Talk:Axion

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axion

Apparantly found: http://www.physorg.com/news84633896.html anescient 19:35, 6 December 2006 (UTC)[reply]

Primary: http://www.iop.org/EJ/abstract/0954-3899/34/1/009 ~Kylu (u|t) 04:18, 7 December 2006 (UTC)[reply]

Physorg.com is a website of dubious credibility, and the press interpretation of this paper is generally sensationalist. These are probably not axions! 18.4.2.3 17:31, 7 December 2006 (UTC)[reply]

How about now? https://www.nature.com/articles/s41586-019-1630-4 204.212.175.30 (talk) 18:56, 7 October 2019 (UTC)[reply]

No. An axion in Condensed Matter Theory is not the same as an axion in Particle Physics, which is the scope of this article. - Sarilho1 (talk) 20:40, 7 October 2019 (UTC)[reply]

I raised the importance level of this article to Medium. Axions are of intense theoretical and experimental interest. They are related to Strong CP Violation which, in turn, relates to the observed matter / antimatter asymmetry of the universe (or Baryon number problem). They are also possibly important for other cosmological effects. Finally, we may be able to experimentally observe them.

Slashdot backs things up. http://science.slashdot.org/article.pl?sid=06/12/06/2212250&from=rss Believe it now? --//Mac Lover ^Talk _C 01:44, 10 December 2006 (UTC)[reply]

Umm... maybe you're kidding, but Slashdot is not a reliable source of information on scientific subjects. --Reuben 07:54, 10 December 2006 (UTC)[reply]

Does anybody else has proof about axions?--//Mac Lover ^Talk _C 03:02, 12 December 2006 (UTC)[reply]

No, axions are still hypothetical particles. Nobody has demonstrated that they exist so far. There are a couple of promising leads (see the article), and other searches in progress, so maybe someday there will be proof of axions - but not now. --Reuben 04:51, 12 December 2006 (UTC)[reply]

The initial wording should be changed for that reason: “ axion (/ˈæksiɒn/) is a hypothetical elementary particle postulated by…” If it’s hypothetical it can’t be something that is. If it is something, then it’s not hypothetical.— Preceding unsigned comment added by 69.181.192.29 (talk) 21:35, 20 June 2023 (UTC)[reply]

I'm not sure I follow your logic. A conjectured concept is still a type of concept. Praemonitus (talk) 05:00, 21 June 2023 (UTC)[reply]

The “idea” can be real, but there is no such thing as a hypothetical thing (maybe in math). It’s either real or it isn’t. Don’t know how it can be anything else. 69.181.192.29 (talk) 07:22, 25 June 2023 (UTC)[reply]

Many RS use the phrase "hypothetical particle" to describe axions, gravitons, neutralinos, etc. Higgs bosons graduated from hypothetial-ity (??), axions not yet AFAICT. HouseOfChange (talk) 08:44, 25 June 2023 (UTC)[reply]

No, what it's saying is this may or may not be a thing, then covering the affirmative case and describing the attempts to verify it. This is a valid part of the scientific process. This article is as appropriate as discussing a notable but hypothetical astronomical object, for example. Praemonitus (talk) 16:31, 25 June 2023 (UTC)[reply]

Please explain in the article![edit]

How is this thingie different from the various kinds of neutrinoss? Both are chargeless, very light and minimally interactive with matter. 195.70.48.242 09:53, 7 December 2006 (UTC)[reply]

Among other reasons: Given that the decay spectrum of the supposed axion is e+e-, the axion must be a boson (and as an effective degree of freedom from chiral condensate it could hardly be anything else). The neutrino is a spin-1/2 fermion.

Well yeah, what the person above said. The axion is a spin-0 boson, the neutrino is a spin-1/2 fermion. The axion holds a very different place in the overall theory of all the particles than the neutrino (by overall model I mean the Standard Model). See the wikipedia page for "List of particles"

Jain[edit]

I have to disagree with removal of the paragraph about Jain's supposed discovery.

