Light propagation and quasinormal modes of a topologically charged Schwarzschild-Klinkhamer wormhole

TL;DR

This work analyzes light propagation and scalar perturbations in a topologically charged Schwarzschild-Klinkhamer wormhole endowed with a global monopole. By combining null geodesics, weak- and strong-field lensing (via Gauss-Bonnet and Bozza–Tsukamoto formalisms), photon-sphere/shadow calculations, and a scalar quasinormal-mode/time-domain study, the authors map how the throat radius $a$ and monopole charge $\bar{\alpha}$ shape observables. They find the strong-field deflection largely depends on $\bar{\alpha}$ and is independent of $a$ at leading order for shadows, while weak-field deflection and Einstein-ring observables encode $\bar{\alpha}$ effects with $a$ entering only higher-order terms; quasinormal spectra and time-domain signals show that increasing $a$ lengthens the ringdown without compromising stability. These results establish potential observational signatures distinguishing this wormhole from Schwarzschild and global-monopole spacetimes, guiding future high-precision lensing and gravitational-wave measurements.

Abstract

In this work, we present a theoretical analysis of null geodesics, critical photon orbits, and shadow formation associated with a wormhole generated by a geometric defect. The propagation of light in this spacetime is examined through the deflection angle in both weak- and strong-field regimes. Analytical expansions are derived in each regime and employed to characterize gravitational lensing observables. By varying the global monopole charge, we evaluate its impact on these observables and determine parameter ranges that may be accessible to current or future observational probes. Finally, we calculate the quasinormal modes as well as the time-domain solution for scalar perturbations as well.

Figures (12)

• Figure 1: Null geodesics are displayed for several combinations of the parameters $a$ and $\Bar{\alpha}$. The dashed curves identify the associated photon spheres, whose radii change with $a$ for fixed $\Bar{\alpha}$.
• Figure 2: Light deflection in the weak-field regime.
• Figure 3: The Gaussian curvature $\mathcal{K}(r,a,\Bar{\alpha})$ evaluated for $M=1$, $\Bar{\alpha} =0.5$ and $a=2.01$. The solid wine marker identifies the radial location at which $\mathcal{K}$ vanishes, defining the boundary between regions of stability and instability for photon motion. The wine dotted marker denotes the photon sphere radius $r_{m}$, which lies entirely within the unstable domain.
• Figure 4: The deflection angle $\hat{\alpha}(\beta,\Bar{\alpha})$ is plotted as a function of the impact parameter $\beta$ for several values of $\Bar{\alpha}$.
• Figure 5: In (a) and (b) we have respectively the regular part of the integration (\ref{['24']}) and the angular deviation as a function of $a/2M$ for $\beta/2M=\frac{3\sqrt{3}}{2}+0.005$ and then we vary the charge on the global monopole.