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Bronnikov K.A.,Institute of Gravitation and Cosmology | Konoplya R.A.,University of Cambridge | Zhidenko A.,Federal University of ABC
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We test the stability of various wormholes and black holes supported by a scalar field with a negative kinetic term. The general axial perturbations and the monopole type of polar perturbations are considered in the linear approximation. Two classes of objects are considered: (i) wormholes with flat asymptotic behavior at one end and anti-de Sitter on the other (Minkowski-anti-de Sitter wormholes) and (ii) regular black holes with asymptotically de Sitter expansion far beyond the horizon (the so-called black universes). A difficulty in such stability studies is that the effective potential for perturbations forms an infinite wall at throats, if any. Its regularization is in general possible only by numerical methods, and such a method is suggested in a general form and used in the present paper. As a result, we have shown that all configurations under study are unstable under spherically symmetric perturbations, except for a special class of black universes where the event horizon coincides with the minimum of the area function. For this stable family, the frequencies of quasinormal modes of axial perturbations are calculated. © 2012 American Physical Society.


Bronnikov K.A.,Institute of Gravitation and Cosmology | Krechet V.G.,Yaroslavl State University | Lemos J.P.S.,University of Lisbon
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We consider stationary, cylindrically symmetric configurations in general relativity and formulate necessary conditions for the existence of rotating cylindrical wormholes. It is shown that in a comoving reference frame, the rotational part of the gravitational field is separated from its static part and forms an effective stress-energy tensor with exotic properties, which favors the existence of wormhole throats. Exact vacuum and scalar-vacuum solutions (with a massless scalar) are considered as examples, and it turns out that even vacuum solutions can be of wormhole nature. However, solutions obtainable in this manner cannot have well-behaved asymptotic regions, which excludes the existence of wormhole entrances appearing as local objects in our Universe. To overcome this difficulty, we try to build configurations with flat asymptotic regions by the cut-and-paste procedure: on both sides of the throat, a wormhole solution is matched to a properly chosen region of flat space at surfaces Σ- and Σ+. It is shown, however, that if we describe the throat region with vacuum or scalar-vacuum solutions, one or both thin shells appearing on Σ- and Σ+ inevitably violate the null energy condition. In other words, although rotating wormhole solutions are easily found without exotic matter, such matter is still necessary for obtaining asymptotic flatness. © 2013 American Physical Society.


Bronnikov K.A.,Institute of Gravitation and Cosmology | Fabris J.C.,Federal University of Espirito Santo | Zhidenko A.,Federal University of ABC
European Physical Journal C | Year: 2011

We study the stability of static, spherically symmetric solutions to the Einstein equations with a scalar field as the source. We describe a general methodology of studying small radial perturbations of scalar-vacuum configurations with arbitrary potentials V(φ) and in particular space-times with throats (including wormholes), which are possible if the scalar is phantom. At such a throat, the effective potential for perturbations Veff has a positive pole (a potential wall) that prevents a complete perturbation analysis. We show that, generically, (i) Veff has precisely the form required for regularization by the known S-deformation method, and (ii) a solution with the regularized potential leads to regular scalar field and metric perturbations of the initial configuration. The well-known conformal mappings make these results also applicable to scalar-tensor and f(R) theories of gravity. As a particular example, we prove the instability of all static solutions with both normal and phantom scalars and V(φ) ≡ 0 under spherical perturbations. We thus confirm the previous results on the unstable nature of anti-Fisher wormholes and Fisher’s singular solution and prove the instability of other branches of these solutions including the anti-Fisher “cold black holes.”. © Springer-Verlag / Società Italiana di Fisica 2011.


Bolokhov S.V.,PFUR | Bronnikov K.A.,Institute of Gravitation and Cosmology | Rubin S.G.,National Research Nuclear University MEPhI
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The Higgs boson of the standard model is described by a set of off-diagonal components of the multidimensional metric tensor, as well as the gauge fields. In the low-energy limit, the basic properties of the Higgs boson are reproduced, including the shape of the potential and interactions with the gauge fields of the electroweak part of the standard model. © 2011 American Physical Society.


Bronnikov K.A.,Institute of Gravitation and Cosmology | Sushkov S.V.,Tatar State University of Humanities and Education
Classical and Quantum Gravity | Year: 2010

We construct examples of static, spherically symmetric wormhole solutions in general relativity with a minimally coupled scalar field whose kinetic energy is negative in a restricted region of space near the throat (of arbitrary size) and positive far away from it. Thus in such configurations a 'ghost' is trapped in the strong-field region, which may in principle explain why no ghosts are observed under usual conditions. Some properties of general wormhole models with the field are revealed: it is shown that (i) trapped-ghost wormholes are only possible with nonzero potentials V(); (ii) in wormholes with two asymptotically flat regions, a nontrivial potential V() has an alternate sign and (iii) a wormhole with two asymptotically flat regions which is mirror symmetric with respect to its throat has necessarily a zero Schwarzschild mass at both asymptotics. © 2010 IOP Publishing Ltd.


