Sunday, 20 May 2007

LHC Roulette

There are no seminars these days that would be interesting enough to report on. To keep blogging, i'm afraid, i have to present you with some musings of my own. I always wanted to spell out my expectations concerning what the LHC would discover. We know for sure that it will reveal the mechanism of electroweak symmetry breaking. But for the first time in many years the outcome of a collider experiment is not obvious before the start. Now that the LHC starting date has been delayed again, it is the perfect time to play guessing games.

This is my pie:Unexpected 40%, Standard Model 40%, Strong Dynamics 15%, Exotics 5%.


Why do I expect Unexpected? Although the Standard Model describes the data perfectly well, it leaves many questions unanswered. And my feeling is that none of its extensions on the market really answers these questions. At least, not more than one at the same time. Of course, the most publicized is the hierarchy problem, which all the current models find difficult to handle. Less discussed, but perhaps more troubling is the question of fermion masses. Electroweak symmetry breaking should produce masses not only to the W and Z, but also to the fermions. We observe striking patterns in fermion masses, but we have no clue where they come form. For example, the up and down quarks are almost degenerate in mass but isospin is badly broken in the third generation. Besides that, there is the question of dark matter. While many models accommodate a dark matter candidate, they rarely explain the striking fact that the baryonic and the dark matter abundances are so close to each other. I maintain the childlike belief that there could be a simple and spectacular answer to some of these question within an ordinary quantum field theory. That there is something we are missing. Something obvious in hindsight, but very tough to pinpoint without a hint from experiment. Like anomalies in the old days.

Next, the worst of all worlds: Standard Model with a fairly light higgs boson. Unfortunately, all the collider data point to this possibility. Fermion masses and dark matter could be the results of some obscure physics at other energy scales. The hierarchy problem could well be the hierarchy fact, leaving us prey to landscape speculations. Really, a nightmare scenario and probably the end of particle physics as we know it.

Strong dynamics with a composite higgs or no higgs at all. This is a very natural possibility. A similar mechanism has been chosen by nature to break the chiral symmetry of QCD. Qualitatively, that breaking could also be described by a scalar field that gets a vev (the linear sigma model). At the deeper level, the scalar turns out to be condensing quark-antiquark pairs. However, it is hard to imagine how strong interactions at TeV could remain hidden from our precise low energy experiments. There are thousand places where the effects could in principle show up: flavour, CP violation, electroweak precision tests. We see none. The most troubling question is: why would nature design a theory with the seemingly sole purpose to hide it from our low-energy eyes? Nevertheless, there is always hope that there is some misunderstanding due to our ignorance of strong interactions.

Finally, Exotics. In this category I put all the crowning achievements of theoretical particle physics in the last 30 years. Supersymmetry, large extra dimensions, Little Higgs, TeV strings, TeV unicorns... Most likely, in a few years all these theories will be given a prominent place in the history of science, along with flogiston and Lamarckian evolution. They all have the same philosophical problem as the TeV scale strong interactions: why would someone take so much trouble to hide their effects from low-energy experiments. Only that they seem far less natural than strong dynamics. Why did i give as much as 5 percent then? Well, there is a large volume effect here ;-)

That's from me. As you can see, i'm naiveness and skepticism in one. If you're more confident about a particular existing model (beyond the Standard Model) you're welcome to lose 1000 dollars in Tommaso's online house of games.

7 comments:

Sushimoto said...

Well, if Supersymmetry were just one year old, proposed say by Arcano Hamelin, a very smart and prestigious theoretician, everybody would be terribly excited about it. The SUSY little hierarchy problem would be simply dismissed as very little, the SUSY option would be considered to be obviously superior and more elegant than any of its competitors and your pie would be drammatically different.

Anonymous said...

You know, for being such educated individuals, we sure can be rather dense.

Its rather ironic that years worth of higher education, and stress going through the junior faculty shuffle and the eventual tenure process and so forth and it all comes down to a roulette wheel --Literally.

If nature decides to give us a solitary scalar higgs and nothing else, well I for one am almost assuredly out of a job =/

mcc said...

Okay, so here is a question about that little pie you gave here. Given our perfect hindsight in this the year 2007, what would it look like if we decided to a draw a pie like this characterizing the finds of the Tevatron?

Jester said...

mcc, i guess my pie would be dominated by "nothing". Again, LEP and others indicate there is no spectacular new physics below 1 TeV.

Bilge said...

Surely, the "unexpected stuff" is exotic, no?!

island said...

I maintain the childlike belief that there could be a simple and spectacular answer to some of these question within an ordinary quantum field theory. That there is something we are missing. Something obvious in hindsight, but very tough to pinpoint without a hint from experiment.

"Hindsight" is right, and I don't think that your belief is "childlike". I also believe that there is something obvious missing, but I don't think that you're going to get physicists to take it seriously unless nothing is found, because the implication of the following physics is that the negative energy solutions have been misinterpreted:

http://www.lns.cornell.edu/spr/2006-02/msg0073320.html

This model very simply resolves the hierarchy problmem, but it will require a comlete collapse of particle theory to invoke this much hindsight:

http://www.lns.cornell.edu/spr/2005-06/msg0069755.html

There are four extremely short but *unaddress* points that I made in a quick series of posts to the moderated research group that are linked to the above address.

Hindsight, something missed, and simplicity... it's exactly as you suspect, although you probably weren't expecting that much time in your hindsight... ;)



Bilge... LLTNS!... how have you been?

aaacss said...

Don't worry anonymous. I'm sure your job will be safe for a long long time. I'm reading "The Computational Universe" and thinking that this thing is probably more complex than we've even begun to imagine. I'm sure we will discover lots, and the biggest discovery may very well be that there is so much more to discover.