Passage of radiation through wormholes of arbitrary shape

TL;DR

This paper analyzes how scalar and electromagnetic waves scatter and resonate in traversable wormholes of arbitrary shape, revealing unique properties such as long-lived quasinormal modes and the absence of superradiance.

Contribution

It provides a detailed study of quasinormal modes and scattering in generic wormhole geometries, demonstrating the impact of shape functions and confirming the accuracy of high-order WKB methods.

Findings

Wormholes with $b'(r) \,\approx\, 1$ have very long-lived quasinormal modes.

Axially symmetric wormholes do not exhibit superradiance.

High-order WKB formula accurately computes scattering and Hawking radiation processes.

Abstract

We study quasinormal modes and scattering properties via calculation of the $S$-matrix for scalar and electromagnetic fields propagating in the background of spherically and axially symmetric, traversable Lorentzian wormholes of a generic shape. Such wormholes are described by the Morris-Thorne ansatz and its axially symmetric generalization. The properties of quasinormal ringing and scattering are shown to be determined by the behavior of the wormhole's shape function $b(r)$ and shift factor $\Phi(r)$ near the throat. In particular, wormholes with the shape function $b(r)$, such that $b'(r) \approx 1$, have very long-lived quasinormal modes in the spectrum. We have proved that the axially symmetric traversable Lorentzian wormholes, unlike black holes and other compact rotating objects, do not allow for superradiance. As a by product we have shown that the 6th order WKB formula used for scattering problems of black or wormholes provides high accuracy and thus can be used for quite accurate calculations of the Hawking radiation processes around various black holes.