This week I’m getting ready for the start next week of the spring semester. I’ll be teaching the second half of our graduate course on Lie Groups and Representations, something I also did a few years ago, at which point I wrote up some notes and put them on-line. This year, since the students covered somewhat different material during the first semester, I’ll be covering some different topics, hoping to both write up some notes on the new topics, and improve the older notes. We’ll see how much of that I have time for. Throughout academia, others are also trying to figure out what they’ll be talking about during the new term, for example see Clifford Johnson’s recent posting. He’s teaching a course on string theory, something about which he seems to be a tad bit defensive. Actually his outline syllabus doesn’t really indicate what he will cover, referring to aspects of perturbative and non-perturbative string theory, gravity and quantum field theory, which pretty much includes most of modern physics. Perhaps, like some of the rest of us, he hasn’t quite yet decided what exactly to talk about…
A future course that some people might be interested in is a summer school to take place in Seattle on Lattice QCD and its Applications.
An American Physics Student in England has a review of QFT textbooks for beginners. He neglects to mention a couple of my favorites (maybe just because they are ones I learned from during my student days): Quantum Field Theory by Itzykson and Zuber, and Pierre Ramond’s Field Theory: A Modern Primer.
I saw the above link first at Dorigo Tommaso’s blog, which also contains all sorts of news about interesting results coming out of the Tevatron, including a new, more accurate value of the W-mass. See for instance here, here, here, and here. About the new W-mass measurement, there’s also a Fermilab press release, and an article in Nature. It may yet turn out that the Tevatron is the place where the Higgs is first seen.
Notes from the talks at last week’s Gottingen Winterschule on Geometric Langlands are now available.
From Peter Teichner’s web-site, a new preprint by him, Hohnold and Stolz describing 8 different models for real K-theory, one of which is in terms of supersymmetric quantum mechanics. The paper is dedicated to the memory of Raoul Bott, whose periodicity theorem is a large part of this story.
From Michael Douglas’s web-site, there are slides from his recent colloquium talk here at Columbia on Supersymmetric Gauge Theory: an overview. He also has a new preprint out with Denef and Kachru entitled Physics of String Flux Compactifications. The autthors go over the arguments for the Landscape and devote significant space to discussing whether or not string theory is testable. They explain why hopes that one could use a statistical, anthropic argument to predict whether supersymmetry breaking happens at low or high scales haven’t worked out. There’s a somewhat mystifying claim that “in fact string/M-theory does predict a definite distribution of gauge theory and matter contents”, referring to various papers which don’t contain anything like a definite string/M-theory prediction of such a distribution.
As for the testability of string theory, the authors first note that while there are all sorts of exotic phenomena that one might imagine finding that are consistent with string theory, none of them are required by string theory, so:
Thus, while string theory can offer experimentalists many exciting possibilities, there is little in the way of guarantees, nor any clear way for such searches to falsify the theory.
They then go on to give what they see as four possibilities for testability:
1. “Swampland” arguments showing that string theory can’t possibly lead to a low energy effective theory that agrees with what we see. Unfortunately, there seems to be no such plausible argument, with all arguments of this kind so far only ruling out string theory as a source for very different physics than what we observe.
2. String theory must be true because there is no other possible theory of quantum gravity. They completely ignore LQG, but do admit that “one should not take this too seriously until it can be proven that alternatives do not exist”, mentioning the possibility of finiteness of N=8 supergravity.
3. Maybe the LHC will discover new physics that clearly is the result of a string theory compactification.
4. Maybe they will be able to make statistical predictions using the landscape.
These seem to me extremely weak and problematic arguments. 3 appears to be little more than wishful thinking that a miracle will happen and save the day, and all efforts over the last few years to pursue 4 seem to lead to insuperable difficulties for very fundamental reasons. In the end, the authors acknowledge this, writing “ultimately convincing evidence for string theory will have to come from observing some sort of exotic physics”, and putting their hopes in string cosmology, especially the hope of seeing networks of cosmic superstrings or signals in the CMB corresponding to non-linearities in the DBI action.
After this dismal summary of the situation and of prospects for the future, the authors decide to end with conclusions more or less directly opposite to the ones their arguments naturally lead to:
We conclude by noting that while the present situation is not very satisfactory, there is every reason to be optimistic… There are many well-motivated directions for improving the situation, and good reasons to believe that substantial progress will be made in the future.
Update: One more. There will be a public debate over the anthropic principle later this month, involving David Gross, Lenny Susskind, and others. More information here.
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