arXiv subjects

K. A. Bronnikov

Publications and source records attributed to K. A. Bronnikov.

At least 127 records · Page 7Linked to original sources

arXiv2001

Measurement of the gravitational constant $G$ in space (Project SEE): sensitivity to orbital parameters and space charge effect

We describe some new estimates concerning the recently proposed SEE (Satellite Energy Exchange) experiment for measuring the gravitational interaction parameters in space. The experiment entails precision tracking of the relative motion of two test bodies (a heavy "Shepherd", and a light "Particle") on board a drag-free space capsule. The new estimates include (i) the sensitivity of Particle trajectories and G measurement to the Shepherd quadrupole moment uncertainties; (ii) the measurement errors of G and the strength of a putative Yukawa-type force whose range parameter λmay be either of the order of a few meters or close to the Earth radius; (iii) a possible effect of the Van Allen radiation belts on the SEE experiment due to test body electric charging. The main conclusions are that (i) the SEE concept may allow one to measure G with an uncertainty smaller than 10^{-7} and a progress up to 2 orders of magnitude is possible in the assessment of the hypothetic Yukawa forces and (ii) van Allen charging of test bodies is a problem of importance but it may be solved by the existing methods.

gr-qc↗

arXiv2001

On Observational Predictions from Multidimensional Gravity

We discuss possible observational manifestations of static, spherically symmetric solutions of a class of multidimensional theories of gravity, which includes the low energy limits of supergravities and superstring theories as special cases. We discuss the choice of a physical conformal frame to be used for the description of observations. General expressions are given for (i) the Eddington parameters $β$ and $γ$, characterizing the post-Newtonian gravitational field of a central body, (ii) p-brane black hole temperatures in different conformal frames and (iii) the Coulomb law modified by extra dimensions. It is concluded, in particular, that $β$ and $γ$ depend on the integration constants and can be therefore different for different central bodies. If, however, the Einstein frame is adopted for describing observations, we always obtain $γ=1$. The modified Coulomb law is shown to be independent of the choice of a 4-dimensional conformal frame. We also argue the possible existence of specific multidimensional objects, T-holes, potentially observable as bodies with mirror surfaces.

gr-qc↗

arXiv2001

Cylindrically Symmetric Solitons with Nonlinear Self-Gravitating Scalar Fields

Static, cylindrically symmetric solutions to nonlinear scalar-Einstein equations are considered. Regularity conditions on the symmetry axis and flat or string asymptotic conditions are formulated in order to select soliton-like solutions. Some non-existence theorems are proved, in particular, theorems asserting (i) the absence of black-hole and wormhole-like cylindrically symmetric solutions for any static scalar fields minimally coupled to gravity and (ii) the absence of solutions with a regular axis for scalar fields with the Lagrangian $L=F(I)$, $I=ϕ^αϕ_α$, for any function $F(I)$ possessing a correct weak field limit. Exact solutions for scalar fields with an arbitrary potential function $V(ϕ)$ are obtained by quadratures and are expressed in a parametric form in a few ways, where the parameter may be either the coordinate $x$, or the $ϕ$ field, or one of the metric coefficients. Soliton-like solutions are shown to exist only with $V(ϕ)$ having a variable sign. Some explicit examples of solutions (including a soliton-like one) and their flat-space limit are discussed.}

gr-qc↗

arXiv2000

See Project for Testing Gravity in Space: Current Status and New Estimates

gr-qc↗

arXiv2000

p-Brane Black Holes as Stability Islands

In multidimensional gravity with an arbitrary number of internal Ricci-flat factor spaces, interacting with electric and magnetic $p$-branes, spherically symmetric configurations are considered. It is shown that all single-brane black-hole solutions are stable under spherically symmetric perturbations, whereas similar solutions possessing naked singularities turn out to be catastrophically unstable. The black hole stability conclusion is extended to some classes of configurations with intersecting branes. These results do not depend on the particular composition of the $D$-dimensional space-time, on the number of dilatonic scalar fields $ϕ^a$ and on the values of their coupling constants. Some examples from 11-dimensional supergravity are considered.

hep-th↗

arXiv1999

Block-Orthogonal Brane Systems, Black Holes and Wormholes

Multidimensional cosmological, static spherically symmetric and Euclidean configurations are described in a unified way for gravity interacting with several dilatonic fields and antisymmetric forms, associated with electric and magnetic p-branes. Exact solutions are obtained when certain vectors, built from the input parameters of the model, are either orthogonal in the minisuperspace, or form mutually orthogonal subsystems. Some properties of black-hole solutions are indicated, in particular, a no-hair-type theorem and restrictions emerging in models with multiple times. From the non-existence of Lorentzian wormholes, a universal restriction is obtained, applicable to orthogonal or block-orthogonal subsystems of any p-brane systems. Euclidean wormhole solutions are found, their actions and radii are explicitly calculated.

