Energy-momentum Tensor Of Scalar Field Research Articles

The Parameterized Post-Friedmannian Framework for Nonminimal Derivative Coupling with General Cosmological Perturbation Metric

We study the parameterization of cosmological model where derivative of an additional scalar field coupled to curvature tensor. We extend the Parameterized Post-Friedmannian framework for interacting dark energy theories to the model. Starting from general cosmological perturbation metric, we derive perturbed energy-momentum tensor for scalar field and parameterized the tensor. Based on the value of the parameters, we compare the model with relevant models in current literature. As the results, we find that parameterization for type 1 theories of dark energy which is explicitly coupled to dark matter, gives only 4 non-zero Parameterized Post-Friedmannian coefficients.

Scalar particle production in a simple Horndeski theory

The scalar particle production through a scalar field nonminimally coupled with geometry is investigated in the context of a spatially homogeneous and isotropic Universe. In this paper, to study the evolution of particle production over time in the case of analytical solutions, we focus on a simple Horndeski theory. We first suppose that the Universe is dominated by a scalar field and derive the energy conservation condition. Then, from the thermodynamic point of view, the macroscopic nonconservation of the scalar field energy-momentum tensor can be explained as an irreversible production of the scalar particles. Based on the explanation, we obtain a scalar particle-production rate and the corresponding entropy. Finally, since the Universe, in general, could be regarded as a closed system satisfying the laws of thermodynamics, we naturally impose some thermodynamic constraints on it. The thermodynamic properties of the Universe can provide additional constraints on the simple Horndeski theory.

Vacuum polarization and classical self-action near higher-dimensional defects

We analyze the gravity-induced effects associated with a massless scalar field in a higher-dimensional spacetime being the tensor product of (d-n)-dimensional Minkowski space and n-dimensional spherically/cylindrically symmetric space with a solid/planar angle deficit. These spacetimes are considered as simple models for a multidimensional global monopole (if ngeqslant 3) or cosmic string (if n=2) with (d-n-1) flat extra dimensions. Thus, we refer to them as conical backgrounds. In terms of the angular-deficit value, we derive the perturbative expression for the scalar Green function, valid for any dgeqslant 3 and 2leqslant nleqslant d-1, and compute it to the leading order. With the use of this Green function we compute the renormalized vacuum expectation value of the field square {langle phi ^{{}2}(x)rangle }_{mathrm{ren}} and the renormalized vacuum averaged of the scalar-field energy-momentum tensor {langle T_{M N}(x)rangle }_{mathrm{ren}} for arbitrary d and n from the interval mentioned above and arbitrary coupling constant to the curvature xi . In particular, we revisit the computation of the vacuum polarization effects for a non-minimally coupled massless scalar field in the spacetime of a straight cosmic string. The same Green function enables to consider the old purely classical problem of the gravity-induced self-action of a classical point-like scalar or electric charge, placed at rest at some fixed point of the space under consideration. To deal with divergences, which appear in consideration of the two problems, we apply the dimensional-regularization technique, widely used in quantum field theory. The explicit dependence of the results upon the dimensionalities of both the bulk and conical submanifold is discussed.

Exact hairy black holes and their modification to the universal law of gravitation

In this paper two things are done. First, it is pointed out the existence of exact asymptotically flat, spherically symmetric black holes when a self interacting, minimally coupled scalar field is the source of the energy momentum of the Einstein equations in four dimensions. The scalar field potential is the recently found to be compatible with the hairy generalization of the Plebanski-Demianski solution of general relativity. This paper describes the spherically symmetric solutions that smoothly connect the Schwarzschild black hole with its hairy counterpart. The geometry and scalar field are everywhere regular except at the usual Schwarzschild like singularity inside the black hole. The scalar field energy momentum tensor satisfies the null energy condition in the static region of the spacetime. The first law holds when the parameters of the scalar field potential are fixed under thermodynamical variation. Secondly, it is shown that an extra, dimensionless parameter, present in the hairy solution, allows to modify the gravitational field of a spherically symmetric black hole in a remarkable way. When the dimensionless parameter is increased, the scalar field generates a flat gravitational potential, that however asymptotically matches the Schwarzschild gravitational field. Finally, it is shown that a positive cosmological constant can render the scalar field potential convex if the parameters are within a specific rank.

Vacuum polarization of a scalar field on lie groups and homogeneous spaces

We propose a method for calculating vacuum means of the scalar field energy-momentum tensor on Lie groups and homogeneous spaces. We use the generalized harmonic analysis based on the method of coadjoint representation orbits.

Renormalized energy-momentum tensor of λ Φ4 theory in curved space-time

Divergenceless expression for the energy-momentum tensor of scalar field is obtained using the momentum cut-off regularization technique. We consider a scalar field with quartic self-coupling in a spatially flat (3+1)-dimensional Robertson-Walker space-time, having arbitrary mass and coupled to gravity. As special cases, energy-momentum tensor for conformal and minimal coupling are also obtained. The energy-momentum tensor is observed to exhibit trace anomaly in curved space-time

On the Energy-Momentum Tensor of the Scalar Field in Scalar–Tensor Theories of Gravity

We study the dynamical description of gravity, the appropriate definition of the scalar field energy-momentum tensor, and the interrelation between them in scalar-tensor theories of gravity. We show that the quantity which one would naively identify as the energy-momentum tensor of the scalar field is not appropriate because it is spoiled by a part of the dynamical description of gravity. A new connection can be defined in terms of which the full dynamical description of gravity is explicit, and the correct scalar field energy-momentum tensor can be immediately identified. Certain inequalities must be imposed on the two free functions (the coupling function and the potential) that define a particular scalar-tensor theory, to ensure that the scalar field energy density never becomes negative. The correct dynamical description leads naturally to the Einstein frame formulation of scalar-tensor gravity which is also studied in detail.