The press release is no longer available on U Buffalo web site, but the original article used by PhysOrg is still there: [1]
What exactly does Jain/Singh paper claim? Literal quote: "the persistent appearance of unusual narrow peaks around Q = 7 ± 1 MeV and 19 ± 1 MeV favours the existence of new short-lived exotic particles." In the very next paragraph: "The present experiment sheds some light on why the numerous previous efforts over more than two decades were not successful in detecting the low-mass, neutral, short-lived nonstandard axions." The word "axion" appears in the article 6 times, and no other possible short-lived exotic particles are mentioned. So they may not claim explicitly that they have discovered the axion ( their data is simply not good enough to make such claims ), but they sure do imply it. --Itinerant1 01:54, 8 December 2006 (UTC)[reply]

This can't possibly be the axion. If it were a particle it must show up as a narrow peak in Fig.2(a) due to the claimed lifetime in Fig.1(a). The width of a particle in the Q graph is 1/lifetime, and the claimed lifetime is so large that it's width must be tiny -- literally a line on the graph (smeared by detector resolution). But instead Fig.2(a) is totally smeared out. This must be some off-shell phenomena or fakes. It is not a particle.

Also, the standard for claiming discovery of a new particle is 5 standard deviations. The reason for this is because we often see fluctuations below this that go away with more data. The small peaks he does claim after massaging his data are only three standard deviations.

So, the claim that it's a particle is dubious. The claim of a discovery is absolutely wrong. This does not meet the criteria for a particle discovery in particle physics. 164.156.227.2 18:18, 8 December 2006 (UTC)[reply]

Axion is also the name of a series of tractors for agrivultural use by geman (combine-)manufacturer Claas.

Interactions[edit]

How can it be that axions have an electromagnetic interaction if the carry no charge? —Preceding unsigned comment added by Ishvara7 (talk • contribs) 02:49, 20 September 2008 (UTC)[reply]

If a particle has a charge, then that means that it couples to the electromagnetic field in a specific way. In terms of Feynman diagrams it means that there is vertex in which two lines coresponding to the particle and one line corresponding to the photon meet. So, if you look at the Feynman diagram of two electron exchanging a photon, you see that at a point where the photon meets an electron, you have a line corresponding to the electron moving toward the point, then there is a line corresponding to the elctron moving away from the point and there is a line corresponding to the exhanged photon.

The Feynman rules assign a weight every vertex, which in this case is the charge. So, this means that the axion cannot interact with photons in this particular way. But axions can interact with photons in another way. Axion couple directly to charged fermions like quarks. So, you can draw the following Feynman diagram as follows. Draw a closed loop representing a virtual quark. Attach a line corresponding to the axion at some point on that loop. Then attach a line corresponding to the photon at some other point oin the loop and then again a line corresponding to a photon on some other point in the loop.

The photon vertex is of the type I explained above, so it is proportional to the charge of the quark and cleary nonzero. The axion coupling to the quark is also nonzero. According to the Feynman rules, you need to integrate over all posible momenta the internal quark loop can have. You then end up with an effective vertex in which the axion line is coupled to two photon lines. Note that if you had attached only one photon line to the quark loop, then the diagram would correspond to an axion changing into a photon, but that violates energy/momentum conservation (this is automatically satisfied if you do the computations, so the result would be zero).

So, you see that while axions do couple to photons, they do that in a different way that charged particles. This coupling allows an axion to decay in two photns (but very slowly due to the small coupling and low mass). It can also lead to a conversion of the axion to a photon in the presense of an electromagnetic field (in thst case on of the photon lines represents the externa electromagnetic field, the axion line represnts the incoming axion, the other photon line represents the outgoing photon). This is the Primakof effect discussed in the article. Count Iblis (talk) 17:55, 20 September 2008 (UTC)[reply]

New evidence?[edit]

What do you say, guys? http://physicsworld.com/cws/article/news/37841 Mac Davis (talk) 20:37, 20 February 2009 (UTC)[reply]

Added caustics[edit]

I added some stuff about caustics, including a reference to pictures of the "Sikivie triangle" on his personal website. I realize that these pictures do not by any stretch constitute solid scientific evidence; you can see a lot of shapes if you squint at the stars. (And Sikivie is no crank, and so doesn't claim otherwise.) Still, I believe that I hedged enough in the article and didn't give it undue weight. 187.143.13.91 (talk) 19:51, 24 June 2010 (UTC)[reply]

Is ADMX actually taking data now?[edit]