hep-th↗

arXiv1999

Electrically Charged Cold Black Holes in Scalar-Tensor Theories

We study the possible existence of charged and neutral black holes in the Bergmann-Wagoner class of scalar-tensor theories (STT) of gravity in four dimensions. The existence of black holes is shown for anomalous versions of these theories, with a negative kinetic term in the Lagrangian. The Hawking temperature of these holes is zero, while the horizon area is (in most cases) infinite. As a special case, the Brans-Dicke theory is studied in more detail, and two kinds of infinite-area black holes are revealed, with finite and infinite proper time needed for an infalling particle to reach the horizon; among them, analyticity properties select a discrete subfamily of solutions, parametrized by two integers, which admit an extension beyond the horizon. The causal structure and stability of these solutions with respect to small radial perturbations is discussed. As a by-product, the stability properties of all spherically symmetric electrovacuum STT solutions are outlined.

gr-qc↗

arXiv1998

Gravitating Brane Systems: Some General Theorems

Multidimensional gravity interacting with intersecting electric and magnetic $p$-branes is considered for fields depending on a single variable. Some general features of the system behaviour are revealed without solving the field equations. Thus, essential asymptotic properties of isotropic cosmologies are indicated for different signs of spatial curvature; a no-hair-type theorem and a single-time theorem for black holes are proved (the latter makes sense in models with multiple time coordinates). The validity of the general observations is verified for a class of exact solutions known for the cases when certain vectors, built from the input parameters of the model, are either orthogonal in minisuperspace, or form mutually orthogonal subsystems. From the non-existence of Lorentzian wormholes, a universal restriction is obtained, applicable to orthogonal or block-orthogonal subsystems of any $p$-brane system.

gr-qc↗

arXiv1998

Cold Scalar-Tensor Black Holes: Causal Structure, Geodesics, Stability

We study the structure and stability of spherically symmetric Brans-Dicke black-hole type solutions with an infinite horizon area and zero Hawking temperature, existing for negative values of the coupling constant $ω$. These solutions split into two classes, depending on finite (B1) or infinite (B2) proper time needed for an infalling particle to reach the horizon. Class B1 metrics can be extended through the horizon only for discrete values of mass and scalar charge, depending on two integers m and n. For even m-n, the space-time is globally regular; for odd m, the metric changes its signature on the horizon but remains Lorentzian. Geodesics are smoothly continued across the horizon, but for odd m timelike geodesics become spacelike and vice versa. Causality problems, arising in some cases, are discussed. Tidal forces are shown to grow infinitely near type B1 horizons. All vacuum static, spherically symmetric solutions of the Brans-Dicke theory with $ω<-3/2$ are found to be linearly stable against spherical perturbations. This result extends to the generic case of the Bergmann-Wagoner class of scalar-tensor theories with the coupling function $ω(ϕ) < -3/2$.

gr-qc↗

arXiv1998

Structure and stability of cold scalar-tensor black holes

We study the structure and stability of the recently discussed spherically symmetric Brans-Dicke black-hole type solutions with an infinite horizon area and zero Hawking temperature, existing for negative values of the coupling constant $ω$. These solutions split into two classes: B1, whose horizon is reached by an infalling particle in a finite proper time, and B2, for which this proper time is infinite. Class B1 metrics are shown to be extendable beyond the horizon only for discrete values of mass and scalar charge, depending on two integers $m$ and $n$. In the case of even $m-n$ the space-time is globally regular; for odd $m$ the metric changes its signature at the horizon. All spherically symmetric solutions of the Brans-Dicke theory with $ω<-3/2$ are shown to be linearly stable against spherically symmetric \pns. This result extends to the generic case of the Bergmann-Wagoner class of scalar-tensor theories of gravity with the coupling function $ω(ϕ) < -3/2$.

gr-qc↗

arXiv1997

Cold black holes in scalar-tensor theories

We study the possible existence of black holes in scalar-tensor theories of gravity in four dimensions. Their existence is verified for anomalous versions of these theories, with a negative kinetic term in the Lagrangian. The Hawking temperature T_H of these holes is zero, while the horizon area is (in most cases) infinite. It is shown that an infinite value of T_H can occur only at a curvature singularity rather than a horizon. As a special case, the Brans-Dicke theory is studied in more detail, and two kinds of infinite-area black holes are revealed, with finite and infinite proper time needed for an infalling particle to reach the horizon.

gr-qc↗

arXiv1997

The Reissner-Nordstrom Problem for Intersecting Electric and Magnetic p-Branes

A multidimensional model with (at most) one curved factor space and n Ricci-flat internal spaces is considered, with arbitrary numbers of dilatonic scalar fields and antisymmetric forms of both electric and magnetic types, associated with p-branes in theories like M-theory. The problem setting covers, in particular, homogeneous cosmologies, static, spherically symmetric and Euclidean models. Exact solutions are obtained when the p-brane dimensions and the dilatonic couplings obey orthogonality conditions in minisuperspace. Conditions for black hole and wormhole existence among static models are formulated. For black holes, a kind of no-hair theorem, leading to F-form selection, is obtained; it is shown that even in spaces with multiple times a black hole may only exist with its unique, one-dimensional time; infinite Hawking temperature is explicitly shown to imply a curvature singularity at an assumed horizon, and such cases among extreme black-hole solutions are indicated.

