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Thin-shells and thin-shell wormholes in new massive gravity
https://repo.scoap3.org/record/33007
Within 2 + 1-dimensional cosmological new massive gravity, we consider thin-shell and thin-shell wormhole construction. For this, we introduce first, the junction conditions apt for the fourth order terms in the action of the theory. Then, by employing some specific static solutions in new massive gravity, we study the characteristics of associated thin-shells and thin-shell wormholes. Our finding suggests that, firstly, there cannot exist any thin-shells regarding our chosen solutions of cosmological new massive gravity, and secondly, the constructed thin-shell wormhole does not need to be symmetric. More importantly, the thin-shell wormhole, if ever forms, possesses null energy density and null angular pressure on its throat which are preferable to their negative-valued counterparts.Forghani, S. DanialTue, 28 May 2019 15:24:50 GMThttps://repo.scoap3.org/record/33007urn:ISSN:1434-6052Springer/Società Italiana di Fisica2019-5-28A note on thin-shell wormholes with charge in F ( R )-gravity
https://repo.scoap3.org/record/27112
In their recent work (Eiroa and Aguirre in Eur Phys J C 76:132, 2016 ), Eiroa and Aguirre introduced thin-shell wormholes in FR=R+αR2 -gravity coupled with the Maxwell electromagnetic field. Here in this note we shall address an interesting feature of their results which has been missed. It will be shown that thin-shell wormhole can not be formed in the black hole spacetime solution of this theory but instead there are rooms for making stable thin-shell wormholes in non-black hole bulk spacetime as was noted in Eiroa and Aguirre ( 2016 ). This study is not a comment on very correct results of Eiroa and Aguirre ( 2016 ) but instead it is a complementary result to their paper.Mazharimousavi, S. HabibTue, 31 Jul 2018 22:53:44 GMThttps://repo.scoap3.org/record/27112urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-7-31Black Holes: Insights and Enigmas
https://repo.scoap3.org/record/26304
Sakalli, IzzetTue, 26 Jun 2018 13:09:49 GMThttps://repo.scoap3.org/record/26304urn:ISSN:1687-7365Hindawi2018-06-26Asymmetric thin-shell wormholes
https://repo.scoap3.org/record/26096
Spacetime wormholes in isotropic spacetimes are represented traditionally by embedding diagrams which were symmetric paraboloids. This mirror symmetry, however, can be broken by considering different sources on different sides of the throat. This gives rise to an asymmetric thin-shell wormhole, whose stability is studied here in the framework of the linear stability analysis. Having constructed a general formulation, using a variable equation of state and related junction conditions, the results are tested for some examples of diverse geometries such as the cosmic string, Schwarzschild, Reissner–Nordström and Minkowski spacetimes. Based on our chosen spacetimes as examples, our finding suggests that symmetry is an important factor to make a wormhole more stable. Furthermore, the parameter γ , which corresponds to the radius dependency of the pressure on the wormholes’s throat, can affect the stability in a great extent.Forghani, S. DanialMon, 11 Jun 2018 10:00:00 GMThttps://repo.scoap3.org/record/26096urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-6-8Classical and Quantum Gravity and Its Applications
https://repo.scoap3.org/record/19680
Hendi, Seyed HosseinTue, 11 Apr 2017 08:16:08 GMThttps://repo.scoap3.org/record/19680urn:ISSN:1687-7365Hindawi2017-04-11Black holes from multiplets of scalar fields in 2 + 1- and 3 + 1 dimensions
https://repo.scoap3.org/record/16810
We obtain classes of black hole solutions constructed from multiplets of scalar fields in 2 + 1/3 + 1 dimensions. The multi-component scalars do not undergo a symmetry breaking so that only the isotropic modulus is effective. The Lagrangian is supplemented by a self-interacting potential which plays significant role in obtaining the exact solutions. In 2 + 1/3 + 1 dimensions, a doublet/triplet of scalars is effective, which enriches the available black hole spacetimes and creates useful Liouville weighted field theoretic models.Mazharimousavi, S. HabibMon, 15 Aug 2016 07:03:40 GMThttps://repo.scoap3.org/record/16810urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-8-13Generation of spherically symmetric metrics in f ( R ) gravity
https://repo.scoap3.org/record/16081
