Wormholes in 4D Einstein–Gauss–Bonnet gravity Jusufi, Kimet; Banerjee, Ayan; Ghosh, Sushant G.
European physical journal. C, Particles and fields,
08/2020, Letnik:
80, Številka:
8
Journal Article
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Recent times witnessed a significant interest in regularizing, a
D
→
4
limit, of EGB gravity initiated by Glavan and Lin Phys. Rev. Lett. 124, 081301 (2020) by re-scaling GB coupling constant as
α
/
...(
D
-
4
)
and taking limit
D
→
4
, and in turn these regularized 4
D
gravities have nontrivial gravitational dynamics. Interestingly, the maximally or spherically symmetric solution to all the regularized gravities coincides in the 4
D
case. In view of this, we obtain an exact spherically symmetric wormhole solution in the 4
D
EGB gravity for an isotropic and anisotropic matter sources. In this regard, we consider also a wormhole with a specific radial-dependent shape function, a power-law density profile as well as by imposing a particular equation of state. To this end, we analyze the flare-out conditions, embedding diagrams, energy conditions and the volume integral quantifier. In particular our −ve branch results, in the limit
α
→
0
, reduced exactly to
vis-
a
`
-vis
4D Morris-Thorne of GR.
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Following the recent theory of
f
(
Q
) gravity, we continue to investigate the possible existence of wormhole geometries, where
Q
is the non-metricity scalar. Recently, the non-metricity scalar and ...the corresponding field equations have been studied for some spherically symmetric configurations in Mustafa (Phys Lett B 821:136612, 2021) and Lin and Zhai (Phys Rev D 103:124001, 2021). One can note that field equations are different in these two studies. Following Lin and Zhai (2021), we systematically study the field equations for wormhole solutions and found the violation of null energy conditions in the throat neighborhood. More specifically, considering specific choices for the
f
(
Q
) form and for constant redshift with different shape functions, we present a class of solutions for static and spherically symmetric wormholes. Our survey indicates that wormhole solutions could not exist for specific form function
f
(
Q
)
=
Q
+
α
Q
2
. To summarize, exact wormhole models can be constructed with violation of the null energy condition throughout the spacetime while being
ρ
≥
0
and vice versa.
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In this paper, we study the deflection of light by a class of charged wormholes within the context of the Einstein-Maxwell-dilaton theory. The primordial wormholes are predicted to exist in the early ...universe, where inflation is driven by the dilaton field. We perform our analysis through optical geometry using the Gibbons-Werner method (GW) by adopting the Gauss-Bonnet theorem and the standard geodesics approach. We report an interesting result for the deflection angle in leading-order terms-namely, the deflection angle increases due to the electric charge Q and the magnetic charge P, whereas it decreases due to the dilaton charge Σ. Finally, we confirm our findings by means of geodesics equations. Our computations show that the GW method gives an exact result in leading-order terms.
Recent progress in the determination of both masses and radii of neutron stars has put strong constraints on the equation of state (EoS) above the nuclear saturation density. Within a confining quark ...matter model, we propose an anisotropic star consisting of a homogeneous and unpaired charge-neutral 3-flavor interacting quark matter with O(ms4) corrections in the context of Einstein-Gauss-Bonnet gravity theory. This generalized model depends only on three free parameters: the bag constant B, the interaction parameter a and the Gauss-Bonnet coupling constant α. Given the underlying EoS, we show the possibility of obtaining the maximal neutron star mass which satisfies the recent observational data for PSR J0751+1807. The numerical analysis of mass-radius relations supports the existence of other massive pulsars with a maximum mass consistent and common radii in the range of R≲(11∼14) Km 1. Furthermore, we discuss the mass vs central mass density (M−ρc) relation for stability, compactness and binding energy in this gravity theory. Our results thus provide circumstantial evidence in favor of super-massive pulsars in EGB gravity.
In this article, we develop a theoretical framework to study compact stars in Einstein gravity with the Gauss–Bonnet (GB) combination of quadratic curvature terms. We mainly analyzed the dependence ...of the physical properties of these compact stars on the Gauss–Bonnet coupling strength. This work is motivated by the relations that appear in the framework of the minimal geometric deformation approach to gravitational decoupling (MGD-decoupling), we establish an exact anisotropic version of the interior solution in Einstein–Gauss–Bonnet gravity. In fact, we specify a particular form for gravitational potentials in the MGD approach that helps us to determine the decoupling sector completely and ensure regularity in interior space-time. The interior solutions have been (smoothly) joined with the Boulware–Deser exterior solution for 5
D
space-time. In particular, two different solutions have been reported which comply with the physically acceptable criteria: one is the mimic constraint for the pressure and the other approach is the mimic constraint for density. We present our solution both analytically and graphically in detail.
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We investigate the deflection of light by a rotating global monopole spacetime and a rotating Letelier spacetime in the weak deflection approximation. To this end, we apply the Gauss-Bonnet theorem ...to the corresponding osculating optical geometries and show that the deflection of light increases in each spacetime due to the presence of the global monopole parameter and the string cloud parameter, respectively. The results obtained for the deflection angle in the equatorial plane generalize known results for the corresponding nonrotating global monopole and Letelier spacetimes as well as the Kerr solution.
We examine the effects of the Rastall parameter on the behaviour of spherically symmetric static distributions of perfect fluid matter. It was claimed by Visser Physics Letters B, 782, 83, (2018) ...that the Rastall proposition is completely equivalent to the Einstein theory. While many authors have raised contrary arguments, our intention is to analyse the properties of Rastall gravity through variation of the Rastall parameter in the context of perfect fluids spheres that may be used to model neutron stars or cold fluid planets. This analysis also serves to counter the claim that Rastall gravity is equivalent to the standard Einstein theory. It turns out that the condition of pressure isotropy is exactly the same as for Einstein gravity and hence that any known solution of the Einstein equations may be used to study the effects of the Rastall dynamical quantities. Moreover, by choosing the well studied Tolman metrics, we discover that in the majority of cases there is substantial deviation from the Einstein case when the Rastall parameter vanishes and in cases where the Einstein model displays defective behaviour, certain Rastall models obey the well known elementary requirements for physical plausibility. These empirical findings do not support the idea that Rastall theory is equivalent to Einstein theory as several deviations in physical behaviour are displayed as counter-examples.
In this work we study the properties of compact spheres made of a charged perfect fluid with a MIT bag model EoS for quark matter. Considering static spherically symmetric spacetime we derive the ...hydrostatic equilibrium equations in the recently formulated four dimensional Einstein–Gauss–Bonnet (4
D
EGB) gravity theory. In this setting, the modified TOV equations are solved numerically with the aim to investigate the impact of electric charge on the stellar structure. A nice feature of 4
D
EGB theory is that the Gauss–Bonnet term has a non-vanishing contribution to the gravitational dynamics in 4
D
spacetime. We therefore analyse the effects of Gauss–Bonnet coupling constant
α
and the charge fraction
β
on the mass–radius (
M
-
R
) diagram and also the mass–central density
(
M
-
ρ
c
)
relation of quark stars. Finally, we conclude that depending on the choice of coupling constant one could have larger mass and radius compared with GR and can also be relevant for more massive compact objects due to the effect of the repulsive Coulomb force.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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