Musings

Oscar Chacaltana, Yuji Tachikawa and I are deep in the weeds of nilpotent orbits. One of the things we had to study were the nilpotent orbits of ${𝔤}_2$, and how they sit in $\mathrm{𝔰𝔬}(8)$. Understanding the answer involves an explicit description of $\mathrm{Spin}(8)$ triality, which I thought was kinda cute. Few people will care about the nilpotent orbits, but the bit about triality and $G_2$ might be of some independent interest. So here it is.

I missed the brouhaha surrounding the LHC Joint Higgs Search Progress Report. But, luckily, there’s still something contentful to add to what’s already been said.

Both groups (ATLAS and CMS) found statistically-significant excesses in two channels, corresponding to

• $H\to \gamma \gamma$
• $H\to Z{Z}^{*}$

with an invariant mass centered around 125 GeV.

The latter decay mode yields a 4-lepton final state where one of the ${\ell }^{+}{\ell }^{-}$ pairs has an invariant mass of 91 Gev, corresponding to the decay of an on-shell $Z$ (the other $Z$ is, necessarily, off-shell). Since the relevant 4-lepton final states have relatively low backgrounds, the experimentalists could have (modestly) improved their results by relaxing their constraint that one of the $Z$s be on-shell. My colleague, Can Kiliç, and collaborators have a recent paper advocating exactly such an analysis.

According to Can, this wouldn’t quite have boosted CERN into $5\sigma$ discovery-territory, but it would have made the result more compelling (or, conversely, less-so, depending on the result).

In fact, Can and co. go a little further, and advocate looking in a number of multi-lepton channels:

• same-sign $2\ell$ (the standard $H\to W{W}^{*}$ search looks for opposite-sign di-leptons)
• $3\ell$
• $4\ell$

with varying amounts of MET. Of course, nothing substitutes for greater integrated luminosity, which is what 2012 is all about.

More here, here and, yes, here.

Here’s an old riddle, that some of you may have heard.

François lives in Lyons, and has two girlfriends: one in Marseilles and another in Paris. He can’t seem to choose between them, so he decides on the following strategy. The trains to Paris and to Marseilles both run once-an-hour. He decides to show up at the railroad station at random times, and takes whichever train comes first.

After several weeks, François finds that, on average, 9 times out of 10, he ends up visiting the girlfriend in Marseilles. Clearly, the Fates have chosen for him, so he dumps the girlfriend in Paris and proposes to the girl in Marseilles.

What’s going on?

Reviving a Halloween tradition on this blog…

I was chatting with our new postdoc, and the conversation went something like this:

Mohammad: So, why aren’t you blogging any more?
Jacques: If I were blogging, I would probably be writing posts about superluminal neutrinos. Surely, that’s not what you want.
Mohammad: Hmmmm….
Jacques: On the other hand, Cohen and Glashow wrote a very nice paper laying that whole miserable subject to rest.

The APS Division of Particles and Fields has a new award for dissertations. Here’s the announcement.

Ten years ago, I put up a web page devoted to my father’s Holocaust survival story. The centerpiece was a 2-hour long video of an interview he did in 1993. Back in 2001, the Sorenson 3 Codec, and QuickTime Streaming, were the cat’s pajamas, so that was how I encoded the video. A decade later, Sorenson 3 won’t play on many installations. So, for this year’s Yom HaShoah, I revamped the web page, and re-encoded the video in H.264.

I’m still using QuickTime Streaming … which doesn’t work on the iPhone/iPad. They don’t support RTSP streaming and, instead, require some new-fangled technology, called HTTP Live Streams, to do streaming video (maybe by the next Yom HaShoah …).

Anyway, in honour of Yom HaShoah, 2011, here’s the revamped page¹.

Tonight, the ALICE collaboration released their first paper. This must be something of a record, as they just started observing Pb-Pb collisions on Nov. 7.

They’ve observed elliptic flow at center-of-mass-energy/nucleon-pair $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. For those who were sceptical, the quark-gluon plasma is still a strongly-coupled liquid, with very low shear viscosity, at LHC energies — more than a order of magnitude larger than the $\sqrt{s_{\mathrm{NN}}}=200$ GeV at RHIC.

As with the proton-proton experiments, they are currently operating at only half the design energy. But, unlike proton-proton, which beat the Tevatron by only a modest factor, the heavy-ion experiments are already probing energies an order-of-magnitude larger than those seen at RHIC.

Below is one of their plots (for $v_2$, integrated over $p_t$). $v_2$ is the coefficient of $\cos (2\varphi )$ in a Fourier series of the azimuthal dependence of the particle multiplicity produced in the collision; the larger $v_2$, the stronger the elliptic flow.

Campus was locked down today. Classes were cancelled. And, most annoyingly, the café in the RLM lobby was closed. Despite rumours of a 2nd gunman, it seems there was only one person (and an AK-47) involved and, mercifully, he was the only casualty.

After much delay, I’m releasing Instiki 0.19.

It’s been 9 months since the previous release, so – naturally – there’s a lot of new stuff to report.

