Thursday, March 03, 2005

A crisis in particle theory?

Peter Woit is worried that particle theory is in trouble, since very few theory papers have made the top 50 most cited list since 1999. According to Peter,

Even more so than last year, this data shows that particle theory and string theory flat-lined around 1999, with a historically unprecedented lack of much in the way of new ideas ever since. Among the top 50 papers, the only particle theory ones written since 1999 are a paper about pentaquarks by Jaffe and Wilczek from 2003 at number 20, the KKLT flux vacua paper at number 29 and a 2002 paper on pp waves at number 32.

How many more years of this will it take before leaders of the particle theory community are willing to publicly admit that there's a problem and start a diiscussion about what can be done about it?

It would seem Peter is living in a different world than me. The problem isn't new ideas, it's the ability to test them which is lacking. Particle theory, particularly of the phenomenological bent, is actually pretty active. Just off the top of my head, here are three very new, very active ideas people have had in particle physics in the last couple of years

1) Split supersymmetry
2) Little Higgs models
3) Warped fermions

Search the arxiv for them, you'll get lots of results. Of course, without an experiment to tell us which new idea is right (or, more likely, that they're all wrong) none of them will get hundreds of citations, but that doesn't imply a lack of new ideas. In fact, it's quite the opposite, there are too many new ideas!

Now assume the LHC turns on and finds solid evidence for option number 2, a little Higgs model, then you can be sure that the original little Higgs papers will rocket up the citition list. Until the LHC turns on, though, we're stuck in a "propose a model, explore some of its consequences, move on" sort of mode. That's precisely the sort of thing that leads to lots of new ideas, and not a lot of citations.

My advice to those who think particle theory is in trouble, read hep-ph on a regular basis :) Of course, particle theory could well be in trouble shortly, it all depends on what the LHC sees, but for now, I'd say it's really quite active. Certainly more active than 5/10 years ago, when there was pretty much SUSY, in the form of the MSSM, and nothing else.

7 comments:

Anonymous said...

Good point.

I think, though, if the LHC finds Higgs and little else (a strong possibility, based on the precision measurements bounds), it will certainly be very, very bad for beyong-thestandard-model particle phenomenology.

In that case, a strong possibility is that string theory wll be the only game in town. However, areas like mathematical investigation of gauge theories, lattice gauge theories (you might like this one ;) ) should still be vibrant.

Anonymous said...

Hi Matthew,

I'm also putting this on my own weblog.

First of all, I think there's a straightforward objective issue here: when was the last year in which, if you put together a list of the 50 most heavily cited particle theory papers, only a couple would date from the last five years? I'm pretty sure you would have to go back to around 1945, when WWII interrupted research for about 5 years. I don't know much about what things were like in the earlier part of the century, but I suspect you might have to go back to the 19th century to find another year in which this happened. If you look at the SPIRES topcites data from ten years ago, you can see that things were very different than now, and if anyone knows of a source of similar data from earlier periods I'd be interested to hear about it. Particle theory is in a new situation, quite unlike any other one of the modern period, and people should be thinking about what this means.

The new ideas you mention, like split supersymmetry, aren't getting a lot of citations because they aren't very promising. They don't really explain any known experimental result, or give definite predictions about what future accelerators will see. If one of these ideas actually gave a definite picture of what will happen at the LHC, it would attract a huge amount of attention and number of citations.

As I mentioned in a previous comment, I think phenomenologists are in a very tough spot and will be for at least the next few years, through no fault of their own. I don't think there is much that can be done about this until there's new experimental data. Whatever overhyping of ideas that is going on amongst phenomenologists is relatively harmless.

String theory is a very different story....

Peter

Matthew said...

I think, though, if the LHC finds Higgs and little else (a strong possibility, based on the precision measurements bounds), it will certainly be very, very bad for beyong-thestandard-model particle phenomenology.
Yes, that would be very bleak, and I agree, it's very possible.
In that case, a strong possibility is that string theory wll be the only game in town.
Yes, but I'd expect that there'd be some fallout for the string theorists as well, if no SUSY is seen at the LHC.
However, areas like mathematical investigation of gauge theories, lattice gauge theories (you might like this one ;) ) should still be vibrant.
I can always hope. If the LHC sees nothing that may acutally be a "good" thing, in that it might help getting a super-B factory built. At least with that there is physics you know you don't understand that the machine can probes. A "known unknown" if you will, versus the "unknown unknown" of a new ultra high energy machine.

Anonymous said...

It's unlikely the LHC will find only the Higgs boson and nothing else. Being a scalar field, the Higgs field receives quadratic divergences to its mass in general due to radiative corrections. Either there is an incredible fine tuning coincidence going on or there is some mechanism to stabilize its mass. All known mechanisms so far, whether it's SUSY, little Higgs, extra dimensions, technicolor or what not requires additional particles at about the TeV scale.

Matthew said...

Either there is an incredible fine tuning coincidence going on
If you believe in the whole landscape picture, then that's exactly what's going on. For the record, I don't believe it, but that doesn't mean it's not possible.

Leucipo said...

"My advice to those who think particle theory is in trouble, read hep-ph on a regular basis"

Er, I do not think that the interior of the prototypical ivory tower is the better place to get perspective. Even a Touchgraw browsing of a field can be misleading.

To me, a bad sign is when I find myself printing from Prola.aps.org instead of arxiv.org. For instance, I have been trapped there last weeks looking for serious modelling on horizontal symmetries and radiative lepton mass generations.
A related clue is lack of the courage to invoke conjectures. Most hep-ph hides behinf the curtain of confidence levels (and I am losing confidence of these "confidence" estimates when nobody tells if they are frequentists or bayesians). Only in the alive neutrino field you can read people invoking phenomenogical relationships, eg to relate the cabbibo angle to the square root of some mass quotient. And even in this case the courage come from papers (Georgi et al.) in the seventees, as it comes the Barr-Zee observation that the leptonic mass have quotients of order alpha.

The new observations, I have not read it in any papers (except perhaps that the top Yukawa coupling is unity). And it is not lack of them: I learnt in the net that also the quotient from tau lepton to the electroweak vacuum is of order alpha (<1%) or that the anomalous momentum of electron is about muon/Z0 (hinting that the structure of loops of radiative mass generation is very similar to the structure of the QED vertex correction). In the seventies, such connections had been published as footnotes or introductory remarks (they didn't know of the 246 GeV nor the Z0, so they couldnt). Nowadays people is afraid even of telling it in the internet.

Leucipo said...

Hmm just if you are wondering, yep, the difference a_muon-a_electron could be also related to some radiative mechanism of mass; it coincides with m_electron/M_W