Quick Links

Posted on June 1, 2011 by woit
  • The big news of the past couple days has been the release of more data by CDF which continues to show a bump in the invariant mass of two jets produced with a W. Resonaances gives an excellent description of this and its possible significance. Tommaso Dorigo remains a skeptic.

    I can’t do better than the two of them on this story, but here’s my summary take on the situation:

    With the new data, this can no longer be written off as a statistical fluke. 3 sigma you can argue away as such a fluke, but not 5 sigma.

    The main reason to be skeptical though hasn’t been the statistical significance, but the possibility that this is due to bad modeling of the background. The signal is being extracted from a huge background, so a small misunderstanding of the background could be its cause. If this is the case, the new data changes nothing, you expect to continue to see the effect as more data is analyzed.

    The fact that Tommaso is a skeptic carries a lot of weight, since he works on the CDF experiment and understands the problems well. In general, experimentalists want the experiments they work on to make great discoveries, so tend to be optimists about their own results. When someone is skeptical about a result of their own experiment, that should give one pause.

    What would really make the case for new physics here more compelling would be if the result is confirmed by one of the other experiments (DO at Fermilab, CMS or ATLAS at the LHC) that should be able to see the same effect if it is there. These groups have a certain motivation to not just confirm their competition’s discovery (raising the question of why they didn’t find this first), but to convincingly shoot it down. This posting by Pauline Gagnon of ATLAS says that they see nothing in their 2010 data. One expects that D0 is hard at work and should soon release whatever they have found. ATLAS and CMS should also be hard at work looking at the much larger 2011 data samples. We’ll know soon the results, but the public comments of Dorigo and Gagnon don’t sound to me like those they would be making if they knew their experiments had preliminary confidential results confirming the CDF anomaly.

    Finally, while there are lots of theory papers out already with supposed models explaining this, none are really compelling. This is not an experimental result with an obviously attractive theoretical explanation.

  • Abstruse Goose has commentary on SUSY here.
  • In gossip of the mathematics world, it looks like Princeton (the IAS) has stolen away number theorist Richard Taylor from Harvard.
  • Video of Graeme Segal’s Felix Klein lectures this spring at Bonn on quantum field theory are now available, and well worth watching.
  • Other interesting video available is Greg Moore’s lectures on geometry, topology and QFT at Rutgers last fall.
  • For pictures from this years Physics of the Universe Summit, see here. Any info beyond the transparencies caught in the pictures seems to be private.
  • The journal Foundations of Physics will be putting out an issue on “Forty Years of String Theory”. So far articles intended for this have appeared on the arXiv from Dean Rickles, Steven Gubser, and, last night, Steven Giddings. The Giddings contribution is entitled Is string theory a theory of quantum gravity?, and provides an unusually hype-free discussion of the relevance of gauge/gravity duality to hopes to use string theory to understand quantum gravity, writing:

    While string theory addresses some problems of quantum gravity, its ability to resolve these remains unclear. Answers may require new mechanisms and constructs, whether within string theory, or in another framework.

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9 Responses to Quick Links

  1. X says:
    June 1, 2011 at 12:59 pm

    I’m not following the phenomenology too closely, but I liked the technirho: http://arxiv.org/abs/1104.0976 Do you know what the major criticisms of that suggestion are that make it not “an obviously attractive theoretical explanation”? It would also explain the absence of the Higgs and presence of EWSB in terms of (relatively) known mechanisms.

  2. Peter Woit says:
    June 1, 2011 at 6:54 pm

    X,

    I’m no expert on this, would love to hear from someone who is. In particular, I’m curious to know if this kind of technicolor signature is something that was investigated before the CDF result. My uninformed impression is that this wasn’t an obvious thing to expect to see with this kind of cross-section.

  3. P. says:
    June 1, 2011 at 9:48 pm

    Well, such technicolor inspired resonances are being searched for. They have their own entries in PDG, and also on p. 138 in Viviana Cavaliere’s thesis you can find a related plot. I think Peter is right in that one would expect somewhat smaller cross sections for this channel (actually the cross section obtained in 1104.0976 is on the lower end of what is compatible with the CDF excess).

