Various things of interest, ordered in terms of increasing mathematical content:
This week Fermilab has hosted a P5 meeting and an annual program review.
At the P5 meeting, Fermilab director Pier Oddone made the case for planning to keep running the Tevatron through FY 2010. He pointed out that the current LHC schedule has “no float” for any possible delays in putting the hardware together, and only allows for 3 months between first beam and physics collisions, drawing the conclusion that it was unlikely the LHC would have physics results competitive with the Tevatron before the currently planned closure date of September 2009. Presentations from D0 and CDF claimed that, if the machine runs through FY2010 and provides them with a projected luminosity of 6.8 fb-1, they should be able to exclude the possibility of existence of the Higgs at 95% confidence level over almost the entire possible range of Higgs masses (if it isn’t there!) or find 3 sigma evidence for its existence in some mass ranges (if it is).
At the program review, there was an overview of particle theory at FNAL from Andreas Kronfeld, and a presentation about the LQCD lattice gauge theory project from Paul MacKenzie. Several interesting documents reviewing the state of the lattice gauge theory work are here.
Over the last few months I’ve often told myself that I should learn more about Howard Georgi’s ideas concerning “unparticles” and try and write something about them. Sabine Hossenfelder has saved me the trouble, you can learn about this here.
Last month there was a symposium at Durham on Twistors, Strings and Scattering Amplitudes, a subject which has seen some exciting activity recently. Zvi Bern reviewed progress on computing multi-loop amplitudes in N=4 gauge theory and in gravity theories. He noted that the recently found unexpected one-loop cancellations in N=8 supergravity (leading to the so-called “no triangle hypothesis”) are not due to supersymmetry and are already there in non-supersymmetric gravity. This leads him to conjecture that other gravity theories will be perturbatively finite, he explicitly mentions N=6 supergravity. Nathan Berkovits discussed multi-loop superstring amplitudes in the pure spinor formalism, ending up by noting that there are possible problems caused by needed regularization of ghosts in this formalism, and they affect high-energy contributions to the 4 point 3-loop amplitudes. Not that I’m saying I think this will happen, but it would be pretty damn funny if it turns out that multi-loop superstring amplitudes aren’t finite, multi-loop supergravity ones are…. There’s also a talk by Jacques Distler, who continues his ceaseless quest to figure out how to make physics available over the web in a form that no virtually no web-browser can display properly.
Finally, I strongly believe in advertising equivariant cohomology as much as possible, for mathematicians and for physicists. The new lecture notes by Matvei Libine are a good place to read about it.
Could it be that the pure spinor formalism is just showing its limitations and shortcomings, as opposed to the string multiloop amplitudes being genuinely nonfinite?
JC,
Sure, it could just be a problem of the formalism, and in any case maybe even within that formalism it can be dealt with. What’s interesting though is that, at higher loops, the standard ideology “string amplitudes finite, (super)gravity infinite” may very well be wrong. Hard to be sure until, in both cases, the amplitudes are better understood.
If somebody ever calculates the correct 3-loop superstring amplitude (or higher) expilicity and it is shown to be genuinely nonfinite, then I wouldn’t be surprised if this ends up being the last nail in the coffin for string theory.
Nobel Laureate Martin Veltman gave an interesting public lecture (not sure how old it is – doesn’t appear to have been mentioned here before, my apologies if it has) where he offered his highly sceptical opinion (in decreasing orders of scepticism) on string theory, supersymmetry, the cosmological constant and the Higgs mechanism in the context of a proposal to motivate the construction of an 800GeV linear collider in Hamburg as a successor to the LHC.
It doesn’t require specialist knowledge and contains interesting remarks about the US direction in particle physics. A video of it is here:
http://pauli.physics.lsa.umich.edu/w/arch/som/sto2001/Veltman/real/n001.htm
It makes for an interesting comparison with his co-laureate and student Gerhard ‘t Hooft (who also gives excellent public lectures, by the way) who is quoted in the recent Physics World article as advising physicists to keep such debates out of the public arena.
“Unparticle” physics remind me of the uncola. But it makes me think that perhaps string theory should be called particle “unphysics”.
Thank you, DB.
I checked out Veltman’s lecture. Though I think his momentum-space
suggestion is totally wrong, he has framed the current state of physics
and its problems in a very sensible way.
That Veltman lecture was 2001, before this blog existed. Courageous stand against string theory for that time. Peter, I know cosmology doesn’t interest you as much, but I hope you also heard his remarks on that topic and general relativity.
If you use this link, you can view the video and slides for Veltman’s lecture simultaneously.
Veltman also makes some nice comments at a lecture I once saw at the CERN library. He was very vocal and corrosive regarding string theory. He basically said that he only trusts things that calculate things (something like this).
I don’t know whether these comments were made before or after this lecture.
Hi Peter,
Thanks for the link, I only just noticed. Yes, the unparticle stuff is a fairly weird development. I’m not planning on looking closer into it though. Some of the comments to my post are also interesting in this regard.
Best,
B.
I have a silly, naive question from a condensed matter person…. It seems like “unparticles” are the HEP equivalent of a condensed matter phase that simply isn’t well-described in terms of quasiparticles. For example, when Fermi liquid theory fails in some strongly correlated electronic materials (e.g. the “local moment” phase in heavy fermion compounds), there appears to be no simple description of the low energy excitations of the resulting phase, at least not in terms of weakly interacting quasiparticles with simple quantum numbers like momentum and angular momentum. Is that basically the idea here?
Concerning the searches for Higgs and supersymmetry at the Tevatron, the D0 and DF teams have just submitted a joint paper about their status. As stated in its conclusions, “the `hint´ of an MSSM Higgs boson at m_a around 160GeV obtained by CDF was not confirmed by D0”. In other words, no Higgs or SUSY so far. This is the link:
http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.0248v1.pdf
JE,
the proceedings you point to do not include the most recent results. CDF has a new result for MSSM Higgs blessed for both the bbH->bbb(b) and the H->tau tau searches. These update previous results based on half the statistics.
As far as the former goes, it is reported in my blog – I wrote about it a month ago. The latter, although blessed, is not accessible online yet to my knowledge. I did write about it today, but I left out the results, because I prefer to leave a chance to the authors to do that first. In any case, your conclusion does hold.
Cheers,
T.
DB, thanks for the link to Veltman’s talk . He certainly has non-conventional povs about validity of GR and there are also interesting discussions at the end.
Peter , what do you think of the talk? Has Veltman read your book or have you
corresponded with him regarding string theory?
Thanks
Doug,
I was hoping someone knowledgeable would answer your question. I haven’t looked closely at what Georgi is doing, but assume you’re basically right, that the point is that there are field-theoretic phenomena not describable by particle-like excitations.
Shantanu,
Haven’t had a chance to look at the Veltman talk. I corresponded a little bit with him when I was trying to get the book published, and he was quite sympathetic. I’d suspect my more mathematical point of view is not to his liking, but that’s he’d agree with much of the critique of string theory. I had the pleasure of meeting him once when I was a postdoc at Stony Brook, and found him to be quite an impressive character.