The article says "ADMX is amidst a series of upgrades and is currently taking data in new mass and coupling ranges.". However, as of a few weeks ago they were still ramping up the magnet after the latest upgrade (personal communication). What verifiable source do we have that the experiment is currently taking data? I can't find any such announcements online. Howard Landman (talk) 17:08, 18 February 2014 (UTC)[reply]

Experiment Limit Reporting[edit]

There's extensive coverage of experimental searches. Should there be a table of limit results, or just current best limits, or do the values not matter since axions haven't been detected? Timetraveler3.14 (talk) 00:55, 15 November 2014 (UTC)[reply]

Yes, having a summary would be nice. Probably not a table but a chart showing regions. 67.198.37.16 (talk) 18:34, 24 November 2019 (UTC)[reply]

Particles and detergents.[edit]

It appears the axion has been named after a brand of detergent.

A few years before, a supermarket display of brightly colored boxes of a laundry detergent named Axion had caught my eye. It occurred to me that “axion” sounded like the name of a particle and really ought to be one.
— Frank Wilczek

Is this trivium too trivial to mention? Kleuske (talk) 14:26, 31 January 2016 (UTC)[reply]

No, its not too trivial, I think its a fun bit of history. (Actually, I remember hearing this too, back in the day.) 67.198.37.16 (talk) 18:33, 24 November 2019 (UTC)[reply]

Assessment comment[edit]

The comment(s) below were originally left at Talk:Axion/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

I raised the importance of this article to Medium from Low. The axion is of intense theoretical and experimental interest. It is related to Strong CP Violation which, in turn, is related to the matter / anitmatter asymmetry of the observed universe (aka the Baryon number problem). As noted, it is experimentally verifiable and has several possible cosmological implications.

Last edited at 23:18, 6 February 2007 (UTC). Substituted at 08:43, 29 April 2016 (UTC)

Why are axions cold?[edit]

From what I've read, axions are interesting in ΛCDM models because they're "cold", have very low velocities. (At least in intergalactic space. Within galaxies they acquire kinetic energy.)

Such a low-mass particle, given even the tiniest bit of energy, would be zipping around like a neutrino, at a velocity indistinguishable from c. How they are produced at a temperature so many orders of magnitude below that of the universe they came from is something I'd like to understand.

It's addressed very briefly on p. 10 of http://www.astro.caltech.edu/~golwala/ph135c/08MooreAxions.pdf, which says:

“

How Can Axions be “Cold”?

Dark matter should be non-relativistic before structure formation
- For m_A = 10⁻⁵ eV at 2.7 K = 2×10⁻⁴ eV
- These “thermal” axions would be relativistic
Also have axions produced at QCD phase transition
- “Non-thermal” axions are cold and form BE condensate

”

An elaboration on this would be a great addition to the article. 71.41.210.146 (talk) 16:04, 10 July 2016 (UTC)[reply]

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News October 2016[edit]

https://www.newscientist.com/article/2110591-physics-tweak-solves-five-of-the-biggest-problems-in-one-go/ "SMASH predicts that the axion should be about ten billion times lighter than the electron. Particles this small could be probed by the CULTASK experiment running in South Korea, or the proposed ORPHEUS experiment in the US and the planned MADMAX experiment in Germany." 68.179.173.92 (talk) 02:22, 28 October 2016 (UTC)[reply]

based on [2]; refs:

[3] which reports results from the [existing] Orpheus experiment ("excludes dark matter axion-like particles with masses between 68.2 and 76.5 μeV and axion-photon couplings greater than 4 x 10^-7 GeV^-1") - which this article could mention ? - Rod57 (talk) 00:00, 23 November 2016 (UTC)[reply]

News July 2017[edit]

http://www.nature.com/nphys/journal/v13/n6/full/nphys4109.html New CAST limit on the axion–photon interaction.

Ultralight axions[edit]

This article does not directly address ultralight axions (ULAs), but they are a valid possibility, and around $m\sim 10^{-22}\,\mathrm {eV}$ they make a particularly attractive dark matter candidate. Should we add a (sub)section about that (perhaps under Properties)? Gneisss (talk) 11:06, 17 December 2017 (UTC)[reply]

What is "PRL"?[edit]

Abbreviation PRL does not seem to be introduced:

GammeV saw no events in a 2008 PRL.

