Zahra Amirabi

Stability of generic cylindrical thin shell wormholes

We revisit the stability analysis of cylindrical thin shell wormholes which have been studied in literature so far. Our approach is more systematic and in parallel to the method which is used in spherically symmetric thin shell wormholes. The stability condition is summarized as the positivity of the second derivative of an effective potential at the equilibrium radius, i.e.

Stability of thin-shell wormholes supported by normal matter in Einstein-Maxwell-Gauss-Bonnet gravity

V^{\prime \prime}\left(a_{0}\right) >0

Higher dimensional thin-shell wormholes in Einstein-Yang-Mills-Gauss-Bonnet gravity

. This may serve as the master equation in all stability problems for the cylindrical thin-shell wormholes.

N-dimensional non-abelian dilatonic, stable black holes and their Born–Infeld extension

Recently in ( Phys. Rev. D 76, 087502 (2007) and Phys. Rev. D 77, 089903(E) (2008)) a thinshell wormhole has been introduced in 5-dimensional Einstein-Maxwell-Gauss-Bonnet (EMGB) gravity which was supported by normal matter. We wish to consider this solution and investigate its stability. Our analysis shows that for the Gauss-Bonnet (GB) parameter � 0, we iterate once more that no stable, normal matter thin-shell wormhole exists.

Effect of the Gauss-Bonnet parameter in the stability of thin-shell wormholes

We present thin-shell wormhole solutions in the Einstein–Yang–Mills–Gauss–Bonnet (EYMGB) theory in higher dimensions d ≥ 5. Exact black hole solutions are employed for this purpose where the radius of the thin shell lies outside the event horizon. For some reasons the cases d = 5 and d > 5 are treated separately. The surface energy–momentum of the thin shell creates surface pressures to resist against collapse and rendering stable wormholes possible. We test the stability of the wormholes against spherical perturbations through a linear energy–pressure relation and plot stability regions. Apart from this restricted stability we investigate the possibility of normal (i.e. non-exotic) matter which satisfies the energy conditions. For negative values of the Gauss–Bonnet (GB) parameter we obtain such physical wormholes.

Black hole and thin-shell wormhole solutions in Einstein-Hoffman-Born-Infeld theory

We find large classes of non-asymptotically flat Einstein–Yang–Mills–Dilaton and Einstein–Yang–Mills–Born–Infeld–Dilaton black holes in N-dimensional spherically symmetric spacetime expressed in terms of the quasilocal mass. Extension of the dilatonic YM solution to N-dimensions has been possible by employing the generalized Wu-Yang ansatz. Another metric ansatz, which aided in finding exact solutions is the functional dependence of the radius function on the dilaton field. These classes of black holes are stable against linear radial perturbations. In the limit of vanishing dilaton we obtain Bertotti–Robinson type metrics with the topology of AdS2×SN–2. Since connection can be established between dilaton and a scalar field of Brans–Dicke type we obtain black hole solutions also in the Brans–Dicke–Yang–Mills theory as well.

New non-Abelian black hole solutions in Born-Infeld gravity

Among other aspects the foremost challenging problems related to thin-shell wormholes [1] are, i) positivity of energy density , and ii) stability against symmetry preserving perturbations. To overcome these problems recently there have been various attempts in Einstein-Gauss-Bonnet (EGB) gravity with Maxwell and Yang-Mills sources [2]. Specifically, with the negative Gauss-Bonnet (GB) parameter (α < 0) we obtained stable thin-shell wormholes, obeying a linear equation of state, against radial perturbations [1, 2]. By linear equation of state it is meant that the energy density (σ) and surface pressure p satisfy a linear relation. To respond the other challenge, however, i.e. the positivity of the energy density (σ > 0), we maintain still a cautious optimism. To be realistic, only in the case of Einstein-Yang-Mills-Gauss-Bonnet (EYMGB) theory and in a finely-tuned narrow band of parameters we were able to beat both of the above stated challenges [2]. Our stability analysis with the unfortunate negative energy density was extended further to cover non-asymptotically flat (NAF) dilatonic solutions [3]. In this Brief Report we show that stability analysis of thin-shell wormholes extends to the case of a generalized Chaplygin gas which has already been considered within the context of Einstein-Maxwell thin-shells wormholes [4]. Due to the accelerated expansion of our universe a repulsive effect of a Chaplygin gas has been considered widely in recent times . From the same token therefore it would be interesting to see how a generalized Chaplygin gas supports a thin-shell wormhole against radial perturbations in Gauss-Bonnet (GB) gravity. For this purpose we perturb the thin-shell radially and reduce the equation into a particle in a potential well problem with zero total energy. The stability amounts to the determination of the negative domain for the potential. We obtain plots that provides us such physical regions indicating stable wormholes. For technical reasons we restrict ourselves only to the 5-dimensional plots. The d−dimensional Einstein Maxwell Gauss Bonnet (EMGB) action without cosmological constant

d-dimensional non-asymptotically flat thin-shell wormholes in Einstein-Yang-Mills-Dilaton gravity

Abstract We adopt the Hoffmann–Born–Infeldʼs (HBI) double Lagrangian approach in general relativity to find black holes and investigate the possibility of viable thin-shell wormholes. By virtue of the non-linear electromagnetic parameter, the matching hypersurfaces of the two regions with two Lagrangians provide a natural, lower-bound radius for the thin-shell wormholes which provides the main motivation to the present study. In particular, the stability of thin-shell wormholes supported by normal matter in higher-dimensional Einstein–HBI–Gauss–Bonnet (EHBIGB) gravity is highlighted.

Generation of spherically symmetric metrics in f(R) gravity

We introduce new black hole solutions to the Einstein-Yang-Mills-Born-Infeld (EYMBI), Einstein-Yang-Mills-Born-Infeld-Gauss-Bonnet (EYMBIGB), and Einstein-Yang-Mills-Born-Infeld-Gauss-Bonnet-Lovelock (EYMBIGBL) gravities in higher dimensions N{>=}5 to investigate the roles of Born-Infeld parameter {beta}. It is shown that these solutions in the limits of {beta}{yields}0 and {beta}{yields}{infinity} represent pure gravity and gravity coupled with Yang-Mills fields, respectively. For 0<{beta}<{infinity} it yields a variety of black holes, supporting even regular ones at r=0.

Black hole solution in third order Lovelock gravity has no Gauss-Bonnet limit

Abstract Thin-shell wormholes in Einstein–Yang–Mills-dilaton (EYMD) gravity are considered. We show that a non-asymptotically flat (NAF) black hole solution of the d -dimensional EYMD theory provides stable thin-shell wormholes which are supported entirely by exotic matter. The presence of dilaton makes the spacetime naturally NAF, and with our conclusion it remains still open to construct wormholes supported by normal matter between two such spacetimes.