The Higgs Discovery

Posted on June 17, 2012 by woit

Just got out of 8 days in the Grand Canyon which was spectacular,

Reliable rumors couldn’t wait, and they indicate that the experiments are seeing much the same thing as last year in this year’s new data: strong hints of a Higgs around 125 GeV. The main channel investigated is the gamma-gamma channel where they are each seeing about a 4 sigma signal.

More later when I reach civilization.

Update: Back in civilization, or at least New York City. The above was the first posting I’ve ever written on an iphone, late at night. Now I have a real keyboard, so I can write a bit more. The “4 sigma signal” refers to the combined 2011 and new 2012 data. To oversimplify the situation, last year both experiments were seeing roughly a 3 sigma excess in gamma-gamma around 125 GeV. This was enough to convince many people that it was highly likely that this was the Higgs. However, that size excess is not completely convincing, it is not unheard of for there to be statistical flukes of such size.

The 2012 data that is being analyzed for ICHEP is of a similar size to the 2011 data. If 2011 was a fluke, you expect to see nothing much around 125 GeV in the 2012 data. If the 2011 signal really was the Higgs you expect the signal to strengthen. What I’m hearing from both experiments is that they are seeing an excess in the new data, strengthening the significance of the signal.

Exactly how much data they’ll have analyzed by ICHEP and exactly what the significance of the signal in the gamma-gamma channel will be (as well as what other channels will show) is still to be seen. CERN will soon have to decide how to spin this: will they announce discovery of the Higgs, or will they wait for some overwhelmingly convincing standard to be met, such as 5 sigma in at least one channel of one experiment? The bottom line though is now clear: there’s something there which looks like a Higgs is supposed to look. Attention will soon move to seeing if this signal is exactly what the SM predicts (e.g. will the excesses in different channels agree with SM predictions?).

More details about this from Philip Gibbs (who is speculating about what will be announced), and from Tommaso Dorigo (who is keeping quiet about what he knows, but providing context for what the ICHEP announcements will mean).

Update: Matt Strassler has more about this here. He provides about 20 links to his own blog, no link to the source of his information (this posting). It appears that this is because I’m a “non-particle-physicist blogger” engaged in a conspiratorial plot with some of the 6000+ people who know this latest news to “subvert the scientific process” by sharing it with others.

Update: There are stories about this at Wired, New Scientist and the New York Times. The New York Times article emphasizes that the Higgs results are now “Shrouded in Secrecy”, with the spokeswoman for ATLAS pleading “Please do not believe the blogs”.

According to Matt Strassler “the experimentalists can’t possibly have their data in presentable form yet, so the rumors can’t be correct in every detail”. To clarify any confusion

“Exactly how much data they’ll have analyzed by ICHEP and exactly what the significance of the signal in the gamma-gamma channel will be (as well as what other channels will show) is still to be seen”

means that the above rumors were based on just part of the data (significantly less than half in the ATLAS case, somewhat more than half in the CMS case).

Update: I think I’m too old to ever really understand Twitter, but it seems that #HiggsRumors is a “Trending Topic”, whatever that means. More explanation available from Jennifer Ouellette, and sensible commentary from Chad Orzel.

Posted in Experimental HEP News, Favorite Old Posts | 88 Comments

Too Much Ain’t Enough Langlands

Posted on June 7, 2012 by woit

I should be packing for my trip, but couldn’t resist one last blog posting, since I’ve recently a run across a lot of interesting Langlands-related material, including:

  • A Symposium this fall at the Fields Institute, in honor of Ngo’s Fields Medal winning work, on Fundamentals of the Langlands Program. They have a symposium blog, and including a video with Jim Arthur who gives a little bit of historical background to the Langlands Program.
  • This past semester the Fields Institute has had a program on Galois Represesentations, with an instructional workshop, lecture series by Michael Harris and Christophe Breuil, and lots more. Some notes are on the instructional workshop page, and lots of audio of the talks are available here (so you can see what trying to learn math will be like when you go blind).
  • To hear from the man himself, there’s something old here (notes here), something from last year here.
  • In recent years Matt Emerton has written some wonderful expository pieces, often on Langlands-related topics, as the answers to questions on MathOverflow. He has collected links to them here.
Posted in Langlands | Comments Off on Too Much Ain’t Enough Langlands

High Drama

Posted on June 7, 2012 by woit

It’s exactly a month until new LHC Higgs results are to be unveiled at ICHEP. The machine has been running well, and right about now should be the cut-off time after which new data will arrive too late for analysis before ICHEP. So the integrated luminosity available for each experiment to analyze will be about 4.5 inverse femtobarns. See Tommaso Dorigo for an explanation of what this means. Very roughly, if the Higgs is there with a mass around 125 GeV, each experiment should see tentative signal similar to last year’s, with the combination of data from both years and both experiments likely reaching the 5 sigma standard necessary to declare discovery. If no signal similar to last year’s is seen, this will seriously re-open the possibility of no Higgs (or a very different Higgs than the SM one). Either way, should be very exciting.

