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I was recently introduced to the dark matter candidate known as "macros," which are theoretically made up of macroscopic clumps of matter rather than of an elementary particle. These apparently can have masses up to $\sim 10^{20}$ grams (perhaps I misread something?). A paper published this year claims that macros could theoretically produce a new type of lightning that is made of a single leader, rather than "regular" lightning which is made of hundreds or thousands of leaders.

Questions:

  1. What is the resolution required to be able to definitively establish the existence of a macro via photographs of lightning, as suggested by the paper published this year?

  2. Are there other ways to probe the existence of macros without depending on photography? Or, are there ways to rule out the existence of macros without photography?

  3. If these macros are made of fermionic matter (maybe they aren't, I'm not sure), then why wouldn't they be ripping through other macroscopic objects, like people or buildings or mountains?

  4. Apparently, the process by which "regular" lightning is generated is not well understood, and yet here we have a proposal for dark matter that may be detected via a new type of lightning. So, how would we, in principle, be able to tell apart the "regular" lightning from a macro-induced lightning strike if the mechanism for "regular" lightning is not well understood.

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As I understand, the macro idea does not propose a specific formation mechanism or microscopic explanation of what the dark matter is. It takes the mass - cross-section parameter space as a phenomenological starting point and asks what constraints could be put on it.

With that in mind...

What is the resolution required to be able to definitively establish the existence of a macro via photographs of lightning, as suggested by the paper published this year?

To answer this question rigorously, you would need to compare the expected distribution of macro lightning strikes, with the distribution of non-macro lighting strikes. The authors don't do this analysis. However, there is some information, since they say that the straightest lightning strike they found in the literature is not straight enough to be a macro. In order to make this claim, they have to know (or assume) that the camera had enough resolution that it could have measured a straighter lightning strike. The camera used for that image was a "Panasonic Lumix DMC-TZ10 compact camera in scene mode."

Are there other ways to probe the existence of macros without depending on photography? Or, are there ways to rule out the existence of macros without photography?

I think this group has written a lot of papers on different ways to test for macros, such as

If these macros are made of fermionic matter (maybe they aren't, I'm not sure), then why wouldn't they be ripping through other macroscopic objects, like people or buildings or mountains?

The last two papers above consider those possibilities.

Apparently, the process by which "regular" lightning is generated is not well understood, and yet here we have a proposal for dark matter that may be detected via a new type of lightning. So, how would we, in principle, be able to tell apart the "regular" lightning from a macro-induced lightning strike if the mechanism for "regular" lightning is not well understood.

I'm not an expert on lightning. The claim in the Starkman et al paper is that the signature of macros is a lightning strike more straight than any that would be produced by a terrestrial mechanism. However, note there is a comment on arxiv by Cooray et al in response to the Starkman et al paper, that questions the lightning signature proposed by Starkman et al: https://arxiv.org/abs/2105.09615. Cooray et al also wrote a follow-up paper proposing a different way to use lightning to look for macros https://arxiv.org/abs/2107.05338

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