Short Items

Posted on May 25, 2010 by woit
  • Beam intensity at the LHC continues to increase with successful collision this morning of beams containing 13 bunches of protons, producing an initial luminosity of about 1.5 x 1029cm-2s-1. This is about a factor of 1000 below the goal for later this year, 2000 below typical luminosities at the Tevatron. The current plan is for proton-proton collisions this year until November 1, then a shift for a while to heavy ions. Integrated luminosity is about 10 nb-1, see a graph here.
  • Last week this result (also see here) from DZero got a lot of attention in the press, including a front page story in the New York Times. The claim is of observation of a CP-violating effect not predicted by the Standard Model, with a significance of 2-3.2 sigma, depending on exactly what numbers you look at. If I had to bet, I’d bet that this, like lots of other purported violations of the SM over the last 35 years, will ultimately disappear. Unfortunately, it seems that CDF is unlikely to be able to confirm or disconfirm this. For blog postings from people who actually know something about this, see here and here.
  • There’s an interesting interview with Shing-Tung Yau at Discover. This fall he has a new book coming out: The Shape of Inner Space.
  • My colleague Brian Greene is keeping very busy, with the World Science Festival here in New York next week, and filming a four-part NOVA series based on is book Fabric of the Cosmos.
  • If I weren’t planning a trip to South America to see another eclipse in July, I’d probably be trying to find an excuse to go to Paris that month, and ICHEP 2010 might do the trick. Now, it seems even physics conferences have blogs.
  • Herbert Neuberger has a very nice survey here, based on a colloquium talk, of our understanding of non-perturbative QCD.
  • Frank Quinn has a long essay here which has quite a few interesting things to say about mathematics, mathematics research, mathematics education, and relations to physics. Quinn is a topologist who has interacted with physicists since the late 80s, in the context of topological quantum field theory. I learned about this from a posting at the n-Category Cafe, where some illustrious commenters have an interesting exchange about TQFT.
  • For a long time now, particle theory has been divided up between phenomenology and string theory, with formal QFT an increasingly marginalized subject. At the same time, more and more mathematicians have been studying QFT long enough to become quite expert at it. In the future it seems conceivable that this will ultimately lead to new discoveries about QFT coming out of math, not physics departments. For an indication of how things are going, take a look at the recent MSRI workshop in honor of Alan Weinstein. Videos of some of the talks are supposed to be available at some point. I’m most looking forward to seeing what Graeme Segal has to say about Geometric aspects of the positivity of energy in quantum field theory, and curious to know what Reshetikhin had to say about Hamiltonian structure of gauge theories (it appears that video of that talk will not be available). Next week Reshetikhin is teaching a master-class on gauge theories in Amsterdam (web-site here), and he taught a course on QFT there last fall

    • Updates:

  • See Resonaances for some news that makes the DZero supposed SM violation look less likely. Some support for the claim came from earlier data showing similar SM violation in another channel, but the latest from CDF is that, with more data, this has gone away.
  • Latest from the LHC is that on Tuesday morning a peak luminosity of about 2 x 1029cm-2s-1 was reached. Integrated luminosity is now about 16 nb-1.
  • Nature has an interview with Brian Greene about the new orchestral work from Philip Glass inspired by his recent children’s book.

    • Update: A more skeptical report on the DZero result from Adrian Cho at Science Magazine is here.

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    16 Responses to Short Items

    1. Jonathan says:
      May 25, 2010 at 3:42 pm

      Where are you heading to to see the eclipse? I’ll be in Chile at the time visiting some groups in Santiago but might see if I can go see the eclipse. That would make the last three in a row!

    2. Peter Woit says:
      May 25, 2010 at 4:28 pm

      Hi Jonathan,

      I’ll be with a group going down to Patagonia from Buenos Aires. In Patagonia the eclipse will be happening near sunset, and the probability of clouds is high, so the plan involves getting on a chartered plane to get above the clouds at eclipse time. Not cheap, but cheaper than the other South American way of seeing the eclipse, which would be to fly to Easter Island and see it there. But those flights, and any place to stay on the Island, are quite expensive.

    3. Coin says:
      May 25, 2010 at 5:53 pm

      “The current plan is for proton-proton collisions this year until November 1, then a shift for a while to heavy ions”

      So I’m not sure I understand what the heavy-ion searches are about.

      The proton collisions, as I understand, the point is to probe the particle spectrum. This will likely require a long, high-luminosity run before anything “new” can be found, because a large number of events have to be logged in order to establish a background which interesting events can be distinguished against.

      The heavy ion collisions though as I understand have nothing to do with the particle-spectrum search, and the goal there is to create a quark–gluon plasma (which I assume, like the exotic particles in the proton searches, will last only a short amount of time and be analyzed only by the particle spray it leaves behind?). Will the heavy ion experiments have the property the proton experiments have, where the machine has to run for a very long time in order for any conclusions to be drawn at all?

      Is there somewhere that would be a good source for learning about how the quark gluon plasma analysis works and exactly what we are hoping to learn from it?

    4. Peter Woit says:
      May 25, 2010 at 6:01 pm

      Coin,

      Good questions. I’ve seen very little about what people will be looking for in heavy ion collisions at LHC energies. Maybe there’s a knowledgeable reader out there…

    5. Tim van Beek says:
      May 26, 2010 at 6:40 am

      In the future it seems conceivable that this will ultimately lead to new discoveries about QFT coming out of math, not physics departments.