    One reason technicolor is not considered an “obviously attractive theoretical explanation” is that technicolor models tend to be in conflict with a lot of other experimental constraints, in particular flavor physics and electroweak precision tests. But many of these things are very hard to actually calculate, so maybe it does work.

    Cheers

  4. anon. says:
    June 2, 2011 at 2:44 pm

    I think that if you had asked technicolor advocates, at almost any point in the last 10 years, at what mass scale they would expect techni-resonances to show up, they would have tended to give you answers much larger than 150 GeV. Even if this state is supposed to be lighter because it’s a techni-pion, it would be coming from something at 300 GeV or so, which is still lighter than any TC advocate would have expected. This scenario — an s-channel resonance decaying to a W plus another resonance — would definitely be a “who ordered that?” moment for the field.

    Electroweak precision and precision flavor physics results are still incredibly difficult to reconcile with technicolor, and most attempts to do so amount to putting lipstick on a pig. Even if the result holds up and proves to be a new s-channel resonance, interpreting it as being related to technicolor would be a real stretch, one not (so far) justified in any way by the data itself.

  5. Bernhard says:
    June 2, 2011 at 3:53 pm

    Peter,

    About Giddings article… One sentence on the very beginning caught my attention:

    “Specifically, string theory naturally regulates the infinite proliferation of ultraviolet divergences in the loop expansion, and, order-by-order in perturbation theory, apparently gives UV finite scattering amplitudes.”

    I´m interested in the “apparently”… Do you know how certain anyone is of this claim? It´s hard to believe one can get “nice”cross-sections out of ST, but perhaps I´m wrong…

  6. Peter Woit says:
    June 2, 2011 at 4:49 pm

    Bernhard,

    The situation with finiteness of multi-loop superstring amplitudes is kind of murky, and during the “String Wars” for some reason I ended up getting into long arguments about it, which you could probably find on my blog, Jacques Distler’s or Clifford Johnson’s. One of my colleagues at Columbia, Phong, is one of the experts in the subject. He and Eric d’Hoker (who I went to grad school with) have shown finiteness at two-loops, in a calculational tour-de-force. The technicalities involved are fearsome. As far as I know, neither they nor anyone else has conclusively shown finiteness at 3 loops or above. One reason this story is complicated is that there are several different possible formalisms to use in the superstring quantization, with different technical problems. The claims made from the early days that string had to be finite at any number of loops could be described perhaps as plausibility arguments.

    To be fair to string theory, you certainly can compute amplitudes perturbatively at the first couple of orders, with very pretty and interesting results (which have little to do with HEP as far as we know…). Of course, the full perturbation series is divergent, you need some non-perturbative formulation to get something fully consistent.

    In any case, what Giddings is claiming is that this is all irrelevant, that the real problem is not UV finiteness of perturbation theory, but the infrared and non-perturbative behavior.

  7. Igor Khavkine says:
    June 2, 2011 at 4:55 pm

    Question for anyone who has watched Graeme Segal’s lectures. Is there anything particular in his lectures that is worth paying attention to? For instance, which, if any, of his comments are particularly new or particularly clear summaries of what’s already known? For the record, having watched the lectures, I found it hard to figure out an answer to these questions. I do have to admit a certain bias in my theoretical interests, which have so far stayed clear of 2-dimensional, topological, Euclidean QFTs, which might have been a drawback.

  8. Peter Woit says:
    June 2, 2011 at 5:14 pm

    Igor,

    One thing worth paying attention to is Segal’s treatment of the relation between the Minkowski and Euclidean formalisms of QFT (he treats this by doing analytic continuation on a space of metrics, not in physical or momentum space as is conventional). Even if you think you’ve never deal with Euclidean QFTs, you probably have, since in order to make calculations well-defined you generally have to do this. This is a fundamental issue about QFTs, and Segal is one of the few people I know who has tried to think it through clearly.

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