A note on viability of nonminimally coupled f(R) theory

Koivisto, Tomi S.

doi:10.1007/s10714-016-2087-5

Cited by 4 publications

(2 citation statements)

References 14 publications

(49 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The particular case f (R, L m ) = f 1 (R) + [1 + λf 2 (R)]L m , suggested in Bertolami et al (2007), was also explored by Ribeiro & Páramos (2014) and , using different dimensionless variables. Note however that some particular models within the class of theories defined by the function f (R, L m ), might present instabilities at the cosmological perturbation level (Tamanini & Koivisto, 2013;Koivisto & Tamanini, 2016). Another very popular theory where matter is non-minimally coupled to gravity, is the so-called f (R, T ) gravity where T is the trace of the energy-momentum tensor.…”

Section: Higher-order Theories and Non-minimal Couplingmentioning

confidence: 99%

Dynamical systems applied to cosmology: Dark energy and modified gravity

et al. 2018

Self Cite

View full text Add to dashboard Cite

The Nobel Prize winning confirmation in 1998 of the accelerated expansion of our Universe put into sharp focus the need of a consistent theoretical model to explain the origin of this acceleration. As a result over the past two decades there has been a huge theoretical and observational effort into improving our understanding of the Universe. The cosmological equations describing the dynamics of a homogeneous and isotropic Universe are systems of ordinary differential equations, and one of the most elegant ways these can be investigated is by casting them into the form of dynamical systems. This allows the use of powerful analytical and numerical methods to gain a quantitative understanding of the cosmological dynamics derived by the models under study. In this review we apply these techniques to cosmology. We begin with a brief introduction to dynamical systems, fixed points, linear stability theory, Lyapunov stability, centre manifold theory and more advanced topics relating to the global structure of the solutions. Using this machinery we then analyse a large number of cosmological models and show how the stability conditions allow them to be tightly constrained and even ruled out on purely theoretical grounds. We are also able to identify those models which deserve further in depth investigation through comparison with observational data. This review is a comprehensive and detailed study of dynamical systems applications to cosmological models focusing on the late-time behaviour of our Universe, and in particular on its accelerated expansion. In self contained sections we present a large number of models ranging from canonical and non-canonical scalar fields, interacting models and non-scalar field models through to modified gravity scenarios. Selected models are discussed in detail and interpreted in the context of late-time cosmology.

show abstract

Section: Higher-order Theories and Non-minimal Couplingmentioning

confidence: 99%

Dynamical systems applied to cosmology: Dark energy and modified gravity

et al. 2018

Self Cite

View full text Add to dashboard Cite

show abstract

“…Tamanini and Koivisto [42] explored the Lagrangian scalar field to model the extended nonminimally coupling between matter and curvature theories, which define the supplement force that comes through non-conservative energy-momentum tensor. Koivisto and Tamanini [43] investigated the noteworthy issues on non-minimal curvature matter with f (R) gravity theories for the feasible stability states. Silva and Páramos [44] examined the analytical results under the perturbation approach in self-stable manner for the feasible dark source structure that are expressed in context of modified f (R) gravity theories with non-minimal coupled curvature matter.…”

Section: Introductionmentioning

confidence: 99%

Complexity factor for anisotropic source in non-minimal coupling metric f(R) gravity

Abbas

Nazar

2018

Eur. Phys. J. C

View full text Add to dashboard Cite

In this outline we recognize the idea of complexity factor for static anisotropic selfgravitating source with generalized f (R) metric gravity theory. In present consideration, we express the Einstein field equations, hydrostatic equilibrium equation, the mass function and physical behavior of f (R) model by using some observational data of well known compact stars like 4U 1820 − 30, SAX J1808.4 − 3658 and Her X − 1. We define the scalar functions through the orthogonal splitting of the Reimann-Christofell tensor and then find the vanishing complexity condition for self-gravitating system with the help of these scalars. It has been found that the vanishing condition for the complexity are pressure anisotropy and energy density inhomogeneity must cancel each other. Moreover, we study the momentous results of an astral object for the vanishing of complexity factor. Finally, these solutions reduced to previous investigation about complexity factor in General Relativity by taking λ = 0.

show abstract

In the realm of the Hubble tension—a review of solutions ^*

Valentino

Mena²,

Pan³

et al. 2021

Class. Quantum Grav.

