  
Levon Pogosian ◽  
Alessandra Silvestri ◽  
Kazuya Koyama ◽  
Gong-Bo Zhao

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