October 31, 2013

Halloween 2013

It’s Halloween, again. Time for another pumpkin.

Posted by distler at 10:23 AM | Permalink | Followups (1)

August 24, 2013

Zombies

Normally, I wouldn’t touch a paper, with the phrase “Boltzmann brains” in the title, with a 10-foot pole. And anyone accosting me, intent on discussing the subject, would normally be treated as one of the walking undead.

But Sean Carroll wrote a paper and a blog post and I really feel the need to do something about it.

Posted by distler at 2:10 PM | Permalink | Followups (22)

August 6, 2013

Maybe this time …

For many years, I tried keeping up with the LQG literature. Though it provided occasional fodder for blogging, it mostly was an exercise in frustration. Years ago, I gave up the effort. Still, occasionally, an LQG paper crosses my radar screen with claims interesting enough to cause me to suspend my better judgement.

One such paper, by Gomes et al, purports to be a significant breakthrough in the understanding of AdS/CFT. They claim to reproduce the conformal anomaly of a boundary CFT from some Loopy formulation (“Shape Dynamics”) of the bulk theory, thereby shedding light on the 1998 computation of Henningson and Skenderis who first reproduced the conformal anomaly from AdS/CFT (a more careful and thorough derivation can be found in a followup paper).

How could I resist?

Posted by distler at 10:59 AM | Permalink | Followups (6)

June 27, 2013

I lost

It’s been 20 years since I had the surreal experience of turning on C-Span late at night to see my future boss, Steve Weinberg, testify before Congress on behalf of the SSC.

Steve, alas, was unsuccessful; the SSC was cancelled, and the High Energy Physics community threw our collective eggs in the basket of the LHC. The SSC, at $\sqrt{s}=40$TeV, was designed as a discovery machine for TeV-scale physics. The LHC, with a design energy of $\sqrt{s}=14$TeV, is the best one could do, using the existing LEP tunnel. It was guaranteed to discover the Higgs. But for new physics, one would have to be somewhat lucky.

Posted by distler at 11:59 AM | Permalink | Followups (23)

September 16, 2012

Uncertainty

Update (10/18/2012) — Mea Culpa:

Sonia pointed out to me that my (mis)interpretation of Ozawa was too charitable. We ended up (largely due to Steve Weinberg’s encouragement) writing a paper. So… where does one publish simple-minded (but, apparently, hitherto unappreciated) remarks about elementary Quantum Mechanics?

Sonia was chatting with me about this PRL (arXiv version), which seems to have made a splash in the news media and in the blogosphere. She couldn’t make heads or tails of it and (as you will see), I didn’t do much better. But I thought that I would take the opportunity to lay out a few relevant remarks.

Since we’re going to be talking about the Uncertainty Principle, and measurements, it behoves us to formulate our discussion in terms of density matrices.

Posted by distler at 12:27 AM | Permalink | Followups (29)

July 24, 2012

Bringing the Web to America

It has long been my conviction that anything appearing on the Wall Street Journal’s Editorial/Op-Ed pages is a lie. In fact, if there’s a paragraph appearing on those pages, in which you can’t spot an evident falsehood or obfuscation, then the problem is that you haven’t studied the topic, at hand, in sufficient depth.

On that note, it comes as no surprise that we “learn” [via Kevin Drum] that the Internet was the creation of private industry (specifically, Xerox PARC), not some nasty Government agency (DARPA). Nor is it surprising that the author of the book about PARC, on which the claims of the WSJ Op-Ed were based, promptly took to the pages of of the LA Times to debunk each and every paragraph. (See also Vint Cerf: “I would happily fertilize my tomatoes with Crovitz’ assertion.”)

Which leaves me little to do, but post a copy of this lecture, from 1999, by Paul Kunz of SLAC. The video quality is really bad, but this is (to my knowledge) the only extant copy. He tells a bit of the pre-history of the internet, and the role high energy physicists played.

As Michael Hiltzik alluded to, in his LA Times piece, AT&T (and, more relevant for Kunz’s story, the Europeen Telecoms) were dead-set against the internet, and did everything they could to smother it in its cradle. High energy physicists (who were, in turn, funded by …) played a surprising role in defeating them. (And yes, unsurprisingly, Al Gore makes a significant appearance towards the end.)

Enjoy ….

Paul Kunz: Bringing the Web to America

And now you know the answer to the trivia question: “What was the first website outside of Europe?”

Update:

For those unfamiliar with how this all works, Gordon Crovitz, the author of the hilariously wrong column in question, is the former publisher of the Wall Street Journal. And the column, itself, is now endlessly echoed and repeated in the wingnutosphere.
Posted by distler at 11:57 PM | Permalink | Followups (1)

July 8, 2012

Astral Pain

Anyone who’s followed this blog, since the early days, has read more than one instance of my complaints about crappy support for Unicode in common programming tools. I’m sad to report that, even in 2012, doing Unicode is (still) harder than it looks.

