Double shadows of reflection-asymmetric wormholes supported by positive energy thin-shells

Abstract

We consider reflection-asymmetric thin-shell wormholes within Palatini f (R) gravity using a matching procedure of two patches of electrovacuum space-times at a hypersurface (the shell) via suitable junction conditions. The conditions for having (linearly) stable wormholes supported by positive-energy matter sources are determined. We also identify some subsets of parameters able to locate the shell radius above the event horizon (when present) but below the photon sphere (on both sides). We illustrate with an specific example that such two photon spheres allow an observer on one of the sides of the wormhole to see another (circular) shadow in addition to the one generated by its own photon sphere, which is due to the photons passing above the maximum of the effective potential on its side and bouncing back across the throat due to a higher effective potential on the other side. We finally comment on the capability of these double shadows to seek for traces of new gravitational physics beyond that described by General Relativity.

3+1 decomposition in modified gravities within the Palatini formalism and some applications

“…The ADM decomposition is also studied by applying the previous Gauss-Codazzi equations. Finally, the corresponding junction conditions for f (R) gravities within the Palatini formalism are established, which coincide with the results obtained in [31] through distributional analysis, and which have been shown to have important consequences in different scenarios, as the deflection of light by compact objects and the formation of (double) shadows [32].…”

“…In comparison to metric f (R) theories, where the Ricci scalar and its first derivative has to be continuos in general [37], and in some particular cases double layers might be allowed [41,42], this not the case for Palatini f (R) gravity, as naturally arise since the field equations remain second order in comparison to the fourth order of metric f (R) gravities. Nevertheless, the theory imposes the continuity of the trace of the energy-momentum tensor which might have important consequences, as was pointed out in [32].…”

“…Hence, the action for f (R) in the Palatini formalism reduces to the Hilbert-Einstein action with a cosmological constant in vacuum, equivalently to the field equations ( 4) and ( 5). Hence, by the induced metric γµν and the normal vector ñµ given in (32), the Ricci scalar R can be expressed in terms of the extrinsic curvature K and the intrinsic curvature (3) R conformally related to the ones of the spacetime hypersurface, as follows:…”

Observational Signature and Additional Photon Rings of Asymmetric Thin-shell Wormhole

“…The authors showed that due to reflection of photons by the wormhole there exist a novel shadow which is different from that of black hole in certain parameters space. Then more examples of asymmetric shin-shell wormhole are studied in [37][38][39], of which the authors named their results as double shadows [37]. It's worth noting that double shadows should be called double critical curves or photon spheres in the context of our article.…”

Revisiting the shadow of braneworld black holes

“…In particular, some interesting results related to the black hole shadows have been found. For examples, one can see the black hole shadows in the regularized 4D Einstein-Gauss-Bonnet gravities in [21][22][23][24], the shadows of black holes in an expanding universe in [25][26][27], the cuspy and fractured black hole shadows in [28,29], the black holes furnished by non-geodesic photons in [30,31] and the novel shadows from the asymmetric thin-shell wormhole in [32][33][34][35][36].…”