Category Archives: research

Happy Higgs Day?

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Dont forget that today there will be big announcements of the latest results from the LHC about the search for the Higgs…(and some of us are hoping for news about what might be the beginning of the search for what lies beyond…)

There are so many live blogs, so follow a few… Like Resonances… for an expert view, Matt Strassler, for another expert view, or Quantum Diaries, for a non-expert view.

Exciting!!

(update… Looks like it is a strong enough set of results, statistically, to call the Higgs discovered… Hurrah! And with possible hints of new physics too? Excellent….)

Further update… A CERN press release is to be found here. Also, looks like any deviation from the standard model Higgs, at least for the decay channels examined so far, is very small… So there’s a lot left to do and understand…

-cvj Click to continue reading this post →

Amsterdam!

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20120703-164422.jpgAmsterdam! I’m here for a workshop for a while. It is on string theory – many aspects – and so the mix of people is a good one overall, with conversations ranging from high energy physics, the LHC (including the Higgs announcement at CERN expected tomorrow) and black holes all the way over to condensed matter and various kinds of exotic physics one can do in the laboratory in that context. It should be an excellent time here… It is good to be back in the city after over a decade, and to catch up with a number of friends and colleagues in the field. I also want to properly explore the city this time, not having done that much exploration last time. (Photo above is a snap taken of the lovely moon that came out last night, with the Amstel and accompanying reflections and so forth… Was pretty to see.)

I’ve been trying to read some notes in preparation for working on a draft of a […] Click to continue reading this post →

Has the Fat Lady Sung?

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The OPERA experiment has reported that they may have found the source of the timing discrepancy that produced the result that neutrinos moved apparently faster than light. It seems that there was a faulty connection that affected the timing measurements. Here’s a physics world article on the matter, along with a link to a CERN press release. (Note that there are some doubts related more directly to the GPS timing signals they used, which on their own would make for even faster neutrinos, but clearly there’s cause to really doubt their strong claim from back in the Fall and take a step back.)

You’ll recall the huge press storm about it last Fall, accompanied by all the usual hysteria about the establishment (this time, Einstein) being overturned. I blogged about it here, with the noncommittal title “No, Uh-uh, Nope, Nuh-uh”. They’ll be doing more experiments later in the year, as will a number of other groups, in order to solidify the results one way or another. It’s clear that most people have decided the whole business is over, and will turn away from it to other things. Some will be pleased, some annoyed, some confused, and so forth.

My hope is (as I discussed in the article I wrote back then) that this gets as much […] Click to continue reading this post →

Scribbling about Quantum Gravity

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So I mentioned that I was doing some more material for the Nova people, via their website. (See here for some earlier material about Multiverses.) They’ve a blog called The Nature of Reality with contributions from many interesting people. Well, now they’re featuring those pencasts I think I told you about in an earlier post.

The pencasts are all about Quantum Gravity, a major research topic in physics. I talk about what it is and why we care about it. I speak and write, scribble and draw and […] Click to continue reading this post →

Tune In!

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Later today, there’ll be a joint seminar by physicists from ATLAS and CMS, the two experimental halls at the Large Hadron Collider (LHC) looking for evidence of the Higgs boson. This will be the first official announcement of the physics seen (or not seen) by the combined results from both independent searches. Neither search has enough data to announce a discovery of anything (as far as I’ve heard) and the combined results would not constitute one either, but people are hoping for at least some nice hints of something suggestive that support each other. We shall see! this is an exciting time, as you’ve read me say before, and so I recommend looking out for what will be announced. Even a negative result (e.g., “we’ve found nothing yet”) […] Click to continue reading this post →

Almost at an End

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I’ve had a fun time over the last few lectures with some more mature topics, pointing the students to things that they will see more (I hope) in the advanced class next semester. We covered the large N Gross-Neveu model in some detail, giving me the opportunity to give a glimpse of several important topics and techniques… at large N the 2 dimensional model’s solution is exact, and it shows important phenomena such as spontaneous chiral symmetry breaking, dynamical mass generation for the fermions and dimensional transmutation. These are all important phenomena shared by (the more difficult to study) quantum chromodynamics, the theory of the strong nuclear interactions. (See an earlier post about some of these properties and what they are… there’s also a mention of a new general level book that goes into some detail on the physics and the history.)

