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roadtrip, frustrated magnets, ultimate

Ed Witten is giving a talk at Stanford on Monday, so I figure it's a good excuse to skip class and take a road trip. His lecture on Twistor Theory on Thursday sounds more interesting, but Thursday is my busiest day of the week and I have to TA, so skipping isn't really an option. Supersymmetric Quantum-Chromodynamic instantons will have to do! Not that I expect to understand much at all of what he might say, but I don't exactly have anything better to do that day.

Journal Club today was about geometrically frustrated magnets. Nothing scarier than a lattice of angry frustrated magnets chasing you!

Started playing Ultimate frisbee, our team is called Disc Amplitude. We had a scrimage on Tuesday, and then we'll have our first real game next Tues. Hopefully, I've figured out most of the rules by now :)

Comments

( 5 comments — Leave a comment )
onhava
Oct. 8th, 2004 05:58 pm (UTC)
Don't underestimate how interesting SUSY QCD instantons are. SUSY QCD with different numbers of colors and flavors displays a huge variety of types of behavior (confining phases, Higgs phases, free electric phases, free magnetic phases, etc.), and there are all sorts of unexpected dualities between these. For N_f <= N_c, it has been known what role instantons play in the theory, but it's been poorly understood for N_f > N_c until Witten's latest paper. (Which I haven't found the time to study at all, I've just been told a bit about it.)

As for why you should care: we know that below a TeV or so dynamics in the real world is described by a non-SUSY gauge theory. We know new physics will occur at the energy scales we're probing soon, and it's a good bet that it will involve either new strongly interacting (SUSY or not) gauge theories, or SUSY. In either case understanding the possible behaviors of gauge theories is very important. But in the non-SUSY case, we really have no hope at present of understanding things in much detail. In the SUSY case we do have that hope.

Another place progress has been made recently is with something called "a-maximization," which brings us a step closer to having a 4-dimensional version of what's called the Zamolodchikov c-theorem in two dimensions. Basically this involves finding a function that monotonically decreases along renormalization group flow. (There are, I think, both weaker and stronger forms of the conjecture.) Again, I don't know that much about this stuff, but there is definitely progress being made toward a general understanding of gauge theory dynamics (however far off that ultimate goal might be).

Twistors, on the other hand, are an idea that I think Penrose was hoping would bring us closer to quantum gravity, but mostly they're useful for studying zero-mass fields of various spins. Lately there's been some excitement about a way of using them to rewrite the perturbation expansion for n-gluon scattering in terms of a smaller number of simpler diagrams, but I understand that this only works so far at tree level for QCD (although at one-loop for N=4 SUSY) and that in the QCD case this technique was basically known before in a different context. There is some hope that this might lead to better ways to calculate in Yang-Mills theory in general, but I don't think this is at all clear yet, from what I've heard.

Then, I'm no expert on any of these things. Maybe you can post a bit about what Witten says.
spoonless
Oct. 9th, 2004 04:57 pm (UTC)
Thanks for the background on why SUSY QCD is important. That makes me even more excited about monday :)

Wish I knew more about this stuff. I've clearly got a lot more to learn.

Twistors, on the other hand, are an idea that I think Penrose was hoping would bring us closer to quantum gravity, but mostly they're useful for studying zero-mass fields of various spins. Lately there's been some excitement about a way of using them to rewrite the perturbation expansion for n-gluon scattering in terms of a smaller number of simpler diagrams, but I understand that this only works so far at tree level for QCD (although at one-loop for N=4 SUSY) and that in the QCD case this technique was basically known before in a different context. There is some hope that this might lead to better ways to calculate in Yang-Mills theory in general, but I don't think this is at all clear yet, from what I've heard.

I've noticed that a lot of Witten's papers within the last year or so have been about Twistor space. So I figured it must be somewhat cool. But in all reality, it's probably a good thing that the Monday talk is the one I can make. That one I'm more likely to take some things home from. And it's more physics than math, so it's also more relevant.

Maybe you can post a bit about what Witten says.

I'll try. You might check pbrane's journal too; I haven't asked him, but I would assume he's going to this too. And if he is, I'm sure he'll be able to say more about it.
amberphlame
Oct. 8th, 2004 09:13 pm (UTC)
have you ever tried disc golf?
a lot more fun than ultimate to me.
:)
spoonless
Oct. 9th, 2004 05:01 pm (UTC)
That's funny, someone was just telling me about disc golf on the way home last night. Where I'm from they play something called "frisbee golf" but from what the folks here describe, disc golf is slightly different.

I've never played either, but I'm sure it's a lot of fun!
fallen_x_ashes
Oct. 22nd, 2004 08:15 pm (UTC)
Envy
I m quite envious that you're going to be able to see Witten, although I'm sure I probably wouldn't be able to understand the lecture at all. :-D

Have fun.
( 5 comments — Leave a comment )

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