The most visible change comes when you unpack the distribution. External dependencies have always been a pain to deal with. With Instiki, we’ve tried to minimized their number; but sometimes they’re unavoidable. With Instiki 0.19, I’ve started using Bundler to manage external dependencies. What that means is that, when you’ve unpacked the distribution, you need to type

ruby bundle

at the commandline, from the main Instiki directory. This will download and install the Rubygems used by Instiki. The list of Rubygems is in the Gemfile. And, if your situation is special, you can tweak that list. If, for instance, you’re using MySQL instead of the default sqlite3 database, you need to add a line

gem "mysql"

to the Gemfile. Users on Dreamhost will find that they need to modify the entry for sqlite3-ruby. But, in general, you should find that you won’t have to muck with it and that the whole installation experience is more hassle-free than before.

The next most visible change is that itex2MML is now a Rubygem (managed by Bundler), so you don’t need to worry about installing it separately. In fact, with 0.19, every Instiki installation now provides an itex-to-MathML translation service as a web service. Perhaps, you’ll find other uses for it, but the main reason for its existence is that …

Instiki now includes a WYSIWYG drawing package, based on SVG-Edit. You can embed SVG figures directly in your wiki pages, and you can embed MathML content in those SVG figures. This has proven really useful to me, personally, what with the ability to export Instiki pages to LaTeX, and export the figures to PDF.

This release is based on Rails 2.3.9. I expect that the next release will be based on Rails 3.

Update: Nested Extensible Arrows

Thanks to some discussions with Frédéric Wang (of Mozilla MathML fame), I’ve improved itex2MML, so that it can now accommodate nested extensible arrows with optional arguments. Users of Instiki 0.19 can update their version of itextomml by typing

ruby bundle update

A certain Professor Xxxx has received quite the internet thrashing for complaining that (cached version) — despite a household income (roughly $450K $400K ) nineeight times the median US household income — he’s really just an ordinary Joe, trying to make ends meet, and will suffer terribly if Congress allows the Bush tax cuts (on incomes over $250K) to expire.

I’m somewhat loath to pile on, as surely every cognitive flaw, exhibited in the post in question, has been more than amply exposed. But something struck me about one of his followup posts (cached version), which seems to speak to a more general bit of nonsense that one hears from those of Professor Xxxx’s ideological persuasion.

He says

So why doesn’t Prof. Krugman say that I’m a whiny loser because I’m complaining that the government needs 50% of the money I spend each month, on things like art camps? It may be that some of the decisions I made that led to these fixed costs were mistakes, but there will be a real impact from this increase in my tax burden. I’ve not seen any critic point out why my Polish-American house cleaner would be better off getting handouts from the government than earning her wage cleaning our house.

Now, arguing that your taxes shouldn’t be raised because, if they are, you’ll respond by employing fewer domestic servants, is probably not the winning sort of argument that a University of Chicago Law professor would teach his students to marshall. But let’s leave that aside. What I want to focus on is the fact that art camp, for apple-cheeked Amy is in peril. Two paragraphs later, he says

Fifth, lost in all of this is the impact of increased taxes on the work-leisure tradeoff. As marginal taxes rise, so does the disincentive to work. I’m asked with some frequency to write, consult, or testify, and when I do, I face the question of whether the effort and time is worth it. I can choose to watch the Steelers or help a hedge fund with a corporate law question. The higher my marginal taxes, the more likely I am to choose the former. This is a losing proposition from a social welfare perspective, no matter what you think of the quality of my advice or the role of hedge funds.

Let’s understand what’s being said here.

If his marginal tax rate is raised from the current 35% to 39% (the rate that prevailed during the Clinton Era), art camp for apple-cheeked Amy will become unaffordable. But, rather than take on that additional consulting gig (which, after taxes, would net him $122/hour, instead of $130/hour) to pay for Amy’s art camp, Professor Xxxx plans to sit on the couch watching football.

Is that really how Professor Xxxx plans to meet this (alleged) financial challenge? If so, he truly does inhabit a different psychological universe. Most of us, when cash-flow gets tight, try to find ways to increase rather than decrease our income.

But, really, who (except for the Xxxx’s) cares whether apple-cheeked Amy gets to go to art camp? What really matters to the rest of us is Professor Xxxx’s contributions to the overall economy. Is it really true that he (and others in his position) will park himself on the couch, watching football, instead of contributing productively to the economy?

Is it really true that raising the top marginal tax rate will hurt GDP, because people like Professor Xxxx will work less hard in response?

My last paper was written almost entirely on an Instiki wiki, transferred to a TeX file (in an SVN repository) only a few days before submission. The 136 figures were prepared using Instiki’s nifty built-in WYSIWYG SVG-editor.

Unfortunately, when it came time to “export” the figures to accompany the TeX file, I realized – to my horror – that there did not exist a tool for converting SVG, with embedded MathML, into PDF. We ended up producing PNG bitmaps (essentially, taking screen shots in the browser). That was time-consuming (thank heavens for a graduate student co-author) and the results were less than completely satisfactory.

So, with the paper squared-away, and the semester well underway, I sat down to put together a better solution.

I received the following in my email, last night (8/30/2010):

Ms. Ref. No.: XXXXXX
Title: XXXXXXXXXXXXXXX
Journal of Geometry and Physics

Dear Professor Jacques Distler,

You agreed to review Manuscript Number XXXXXX for
Journal of Geometry and Physics on . Your completed
review was due by 12 Oct 2010.

Your review is now -42 days late. Therefore I would
be grateful if you would submit you review as soon
as possible at the Elsevier Editorial System at
http://ees.elsevier.com/geophy/. Please login as a
Reviewer using the following username and password:

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Gogol Bordello are my current favourite band … by far.