For the other story people are following, the death of SUSY, see Nima Arkani-Hamed’s recent talk. He lists as “High Drama for 2012” not just the Higgs, but also SUSY results on stops, gluinos and multileptons. Here I think most people have given up hope that evidence for SUSY will be found, so the high drama is the human one of how SUSY advocates will react as remaining possible SUSY hiding places are mopped up. The conference was in honor of Savas Dimopoulos, who has been working on SUSY models for more than 30 years, so Arkani-Hamed’s talk didn’t even acknowledge the possibility of no SUSY. He described the 2 alternatives available to physics as “natural SUSY”, which is just about ruled out, and various versions of “split supersymmetry”, where superpartner masses can be pushed arbitrarily high, out of the reach of the LHC or any conceivable experiment. He didn’t mention the version one commenter here recently brought up, “super-split supersymmetry”, which was an April Fool’s joke, but may be the direction the field is headed.

Tommaso notes that the new data has been blinded by the experiments, meaning that even those working with it don’t know anything about what the final result will be until the last stage of the analysis. Whenever that might be, I’m hoping reliable rumors will soon ensue.

I’m heading out on vacation tomorrow, to the bottom of the Grand Canyon, out of reach of the internet until about June 18th. During this time I’ll have to shut off comments here. So, hold your reliable rumors until I get back….

Update: Seems that some of these reliable rumors just won’t wait. Whatever Tommaso says about CMS blinding its data, either that’s not the case at ATLAS, or some of it is now unblinded. I hear that the first chunk of gamma-gamma data is showing some signs (2 sigma) of a signal at about the same place as last year’s data. Analysis of more data is proceeding, and very soon people at ATLAS will know whether there’s a signal there. High drama….

Posted in Experimental HEP News | 4 Comments

25 Years of Topological Quantum Field Theory

Posted on May 31, 2012 by woit

It occurred to me today that right about now is the time someone should have chosen as the date for a celebration of the 25th anniversary of the birth of the idea of “Topological Quantum Field Theory”, as well as some much less well-known ideas about the relationship of QFT and mathematics that still await full investigation.

Just about 25 years ago, from May 12-16 1987, there was a remarkable conference that I attended at Duke, to celebrate the “Mathematical Heritage of Hermann Weyl”, two years after the centenary of his birth. The proceedings were published a year or so later. At this conference, Michael Atiyah gave an amazing talk with the title New invariants for manifolds of dimensions 3 and 4. In it he unveiled a vista of new ideas about topology that would dominate the subject for years to come. For symplectic manifolds he described Andreas Floer’s unpublished new ideas about what came to be known as “Floer Homology” and how these gave new invariants of such manifolds and their Lagrangian submanifolds, invariants related to very recent work of Gromov (now known as “Gromov-Witten invariants”). Replacing 1d (Lagrangian paths) and 2d (pseudo-holomorphic curves) objects in a symplectic manifold by 3d (flat connections) and 4d (instantons) objects in a space of connections on a 4d manifold gave yet another whole new world of mathematics. This is the subject of Floer Homology and Donaldson invariants for 4d manifolds, possibly with boundary, (and was based on work of Floer and Donaldson that was still unpublished). Finally, the Euler characteristic of Floer Homology was identified with a new invariant due to Casson (also unpublished, it seemed like nothing Atiyah was talking about was yet written up), which was a 3d invariant that fit beautifully into the whole picture.

There’s a copy of Atiyah’s write-up of the talk online here (perhaps the AMS will ignore any intellectual property issues here for the greater good). I see that, increasingly like everything else in the world, electronic access to the book is controlled by Google, see Google Play, which I didn’t even know existed.

An inspiration for Floer had been Witten’s ground-breaking paper “Supersymmetry and Morse Theory”, which dealt with the relationship between Morse theory and some supersymmetric quantum mechanics models. Atiyah explained some of these ideas in the talk and towards the end conjectured that quantum field theories were part of the story. His conjectural QFTs would have Floer homology as their ground states and would turn out to be the basic examples of TQFTs. After repeated prodding from Atiyah, Witten a year later produced such theories as twisted N=2 supersymmetric QFTs: a sigma model for the symplectic manifold case, and a supersymmetric Yang-Mills theory for the 4d case. In his final remarks, Atiyah raised the issue of knot invariants and the Jones polynomial, suggesting that this too would have a QFT interpretation, something that came to fruition a couple years later with Witten’s Chern-Simons theory that won him a Fields medal. Witten was at the talk, and I recall him coming down to the podium to ask Atiyah some questions about the Jones polynomial immediately after the lecture.

