$f({\sf R})$ Gravity Wormholes sourced by a Phantom Scalar Field

We study the tideless traversable wormholes in the f(R) gravity metric formalism. First we consider three shape functions of wormholes and study their viabilities and structures. The connection between the f(R) gravity model and wormhole shape function has been studied and the dependency of the f(R) gravity model with the shape function is shown. We also obtain a wormhole solution in the f(R) gravity Starobinsky model surrounded by a cloud of strings. In this case, the wormhole shape function depends on both the Starobinsky model parameter and the cloud of strings parameter. The structure and height of the wormhole is highly affected by the cloud of strings parameter, while it is less sensitive to the Starobinsky model parameter. The energy conditions have been studied and we found the ranges of the null energy condition violation for all wormhole structures. The quasinormal modes from these wormhole structures for the scalar and Dirac perturbations are studied using higher order WKB approximation methods. The quasinormal modes for the toy shape functions depend highly on the model parameters. In case of the Starobinsky model's wormhole the quasinormal frequencies and the damping rate increase with an increase in the Starobinsky model parameter in scalar perturbation. Whereas in Dirac perturbation, with an increase in the Starobinsky model parameter the quasinormal frequencies decrease and the damping rate increases. The cloud of strings parameter also impacts prominently and differently the quasinormal modes from the wormhole in the Starobinsky model.

Section: Introductionmentioning

confidence: 99%

Tideless traversable wormholes surrounded by cloud of strings in f(R) gravity

Gogoi

Goswami

2023

“…In this context, exotic matter is reduced or even not needed when wormholes solutions are realized on alternative theoretical frameworks. Traversable wormholes have been found in many modified gravitational theories, such as in f (R) gravity [12][13][14][15][16][17][18], f (R, T ) gravity [19][20][21][22], modified teleparallel gravity [23], non-minimal couplings [24,25], extra fundamental fields [26][27][28][29][30][31], Einstein-Gauss-Bonnet gravity [32][33][34], Einstein-Scalar-Gauss-Bonnet gravity [35,36], Brans-Dicke theory [37][38][39], Randal-Sundrum model [40], braneworld configurations [41], metric-Palatini gravity [42,43], with thin shells [44][45][46][47][48], Einsteinian Cubic gravity [49], Einstein-Dirac-Maxwell [50], massive JCAP11(2023)055 gravity [51] and by disformal transformations [52][53][54][55][56],...…”

Section: Introductionmentioning

confidence: 99%

Stealth Ellis wormholes in Horndeski theories

Bakopoulos,

Chatzifotis,

Erices

et al. 2023

In this work we are revisiting the well studied Ellis wormhole solution in a Horndeski theory motivated from the Kaluza-Klein compactification procedure of the more fundamental higher dimensional Lovelock gravity. We show that the Ellis wormhole is analytically supported by a gravitational theory with a non-trivial coupling to the Gauss-Bonnet term and we expand upon this notion by introducing higher derivative contributions of the scalar field. The extension of the gravitational theory does not yield any back-reacting component on the spacetime metric, which establishes the Ellis wormhole as a stealth solution in the generalized framework. We propose two simple mechanisms that dress the wormhole with an effective ADM mass. The first procedure is related to a conformal transformation of the metric which maps the theory to another Horndeski subclass, while the second one is inspired by the spontaneous scalarization effect on black holes.

“…The most intensely studied approach however is the one according to which the energy conditions are violated not by the actual matter but by an effective energy-momentum tensor arising in the context of a modified theory of gravity. These theories include f (R) theories [45][46][47][48][49][50], extra dimensions [51][52][53], brane-world models [54][55][56][57][58], non-minimally coupled scalar-tensor theories [59][60][61][62][63], or higher-derivative gravitational theories [64][65][66][67][68][69][70][71][72] to mention a few indicative works. The stability behaviour of the wormhole solutions emerging in the context of different theories has also undergone an intensive study over the years [73][74][75][76][77][78] resulting at times to no-go theorems [79,80] and forcing us to move to theories beyond GR for viable solutions.…”

Section: Introductionmentioning

confidence: 99%

Traversable wormholes in beyond Horndeski theories

Bakopoulos

Charmousis

Kanti

2022

We construct a large class of explicit, asymptotically flat and regular wormhole solutions in higher order scalar tensor theories. The solutions are vacuum solutions of scalar tensor theory and no matter (exotic or regular) is introduced in order to support them. They are constructed via a general disformal transformation of a seed black hole solution. The seed solutions belong to a particular Horndeski theory which requires the presence of all extended Galileons and has a higher dimensional Lovelock origin. As a result, the resulting wormholes are always solutions of general beyond Horndeski theory. The particular class of wormholes we study are parametrised by their ADM mass and two coupling constants of the theory, one related to their higher dimensional Lovelock origin and one to the disformal transformation itself. The latter of the coupling constants affects the throat size of the wormhole solutions, thus giving them a compact or non-compact nature, as well as their properties.