Nonminimal Coupling Of Scalar Field Research Articles

Non-minimal coupling, negative null energy, and effective field theory

The non-minimal coupling of scalar fields to gravity has been claimed to violate energy conditions, leading to exotic phenomena such as traversable wormholes, even in classical theories. In this work we adopt the view that the non-minimal coupling can be viewed as part of an effective field theory (EFT) in which the field value is controlled by the theory’s cutoff. Under this assumption, the average null energy condition, whose violation is necessary to allow traversable wormholes, is obeyed both classically and in the context of quantum field theory. In addition, we establish a type of "smeared" null energy condition in the non-minimally coupled theory, showing that the null energy averaged over a region of spacetime obeys a state dependent bound, in that it depends on the allowed field range. We finally motivate our EFT assumption by considering when the gravity plus matter path integral remains semi-classically controlled.

Non-minimal unimodular inflation

We study an extension of the unimodular cosmological inflation in the context of the non-minimal coupling of a generic scalar field with gravitational sector. We consider the non-minimal coupling of the scalar field and gravity as the only source of energy–momentum tensor in this setup. Without introducing new particles other than those already existing in electroweak theory, the generic scalar field’s non-minimal coupling is responsible for the generation of the seeds of perturbations for structure formation and the observed Cosmic Microwave Background anisotropies in this scenario. We calculate inflation parameters in both the Jordan and Einstein frames, and then we study primordial spectral indices for slow-roll parameters in Einstein’s frame at the first and second orders. The numerical results of this model are consistent with the Planck2018 and BICEP/Keck joint data sets in some subspaces of the model parameters space. By considering a sufficient amount of inflation, we estimate the strength of the non-minimal coupling parameter, ξ, to find appropriate new constraints on the values of this parameter. By comparing the numerical values of the inflation observables in two frames and also with observation, we comment on the issue of frames in this framework.

Nonlinearity analysis for cosmological inflation with minimal and non-minimal coupling of scalar field from horndeski theory for special cases: de sitter expansion and decaying scalar field

In this work, we consider De Sitter expansion and decaying scalar field in cosmological model with combination of minimal and non-minimal coupling of scalar field from Horndeski theory. As a continuity of the previous work, after the background solution and condition obtained, we continue the analysis to the nonlinearity aspect of perturbations via the spectral index of the perturbations. Spectral index of the perturbations and tensor to-scalar ratio of these special cases give sign of inflation model.

Inflation and Reheating in f(R,h) theory formulated in the Palatini formalism

A new model for inflation using modified gravity in the Palatini formalism is constructed. Here non-minimal coupling of scalar field h with the curvature R as a general function f(R,h) is considered. Explicit inflation models for some choices of f(R,h) are developed. By writing an equivalent scalar-tensor action for this model and going over to Einstein frame, slow roll parameters are constructed. There exists a large parameter space for different choices of f(R,h) and potentials which satisfy values of n s and limits on r compatible with Planck 2018 data. Further, we calculate reheating temperature and the number of e-folds at the end of reheating for different values of equation of state parameter for all the constructed models.

Non-linearity analysis for cosmological inflation model with minimal and non-minimal coupling of scalar field from Horndeski theory

In this work, we analyze the non-linearity aspect of perturbations generated in early times for cosmological inflation model with minimal and non-minimal couplings of scalar field from Horndeski theory. We study the spectral index of the perturbations and tensor-to-scalar ratio and can be seen as the evidence for inflation for some responsible coupling constant. We get the sign of non-linearity from the spectral index and tensor-to-scalar ratio for this model, and this result can be analyzed further to find non-Gaussianity.

Cosmological inflation with minimal and non-minimal coupling of scalar field from Horndeski theory

We consider a cosmological model with combination of minimal and non-minimal coupling of scalar field by considering a set of particular coefficient function from Horndeski theory. We study cosmological inflation from the background solution and get the responsible coupling constant regarding the slow-roll inflation parameters. Then we compare the result with the stability conditions to get the exact value of coupling constant for this cosmological model.

Hawking Radiation for Non-Minimally Coupled Matter from Generalized 2-D Black Hole Models

It is well known that spherically symmetric reduction of general relativity (SSG) leads to non-minimally coupled scalar matter. We generalize (and correct) recent results to Hawking radiation for a class of dilaton models which share with the Schwarzschild black hole non-minimal coupling of scalar fields and the basic global structure. An inherent ambiguity of such models (if they differ from SSG) is discussed. However, for SSG we obtain the rather disquieting result of a negative Hawking flux at infinity, if the usual recipe for such calculations is applied.

Hierarchies from supergravity

We discuss a non-minimal coupling of scalar fields to supergravity. As well as spontaneous local supersymmetry breaking and a vanishing cosmological constant we can obtain a gravitino mass ∼ 100 GeV without introducing a mass scale different from the Planck scale.