The Duke conference was also significant to me for personal reasons. At the time I was a postdoc at the ITP in Stony Brook, looking for a job and trying to figure out my future. It was becoming clear that physics departments didn’t want to hear from any young theorists interested in mathematics who weren’t doing string theory. I had been spending a lot of time at Stony Brook learning more mathematics and talking to some of the geometers there, who were housed on the floor below the ITP. My trip to the conference at Duke was motivated partly by a desire to visit my grandparents who were in North Carolina for the summer, as well as a plan to investigate prospects for a career change into mathematics. The Atiyah talk bowled me over, convincing me that the intersection of mathematics and QFT had an exciting future. Getting to know a bit more about the mathematical community showed me it could be a great place to work, in many ways much more welcoming and open to new ideas than the physics community. I soon moved up to Cambridge for a year, where the Harvard Physics department let me use a desk, and found a part-time job teaching calculus at Tufts.

What’s remarkable to me now looking at the conference volume is how much exciting material was being discussed, in addition to the fantastic Atiyah talk. Raoul Bott gave a wonderful talk on Borel-Weil-Bott (and its relation to quantization), David Vogan on representation theory in general (and its relation to quantization). Roger Howe has a contribution also about deep connections between quantum mechanics and what he calls the “oscillator representation”. Jim Lepowsky was talking about Kac-Moody Lie algebras, vertex operators and the Monster group, Is Singer about quantizing gauge theory and string theories, and there were a host of other wonderful talks on topology and geometry.

One topic that I didn’t really appreciate at all at the time was that of Langlands theory. Langlands himself was there, talking about Shimura varieties, and James Arthur talked about the Trace formula and its applications to Langlands theory. I think I may have missed Witten’s talk, since I don’t remember it, but his contribution to the conference proceedings is about how to abstractly think about the theory of 2-d free fermions, in a form that makes sense on an arbitrary curve. A few weeks later (June 23), his amazing paper Quantum Field Theory, Grassmanians and Algebraic Curves was submitted to Communications in Mathematical Physics. If I had to point to a paper that truly looks like 21st century work that fell by accident into the 20th century, this would be it. It gives some strikingly different ways of thinking about QFT in 2d, including tantalizing connections to the structures (“automorphic representations”) that show up in Langlands theory, and has provided inspiration to many people over the years, including the geometric Langlands program. Atiyah’s lecture pointed to new ideas relating QFT to cutting edge geometry and topology, ideas that quickly led to lots of progress, while Witten’s ideas related QFT to representation theory and Langlands theory, in ways that we still have yet to fathom.

Posted in Favorite Old Posts, Uncategorized | 14 Comments

Friedrich Hirzebruch 1927-2012

Posted on May 29, 2012 by woit

The German mathematician Friedrich (Fritz) Hirzebruch passed away a couple days ago, at the age of 84. Hirzebruch was perhaps the most important mathematician in the Germany of the postwar period, responsible for the founding of the Max Planck Institute in Bonn, as well as the yearly Bonn Arbeitstagung conference. The Mathematics Genealogy Project lists him as having 52 Ph.D. students and 368 descendants. There’s a wonderful interview and article about him at the Simons Foundation web-site.

Hirzebruch’s first great mathematical achievement was the proof in 1954 of the generalization of the classical Riemann-Roch theorem to higher dimensional complex manifolds, now known as the Hirzebruch-Riemann-Roch theorem. This used the new techniques of sheaf cohomology and was one of the centerpieces of the explosion of new results in geometry and topology during the 1950s. Further generalization of this led to the Grothendieck-Riemann-Roch theorem, and the Atiyah-Singer index theorem. Hirzebruch’s monograph on the subject Topological Methods in Algebraic Geometry was the essential textbook in this area for many years.

The last time I heard Hirzebruch talk was at the celebration of Atiyah’s 80th birthday in Edinburgh, where Hirzebruch gave a talk about his interactions with Atiyah. He displayed some of their correspondence from this period, which makes fascinating reading and is now available here.

With the loss of Raoul Bott a few years ago, and now Fritz Hirzebruch, the math and physics communities are deprived of two of the great figures who built parts of modern mathematics that appear crucially in the structure of the Standard Model. Much of this connection between math and physics remains a mystery, and it’s too bad they won’t be around to help make progress unraveling it.