Bronnikov K.A.,Institute of Gravitation and Cosmology | Zaslavskii O.B.,University of Kharkiv
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

We study the conditions of a possible static equilibrium between spherically symmetric, electrically charged or neutral black holes and ambient matter. The following kinds of matter are considered: (1) neutral and charged matter with a linear equation of state pr=wρ (for neutral matter the results of our previous work are reproduced), (2) neutral and charged matter with pr∼ρm, m>1, and (3) the possible presence of a "vacuum fluid" (the cosmological constant or, more generally, anything that satisfies the equality T00=T11 at least at the horizon). We find a number of new cases of such an equilibrium, including those generalizing the well-known Majumdar-Papapetrou conditions for charged dust. It turns out, in particular, that ultraextremal black holes cannot be in equilibrium with any matter in the absence of a vacuum fluid; meanwhile, matter with w>0, if it is properly charged, can surround an extremal charged black hole. © 2011 American Physical Society.


Bronnikov K.A.,National Research Nuclear University MEPhI | Korolyov P.A.,Institute of Gravitation and Cosmology
Gravitation and Cosmology | Year: 2015

We construct explicit examples of globally regular static, spherically symmetric solutions in general relativity with scalar and electromagnetic fields describing traversable wormholes with flat and AdS asymptotics and regular black holes, in particular, black universes. (A black universe is a regular black hole with an expanding, asymptotically isotropic space-time beyond the horizon.) The existence of such objects requires invoking scalars with negative kinetic energy (“phantoms, ” or “ghosts”), which are not observed under usual physical conditions. To account for that, the so-called “trapped ghosts” were previously introduced, i.e., scalars whose kinetic energy is only negative in a restricted strong-field region of space-time and positive outside it. This approach leads to certain problems, including instability (as is illustrated here by derivation of an effective potential for spherical pertubations of such systems). In this paper, we use for model construction what we call “invisible ghosts, ” i.e., phantom scalar fields sufficiently rapidly decaying in the weak-field region. The resulting configurations contain different numbers of Killing horizons, from zero to four. © 2015, Pleiades Publishing, Ltd.


Ivashchuk V.D.,Institute of Gravitation and Cosmology
European Physical Journal C | Year: 2016

We consider a gravitational model in dimension D with several forms, l scalar fields and a Λ -term. We study cosmological-type block-diagonal metrics defined on a product of an 1-dimensional interval and n oriented Einstein spaces. As an electromagnetic composite brane ansatz is adopted and certain restrictions on the branes are imposed the conformally covariant Wheeler–DeWitt (WDW) equation for the model is studied. Under certain restrictions, asymptotic solutions to the WDW equation are found in the limit of the formation of the billiard walls. These solutions reduce the problem to the so-called quantum billiard in (n+ l- 1) -dimensional hyperbolic space. Several examples of quantum billiards in the model with electric and magnetic branes, e.g. corresponding to hyperbolic Kac–Moody algebras, are considered. In the case n= 2 we find a set of basis asymptotic solutions to the WDW equation and derive asymptotic solutions for the metric in the classical case. © 2016, The Author(s).


Bronnikov K.A.,Institute of Gravitation and Cosmology | Skvortsova M.V.,Institute of Gravitation and Cosmology
Gravitation and Cosmology | Year: 2013

To explain the recently reported large-scale spatial variations of the fine structure constant α, we apply some models of curvature-nonlinear multidimensional gravity. Under the reasonable assumption of slow changes of all quantities as compared with the Planck scale, the original theory reduces to a multiscalar field theory in four dimensions. On this basis, we consider different variants of isotropic cosmological models in both the Einstein and Jordan conformal frames. One of the models turns out to be equally viable in both frames, but in the Jordan frame themodel predicts simultaneous variations of α and the gravitational constant G, equal in magnitude. Large-scale small inhomogeneous perturbations of these models allow for explaining the observed distribution of α values. © 2013 Pleiades Publishing, Ltd.


Bronnikov K.A.,Institute of Gravitation and Cosmology | Elizalde E.,Consejo Superior de Investigaciones Cientificas ICE CSIC IEEC Campus UAB
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

The properties of static, spherically symmetric configurations are considered in the framework of two models of nonlocally corrected gravity, suggested in S. Deser and R. Woodard, Phys. Rev. Lett. 99, 111301 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.111301 and S. Capozziello, Phys. Lett. B 671, 193 (2009)PYLBAJ0370-269310.1016/j.physletb.2008.11.060. For the first case, where the Lagrangian of nonlocal origin represents a scalar-tensor theory with two massless scalars, an explicit condition is found under which both scalar fields are canonical (nonphantom). If this condition does not hold, one of the fields exhibits a phantom behavior. Scalar-vacuum configurations then behave in a manner known for scalar-tensor theories. In the second case, the Lagrangian of nonlocal origin exhibits a scalar field interacting with the Gauss-Bonnet (GB) invariant and contains an arbitrary scalar field potential. It is found that the GB term, in general, leads to violation of the well-known no-go theorems valid for minimally coupled scalar fields in general relativity. It is shown, however, that some configurations of interest are still forbidden-whatever be the scalar field potential and the GB-scalar coupling function, namely, "force-free" wormholes (such that gtt=const) and black holes with higher-order horizons. © 2010 The American Physical Society.

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