24 research outputs found

### Analytical approximation for $< \phi^2 >$ of a quantized scalar field in ultrastatic asymptotically flat spacetimes

Analytical approximations for of a quantized scalar field in
ultrastatic asymptotically flat spacetimes are obtained. The field is assumed
to be both massive and massless, with an arbitrary coupling $\xi$ to the scalar
curvature, and in a zero or nonzero temperature vacuum state. The expression
for is divided into low- and high-frequency parts. The expansion
for the high-frequency contribution to this quantity is obtained. This
expansion is analogous to the DeWitt-Schwinger one. As an example, the
low-frequency contribution to $$ is calculated on the background of
the small perturbed flat spacetime in a quantum state corresponding to the
Minkowski vacuum at the asymptotic. The limits of the applicability of these
approximations are discussed.Comment: revtex4, 9 page

### Quantum-corrected ultraextremal horizons and validity of WKB in massless limit

We consider quantum backreaction of the quantized scalar field with an
arbitrary mass and curvature coupling on ultraextremal horizons. The problem is
distinguished in that (in contrast to non-extremal or extremal black holes) the
WKB approximation remains valid near $r_{+}$ (which is the radius of the
horizon) even in the massless limit. We examine the behavior of the
stress-energy tensor of the quantized field near $r_{+}$ and show that
quantum-corrected objects under discussion do exist. In the limit of the large
mass our results agree with previous ones known in literature.Comment: revtex4, 9 page

### Inhomogeneous compact extra dimensions and de Sitter cosmology

In the framework of multidimensional $f(R)$ gravity, we study the metrics of
compact extra dimensions assuming that our 4D space has the de Sitter metric.
Manifolds described by such metrics could be formed at the inflationary and
even higher energy scales. It is shown that in the presence of a scalar field,
varying in the extra factor space $\mathbb{M}_2$, it is possible to obtain a
variety of inhomogeneous metrics in $\mathbb{M}_2$. Each of these metrics leads
to a certain value of the 4D cosmological constant $\Lambda_4$, and in
particular, it is possible to obtain $\Lambda_4 =0$, as is confirmed by
numerically obtained solutions. A nontrivial scalar field distribution in the
extra dimensions is an important feature of this family of models.Comment: 15 pages, 9 figure

### Sub-Planckian scale and limits for $f(R)$ models

We study the Universe evolution starting from the sub-Planckian scale to
present times. The requirement for an exponential expansion of the space with
the observed metric as a final stage leads to significant restrictions on the
parameter values of a $f(R)$-function. An initial metric of the Universe is
supposed to be maximally symmetric with the positive curvature

### Propagation of Gravitational Waves in Chern-Simons Axion Einstein Gravity

In this paper we shall investigate the propagation of gravitational waves in
a flat Friedman-Robertson-Walker background, in the context of a string
motivated corrected Einstein gravity. Particularly, we shall consider a
misalignment axion Einstein gravity in the presence of a string originating
Chern-Simons coupling of the axion field to the Chern-Pontryagin density in
four dimensions. We shall focus our study on the propagation of the
gravitational waves, and we shall investigate whether there exists any
difference in the propagation of the polarization states of the gravitational
waves. As we demonstrate, the dispersion relations are different in the
Right-handed mode and the Left-handed mode. Finally, we compare the propagation
of the axion Chern-Simons Einstein theory with that of standard $F(R)$ gravity.Comment: PRD Accepted. arXiv admin note: text overlap with arXiv:1907.0162

### Analytical approximation of the stress-energy tensor of a quantized scalar field in static spherically symmetric spacetimes

Analytical approximations for ${}$ and ${}$ of a
quantized scalar field in static spherically symmetric spacetimes are obtained.
The field is assumed to be both massive and massless, with an arbitrary
coupling $\xi$ to the scalar curvature, and in a zero temperature vacuum state.
The expressions for ${}$ and ${}$ are divided into
low- and high-frequency parts. The contributions of the high-frequency modes to
these quantities are calculated for an arbitrary quantum state. As an example,
the low-frequency contributions to ${}$ and ${}$ are
calculated in asymptotically flat spacetimes in a quantum state corresponding
to the Minkowski vacuum (Boulware quantum state). The limits of the
applicability of these approximations are discussed.Comment: revtex4, 17 pages; v2: three references adde

### Self-force of a point charge in the space-time of a massive wormhole

We consider the self-potential and the self-force for an electrically charged
particle at rest in the massive wormhole space-time. We develop general
approach for the renormalization of electromagnetic field of such particle in
the static space-times and apply it to the space-time of the wormhole with
parameter of the mass, $m$. The self-force is found in manifest form; it is an
attractive force. We discus the peculiarities due to massive parameter of the
wormhole.Comment: 10 pages, 1 figure text correcte

### Self-force on a scalar point charge in the long throat

An analytic method is presented which allows for the computation of the
self-force for a static particle with a scalar charge in the region of an
ultrastatic spacetime which one can call the long throat. The method is based
on the approximate WKB solution of a radial mode equation for a scalar field.
This field is assumed to be massless, with a coupling $\xi$ to the scalar
curvature is satisfying the condition $\xi>1/8$.Comment: 11 pages, 1 figur