Update: The New York Times has a very good obituary of Hirzebruch here.

Posted in Obituaries | 10 Comments

Welcome to the Multiverse

Posted on May 21, 2012 by woit

Multiverse Mania makes the big time this week, with a cover story Welcome to the Multiverse by Brian Greene in Newsweek. While the title indicates that the Multiverse is here and part of our scientific world-view, the subtitle is a bit cagier: “The latest developments in cosmology point toward the possibility that our universe is merely one of billions.”

The article is pretty uniformly a promotional piece for multiverse mania, although buried fairly deep in the piece is something a bit more skeptical:

because the proposal is unquestionably tentative, we must approach it with healthy skepticism and invoke its explanatory framework judiciously.

Imagine that when the apple fell on Newton’s head, he wasn’t inspired to develop the law of gravity, but instead reasoned that some apples fall down, others fall up, and we observe the downward variety simply because the upward ones have long since departed for outer space. The example is facetious but the point serious: used indiscriminately, the multiverse can be a cop-out that diverts scientists from seeking deeper explanations. On the other hand, failure to consider the multiverse can place scientists on a Keplerian treadmill in which they furiously chase answers to unanswerable questions.

Which is all just to say that the multiverse falls squarely in the domain of high-risk science. There are numerous developments that could weaken the motivation for considering it, from scientists finally calculating the correct dark-energy value, or confirming a version of inflationary cosmology that only yields a single universe, or discovering that string theory no longer supports a cornucopia of possible universes. And so on.

I don’t see how we’re anywhere near finding such a version of inflation or getting rid of the string theory landscape, so the only hope of getting any evidence against the multiverse seems to be to calculate the cosmological constant. The multiverse thus looks to be pretty much impregnable and immune to any conceivable scientific challenge. A few years ago, pieces like this would hold out hope that the LHC would discover something encouraging for the multiverse, but now the LHC isn’t even mentioned. The only possible positive evidence suggested is seeing remnants of bubble collisions in the CMB, but the very likely eventuality of not seeing such a thing doesn’t count as evidence against the multiverse idea.

So, I fear Brian is right: Welcome to the Multiverse, physics is going to be stuck with it for a very long time…

Posted in Multiverse Mania | 94 Comments

Higgs Update

Posted on May 21, 2012 by woit

The announcement of new Higgs results from the LHC is now scheduled for about a month and a half from now, July 7th, 9:30 and 10am Melbourne time, at ICHEP2012. The LHC is performing well, with nearly 2.5 fb-1 of integrated luminosity/experiment. With only 2-3 weeks more of data collection before the cutoff for what can be analyzed in time to be made public July 7, one can expect the July announcements to be based on perhaps 4-5 fb-1 per experiment. Rough estimates show that, combining last year’s 5 fb-1 at 7 TeV and this year’s expected data, if the SM Higgs really is there at 125 GeV, each experiment should see a signal of 4 sigma significance. This is not quite the 5 sigma significance traditionally set for a discovery claim, but very close.

It thus looks possible that a discovery claim will require combining the results from CMS and ATLAS. The LHC Higgs Combination Group has been hard at work for the last couple years, developing methods for combining results from the two experiments. This time, they will be ready to quickly combine all the data from the two experiments, and maybe this will be what gives the 5 sigma needed for CERN to claim discovery. I don’t know what the plan is for when they will be provided with the CMS/ATLAS data, or when they plan to announce a result.

The LHC-HCG is competing with Philip Gibbs, who today released a Higgs Combination Java Applet which allows anyone to produce their own data combinations. If the LHC-HCG can’t produce a combination by 10:30am July 7, CERN should perhaps consider getting Philip’s applet properly set up and having DG Heuer publicly press the right button, allowing CERN to claim the Higgs discovery before Philip does.

Posted in Experimental HEP News | 15 Comments

Latest from the Rumor Mill

Posted on May 16, 2012 by woit

There’s at least one thing about string theory that has changed dramatically since my book was written back in 2002 or so. At the time I accumulated various numbers showing the way hiring in particle theory at leading institutions in the US had been dominated by string theory hires. Overall, at that time about 20 people/year were getting tenure-track positions, roughly half in string theory half in phenomenology. This data came from the Theoretical Particle Physics Jobs Rumor Mill, and Erich Poppitz has done an excellent job of putting some statistics together based on this data (see here). In recent years Erich’s data shows a much lower number of such positions (10-15/year), due to some combination of the bad economy and lack of enthusiasm for particle theory by other physicists. The number of string theorists getting positions had come down to about 2/year, then down to only one last year.

