scholarly journals PPN parameters in gravitational theory with nonminimally derivative coupling

2017 ◽  
Vol 26 (02) ◽  
pp. 1750005 ◽  
Author(s):  
Zhu Yi ◽  
Yungui Gong
Keyword(s):  
Scalar Field ◽  
Gravitational Theory ◽  
Kinetic Term ◽  
Nonminimal Coupling ◽  
Derivative Coupling ◽  
Tensor Theory ◽  
Experimental Constraint ◽  
Stress Energy ◽  
Ppn Parameters ◽  
Dynamical Dark Energy

The nonminimal coupling of the kinetic term to Einstein’s tensor helps the implementation of inflationary models due to the gravitationally enhanced friction. We calculate the parametrized post-Newtonian (PPN) parameters for the scalar–tensor theory of gravity with nonminimally derivative coupling. We find that under experimental constraint from the orbits of millisecond pulsars in our galaxy, the theory deviates from Einstein’s general relativity in the order of [Formula: see text], and the effect of the nonminimal coupling is negligible if we take the scalar field as dynamical dark energy. With the assumed conditions that the background scalar field is spatially homogeneous and evolves only on cosmological timescales and the contribution to stress–energy in the solar system from the background scalar field is subdominant, the scalar field is required to be massless.

scholarly journals RECONSTRUCTING A STRING-INSPIRED NONMINIMALLY COUPLED QUINTOM MODEL

2009 ◽  
Vol 18 (08) ◽  
pp. 1291-1301 ◽  
Author(s):  
M. R. SETARE ◽  
J. SADEGHI ◽  
A. R. AMANI
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
String Theory ◽  
Scalar Curvature ◽  
Recent Work ◽  
Nonminimal Coupling ◽  
Tachyon Field ◽  
Dynamical Dark Energy

Motivated by the recent work of Zhang and Chen,1we generalize their work to the nonminimally coupled case. We consider a quintom model of dark energy with a single scalar field T given by a Lagrangian inspired by a tachyonic Lagrangian in string theory. We consider nonminimal coupling of the tachyon field to the scalar curvature, and then we reconstruct this model in the light of three forms of parametrization for dynamical dark energy.

scholarly journals Decaying Cosmological Constant and the Choice of a Conformal Frame

1999 ◽  
Vol 183 ◽  
pp. 310-310
Author(s):  
Yasunori Fujii
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Scalar Tensor Theory ◽  
Nonminimal Coupling ◽  
Tensor Theory ◽  
Theory Of Gravity ◽  
To Come ◽  
Hilbert Action

A solution of the cosomlogical constant problem seems to come from a version of the scalar-tensor theory of gravity, which is characterized by a “nonminimal coupling“ in place of the standard Einstein-Hilbert action, where ɸ is the scalar field while ξ a constant. One then encounters an inherent question never fully answered: How can one single out a right conformai frame?

scholarly journals Warm Inflation with Nonminimal Derivative Coupling

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Kourosh Nozari ◽  
M. Shoukrani ◽  
N. Rashidi
Keyword(s):  
Scalar Field ◽  
Observational Data ◽  
Kinetic Term ◽  
Model Parameters ◽  
Detailed Calculation ◽  
Data Set ◽  
Derivative Coupling ◽  
Warm Inflation ◽  
Inflation Model ◽  
Planck Satellite

We study the effects of the nonminimal derivative coupling on the dissipative dynamics of the warm inflation where the scalar field is nonminimally coupled to gravity via its kinetic term. We present a detailed calculation of the cosmological perturbations in this setup. We use the recent observational data from the joint data set of WMAP9 + BAO +H0and also the Planck satellite data to constrain our model parameters for natural and chaotic inflation potentials. We study also the levels of non-Gaussianity in this warm inflation model and we confront the result with recent observational data from the Planck satellite.

Tachyon cosmology with nonminimal derivative coupling

2012 ◽  
Vol 90 (10) ◽  
pp. 999-1005 ◽  
Author(s):  
A. Banijamali ◽  
J. Sadeghi ◽  
H. Vaez
Keyword(s):  
Asymptotic Behavior ◽  
Scalar Field ◽  
Cosmic Time ◽  
Gravitational Theory ◽  
Initial Time ◽  
Tachyon Field ◽  
Einstein Tensor ◽  
Cosmological Singularity ◽  
Derivative Coupling

In this paper we study a gravitational theory in which tachyons play the role of a scalar field. Also, nonminimal derivative coupling between tachyons and the Einstein tensor is considered in the model. We show that at the initial time, tachyon field behavior is exponential and its behavior at late times is liner in cosmic time. We investigate the asymptotic behavior of scale factor a(t) = eα(t) and show that in the limit t → ∞ it is impossible to have a constant [Formula: see text] and the model has an initial cosmological singularity (i.e., a ∝ (t – ti)2/β) in the limit t – ti.

scholarly journals Inflation driven by scalar field and solid matter

2019 ◽  
Vol 28 (04) ◽  
pp. 1950072
Author(s):  
Peter Mészáros
Keyword(s):  
Scalar Field ◽  
Rotational Symmetry ◽  
Kinetic Term ◽  
Nonlinearity Parameter ◽  
Energy Tensor ◽  
Solid Matter ◽  
Slow Roll ◽  
Stress Energy ◽  
Simple Generalization ◽  
Different Shapes

