Singularity structure being valid for all QFTs?

[Suekdccia]

TL;DR Summary

Singularity structure being valid for all QFTs? Even for more general theories?

I'm trying to understand this paper (https://arxiv.org/abs/1709.02813) in which the authors try to build a wavefunction for the universe without assuming locality and unitarity, so they would be rather emergent from geometrical constructs called "polytopes" and not assumed from the start (they tried to do the same with Lorentz invariance as well: https://arxiv.org/abs/1811.01125)

In the abstract it's said that the singularity structure of the toy model for the wavefunction of the universe that they used is universal and valid for all theories. Later, near the end (page 65) it says that again. Also, they say in page 56 that the geometric framework to compute the wavefunction of the universe doesn't make any reference to the underlying theory. I get that the singularities they are talking about refer to the poles found in correlators in quantum field theories (although they would be referring to cosmological correlators instead, as the paper is intended to apply to cosmology) and that they would be universal in the sense that correlators in any quantum field theory will have these singularities

However, what do the authors mean saying that it would be valid for all theories being universal for all of them or that they do not make any reference to the underlying theory?. I mean, do they only refer to all possible QFTs? Or are they referring more generally to the possible fundamental theories that could describe the universe (i.e. quantum gravity theories or theories of everything like string theory)?

For instance, in these presentations ("A Timeless History of Time" & "Bootstrapping large graviton non-Gaussianity" by Enrico Pajer), in the context of the cosmological bootstrap program, which is related to the previous papers, it is indicated that physicists could use the cosmological singularity correlators to study correlators from UV-complete theories and non-perturbative QFT. Does it mean then that all possible theories of fundamental high energy physics could be studied in this framework through these singularity correlators?

 

[PeterDonis]

Moderator's note: Thread level changed to "A". @Suekdccia the references you give cannot be usefully discussed at the "I" level. If you do not have the requisite background for an "A" level discussion, you are not going to be able to make much sense of these references.

 

[Suekdccia]

Moderator's note: Thread level changed to "A". @Suekdccia the references you give cannot be usefully discussed at the "I" level. If you do not have the requisite background for an "A" level discussion, you are not going to be able to make much sense of these references.

The papers are indeed advanced but I thought that the specific things that I was asking about (singularity correlators and their validity for more general theories than QFTs) required an intermediate level. Sorry about that

 

[bhobba]

The papers are indeed advanced but I thought that the specific things that I was asking about (singularity correlators and their validity for more general theories than QFTs) required an intermediate level. Sorry about that

Those papers are beyond my level, which taps out at Quantum Field Theory for the Gifted Amateur. As a mentor, I have received complaints from those who may be able to help that they can't understand your issue. I certainly can't, but I only have beginner—to intermediate knowledge of QFT and a smattering of cosmology.

String theory, for example, is a QFT. We have a folk from Wienberg that says all theories will look like a QFT at large enough distances. This would seem to place constraints on non-QFT theories. That's just my initial take.

Bottom line is at present those with enough knowledge to answer your issues can't understand what they are. I certainly can't. Can I please ask you to repost it? A much better query would be can someone help me understand the following papers?

And Peter's point is indeed valid. I know there is a common misconception that if you can't explain an idea to a freshman college student (I think it was Feynman who said it), then you don't understand it. I know what Feynman was getting at, but there is a famous story about how even he could not understand some stuff, and his sister, Joan, also a physicist, told him to work it out for himself, which he did. Very few people are in Feynman's class, and the vast majority have to accept that some things may be beyond their present understanding. It certainly applies to me.

Thanks
Bill

 

[PeterDonis]

I thought that the specific things that I was asking about (singularity correlators and their validity for more general theories than QFTs) required an intermediate level.

No, they're not. You are talking about advanced speculations.

 

[PeterDonis]

We have a folk from Wienberg that says all theories will look like a QFT at large enough distances. This would seem to place constraints on non-QFT theories.

Not really, no--Weinberg's point was actually that the fact that our best current theories are QFTs tells us nothing useful about what theories at the next underlying level will look like.

 

[bhobba]

Not really, no--Weinberg's point was actually that the fact that our best current theories are QFTs tells us nothing useful about what theories at the next underlying level will look like.

Valid point.

Thanks
Bill