Monday, 26 May 2008

Sagrada Familia et al.

I have not reported much from CERN in May because I was away most of the time. Last week I was enjoying my holidays in Barcelona. One of the numerous tourist attractions there is a cool science museum with a planetarium, physics toys, dinosaur skeletons, gaudy fish and octopussies. What kids seemed to like the most, however, was a temporary exhibition of particle physicists in their natural habitat who were attracted to that place by the conference Planck'08. On the photo you can see the exhibits observed by an intrigued American tourist. The physicists are kept behind a provisional fence so that tourists do not feed them (scientists in general require a carefully selected diet of coffee and cookies).

Planck is an annual European meeting centered around model building beyond the Standard Model. It usually gives a fair overview of what's new in the field. A short glance at the program reveals that there is not much. I could often hear this unpleasant sound of an empty barrel being scraped. Nevertheless, there were a few noteworthy talks too. Amusingly, most of the theoretical developments these days happens in the queer corner of particle physics. For more than 30 years particle physics was focused on very well motivated extensions of the Standard Model, which didn't get us very far. The recent trend, prompted by Howard Georgi's joke, is to play with perfectly unmotivated models instead. The hope is that shooting at random will prove, if not more successful, at least more fun. Thus, there's much a do about unparticles and its close relatives - the hidden valley models. A new member of the family proposed by Markus Luty is called quirks. This is an extension of the Standard Model with a hidden sector being a QCD-like confining theory. Unlike the ordinary QCD where some light quarks are much lighter than the QCD scale ~1 GeV, that hidden sector has a small (much less than TeV) confinement scale but heavy (more than TeV) quarks. The resulting phenomenology is weird. In QCD, two quarks flying apart form a string in between them whose energy density soon becomes large enough to pull new quarks out of the vacuum. For quirks this is not the case, so that a string between two quirks does not break and may stretch to macroscopic sizes. Markus is currently investigating the collider signals of his quirky scenario.

Besides that, I would mention Gia Dvali who keeps pushing his huge-number-of-degrees-of-freedom solution to the hierarchy problem, Riccardo Rattazzi who made some progress in understanding of the conformal field theories of the Luty-Okui type, and John Terning who explores the AdS/CFT approach to unparticles and hidden valley. Yet the overall impression is that theorists are regrouping their forces while waiting for the LHC. The real game will begin in a year or so.

Sunday, 11 May 2008

Pauli's Other Exclusion Principle

As I am currently stretched between continents, I ponder over the differences between the US and Europe. Apart from the taste of food and the size of humans, there seems to be a fundamental difference at the level of particle physics. Let's have a closer look at the time and place of discoveries of elementary particles:
  • Tau neutrino, 2000, Fermilab, United States
  • Top quark, 1995, Fermilab, United States
  • W and Z bosons, 1983, CERN, Switzerland
  • Gluon, 1979, DESY, Germany
  • Bottom quark, 1977, Fermilab, United States
  • Tau, 1975, SLAC, United States
  • Charm quark, 1974, SLAC/Brookhaven, United States
  • Up, down, and strange quarks, 1968, SLAC, United States
  • Muon neutrino, 1962, Brookhaven, United States
  • Electron neutrino, 1956, Los Alamos, United States
  • Muon, 1936, Caltech, United States
  • Photon, 1905, Patent Office in Bern, Switzerland
  • Electron...let's skip that one for simplicity...
This can be summarized as Pauli's other exclusion principle:

Fermions are discovered in the US, whereas bosons are discovered in Europe.
Pauli's other exclusion principle has been confirmed in numerous experiments, sometimes un a quite spectacular way. Around 1974, the most powerful accelerator in the world was the ISR at CERN who produced charmonium in commercial quantities. However, since a discovery of the J/Psi particle at CERN would contradict Pauli's other exclusion principle, the experiment set its cuts so as to reject events with pT < 3.2 GeV (the mass of the J/Psi particle is 3.1 GeV). Later on, some significant efforts were invested to miss the Upsilon particle. The cancellation of the SSC can also be explained by Pauli's other exclusion principle: the SSC would be able to discover the Higgs boson.

Since, there is no more doubt that Pauli's other exclusion principle is a fundamental law of nature, it can be used to formulate predictions. One obvious implication is that Higgs searches at the Tevatron are pointless, and resources should be reallocated to searches for new heavy quarks. The Higgs boson, if it exists, will be discovered at the LHC. The new physics at the LHC, however, is severely constrained. Typical solutions to the hierarchy problem predict new fermions at the TeV scale. The little Higgs or extra dimensional scenarios predict a vector-like partner of the top quark at accessible energies, while supersymmetry predicts fermionic partners of the gauge bosons. On the other hand, the Standard Model with a light Higgs is perfectly consistent with Pauli's other exclusion principle...

Thanks to Jose Ramon for pointing out the facts to me.

Monday, 5 May 2008

Crackpot for Dummies

These days it is hard to sound absurd in particle physics. When none of them along the line know what any of it is worth, you are in constant danger of being taken seriously. But if you're really determined to convince everybody that your idea is nonsense, the short tutorial below might prove handy. It is not enough to just come up with a pile of nonsense - presentation is the key. The tutorial is illustrated with examples from the seminar a week ago by John Moffat who has achieved a certain perfection in the art.

1. First of all, of course, you need a great nonsensical idea. That's the easiest part. Take any long-standing problem and write down a bold solution. For example, find a mechanism of breaking the electroweak symmetry without introducing any new degrees of freedom and without violating unitarity.
2. Your solution should rely on technical terms that have no meaning to anyone else but you.
Symmetry breaking fermion loop measure sounds just perfect. Never try to explain the meaning of that - you can always refer to your 11 previous publications in case somebody asks.
3. On the other hand, you should elaborate on trivial points. For example, you can explain at length why in a theory without a Higgs particle there is no quadratic divergences to the Higgs mass.
4. It is useful to formualate your predictions using as many digits as possible. For example, you could give the value of the non-local electroweak energy scale to be 541.189 GeV.
5. Make clear that your idea explains any experimental discrepancy that is actually on the market.
6. To make connection with the rest of theoretical physics you should often mention string theory, supersymmetry, little higgs and everything else, noting each time that your idea is none of the above.
7. To whatever question from the audience you should reply by repeating the last sentence you just said.

But seriously...fringe or non-mainstream ideas are important, even when they're weird, and even when they're not quite right at the end of the day. That's provided you make an attempt to explain your point and face criticism. Otherwise, all you get is a ridicule. At least here at CERN, where jester is at loose.