Tag Archives: DoingScience

Amplitudes 2017

I’ve been at Amplitudes this week, in Edinburgh. There have been a lot of great talks, most of which should already have slides online. (They’ve been surprisingly quick about getting slides up this year, with many uploaded before the corresponding talks!) Recordings of the talks should also be up soon.

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We also hiked up local hill Arthur’s Seat on Wednesday, which was a nice change of pace.

I’ll have more time to write about the talks later, a few of them were quite interesting. For now, take a look at some of the slides if you’re curious.

Visiting LBNL

I’ve been traveling this week, giving a talk at Lawrence Berkeley National Laboratory, so this will be a short post.

In my experience, most non-scientists don’t know about the national labs. In the US, the majority of scientists work for universities, but a substantial number work at one of the seventeen national labs overseen by the Department of Energy. It’s a good gig, if you can get it: no teaching duties, and a fair amount of freedom in what you research.

Each lab has its own focus, and its own culture. In the past I’ve spent a lot of time at SLAC, which runs a particle accelerator near Stanford (among other things). Visiting LBNL, I was amused by some of the differences. At SLAC, the guest rooms have ads for Stanford-branded bed covers. LBNL, meanwhile, brags about its beeswax-based toiletries in recyclable cardboard bottles. SLAC is flat, spread out, and fairly easy to navigate. LBNL is a maze of buildings arranged in tight terraces on a steep hill.

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I forgot to take a picture, but someone appears to have drawn one.

While the differences were amusing, physicists are physicists everywhere. It was nice to share my work with people who mostly hadn’t heard about it before, and to get an impression of what they were working on.

PSI Winter School 2017

It’s that time of year again! Perimeter Scholars International, Perimeter’s Master’s program in theoretical physics, is holding its Winter School up in Ontario’s copious backwoods.

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Ominous antlered snowmen included

Like last year, the students are spending mornings and evenings doing research supervised by PI grad students, postdocs, and faculty, and the afternoons on a variety of winter activities, including skiing and snowshoeing.

Last year, my group worked on the “POPE”, a proposal by Basso, Sever, and Vieira, and we ended up getting a paper out of it. This year, I’ve teamed up with Freddy Cachazo on a gravity-related project. We’ve got a group of enthusiastic students and are making decent progress, I’ll have more to say about it next week.

Next Year in Copenhagen!

As some of you might be aware, this is my last year at the Perimeter Institute. It’s been great, but the contract was only for three years, and come August I’ll be heading elsewhere.

Determining that “elsewhere” was the subject of an extensive job search. Now that the search has resolved, I can tell you that “elsewhere” is the Niels Bohr International Academy at the Niels Bohr Institute in Copenhagen, where I’ll be starting a three-year postdoc job in the fall.

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Probably in the building on the left

There are some pretty stellar amplitudes people at NBIA, so I’m pretty excited to be going there. It’s going to be a great opportunity to both build on what I’ve been doing and expand beyond. They’re also hiring several other amplitudes-focused postdocs this year, so overall it should be a really fun group.

It’s also a bit daunting. Moving to Canada from the US was reasonably smooth, I could drive most of my things over in a U-Haul truck. Moving to Denmark is going to be quite a bit more complicated. I’ll need to learn a new language and get used to a fairly different culture.

I can take solace in the fact that in some sense I’m retracing my great-grandfather’s journey in the opposite direction. My great-grandfather worked at the Niels Bohr Institute on his way out of Europe in the 1930’s, and made friends with the Bohrs along the way, before coming to the US. I’ll get a chance to explore a piece of family history, and likely collaborate with a Bohr as well.

Hexagon Functions Meet the Amplituhedron: Thinking Positive

I finished a new paper recently, it’s up on arXiv now.

This time, we’re collaborating with Jaroslav Trnka, of Amplituhedron fame, to investigate connections between the Amplituhedron and our hexagon function approach.

The Amplituhedron is a way to think about scattering amplitudes in our favorite toy model theory, N=4 super Yang-Mills. Specifically, it describes amplitudes as the “volume” of some geometric space.