--Mortense (talk) 21:09, 11 October 2018 (UTC)[reply]

Physics Review Letters 67.198.37.16 (talk) 18:30, 24 November 2019 (UTC)[reply]

Is it possible to "compose dark matter"?[edit]

Regarding:

"...said axions would only partially compose dark matter."

Should it be the following?

"...said axions would only partially be composed of dark matter."

--Mortense (talk) 21:21, 11 October 2018 (UTC)[reply]

No. 67.198.37.16 (talk) 18:30, 24 November 2019 (UTC)[reply]

To explain a bit more: if X composes Y, then Y is composed of X. by saying "axions would only partially compose dark matter" the quote is saying that dark matter cannot be only axions, but must include at least one more thing.

--Rpresser 18:47, 12 January 2021 (UTC)[reply]

Detected?[edit]

This says that an axion has been detected. Bubba73 ^{You talkin' to me?} 20:26, 8 October 2019 (UTC)[reply]

No, I've already answered that. That is about Axion insulators. They are axions in the context of Condensed Matter Physics (bidemensional pseudo-particles that arise as excitations in solids), not in Particle Physics where they are postulated to solve the CP problem in QCD. Sure, this discovery can be mentioned in the article (Nature article for references), my preference would be either in the Experiments section or in a new one small one about axions in CMP, as it might help particle physicists in their search, but it is not a actual discovery of an axion as an elementary particle. - Sarilho1 (talk) 08:47, 9 October 2019 (UTC)[reply]

Thank you. Bubba73 ^{You talkin' to me?} 15:11, 9 October 2019 (UTC)[reply]

What's the Lagrangian?[edit]

Without a Lagrangian form for the axion, its hard to understand the geometry of the thing. This seems to be a major shortcoming of this article!? 67.198.37.16 (talk) 18:29, 24 November 2019 (UTC)[reply]

The form of the Lagrangian is determined by the response fields - the ones that yield the equations ∇·𝐃 = ρ, ∇×𝐇 - ∂𝐃/∂t = 𝐉 for the electrical sources ρ and 𝐉. From the equations posted, these are 𝐃 = ε₀(𝐄 - κθc𝐁) and 𝐇 = (𝐁 + κθ𝐄/c)/μ₀, where ε₀μ₀ = 1/c², and are always derived from the Lagrangian density ℒ(𝐄, 𝐁) - when expressed as a function of 𝐄 and 𝐁 - as 𝐃 = ∂ℒ/∂𝐄 and 𝐇 = -∂ℒ/∂𝐁, so that ℒ = ½ (ε₀E² - B²/μ₀) - κθε₀c𝐁·𝐄, which is the Maxwell-Lorentz Lagrangian density plus an axial term -κθε₀c𝐁·𝐄.

The fields - as always - are those associated with the electric potential φ and magnetic potential 𝐀, defined as 𝐁 = ∇×𝐀, 𝐄 = -∂𝐀/∂t - ∇φ, because it is a gauge field. So you always have the equations ∇·𝐁 = 0 and ∇×𝐄 + ∂𝐁/∂t = 𝟎, as identities. The equations cited in the article, for "magnetic" sources (which I'll label here as σ and 𝐊 respectively for charge and current density), would actually be those for the 𝐃 and 𝐇 fields: ∇·𝐇 = σ and c² ∇×𝐃 + ∂𝐇/∂t = -𝐊, while for bona fide magnetic sources they would have been ∇·𝐁 = μ₀σ and ∇×𝐄 + ∂𝐁/∂t = -μ₀𝐊, expressing the degree of non-derivability of the fields (𝐁,𝐄) from potentials - hence the scare quotes. Such equations arise, normally, when describing fields inside a medium, where the response fields (𝐃,𝐇) are not strictly proportional to (𝐁,𝐄). So, in that sense, there's nothing novel or special about (σ,𝐊) and they're tangential to the main issue being raised in the article.

