Talk:Chiral anomaly

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Random references

I get the impression you're just adding random links to papers containing the phrase "chiral anomaly" and not to introductory papers on chiral anomaly. Phys 17:35, 11 Jan 2005 (UTC)

Not really random, but neither introductary. Feel free to change or delete. If I would have a good introductary paper, I would have put it on the top. I'm doing title searches at arxiv.org and then read the papers and link to the (IMHO) best matches. Even as this doesn't yield introductary papers, it gives further reading where the topic is of interest.

I apologize if you consider these papers bad matches.

Pjacobi 17:54, 2005 Jan 11 (UTC)

I'm sorry. But I still think arxiv isn't exactly the best place for introductory papers. Most of the papers there are on research. Phys 19:00, 11 Jan 2005 (UTC)

It would be helpful to explain your assumption that introductory papers are good and research papers are not good. It is not evident to me that this is a shared assumption. --Tagishsimon (talk)

I guess I didn't make my point clearly enough. I did not say research papers are not good. What I intended to write was research papers often don't make good introductory papers. But clearly, reading research papers is necessary for someone working in the field. Phys 19:30, 11 Jan 2005 (UTC)

No gauge fields

I believe that the chiral anomaly does not need to involve gauge fields at all. Many examples of interesting theories with chiral anomalies DO have gauge fields (such as the baryon number violation example in this article). However, the lack of a necessary connection means that this article is a bit misleading at the moment. Any objections to a rewrite? matt 12 July 2005

Adler-Bell-Jackiw

Is the Adler-Bell-Jackiw another name for Chiral anomalies, or just a subset of them? Njerseyguy (talk) 19:20, 8 June 2009 (UTC)[reply]

A subset of them. 67.198.37.16 (talk) 01:18, 5 December 2020 (UTC)[reply]

Theoretical, observed or both

The article is unclear is to whether or not chiral anomalies have been observed, and if so, when, where, and how were they first discovered. Z gin der 2014-06-23T17:31:46Z

They are observed, in the sense that the neutral pion decays, and the chiral anomaly provides the mathematical foundation for this. Neutral pions were observed long ago. The Adler-Bell-Jackiw thing dates to the mid-1970's I think. Here's the long story: the pion was discovered to have negative parity an the 1950's (see article on parity (physics))... mumble mumble chirality... For the neutral pion to decay, the axial current

{\overline {\psi }}\gamma ^{5}\gamma ^{\mu }\psi

cannot be conserved, and the conventional way to make it non-conserved is via the Adler-Bell-Jackiw chiral anomaly. Some details: https://physics.stackexchange.com/questions/16877/chiral-anomaly-and-decay-of-the-pion ... oh but wait, then there's this, straight from the Delphic oracle: http://www.scholarpedia.org/article/Axial_anomaly

You are absolutely right, though; the lede to this article should state this out loud and up front. In principle, I'm supposed to be familiar enough with this stuff to be able to write that lede. In practice, I can't without making a mistake or two. 67.198.37.16 (talk) 01:32, 5 December 2020 (UTC)[reply]

I just now wrote a giant informal introduction. I think its 100% correct and also not misleading. But what do I know... I screw up all the time. 67.198.37.16 (talk) 03:37, 5 December 2020 (UTC)[reply]

Malformed sentence

I think this sentence from the introduction is malformed.

Such events are expected to be prohibited according to classical conservation laws, but we know there must be ways they can be broken, because the observable universe contains more matter than antimatter, we have evidence of charge-parity non-convervation ("CP violation"), and possibly other imbalances which must have been caused by breaking of a chiral law of this kind.

In particular, the commas after "the ways they can be broken". Is "because the observable universe contains more matter than antimatter" a reason why we know conservation laws must be broken? or a reason that we have evidence for charge-parity non-conversation. Surelyourejoking (talk) 08:11, 5 April 2018 (UTC)[reply]

It appears to have been fixed. 67.198.37.16 (talk) 00:17, 5 December 2020 (UTC)[reply]

Dubious claim

"we know there must be ways they can be broken, because the observable universe contains more matter than antimatter" This is not accurate. The matter-antimatter asymmetry may hint that there are new physics that can violate these conservation laws, but we have no direct or indirect evidence regarding the initial conditions of the observable universe, for example, with regard to baryon number or lepton number. So, this is mere speculation One hypotheses is that these numbers, or a combination of them such as B-L are not conserved in some form of high energy new physics that leads to this asymmetry, but this is pure speculation and it is equally possible given the available data that the initial conditions had baryon number and lepton number (which are measures of matter-antimatter asymmetry) that were very close to what they are now, even though that is a less "beautiful" hypotheses. For now, I have added a citation needed tag, but really, the claim needs to be moderated. Ohwilleke (talk) 18:15, 10 August 2018 (UTC)[reply]

Someone fixed this to say "Many physicists suspect that..." which was the intent. 67.198.37.16 (talk) 00:16, 5 December 2020 (UTC)[reply]

Electroweak burning?

Electroweak burning redirects here but there is absolutely no mention of it in the article. Has this been misdirected, or does it need to be added? 106.69.217.22 (talk) 03:32, 14 December 2021 (UTC)[reply]

Chiral Anomaly

It is unclear to me, as a non-particle physicist, how the pion decay violates the chiral anomaly. I have tried looking up the papers, but it is all about pertubation theory and how some terms do not conserve the axial current. But in the end, it should be understandable from a triangle diagram, how the non-conservation of the axial current comes to be. Can someone give an intuitive explanation on the triangle diagram, what the anomalous characteristic is? Can I already see from just looking at the input and output particles (pion/photons) that for a hypothetically massless pion the transition should be forbidden? 2001:7C0:2012:30:DD7D:9A22:18F6:3CC5 (talk) 14:40, 8 March 2022 (UTC)SomeGuy[reply]

I'm not sure what you are after, and less sure how to improve the article. The triangle diagram you see demonstrates clearly that the pion, corresponding to an axial current does decay to something (two photons), so that current is not conserved. The amount by which it is not conserved (anomaly) is an operator involving two photons. Cuzkatzimhut (talk) 15:32, 9 March 2022 (UTC)[reply]

"Informal" "introduction"

The "informal introduction" is neither informal nor an introduction. It's a mess of unexplained jargon. 2001:A61:3017:E001:E82D:9620:1F94:EF30 (talk) 00:04, 20 September 2023 (UTC)[reply]