The hiring season is not yet over and not all the data is in, but so far the Rumor Mill shows no job offers to string theorists at all. Job offers are going pretty exclusively to phenomenologists and cosmologists, with phenomenologists allowed to stray into formal theory if they work on topics related to N=4 SYM and its superconformal invariance (including the hot topic of amplitudes). Marcus at PhysicsForums has patched some of the Rumor Mill links for better accuracy.

One thing hasn’t changed though since 2002: there’s a much larger number of talented and accomplished candidates than there are jobs, and departments are playing it safe, offering the few jobs available only to people working in a small number of areas that are conventionally agreed to be “hot”. As always, if you’re working on some idea that’s not in the narrow mainstream, there’s no chance you’ll get hired into a permanent position at a US institution.

Update: There is one string theorist now with a job offer it seems, with Princeton making an offer to Simone Giombi, who works on the hot topic of higher spins. So, at least Princeton has not given up….

Posted in Uncategorized | 26 Comments

The Smell of SUSY

Posted on May 16, 2012 by woit

The implications of the failure to find SUSY at the LHC are beginning to sink into the particle physics community: the paradigm that dominated the subject for the past 30 years has collapsed in the face of experimental (non)-evidence, threatening to take down the life’s work of hundreds if not thousands of theorists. For some recent attempts to quantify what is going on, from some people with much more statistical expertise than me, see Philip Gibbs and Tommaso Dorigo. By now a significant number of SUSY analyses of the full 2011 dataset have been completed, with negative results. By the end of the year there will be more data, but just a factor of 2-3 more, at about 14% higher energy. To believe that these sorts of increases will turn no signal into a signal requires a willingness to engage in a rather large amount of wishful thinking. The 62% jump in 2014 to 6.5 TeV/beam is more significant, but it’s hard to see an argument for why this should do the trick, and the wait for these results will be discouragingly long, probably until 2015. How many SUSY enthusiasts will keep the faith?

A small number of theorists though still claim all is well, with one group producing a new paper claiming the full 5 inverse femtobarn results show Chanel No5 (fb^-1): The Sweet Fragrance of SUSY. Last year the same authors were claiming to detect Profumo di SUSY in the first inverse femtobarn, and argued that 5 times more data would be conclusive. To quantify the SUSY smells they are advertising, one can plot as a function of time their published predictions for the parameter $M_{1/2}$ which determines the gluino mass.

arXiv:1007.5100 455 GeV (“Golden Point”)
arXiv:1009.2981 455-481 GeV (“Golden Strip”)
arXiv:1111.0236 512 GeV (“Universe F-U2”)
arXiv:1111.4204 518 GeV (“Profumo di SUSY”)
arXiv:1203.1918 610 GeV (“Aroma of Stops and Gluinos”)
arXiv:1205.3052 708 GeV (“The Sweet Fragrance of SUSY”)

It’s rather easy to extrapolate to the future what these authors will be claiming the SUSY masses are, harder to extrapolate how they’ll be describing the smell. The rest of the particle physics community I suspect is already using very different terms for this.

Update: According to this report from Pheno 2012

As pointed out by Rahmat Rahmat (yes, that’s his name—in my notes I list him as Rahmat2) and Csaba Csaki, respectively from University of Mississippi and Cornell University, the LHC should have detected some signature of SUSY by now, especially if the MSSM is correct. As Csaki said, “SUSY is a wonderful woman who does not return my letters. It makes you wonder if she even exists!”

Posted in This Week's Hype | 19 Comments

Igor Frenkel 60th Birthday Conference

Posted on May 14, 2012 by woit

This week Yale is hosting a conference on Perspectives in Representation Theory, in honor of Igor Frenkel’s 60th birthday. I’m planning to take the train up there and attend some of the talks tomorrow and Wednesday. Frenkel has been a pioneer in the field of representation theory, especially in the area of infinite-dimensional algebras whose representations are significant for understanding low-dimensional QFT, string theory and topological QFT. He started his career in the early 1980s, with many important results relevant to understanding affine Lie algebras. These became central in the explosion of interest among physicists in 2d conformal QFTs after 1984 due to their importance in string theory. Frenkel’s later work has covered a wide variety of topics, with one theme that of trying to understand higher-dimensional generalizations of affine Lie algebras and their potential application to QFTs in higher space-time dimensions than 2. He has also promoted the themes of “categorification” and geometric incarnation of representations that are now central to much research in this area.

Pavel Etingof and other students and collaborators of Frenkel have put together a wonderful document, On the work of Igor Frenkel, which gives much more detail about the many topics of his mathematical research.

Update: Videos of the talks are now available here.

Posted in Uncategorized | 1 Comment