      Is it a coincidence that this statement is similar to the closing words of the (draft of the) preface of “Mathematical Foundations of Quantum Field and Perturbative String Theory” that you can read here ? (Last paragraph on the page, right above the “authors” list).

    6. Bill K says:
      May 26, 2010 at 7:06 am

      Why, recreating the conditions of the Big Bang, of course. 🙂

      Knowledgeable I’m not, but I can point you to a good summary of what they’ll be looking for:

      http://www.bnl.gov/npp/docs/Hunting%20the%20QGP.pdf

      And I have some opinions. Under the constraints that the LHC is currently operating, I think ALICE is much more likely to produce new and interesting physics than the other experiments. And I think the two months they’ve allocated for it is far too little. Switching over to lead will be more than just flipping a switch – another lengthy tuning process will be needed.

    7. Peter Woit says:
      May 26, 2010 at 7:16 am

      Bill K,

      I’d be curious to see something more LHC-specific. What will the LHC see that RHIC can’t? What will this tell us? Are their predictions of AdS/CFT and other methods that will be tested?

    8. Anonymous Grad Student says:
      May 27, 2010 at 3:00 am

      I attended the MSRI workshop. Forgot I had made some sketchy notes of Graeme Segal’s talk. Here are some scans to tide you over till the video is posted. (No notes for Reshetikhin’s talk, sorry.)

      http://i46.tinypic.com/2s6pjs7.jpg
      http://i46.tinypic.com/r8ukid.jpg
      http://i46.tinypic.com/e9c2md.jpg

    9. Anonymous Grad Student says:
      May 27, 2010 at 3:31 am

      Also, there were no results in Reshetikhin’s talk. He gave the impression that he’s still in the process of learning gauge theory, and just gave some examples of them. I think the talk even ended with “Results: to come”. Possibly why the video isn’t being posted.

      Should have mentioned, take the notes above with a grain of salt. I’m sure there some misrepresentation in there, especially towards the end 🙂

    10. Adam Helfer says:
      May 27, 2010 at 9:14 am

      AGS,

      Your notes look interesting, but I couldn’t tell specifically what was going on. Was Segal trying to look at properties of Hamiltonians of quantum fields in curved space-time? If so, in the case of generic space-times (no timelike Killing vector), these Hamiltonians are pathological, even for linear quantum fields. They’re not only non-positive, they’re unbounded below (this is an ultraviolet problem) and they do not exist as self-adjoint operators, but rather in the weak sense.

    11. Peter Woit says:
      May 27, 2010 at 2:28 pm

      AGS,

      Thanks a lot for the notes and the report!

      Adam,

      I think what Segal is interested in is trying to make sense of “Wick Rotation” for a curved space-time. Euclidean signature methods are needed in the path integral formulation of QFT, so having an appropriate notion of how to analytically continue from Minkowski to Euclidean signature is crucial. Even in flat space this is an interesting question which I’m not convinced is resolved when one has spinor fields.

      One could imagine thinking about this by complexifying space-time, and looking at holomorphic objects, but Segal is doing something different. He’s taking a fixed space-time manifold and complexifying the space of metrics on it. From what I can tell, he has some good understanding of what happens in d=2, which is interesting for 2d QFT and string theory, not sure what he has for d=4.

    12. JE says:
      May 27, 2010 at 3:08 pm

      Surely off-topic and not really sure of its significance, but just in case… news reports broke in Spain announcing that Professor Francisco Santos of the University of Santander has disproved the Hirsch Conjecture.

    13. Coin says:
      May 27, 2010 at 3:35 pm

      JE, that is very interesting… Wikipedia’s “Hirsch Conjecture” article seems to have some information on this already (they link a blog post by Gil Kalai who noticed this as early as May 10):

      The result is to be presented at the conference 100 Years in Seattle: the mathematics of Klee and Grünbaum… a counter-example was found, using a 43-dimensional polytope of 86 facets with a diameter of more than 43.

      The conference starts July 28, the abstract for Santos’ paper is here.

    14. Adam Helfer says:
      May 27, 2010 at 3:36 pm

      Peter,

      Thanks. I suppose I should wait for MSRI to finish posting the video before going too far in discussing this, but if one doesn’t have some very strong link between the physical metric and whatever the auxiliary structure is (in this case, apparently the space of complexified metrics), it’s hard to see what the physical content of the mathematics is.

      On the issue of Euclideanization (or, to put it in more physical terms, the pseudo-Lorentzianization) of Minkowski space, I don’t know if this comment helps, but the two two-component spinor spaces, that is, the primed and unprimed spaces, have well-defined analytic continuations. What changes is the way these spaces are related to the relevant sense of choices of orientation. In each case, the two spin spaces essentially correspond to the two eigenspaces of the duality operator on two-forms. In the Lorentzian signature, the eigenvalues are plus or minus i, and the spaces are conjugates of each other, and neither is preferred (without more information). In Euclidean signature, however, the eigenvalues are plus or minus one, and so there is an invariant distinction.

    15. Researcher says:
      June 3, 2010 at 2:31 pm

      Another, very sad short item: Vladimir Arnold, a great Russian mathematician, passed away today in Paris, France.

    16. Anonymous Grad Student says:
      June 9, 2010 at 2:48 pm

      Just a heads up. The video for Graeme Segal’s talk (along with others from the conference) is now available.
      http://www.msri.org/communications/vmath/VMathVideos/VideoInfo/4666/show_video

      I couldn’t get the streaming video to work, but the download link works fine.

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