Here’s something you might expect: if something is a volume, it should be positive, right? You can’t have a negative amount of space. So you’d naturally guess that these scattering amplitudes, if they’re really the “volume” of something, should be positive.

“Volume” is in quotation marks there for a reason, though, because the real story is a bit more complicated. The Amplituhedron isn’t literally the volume of some space, there are a bunch of other mathematical steps between the geometric story of the Amplituhedron on the one end and the final amplitude on the other. If it was literally a volume, calculating it would be quite a bit easier: mathematicians have gotten very talented at calculating volumes. But if it was literally a volume, it would have to be positive.

What our paper demonstrates is that, in the right regions (selected by the structure of the Amplituhedron), the amplitudes we’ve calculated so far are in fact positive. That first, basic requirement for the amplitude to actually literally be a volume is satisfied.

Of course, this doesn’t prove anything. There’s still a lot of work to do to actually find the thing the amplitude is the volume of, and this isn’t even proof that such a thing exists. It’s another, small piece of evidence. But it’s a reassuring one, and it’s nice to begin to link our approach with the Amplituhedron folks.

This week was the 75th birthday of John Schwarz, one of the founders of string theory and a discoverer of N=4 super Yang-Mills. We’ve dedicated the paper to him. His influence on the field, like the amplitudes of N=4 themselves, has been consistently positive.

Four Gravitons in China

I’m in China this week, at the School and Workshop on Amplitudes in Beijing 2016.

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It’s a little chilly this time of year, so the dragons have accessorized

A few years back, I mentioned that there didn’t seem to be many amplitudeologists in Asia. That’s changed quite a lot over just the last few years. Song He and Yu-tin Huang went from postdocs in the west to faculty positions in China and Taiwan, respectively, while Bo Feng’s group in China has expanded. As a consequence, there’s now a substantial community here. This is the third “Amplitudes in Asia” conference, with past years meeting in Hong Kong and Taipei.

The “school” part of the conference was last week. I wasn’t here, but the students here seem to have enjoyed it a lot. This week is the “workshop” part, and there have been talks on a variety of parts of amplitudes. Nima showed up on Wednesday and managed to talk for his usual impressively long amount of time, finishing with a public lecture about the future of physics. The talk was ostensibly about why China should build the next big collider, but for the most part it ended up as a more general talk about exciting open questions in high energy physics. The talks were recorded, so they should be online at some point.

Jury-Rigging: The Many Uses of Dropbox

I’ll be behind the Great Firewall of China next week, so I’ve been thinking about various sites I won’t be able to access. Prominent among them is Dropbox, a service that hosts files online.

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A helpful box to drop things in

What do physicists do with Dropbox? Quite a lot.

For us, Dropbox is a great way to keep collaborations on the same page. By sharing a Dropbox folder, we can share research programs, mathematical expressions, and paper drafts. It makes it a lot easier to keep one consistent version of a document between different people, and it’s a lot simpler than emailing files back and forth.

All that said, Dropbox has its drawbacks. You still need to be careful not to have two people editing the same thing at the same time, lest one overwrite the other’s work. You’ve got the choice between editing in place, making everyone else receive notifications whenever the files change, or editing in a separate folder, and having to be careful to keep it coordinated with the shared one.

Programmers will know there are cleaner solutions to these problems. GitHub is designed to share code, and you can work together on a paper with ShareLaTeX. So why do we use Dropbox?

Sometimes, it’s more important for a tool to be easy and universal, even if it doesn’t do everything you want. GitHub and ShareLaTeX might solve some of the problems we have with Dropbox, but they introduce extra work too. Because no one disadvantage of Dropbox takes up too much time, it’s simpler to stick with it than to introduce a variety of new services to fill the same role.

This is the source of a lot of jury-rigging in science. Our projects aren’t often big enough to justify more professional approaches: usually, something hacked together out of what’s available really is the best choice.

For one, it’s why I use wordpress. WordPress.com is not a great platform for professional blogging: it doesn’t give you a lot of control without charging, and surprise updates can make using it confusing. However, it takes a lot less effort than switching to something more professional, and for the moment at least I’m not really in a position that justifies the extra work.