1,118

700

View full text Add to dashboard Cite

The simplest ΛCDM model provides a good fit to a large span of cosmological data but harbors large areas of phenomenology and ignorance. With the improvement of the number and the accuracy of observations, discrepancies among key cosmological parameters of the model have emerged. The most statistically significant tension is the 4σ to 6σ disagreement between predictions of the Hubble constant, H 0, made by the early time probes in concert with the ‘vanilla’ ΛCDM cosmological model, and a number of late time, model-independent determinations of H 0 from local measurements of distances and redshifts. The high precision and consistency of the data at both ends present strong challenges to the possible solution space and demands a hypothesis with enough rigor to explain multiple observations—whether these invoke new physics, unexpected large-scale structures or multiple, unrelated errors. A thorough review of the problem including a discussion of recent Hubble constant estimates and a summary of the proposed theoretical solutions is presented here. We include more than 1000 references, indicating that the interest in this area has grown considerably just during the last few years. We classify the many proposals to resolve the tension in these categories: early dark energy, late dark energy, dark energy models with 6 degrees of freedom and their extensions, models with extra relativistic degrees of freedom, models with extra interactions, unified cosmologies, modified gravity, inflationary models, modified recombination history, physics of the critical phenomena, and alternative proposals. Some are formally successful, improving the fit to the data in light of their additional degrees of freedom, restoring agreement within 1–2σ between Planck 2018, using the cosmic microwave background power spectra data, baryon acoustic oscillations, Pantheon SN data, and R20, the latest SH0ES Team Riess, et al (2021 Astrophys. J. 908 L6) measurement of the Hubble constant (H 0 = 73.2 ± 1.3 km s−1 Mpc−1 at 68% confidence level). However, there are many more unsuccessful models which leave the discrepancy well above the 3σ disagreement level. In many cases, reduced tension comes not simply from a change in the value of H 0 but also due to an increase in its uncertainty due to degeneracy with additional physics, complicating the picture and pointing to the need for additional probes. While no specific proposal makes a strong case for being highly likely or far better than all others, solutions involving early or dynamical dark energy, neutrino interactions, interacting cosmologies, primordial magnetic fields, and modified gravity provide the best options until a better alternative comes along.

show abstract

A note on viability of nonminimally coupled f(R) theory

Abstract: Consistency conditions for nonminimally coupled f (R) theories have been derived by requiring the absence of tachyons and instabilities in the scalar fluctuations. This note confirms these results and clarifies a subtlety regarding different definitions of sound speeds.

Cited by 4 publications

References 14 publications

Dynamical systems applied to cosmology: Dark energy and modified gravity

Dynamical systems applied to cosmology: Dark energy and modified gravity

Complexity factor for anisotropic source in non-minimal coupling metric f(R) gravity

In the realm of the Hubble tension—a review of solutions ^*

Contact Info

Product

Resources

About

A note on viability of nonminimally coupled f(R) theory

Abstract: Consistency conditions for nonminimally coupled f (R) theories have been derived by requiring the absence of tachyons and instabilities in the scalar fluctuations. This note confirms these results and clarifies a subtlety regarding different definitions of sound speeds.

Cited by 4 publications

References 14 publications

Dynamical systems applied to cosmology: Dark energy and modified gravity

Dynamical systems applied to cosmology: Dark energy and modified gravity

Complexity factor for anisotropic source in non-minimal coupling metric f(R) gravity

In the realm of the Hubble tension—a review of solutions *

Contact Info

Product

Resources

About

In the realm of the Hubble tension—a review of solutions ^*