The other thing I took some time to explore was the diagrammatics of the model, and the interesting patterns that emerge […] Click to continue reading this post →

Infinity Coincidence

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So here’s an interesting sequence of events. On Tuesday in the QFT class I finished the lecture on Renormalization Group Flow, and the idea of a “beta function”, unpacking the results we’d accumulated from QED and quartic scalar field theory to use as illustration. The key result, for those of you about to scroll away (or the few of you who have not, but are hovering over the scroll bar), is as follows. Never mind what a beta function is right now. The issue at hand concerns whether it is positive or negative for a force of interaction being studied. A positive beta function tells you that the strength of the interaction between constituent things (particles, etc) gets weaker as you work at lower energies… This is an important result in understanding how Nature behaves in a variety of situations… one way of seeing variety is to look at different energy scales, and sometimes what seems familiar takes on different character. The converse is true… that positive beta function tells you that the interaction gets stronger at higher energies… Energy is also rather like the inverse of distance scale too, so high energy is akin to shorter distance scales (higher resolution), and low energy like longer distance scales (grainier resolution). In other words, looking at stuff in really tiny detail means using higher energy… and the nature of that stuff can change when you look at that sort of resolution since the way things interact changes… For electromagnetism, for example, we see that it gets stronger the closer we look, digging more deeply into the structure of the atom, say, probing the charged constituents of the nucleus once we’ve understood electrons. The result is that you see the electromagnetic interaction changes, ultimately turning into something else… (it merges with one of the nuclear forces, in fact…but that’s a story for another day)

So anyway one of the things I ended the class with was the idea that if you had a negative beta […] Click to continue reading this post →

QFT Rocks!

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I’m having a blast teaching the introductory quantum field theory class, as you may have gathered from several previous posts. It has been taking a lot of time, but I’ve been doing detailed computations with the students (and hence taking up a lot of preparation time) to make sure they really get how to compute in a quantum field theory (such as Quantum Electrodynamics (QED)) and see how it connects to the real world. Having spent time on the electron anomalous magnetic moment computation (I told you about that spectacular feature of QED earlier) we went back to basics to discuss in more detail the nature of the physics that is to be extracted from what are called one-loop diagrams – diagrams of the sort I drew before that have a closed loop in them.

This is where I get to try to clear up a huge conceptual issue that still afflicts most people’s popular-level knowledge of quantum field theory due to poor writing – the nonsense often spouted about there being “hidden infinities” and so on and so forth. Covering the poorly-named “renormalization” procedure and treating it in a more physical way to see that the whole “infinity” business is dreck can be fun, since it allows for an emphasis on a lot of the key issues I care about in the science that we do, such as the idea of effective field theory, the importance of separation of scales in your physics, and most importantly the reminder: Let’s not confuse the tools we use to describe Nature with Nature itself.

I like to use that phrase, and it comes back again and again, whether it is to do with […] Click to continue reading this post →

Southern California Strings Seminar

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The next Southern California Strings Seminar is on Friday 21st October! The website is here. It is going to be held over at UCLA this time, and I expect it’ll be fun and informative, as these regional meetings have proven to be. This time it is a one-day event again. You may recall that the last one, on May 6th, was over at USC. See here. There’s a random picture from it above left.

Apologies to anyone who was […] Click to continue reading this post →

Landmarks

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We reached certain key landmarks in the quantum field theory class last week. Not only did we uncover how the Dirac equation predicts that the electron’s spin couples to a background magnetic field, but that it is (to a first approximation) twice the coupling that its angular momentum couples with. This is a remarkable output (once again) from that wonderful equation, the result of putting together Quantum Mechanics and Special Relativity. (I’ve discussed other properties of it before, here.) Makes you wonder, doesn’t it? If finding an equation that puts together QM and SR results in so many marvellous things about Nature just falling out so nicely (recall that spin, and also antimatter are also inevitable predictions of the Dirac equation), doesn’t it make you just thirst to know what we’ll learn (predict, explain, discover) when we find how Quantum Mechanics and General Relativity fit together? This is one of the great motivations for the work my research community does, in case you sometimes find yourself wondering – the quest for finding how Nature combines the two things together to make what we call Quantum Gravity. We’ve found one way, on the page, that you can put together QM and GR for sure (you’ve heard of it, it is called string theory) but it’s not yet clear if this form of quantum gravity is the one Nature chooses to work with, and in any case we need to work on it a lot more to understand what we’ve got, as it surely isn’t complete yet. There are huge pieces of the puzzle missing.

Anyway, the next thing we did was the classic computation of the first quantum correction to the “twice” I mentioned above. This is the computation of the famous […] Click to continue reading this post →

AdS Vs CMT

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So there are two workshops going on here at the KITP in Santa Barbara that pertain to issues in condensed matter physics. (You may recall that I am here for some of the week, and in LA at USC for the rest of the week – adds up to a full week each week.) One is Holographic Duality and Condensed Matter Physics (often referred to as AdS/CMT), concerning applications (I’ve told you about this here before) of techniques from string theory to issues in condensed matter theory and experiment, and the other is Topological Insulators and Superconductors. there are people from both communities on both workshops, and so it is an exciting and interesting time.