The "magnetic" sources that arise in the equations cited in the article are not independent of θ, as they would be zero, too, if all of the constitutive coefficients μ₀, ε₀, κ and θ were all constants, with θ = 0; or (σ,𝐊) = κθc (ρ,𝐉), if θ ≠ 0. For the axion, however, θ is promoted to a field in its own right (and for non-constant θ, there'd be additional contributions to (σ,𝐊) from the derivatives of θ). The axion equation comes from adding a "kinetic" term ½(|∇θ|² - (∂θ/∂t)² - m²θ²) into the Lagrangian density for θ, with a suitable coefficient. The one that matches the axial law cited would be ε₀c, so that the total Lagrangian density would be ℒ = ½ (ε₀E² - B²/μ₀) - κθε₀c𝐁·𝐄 + ½ε₀c (|∇θ|² - (∂θ/∂t)² - m²θ²). — Preceding unsigned comment added by 2603:6000:AA4D:C5B8:0:3361:EAF8:97B7 (talk) 18:41, 29 January 2022 (UTC)[reply]

Rotation?[edit]

The article states

With or without monopoles, incorporating the axion into Maxwell's equations has the effect of rotating the electric and magnetic fields into each other.

but the matrix provided is not a rotation matrix (although it is “deceptively” written out to resemble one, but the determinant is not 1, but rather $1+\tan ^{2}\xi$ ).

A more fair representation would probably be the following:

{\begin{bmatrix}\mathbf {E'} \\c\mathbf {B'} \\\end{bmatrix}}={\begin{bmatrix}1&\tan \xi \\-\tan \xi &1\\\end{bmatrix}}{\begin{bmatrix}\mathbf {E} \\c\mathbf {B} \\\end{bmatrix}}

LvdT88 (talk) 12:05, 19 June 2020 (UTC)[reply]

Extensive edit by new user[edit]

I reverted this edit because parts of it are problematic. For example, it adds a lot of prose explanation without citing those explanations to RS; presumably they come from a knowledgeable user but Wikipedia doesn't use that free-flowing essay style. There is also a problem in the weight it gives to one experiment called MADMAX, which does not seem more notable than many other experiments. I would like to see these suggestions for axions given in smaller segments with more RS cited. Also, JaxRed should disclose any COI wrt MADMAX or axion physics. HouseOfChange (talk) 21:54, 24 November 2020 (UTC)[reply]

The change only adds a small section on the experiment, which is notable due to its high sensitivity to axions in the range in which they are predicted to most likely make up dark matter. Scienceperson42 (talk) 17:30, 28 October 2022 (UTC)[reply]

"Quantum Squeezing" experiment at Yale[edit]

https://www.techexplorist.com/new-faster-method-seeking-out-dark-matter/37783/

I don't see mention of this one, and it sounds kinda interesting.... For the regulars here to decide if it should be added. --Pete Tillman (talk) 00:39, 15 February 2021 (UTC)[reply]

Tillman, The Yale haloscope actually has its own wikipedia page at Axion Dark Matter Experiment. Maybe there should be better linkage between here and there? HouseOfChange (talk) 04:07, 15 February 2021 (UTC)[reply]

Yes, I should think so! Are you a regular here? As an antique geologist, whose formal physics education ended, hem, not long after the middle of the last century -- maye you could take care of it? Or a page regular?

Thanks for pointing this out. I am cheering the axion discovery(?) on. Since the physicist, whose name escapes me but who won his Nobel for work done when he was an undergraduate[!!], is a personal hero of mine. Looking forward to reading his new pop-sci book.... Cheers, Pete Tillman (talk) 21:50, 17 February 2021 (UTC)[reply]

mass[edit]

It seems to me that this article is covering widely different points considering that the axion mass proposed varies by 17 orders of magnitude by section, without any summary putting it into perspective. -- MGChecker (talk) 00:42, 29 October 2022 (UTC)[reply]

Equations of axion electrodynamics[edit]

I'm an active researcher who has published four papers on axions. For many years, this Wikipedia page has presented a set of equations due to Visinelli as "the" equations of axion electrodynamics. The problem is that these equations are completely different from the standard set that the whole field uses, and furthermore they are totally theoretically unmotivated. They do not come from an action, do not emerge from deeper theories like string theory, and cannot imply a solution of the strong CP problem. This is a common problem with Wikipedia articles on theoretical physics: they doesn't contain the standard textbook material, but they do contain all sorts of random claims from obscure papers. Many junior researchers have been misled this way. I'm not a Wikipedia insider, but I've fixed the issue and hope that my fix won't be reverted. 73.158.248.187 (talk) 01:33, 9 September 2023 (UTC)[reply]