Heterotic Beast is my math-enabled Forum software. It runs on Rails 3.1.6 and Ruby 1.9.3, so you’d think that all would be good. Which was why I was surprised that this post was ill-formed.

Posted by distler at 11:28 AM | Permalink | Followups (19)

June 1, 2012

Normal Coordinate Expansion

I’ve been spending several weeks at the Simons Center for Geometry and Physics. Towards the end of my stay, I got into a discussion with Tim Nguyen, about Ricci flow and nonlinear $\sigma$-models. He’d been reading Friedan’s PhD thesis, alongside Kevin Costello’s book. So I pointed him to some old notes of mine on the normal coordinate expansion, a key ingredient in renormalizing nonlinear $\sigma$-models, using the background-field method.

Then it occurred to me that the internet would be a much more useful place for those notes. So, since I have some time to kill, in JFK, here they are.

Posted by distler at 8:12 PM | Permalink | Followups (1)

April 7, 2012

Such a sweet looking old lady…

Posted by distler at 2:39 AM | Permalink | Followups (4)

March 14, 2012

Spring Break

I could be back in Austin, chillin’ at SXSW. Instead, I’m here in College Station, at a workshop on higher-dimensional CFTs.

I’ll be giving a talk, on Thursday, which will be a lot like the one I gave in Munich, two weeks ago. The only advantage will be that the paper, that I alluded to previously, is finally be out.

There are, I’ll admit, some compensations. Andreas Stergiou gave a very nice talk, today, about his work with Ben Grinstein and Jean-François Fortin on theories with scale but not conformal invariance. They have to work in $4-ϵ$ dimensions, and need to go to 3 loops to find a violation of conformal invariance. Aside from their complexity, (interacting, unitary and Poincaré-invariant) scale invariant QFTs are weird. They are manifested as Renormalization Group limit cycles (or, even crazier, quasi-periodic motion on a torus), rather than fixed points. Fixed-point theories really are conformally-invariant.

Posted by distler at 1:04 AM | Permalink | Followups (1)

March 8, 2012

Daya Bay

Congratulations to the Daya Bay Experiment for their announcement of the first measurement of a non-zero value of the neutrino mixing angle, ${\theta }_{1,3}$

${\mathrm{sin}}^{2}\left(2{\theta }_{1,3}\right)=0.092±0.017.$

which is $5.2\sigma$ away from zero. Since there was no good theoretical reason to expect this mixing angle to vanish, it’s pleasing to see the first definitive experimental results on its value.

One thing, though, that annoys me about the coverage that I’ve seen is the blithe assertion that neutrino masses (and mixing angles) are now “part of the Standard Model.” That is an incredibly dumb thing to say. Yes, it’s true that one can write down a dimension-5 operator, using only Standard Model fields, which gives neutrinos a mass (and which, if non-diagonal in the flavour eigenstate basis, leads to neutrino mixing, too). That operator looks like

(1)$\frac{{c}_{\mathrm{ij}}}{M}{ϵ}^{\alpha \beta }\left(h,{\psi }_{\alpha }^{i}\right)\left(h,{\psi }_{\beta }^{j}\right)+\text{h.c.}$

where $h$ is the Higgs doublet, ${\psi }^{i}$ are the lepton doublets, and $\left(\cdot ,\cdot \right)$ is the skew-symmetric bilinear form on the fundamental representation of $\mathrm{SU}\left(2\right)$. The complex symmetric $3×3$ matrix, ${c}_{\mathrm{ij}}$, is dimensionless. If we assume that its entries are $O\left(1\right)$, then the mass scale, $M$, suppressing this operator, is enormous, $M\sim {10}^{15}\text{GeV}$. This operator is no more a “part of the Standard Model” than is the dimension-6 operator (also expressible, purely in terms of Standard Model fields) which mediates proton decay. Both are suppressed by GUT-scale masses, indicating that have to do with short-distance physics, well beyond the Standard Model’s ${M}_{\mathrm{EW}}\sim 250\text{GeV}$.

Posted by distler at 11:41 PM | Permalink | Followups (27)

January 27, 2012

G2 and Spin(8) Triality

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 $\mathrm{𝔰𝔬}\left(8\right)$. Understanding the answer involves an explicit description of $\mathrm{Spin}\left(8\right)$ 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.

Posted by distler at 2:09 PM | Permalink | Followups (12)

December 20, 2011

Higg Non-News

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.

Posted by distler at 5:04 PM | Permalink | Followups (4)

December 19, 2011

Vivian Distler 1965-2011

More here, here and, yes, here.

Posted by distler at 4:55 PM | Permalink | Followups (8)

November 19, 2011

Jitter

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?

Posted by distler at 11:46 AM | Permalink | Followups (14)