Talk:Beyond the Standard Model

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This article was nominated for deletion on March 5, 2006. The result of the discussion was keep.

[edit] General Discussion

I'm not sure what the purpose of this article is about. Perhaps it is a little too ambitious and is trying to list/detail every beyond the standard model theory and test rather than trying to list the motivations for the work.

In addition, there are many mistakes (that anyone could have made in undertaking such an expansive task)... for instance the only dimension 5 operator in the SM are neutrino masses (the other ones are not Lorentz invariant). I'm hesitating to correct them because I'm pretty sure that this is not the place for a list of those operators.

[edit] Possible organisational strategy

May be starting with a simple discussion of the failings of the SM -- mainly that there are 20+ parameters of the SM that have no explanation. May be also state the need to extend the SM to accommodate the Standard Model of Cosmology. Perhaps finally a word on neutrino masses.

In its own section, the parameters of the SM can be listed in a simple fashion and what physicists view as needing to be explained: gauge couplings (gauge coupling unification?), fermion masses/mixings (hierarchical structure), strong CP (axion?), higgs mass (hierarchy problem), etc...

Then similar fashion do the interface between the SM and the SM of cosmology: inflation, dark matter, CC problem, baryogenesis, etc (is there anything else?)

Finally, if needed, there could be links to beyond the standard model constraints, theories, etc.

-- jay 04:46, 7 March 2006 (UTC)

I tend to agree with most of this. In particular, insofar as this is a general-use encyclopedia article, we need to start out by explaining the issues in terms that someone with relatively limited knowledge could understand, and only later get to the technical details. -- SCZenz 19:09, 8 March 2006 (UTC)

Yeah, this article, as it currently stands, bites off more than it can chew. It looks more like the table of contents for a book, than an article. linas 03:40, 9 March 2006 (UTC)

There may be some advantages to this style, though. It is now not so difficult to expand some sections and make them articles in their own right. They can then be moved and linked from here.Count Iblis 13:17, 9 March 2006 (UTC)

The article contains a lot of useful information. In particular, the list of operators and terms in the standard model is a good reference, despite a few errors. However, these lists are good references for information about the standard model, ie, if I were to look for them I'd look on the Standard Model page, not here. So I'd suggest incorporating them onto the SM page, which is a bit short on details of the operators/interactions anyway. Then this page can concentrate on, as its title suggests, ways to go beyond the standard model. I don't really know where neutrino masses fit in there, although they have their own page which I'd guess should be linked to the SM page and this page. JarahE 22:55, 3 April 2006 (UTC)

[edit] A physics question

Reading this article made me wonder something, probably it's got an obvious answer (I've only thought about it for 5 minutes), but I'd guess that for you people that understand 4d physics it'd take less. In school they taught us that there are only 3 flavors because neutrinos used to be massless when I was young (before Jay came) so you'd see the extra flavors running around loops, now that neutrinos are massive that argument's gone. Then there's the argument about big Yukawa couplings, this is based on a single scalar Higgs and its not very convincing. But would the following be an experimental ramification of more flavors?

Neutrinos are different from the other fermions in that their mass matrix has really big mixing angles. So if there are extra generations waiting up there, say one every few orders of magnitude until the Planck scale (so much for asymptotic freedom, but really its pretty useless to free the SU(2) and not the U(1) anyway, unless you like GUTs) then you'd expect them to have big mixing angles with the 3 generations we know. My first question is if this is ruled out experimentally. My second is if this is just what you'd want for the see-saw mechanism (which seems to suppose some supermassive neutrinos anyway)? That is, are the neutrinos we know light because they have big mixing angles, and so they get to use the see-saw and their friends don't?

The bigger question then would be whether you can turn this argument around and try to use low energy physics, like neutrino oscillation, to learn about neutrino generations that are way too massive to be formed anywhere but the big bang or a black hole? Anyway, I'd suspect that I'm wrong, or this is the whole point of the see-saw idea so it's old news, or both (or maybe the big mixing angle is a red herring, and the different thing here is that I'm not using a GUT scale but just considering a long progression of extra generations, which to me seems more Hierarchy-free). In which case I'd just like to say that I'm hoping for evidence for more flavors at the LHC, an infinite number seems easier to explain than 3. JarahE 18:01, 4 April 2006 (UTC)

I don't think we're that different in age... I think your question comes down a little bit to semantics -- specifically what does one mean when one says "neutrino".

If you mean something like our neutrino which is part of an anomaly free chiral family, then there are only 3 generations of neutrinos -- you'd see them running around in various loops and causing deviations in the couplings of the W&Z (to decouple chiral fermions requires symmetry breaking and to make all of the fermions heavy enough, you have to go to strong couplings since we've measured the electroweak vev).

If you mean a dirac lepton doublet, then they are allowed and can be made however heavy you want. However, their effects are pretty negligible (you can integrate them out to figure out what they actually do and it isn't much). They could become interesting when they start becoming 1 to 10 TeV-ish. (having the Z mediating flavour changing processes)

You could also think about sterile neutrinos... but they are pretty invisible once you make the active (ie the ones who couple to the Z) light enough.

jay 21:39, 6 April 2006 (UTC)

Good, of course it does depend on the theory that I have in mind. I'm thinking of adding full generations, with all of the same charges and particles as SM generations so you get the same anomaly cancellation in each generation. But I want each successive generation to be more massive than the previous one, and in particular I want the neutrinos in generations 4 and up to be sufficiently massive that the deviations to the W&Z couplings haven't yet been excluded, but maybe would show up at the LHC. As they're massive, I guess I have to decide whether they have Majorana mass terms or if they are part of full Dirac spinors. I'm really interested in both possibilities, but I think I prefer Dirac for aesthetic reasons (for example, so that F=B+L meaning that parity is always plus or minus one).

You point out that light (less than the W mass) Weyl neutrinos of all generations contribute to these couplings, this is what I remembered from school (I remember they can each run around a loop and you get a factor equal to the number of generations which matches experiment very well, but it was important that the neutrinos were light). My extra neutrinos are not at all light. The big Yukawa coupling responsible for these high masses doesn't bother me. I don't even think that the coupling has to be big if you just add more scalars with big VEVs to give the masses. However, in practice I think that fundamental scalars are like epicycles, they can solve any problem but we've never seen one. I hope that at the LHC we'll kill the Higgs sector of the SM. I don't know what can replace it, maybe masses come from some internal degree of freedom like quantum gravity fuzzball orbitals or from vibrating string modes (but with generation-indep quantum numbers) or from internal directions wrapping some compactification cycles, its not clear to me that they should have perturbative gravity-free explanations, and if they do, I don't see why it should be a single scalar Higgs (with lots of Yukawa couplings, which are like VEVs of other scalars anyway so you don't really save anything by considering a single Higgs), so I don't worry about the big Yukawa couplings in the Higgs scenario. If we find a single scalar Higgs at the LHC, I'll start worrying.

Summary: I want usual SM generations (maybe an infinite number) with high masses, and I don't care about the big Yukawa coupling because I don't want the masses to come from the SM Higgs. Is this excluded?

Thanks for your answer! Sorry to be a bit longwinded JarahE 22:48, 6 April 2006 (UTC)