In D -dimensional spherically symmetric f ( R ) gravity there are three unknown functions to be determined from the fourth order differential equations. It is shown that the system remarkably may be integrated to relate two functions through the third one to provide a reduction to second order equations accompanied with a large class of potential solutions. The third function, which acts as the generator of the process, is F(R)=df(R)dR . We recall that our generating function has been employed as a scalar field with an accompanying self-interacting potential previously, which is entirely different from our approach. Reduction of f ( R ) theory into a system of equations seems to be efficient enough to generate a solution corresponding to each generating function. As particular examples, besides the known ones, we obtain new black hole solutions in any dimension D . We further extend our analysis to cover non-zero energy-momentum tensors. Global monopole and Maxwell sources are given as examples.Amirabi, Z.Mon, 20 Jun 2016 09:33:42 GMThttps://repo.scoap3.org/record/16081urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-6-20Cloud of strings as source in 2+1 -dimensional fR=Rn gravity
https://repo.scoap3.org/record/14441
We present three parameters exact solutions with possible black holes in 2+1 -dimensional fR=Rn modified gravity coupled minimally to a cloud of strings. These three parameters are n , the coupling constant of the cloud of strings ξ , and an integration constant C . Although in general one has to consider each set of parameters separately, for n an even integer greater than one we give a unified picture providing black holes. For n≥1 we analyze a null/timelike geodesic within the context of particle confinement.Mazharimousavi, S. HabibTue, 23 Feb 2016 11:59:22 GMThttps://repo.scoap3.org/record/14441urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-2-23Hypocycloidal throat for 2+1 -dimensional thin-shell wormholes
https://repo.scoap3.org/record/12732
Recently we have shown that for 2+1 -dimensional thin-shell wormholes a non-circular throat may lead to a physical wormhole in the sense that the energy conditions are satisfied. By the same token, herein we consider an angular dependent throat geometry embedded in a 2+1 -dimensional flat spacetime in polar coordinates. It is shown that, remarkably, a generic, natural example of the throat geometry is provided by a hypocycloid. That is, two flat 2+1 dimensions are glued together along a hypocycloid. The energy required in each hypocycloid increases with the frequency of the roller circle inside the large one.Mazharimousavi, S. HabibThu, 19 Nov 2015 13:48:48 GMThttps://repo.scoap3.org/record/12732urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-11-19Screening of the Reissner–Nordström charge by a thin-shell of dust matter
https://repo.scoap3.org/record/11108
A concentric charged thin-shell encircling a Reissner–Nordström black hole screens the electric/magnetic charge completely to match with an external Schwarzschild black hole. The negative mass thin-shell is shown to be stable against radial perturbations. It is shown further that by reversing the roles of inside Reissner–Nordström and outside Schwarzschild geometries the mass of the appropriate shell becomes positive.Mazharimousavi, S. HabibThu, 16 Jul 2015 15:00:18 GMThttps://repo.scoap3.org/record/11108urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-7-173+1 -dimensional thin shell wormhole with deformed throat can be supported by normal matter
https://repo.scoap3.org/record/10776
From the physics standpoint the exotic matter problem is a major difficulty in thin shell wormholes (TSWs) with spherical/cylindrical throat topologies. We aim to circumvent this handicap by considering angle dependent throats in 3+1 dimensions. By considering the throat of the TSW to be deformed spherical, i.e., a function of θ and φ , we present general conditions which are to be satisfied by the shape of the throat in order to have the wormhole supported by matter with positive density in the static reference frame. We provide particular solutions/examples to the constraint conditions.Mazharimousavi, S. HabibMon, 22 Jun 2015 18:09:54 GMThttps://repo.scoap3.org/record/10776urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-6-20A topological metric in 2+1 dimensions
https://repo.scoap3.org/record/10557
A real-valued triplet of scalar fields as a source gives rise to a metric which tilts the scalar, not the light cone, in 2+1 dimensions. The topological metric is static, regular, and it is characterized by an integer κ=±1,±2,… The problem is formulated as a harmonic map of Riemannian manifolds in which the integer κ equals the degree of the map.Mazharimousavi, S. HabibWed, 03 Jun 2015 11:37:04 GMThttps://repo.scoap3.org/record/10557urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-6-4Quantum Probes of Timelike Naked Singularities in <math id="M1" xmlns="http://www.w3.org/1998/Math/MathML"><mn>2</mn><mo>+</mo><mn>1</mn></math> -Dimensional Power-Law Spacetimes
