A possible quantum field theory of tachyons?

[PeterDonis]

TL;DR

A paper claims to have found a consistent quantum field theory of tachyons.

I have come across the following paper (arxiv preprint link, it looks like it is published in Phys Rev D) that claims to have found a consistent quantum field theory of tachyons, overcoming three issues which have been said in previous literature to make such a theory impossible:

https://arxiv.org/abs/2308.00450

I am wondering if any PF experts have seen this paper and have any comment on its claims.

 

[Mordred]

I've never encountered this paper before it's interesting but I think I will need to examine it's reference papers to answer several questions it brings to mind. In particular those relating to the negative mass, negative energy terms. Which this paper seems to indicate that the antitachyon addresses which I find questionable as the antitachyon should have the same energy density and mass as it's partner.

Unless I'm misreading this paper


Edit found the relations I needed article in post 4.

 

[Vanadium 50]

PRD will accept a result with one referee; PRL usually requires two. Of course there are exceptions.

I don't particularly care for this kind of theory paper, as it tends to be completely disconnected from experiment. But I will say that they could be much clearer about what a tachyon is. (e.g. which kinematic quantities are real and which are complex)

 

[Mordred]

Yeah I agree this paper is rather lacking on numerous details. I couldn't even begin to imagine how you would handle IR and UV divergence let alone any involvement on the CKMS mass mixing matrix. It seems to rely on the antitachyon for any potential means of detection. I've looked over a couple of its references and some of it helps a bit but doesn't really fill in the blanks.
This reference the paper looks at helps detail the superluminal tachyon, antitachyon it does help make the OP paper a little clearer

https://arxiv.org/abs/2209.01836

May be helpful.

One related question however is how can a subluminal observer ever measure a superluminal particle to begin with ?

 

[Vanadium 50]

how can a subluminal observer ever measure a superluminal particle to begin with ?

I have, on and off, been working on just that. Since it is not published, it is not fodder for PF discussion. What I can say is:

• There is an experimental signature
• There are regions of parameter space where they are not already excluded
• It may be possible to avoid causality problems - there is a little-recognized assumption that may or may not be true.

These tachyons have real energy-momentum four-vectors and thus imaginarty mass. This is necessary for the experimental signature.

I do not believe tachyons exist, but that is not a good reason to avoid the search. It is, however, a good reason to do other things than finish the paper.

 

[Vanadium 50]

PS When I posted this, the timestamp was "in a moment".
Life imitates art.

 

[Mordred]

Fair enough, I haven't followed any of the tachyonic studies in years. Mainly as I too don't feel they exist and needed to focus my studies elsewhere.
However as you say we cannot discount the possibility lol.

Hence part of my reason to dig through the papers references on the issues it mentions.

Edit: wouldn't be the first time studying theories I don't believe likely. You always end up learning something new regardless . Provided it's a theory that has numerous peer reviewed literature naturally (at least for me)

 

[Demystifier]

TL;DR Summary: A paper claims to have found a consistent quantum field theory of tachyons.

I have come across the following paper (arxiv preprint link, it looks like it is published in Phys Rev D) that claims to have found a consistent quantum field theory of tachyons, overcoming three issues which have been said in previous literature to make such a theory impossible:

https://arxiv.org/abs/2308.00450

I am wondering if any PF experts have seen this paper and have any comment on its claims.

The paper has recently been criticized in: https://arxiv.org/abs/2406.14225

 

[Mordred]

Well there's the details involving renormalization lol. Good rebuttal paper

 

[Vanadium 50]

As I mentioned, I do not care for this kind of theoretical physics, untethered to data. However, from a math-y point of view, tachyons are trouble.

As a tachyon loses energy, it speeds up. So what's the ground state? It is not unique as it can point in any direction. This makes a big old mess.

As a more math-y level, we can sometimes replace coupled differential equations with complex numbers. This is a huge simplification. QM does this. When you try and do it again with tachyons, you build in cross-terms: an i from QM multiplies a tachyonic i and you get a real number. That may be real (no pun intended) or it may be an artifact of overusing this trick. I don't think this been completely worked through, much less solved.

 

[Mordred]

Mind if I steal the term math-y lol. I suspect further counter papers to the last counter paper so I agree there is a lot of details yet to resolve. I've been looking over the last paper on the LSZ including the UV cutoff it provided. It's a good exercise if anything and I can use the practice as time allows.
The momentum relations you mentioned are definitely problematic to say the least.

 

[Vanadium 50]

Mind if I steal the term math-y lol.

Happy to rent it to you.

The momentum relations you mentioned are definitely problematic to say the least.

Yes, they are. "What does it mean to be a tachyon" is not a question with a single well-defined answer. "What does imaginary momentum mean, if anything" is at least as troubling. "How do tachyons and tardyons exchange complex momenta" is so poorly defined I don't think it means anything at all. It's all a mess.

I believe that a tachyon should have real 4-momenta and purely imaginary mass. That's still a mess, but it is the smallest possible mess.

And that's just a classical theory. Try quantifying it. Your brain will hurt trying to figure out what commutes and what does not.

 

[Vanadium 50]

For fun, think about the following question - a tachelectron is defined to have q = -e and mass $im_e$. Does it bind to an ordinary proton? If so, what are the energy levels? What is the mass of the combined system? Does the combined system travel faster or slower than light?

 

[Demystifier]

Tachyon fields do not propagate faster than light. https://www.physicsforums.com/threads/why-is-there-nothing-faster-than-light.1053365/#post-6906691

 

[Vanadium 50]

As the poster of that paper points out tachyonic fields are not the same as tachyon particles.