gr-qc↗

arXiv1997

Integrable Multidimensional Cosmology for Intersecting $p$-Branes

A multidimensional field model describing the behaviour of (at most) one Einstein space of non-zero curvature and n Ricci-flat internal spaces is considered. The action contains several dilatonic scalar fields and antisymmetric forms. The problem setting covers various problems with field dependence on a single space-time coordinate, in particular, isotropic and anisotropic homogeneous cosmologies. When the forms are chosen to be proportional to volume forms of p-brane factor spaces, a Toda-like Lagrange representation arises. Exact solutions are obtained when the p-brane dimensions and the dilatonic couplings obey some orthogonality conditions. General features and some special cases of cosmological solutions are discussed. It is shown, in particular, that all hyperbolic models with a 3-dimensional external space possess an asymptotic with the external scale factor a(t) is proportional to |t| (the cosmic time), while all internal scale factors and all scalar fields tend to finite limits. For D=11 a family of models with one 5-brane and three 2-branes is described.

gr-qc↗

arXiv1997

Intersecting electric and magnetic p-branes: spherically symmetric solutions

We consider a D-dimensional self-gravitating spherically symmetric configuration of a generalized electro-magnetic n-form F and a dilatonic scalar field, admitting an interpretation in terms of intersecting p-branes. For theories with multiple times, selection rules are obtained, which obstruct the existence of p-branes in certain subspaces. General static solutions are obtained under a specific restriction on the model parameters, which corresponds to the known "intersection rules". More special families of solutions (with equal charges for some of the F-field components) are found with weakened restrictions on the input parameters. Black-hole solutions are determined, and it is shown that in the extreme limit the Hawking temperature may tend to zero, a finite value, or infinity, depending on the p-brane intersection dimension. A kind of no-hair theorem is obtained, claiming that black holes cannot coexist with a quasiscalar component of the F-field.

gr-qc↗

arXiv1995

ON SPHERICALLY SYMMETRIC SOLUTIONS IN D-DIMENSIONAL DILATON GRAVITY

Exact static, spherically symmetric solutions to the Einstein-Abelian gauge-dilaton equations, in $D$-dimensional gravity with a chain of $n$ Ricci-flat internal spaces are considered, with the gauge field potential having three nonzero components: the temporal, Coulomb-like one, the one pointing to one of the extra dimensions, and the one responsible for a radial magnetic field. For dilaton coupling implied by string theory an $(n+5)$-parametric family of exact solutions is obtained, while for other dilaton couplings only $(n+3)$-parametric ones. The geometric properties and special cases of the solutions are discussed, in particular, those when there are horizons in the space-time. Two types of horizons are distinguished: the conventional black-hole (BH) ones and those at which the physical section of the space-time changes its signature ({\it T-horizons}). Two theorems are proved, one fixing the BH and T-horizon existence conditions, the other discarding the possibility of a regular center. Different conformal gauges are used to characterize the system from the $D$-dimensional and 4-dimensional viewpoints.

gr-qc↗

arXiv1995

VACUUM STATIC, AXIALLY SYMMETRIC FIELDS IN D-DIMENSIONAL GRAVITY

Vacuum static, axially symmetric space-times in $D$-dimensional general relativity with a Ricci-flat internal space are discussed. It is shown, in particular, that some of the monopole-type solutions are free of curvature singularities and their source can be a disk membrane bounded by a ring with a string or branching type singularity. Another possibility is a wormhole configuration where a particle can penetrate to another spatial infinity by passing through a ring with a string or branching type singularity. The results apply, in particular, to vacuum and scalar-vacuum configurations in conventional general relativity.

gr-qc↗

arXiv1994

Vacuum Weyl Cosmologies in D Dimensions

Vacuum cosmological models are considered in the context of a multidimensional theory of gravity with integrable Weyl geometry. A family of exact solutions with a chain of internal spaces is obtained. Models with one internal space are considered in more detail; nonsingular models are selected.

gr-qc↗

arXiv1994

Extra Dimensions and Possible Space-Time Signature Changes

Exact static, spherically symmetric solutions to the Einstein-Maxwell-scalar equations, with a dilatonic-type scalar-vector coupling, in $D$-dimensional gravity with a chain of $n$ Ricci-flat internal spaces are considered, with the Maxwell field potential having two nonzero components: the temporal, Coulomb-like one and the one pointing to one of the extra dimensions. The properties and special cases of the solutions are discussed, in particular, those when there are horizons in the space-time. Two types of horizons are distinguished: the conventional black-hole (BH) ones and those at which the physical section of the space-time changes its signature (the latter are called {\it T-horizons}). Two theorems are proved, one fixing the BH- and T-horizon existence conditions, the other claiming that the system under study cannot have a regular center. The stability of a selected family of solutions under spherically symmetric perturbations is studied. It is shown that only black-hole solutions are stable, while all others, in particular, those with T-horizons are unstable.

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