https://repo.scoap3.org/record/9978
The formation of naked singularities in 2+1 -dimensional power-law spacetimes in linear Einstein-Maxwell and Einstein-scalar theories sourced by azimuthally symmetric electric field and a self-interacting real scalar field, respectively, are considered in view of quantum mechanics. Quantum test fields obeying the Klein-Gordon and Dirac equations are used to probe the classical timelike naked singularities developed at r=0 . We show that when the classically singular spacetimes probed with scalar waves, the considered spacetimes remain singular. However, the spinorial wave probe of the singularity in the metric of a self-interacting real scalar field remains quantum regular. The notable outcome in this study is that the quantum regularity/singularity cannot be associated with the energy conditions.Mazharimousavi, S. HabibWed, 22 Apr 2015 19:29:52 GMThttps://repo.scoap3.org/record/9978urn:ISSN:1687-7365Hindawi Publishing Corporation2015-04-192+1 -dimensional traversable wormholes supported by positive energy
https://repo.scoap3.org/record/9249
We revisit the shapes of the throats of wormholes, including thin-shell wormholes (TSWs) in 2+1 dimensions. In particular, in the case of TSWs this is done in a flat 2+1 -dimensional bulk spacetime by using the standard method of cut-and-paste. Upon departing from a pure time-dependent circular shape i.e., r=at for the throat, we employ a θ -dependent closed loop of the form r=Rt,θ, and in terms of Rt,θ we find the surface energy density σ on the throat. For the specific convex shapes we find that the total energy which supports the wormhole is positive and finite. In addition, we analyze the general wormhole’s throat. By considering the specific equation of r=Rθ instead of r=r0=const., and upon certain choices of functions for Rθ , we find the total energy of the wormhole to be positive.Mazharimousavi, S. HabibTue, 17 Feb 2015 19:58:02 GMThttps://repo.scoap3.org/record/9249urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-2-18Counter-rotational effects on stability of 2+1 -dimensional thin-shell wormholes
https://repo.scoap3.org/record/4081
The role of angular momentum in a 2+1 -dimensional rotating thin-shell wormhole (TSW) is considered. Particular emphasis is given to stability when the shells (rings) are counter-rotating. We find that counter-rotating halves make the TSW supported by the equation of state of a linear gas more stable. Under a small velocity dependent perturbation, however, it becomes unstable.Mazharimousavi, S. HabibMon, 22 Sep 2014 11:06:12 GMThttps://repo.scoap3.org/record/4081urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-9-23Thin-shell wormholes supported by total normal matter
https://repo.scoap3.org/record/4079
The Zipoy–Voorhees–Weyl (ZVW) spacetime characterized by mass ( M ) and oblateness ( δ ) is proposed in the construction of viable thin-shell wormholes (TSWs). A departure from spherical/cylindrical symmetry yields a positive total energy in spite of the fact that the local energy density may take negative values. We show that oblateness of the bumpy sources/black holes can be incorporated as a new degree of freedom that may play a role in the resolution of the exotic matter problem in TSWs. A small velocity perturbation reveals, however, that the resulting TSW is unstable.Mazharimousavi, S. HabibMon, 22 Sep 2014 11:06:10 GMThttps://repo.scoap3.org/record/4079urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-9-23Microscopic thin-shell wormholes in magnetic Melvin universe
https://repo.scoap3.org/record/2512
We construct thin-shell wormholes in the magnetic Melvin universe. It is shown that in order to make a TSW in the Melvin spacetime the radius of the throat cannot be larger than 2B0 , in which B0 is the magnetic field constant. We also analyze the stability of the constructed wormhole in terms of a linear perturbation around the equilibrium point. In our stability analysis we scan a full set of the Equation of States such as Linear Gas, Chaplygin Gas, Generalized Chaplygin Gas, Modified Generalized Chaplygin Gas, and Logarithmic Gas. Finally we extend our study to the wormhole solution in the unified Melvin and Bertotti–Robinson spacetime. In this extension we show that for some specific cases, the local energy density is partially positive but the total energy which supports the wormhole is positive.Mazharimousavi, S. HabibMon, 19 May 2014 16:39:06 GMThttps://repo.scoap3.org/record/2512urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-5-20A scan of f(R) models admitting Rindler-type acceleration