The KITP Fall picnic was yesterday, and this means that there’s the traditional football (i.e. soccer) contest between workshops. Not to resolve physics issues, you understand, but to blow off some steam before getting down to the business of eating all the food… Well, at the top of this post and in the following, you can see some pictures of the process of the string theory crowd getting slaughtered for a change:

The score was 5-0.

The KITP Director, David Gross, who has presided over very many matches where the […] Click to continue reading this post →

Looking Back and Forth

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Somehow after Wednesday I lost track of time, in a sense, in the natural course of having another very busy week. There were several things competing for time, and some of them may be of interest to you. (Left: Some lovely pink gladiolus flowers that have sprung up in my garden.) The Nobel Prizes kept coming, of course, with some very interesting winners announced. In addition to the ones I mentioned already in two earlier posts, I’ve got to find some people among our faculty who’ll be willing to spend 10 to 15 minutes making some informal remarks about the Who/What/Why aspects of the prize at one of two lunches I’ll be hosting in the coming weeks about the Nobel Prize. I’ve mentioned this before. It is an annual event I’ve tried to get going as part of the Dornsife Commons (formerly known as College Commons) series. I’ve locked in Physics and Peace, and want to get people for all the others. This year I know that if I have problems with Chemistry, I can step in if need be, although I’d rather not have to do that – I want to broaden participation, not do everything myself. Look out for those lunches (see here) and come along!

Speaking of doing everything myself, I’ve been continuing the weeks long struggle to get support, interest, and participation for the Science Film Competition I told you about earlier. Having spent a lot of time meeting with many faculty and other parties to build support and understanding, getting lots of faculty to make announcements (one time even coming down from Santa Barbara to campus to give a ten minute announcement in a class at the film school and going up again after!) and so forth – and thanks everyone who has helped! – I decided to amplify my focus on tackling […] Click to continue reading this post →

Quasicrystals!

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Wow! WOW!

As you can tell, I am very pleased about the 2011 Chemistry Nobel Prize announcement. I’d love to tell you a bit more about why, but I’m supposed to be working on something urgently right mow, and so will try to do so later. The key thing is that I think the discovery of quasicrystals is fantastic and very visual example of how we can dream up a mathematical structure just because it is interesting and beautiful (Penrose tilings, independently discovered by Roger Penrose as the answer to a mathematical puzzle, (see two dimensional version on left) but also showing up in Islamic tiling patterns from much earlier) and then find later that Nature has exploited that same pattern to make something- a new form of matter (the quasicrystals themselves… The subject of today’s prize to Dan Shechtman – image below on right is of a silver and aluminium quasicrystal compound. Both images here are from wikimedia commons.).

I was in love with these things when I was an undergraduate, not long after their discovery, […] Click to continue reading this post →

Breakfast Guy

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I’ve no idea who he was, but he made for an interesting subject for several minutes*, sitting eating his breakfast with his (I think) wife. I was staying at a hotel and having breakfast, just North of Santa Barbara. The person I set out wanting to draw (very interesting face) was sitting right opposite me, at the same table as me, looking over regularly, and so it seemed a bad idea to try to sketch him. Also, he turned out to be a physicist also visiting at the KITP for a workshop, and so it could have ended up quite awkward.

It was a pretty good week at the workshop. I had a number of interesting conversations with young people trying out ideas and calculations, who’ve actually read (!) various papers of mine, and so had questions and […] Click to continue reading this post →

Heretic…?

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We had a really interesting discussion of the quantum physics of de Sitter spacetime yesterday here in Aspen, starting with a review of the behaviour of scalar fields in such a background, led by Don Marolf, and then, after lunch, an open-ended discussion led by Steve Shenker. This is all quite difficult, and is of course quite relevant, since a piece of de Sitter is relevant to discussions of inflation, which seems (from cosmological observations) to have been a dominant phase of the very early universe. As the most symmetric space with positive cosmological constant, de Sitter may also be relevant to the universe today, since dark energy (first recognized after 1998’s observations of the universe’s accelerating expansion) may well accounted for by a positive cosmological constant.

So we need to understand this type of spacetime really well… and it seems that we don’t. Now there’ve been a lot of people looking at all this and doing really excellent work, and they understand various issues really well – I am not one of them, as I’ve not worked on this in any detail as yet. Do look at the papers of Marolf, and of Shenker, and collaborators, and references therein, and catch up with what’s been going on in your own way. For what it is worth, the sense that I get is that we’re trying to solve very difficult issues of how to interpret various quantum features of the spacetime and getting a lot of puzzles by trying to make it look a lot like things we’ve done before.

Now, we may solve all these puzzles…. but my current take on this all is that we’re […] Click to continue reading this post →