# Towards traversable wormholes from force-free plasmas

### Submission summary

 As Contributors: Nabil Iqbal · Simon Ross Arxiv Link: https://arxiv.org/abs/2103.01920v3 (pdf) Date submitted: 2021-10-07 15:49 Submitted by: Iqbal, Nabil Submitted to: SciPost Physics Academic field: Physics Specialties: High-Energy Physics - Theory Approach: Theoretical

### Abstract

The near-horizon region of magnetically charged black holes can have very strong magnetic fields. A useful low-energy effective theory for fluctuations of the fields, coupled to electrically charged particles, is force-free electrodynamics. The low energy collective excitations include a large number of Alfven wave modes, which have a massless dispersion relation along the field worldlines. We attempt to construct traversable wormhole solutions using the negative Casimir energy of the Alfven wave modes, analogously to the recent construction using charged massless fermions. The behaviour of massless scalars in the near-horizon region implies that the size of the wormholes is strongly restricted and cannot be made large, even though the force free description is valid in a larger regime.

###### Current status:
Editor-in-charge assigned

In this resubmission we correct some small typos and make small clarifications requested by the referee.

### List of changes

Before equations (63) and (66) we correct the mode-numbering of the frequencies in the inline formula for \omega.

We add footnote 7 on page 6 to explain a potential subtlety in the lowest mode.

### Submission & Refereeing History

Resubmission 2103.01920v3 on 7 October 2021
Submission 2103.01920v1 on 25 March 2021

## Reports on this Submission

### Report

Dear Authors,

Thank you for answering my questions. The result about the Casimir energy in AdS is very important and can have a big significance for the field of wormhole study in general. This is why I want to make sure it is indeed determined by $m^2 R l$ as you claim.
Now I completely agree with your results for the even spectrum of periodic BC.
However, I noticed that that the Dirichlet spectrum, eqns. (63), (64) have a problem: for large $r$, the corrections $\delta \omega$ behave as $r^{1-2 \alpha_-}$, so it grows faster than the original, linear in $r$, answer. So the approximation breaks down. How does it affect the final answer for the Casimir energy?
Also it would be useful to check if the same happens with the odd spectrum for periodic BC.