https://repo.scoap3.org/record/1639
As a manifestation of a large distance effect Grumiller modified Schwarzschild metric with an extraneous term reminiscent of Rindler acceleration. Such a term has the potential to explain the observed flat rotation curves in general relativity. The same idea has been extended herein to the larger arena of f(R) theory. With particular emphasis on weak energy conditions (WECs) for a fluid we present various classes of f(R) theories admitting a Rindler-type acceleration in the metric.Mazharimousavi, S. HabibFri, 14 Mar 2014 17:49:17 GMThttps://repo.scoap3.org/record/1639urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-3-15Thin-shell wormholes from the regular Hayward black hole
https://repo.scoap3.org/record/1602
We revisit the regular black hole found by Hayward in 4 -dimensional static, spherically symmetric spacetime. To find a possible source for such a spacetime we resort to the nonlinear electrodynamics in general relativity. It is found that a magnetic field within this context gives rise to the regular Hayward black hole. By employing such a regular black hole we construct a thin-shell wormhole for the case of various equations of state on the shell. We abbreviate a general equation of state by p=ψ(σ) where p is the surface pressure which is a function of the mass density (σ) . In particular, linear, logarithmic, Chaplygin, etc. forms of equations of state are considered. In each case we study the stability of the thin shell against linear perturbations. We plot the stability regions by tuning the parameters of the theory. It is observed that the role of the Hayward parameter is to make the TSW more stable. Perturbations of the throat with small velocity condition are also studied. The matter of our TSWs, however, remains exotic.Halilsoy, M.Wed, 12 Mar 2014 17:46:58 GMThttps://repo.scoap3.org/record/1602urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-3-13Quantum probes of timelike naked singularities in the weak field regime of f ( R ) global monopole spacetime
https://repo.scoap3.org/record/1171
The formation of a naked singularity in f ( R ) global monopole spacetime is considered in view of quantum mechanics. Quantum test fields obeying the Klein-Gordon, Dirac and Maxwell equations are used to probe the classical timelike naked singularity developed at r = 0. We prove that the spatial derivative operator of the fields fails to be essentially self-adjoint. As a result, the classical timelike naked singularity formed in f ( R ) global monopole spacetime remains quantum mechanically singular when it is probed with quantum fields having different spin structures. Pitelli and Letelier ( Phys. Rev. D 80 (2009) 104035) had shown that for quantum scalar ( spin 0) probes the general relativistic global monopole singularity remains intact. For specific modes electromagnetic ( spin 1) and Dirac field ( spin 1 / 2) probes, however, we show that the global monopole spacetime behaves quantum mechanically regular. The admissibility of this singularity is also incorporated within the Gubser’s singularity conjecture.O. GurtugSat, 01 Feb 2014 03:10:05 GMThttps://repo.scoap3.org/record/1171urn:ISSN:1029-8479Springer/SISSA2014-01-31A new Einstein-nonlinear electrodynamics solution in <math><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math> dimensions
https://repo.scoap3.org/record/1121
We introduce a class of solutions in 2+1 -dimensional Einstein–Power–Maxwell theory for a circularly symmetric electric field. The electromagnetic field is considered with an angular component given by Fμν=E0δμtδνθ for E0= constant. First, we show that the metric for zero cosmological constant and the Power–Maxwell Lagrangian of the form of FμνFμν coincides with the solution given in 2+1 -dimensional gravity coupled with a massless, self-interacting real scalar field. With the same Lagrangian and a non-zero cosmological constant we obtain a non-asymptotically flat wormhole solution in 2+1 dimensions. The confining motions of massive charged and chargeless particles are investigated too. Secondly, another interesting solution is given for zero cosmological constant together with the conformal invariant condition. The formation of a timelike naked singularity for this particular case is investigated within the framework of the quantum mechanics. Quantum fields obeying the Klein–Gordon and Dirac equations are used to probe the singularity and test the quantum mechanical status of the singularity.Mazharimousavi, S. HabibTue, 28 Jan 2014 13:42:35 GMThttps://repo.scoap3.org/record/1121urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-1-29