Solid inflation is a cosmological model where inflation is driven by fields which enter the Lagrangian in the same way as body coordinates of a solid matter enter the equation of state, spontaneously breaking spatial translational and rotational symmetry. We construct a simple generalization of this model by adding a scalar field with standard kinetic term to the action. In our model, the scalar power spectrum and the tensor-to-scalar ratio do not differ from the ones predicted by the solid inflation qualitatively, if the scalar field does not dominate the solid matter. The same applies also for the size of the scalar bispectrum measured by the nonlinearity parameter, although our model allows it to have different shapes. The tensor bispectra predicted by the two models do not differ from each other in the leading order of the slow-roll approximation. In the case when contribution of the solid matter to the stress-energy tensor is much smaller than the contribution from the scalar field, the tensor-to-scalar ratio and the nonlinearity parameter are amplified by factors [Formula: see text] and [Formula: see text], respectively.

scholarly journals FERMIONIC AND SCALAR FIELDS AS SOURCES OF INTERACTING DARK MATTER–DARK ENERGY

2011 ◽  
Vol 20 (13) ◽  
pp. 2543-2558 ◽  
Author(s):  
SAMUEL LEPE ◽  
JAVIER LORCA ◽  
FRANCISCO PEÑA ◽  
YERKO VÁSQUEZ
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Analytical Solution ◽  
Scalar Fields ◽  
Nonminimal Coupling ◽  
Field Equations ◽  
Fermionic Field ◽  
Minimal Coupling ◽  
Constant Type

From a variational action with nonminimal coupling with a scalar field and classical scalar and fermionic interaction, cosmological field equations can be obtained. Imposing a Friedmann–Lemaître–Robertson–Walker (FLRW) metric, the equations lead directly to a cosmological model consisting of two interacting fluids, where the scalar field fluid is interpreted as dark energy and the fermionic field fluid is interpreted as dark matter. Several cases were studied analytically and numerically. An important feature of the non-minimal coupling is that it allows crossing the barrier from a quintessence to phantom behavior. The insensitivity of the solutions to one of the parameters of the model permits it to find an almost analytical solution for the cosmological constant type of universe.

scholarly journals Spinning boson stars and hairy black holes with nonminimal coupling

2018 ◽  
Vol 27 (11) ◽  
pp. 1843009 ◽  
Author(s):  
Carlos A. R. Herdeiro ◽  
Eugen Radu
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Scalar Field ◽  
Coupling Parameter ◽  
Nonminimal Coupling ◽  
Boson Stars ◽  
Hairy Black Holes ◽  
Black Hole Solutions ◽  
Hairy Black Hole ◽  
Coupled Theory

We obtain spinning boson star solutions and hairy black holes with synchronized hair in the Einstein–Klein–Gordon model, wherein the scalar field is massive, complex and with a nonminimal coupling to the Ricci scalar. The existence of these hairy black holes in this model provides yet another manifestation of the universality of the synchronization mechanism to endow spinning black holes with hair. We study the variation of the physical properties of the boson stars and hairy black holes with the coupling parameter between the scalar field and the curvature, showing that they are, qualitatively, identical to those in the minimally coupled case. By discussing the conformal transformation to the Einstein frame, we argue that the solutions herein provide new rotating boson star and hairy black hole solutions in the minimally coupled theory, with a particular potential, and that no spherically symmetric hairy black hole solutions exist in the nonminimally coupled theory, under a condition of conformal regularity.

GALACTIC AND ASTROPHYSICAL SIZES FROM SCALAR-TENSOR THEORY OF GRAVITY

2004 ◽  
Vol 13 (02) ◽  
pp. 359-371 ◽  
Author(s):  
GIUSEPPE BASINI ◽  
MARCO RICCI ◽  
FULVIO BONGIORNO ◽  
SALVATORE CAPOZZIELLO
Keyword(s):  
Scalar Field ◽  
Spiral Galaxies ◽  
Weak Field ◽  
Newtonian Potential ◽  
Scalar Tensor Theory ◽  
Field Limit ◽  
Weak Field Limit ◽  
Tensor Theory ◽  
Flat Rotation Curves ◽  
Theory Of Gravity

We investigate the weak-field limit of scalar-tensor theory of gravity and show that results are directly depending on the coupling and self-interaction potential of the scalar field. In particular, corrections are derived for the Newtonian potential. We discuss astrophysical applications of the results, in particular the flat rotation curves of spiral galaxies.

scholarly journals Thick branes in the scalar–tensor representation of f(R, T) gravity

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
João Luís Rosa ◽  
Matheus A. Marques ◽  
Dionisio Bazeia ◽  
Francisco S. N. Lobo
Keyword(s):  
Scalar Field ◽  
Matter Field ◽  
Energy Tensor ◽  
Tensor Representation ◽  
Observable Universe ◽  
Brane Model ◽  
Gravitational Fields ◽  
Stress Energy ◽  
Tensor Representations ◽  
The Stability

AbstractBraneworld scenarios consider our observable universe as a brane embedded in a five-dimensional bulk. In this work, we consider thick braneworld systems in the recently proposed dynamically equivalent scalar–tensor representation of f(R, T) gravity, where R is the Ricci scalar and T the trace of the stress–energy tensor. In the general $$f\left( R,T\right) $$ f R , T case we consider two different models: a brane model without matter fields where the geometry is supported solely by the gravitational fields, and a second model where matter is described by a scalar field with a potential. The particular cases for which the function $$f\left( R,T\right) $$ f R , T is separable in the forms $$F\left( R\right) +T$$ F R + T and $$R+G\left( T\right) $$ R + G T , which give rise to scalar–tensor representations with a single auxiliary scalar field, are studied separately. The stability of the gravitational sector is investigated and the models are shown to be stable against small perturbations of the metric. Furthermore, we show that in the $$f\left( R,T\right) $$ f R , T model in the presence of an extra matter field, the shape of the graviton zero-mode develops internal structure under appropriate choices of the parameters of the model.

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