Posts with this logo use 
Low-functioning pinhead...
May 6, 2008
Around the Blogs
Probably everyone else knew, but I was pleased to learn that Dmitry Podolsky has a new blog. Dmitry’s main focus is on cosmology (he was a student of Starobinski), but his blog runs the gamut of subjects, and he’s been churning out posts of very high quality. His latest is on the limits of validity of cosmological perturbation theory, a subject which has seen several interesting papers, since I last blogged about it.
Adam FalkowskiJester has a scathing review of a CERN seminar/recent paper by John Moffat. Moffat wants to avoid introducing a Higgs (or other new degrees of freedom) into the Standard Model, by having the theory become nonlocal at a scale of about a TeV (more precisely, at GeV (!)). Nonlocality is a sort of magic pixie dust that makes all of the obvious problems go away. The scattering amplitude for longitudinal W-bosons grows like , violating the unitarity bound above a TeV or so? No problem: in Moffat’s nonlocal theory, the amplitude just vanishes for TeV. This, in turn, violates the Cerulus-Martin bound1, ? Don’t worry …
I suppose I could go on in this vein, but someone will doubtless come along and accuse me of bias. Suffice to say that introducing nonlocality in some willy-nilly fashion like this is bad mojo. And, even were it totally unfair, Jester’s account is wittier than mine.
1 The bound requires analyticity of the elastic scattering amplitude in the cut plane and its polynomial boundedness in . The latter, at least for forward scattering, is intimately connected with causality. In addition to local quantum field theory, both perturbative string scattering amplitudes and various conjectured nonperturbative extensions satisfy the Cerulus-Martin bound, though, to be fair, the latter conjecture violates polynomial boundedness, which is rather suspicious.
May 2, 2008
Faulty Memory
Golem has been experiencing intermittent memory problems for a little over a year, now. Originally, I ascribed the problems to cosmic rays. But their persistence seemed to belie that interpretation.
April 17, 2008
Gauge Mediation
I was remiss (read: lazy, overworked, or whatever) in not writing, earlier, about Meade, Seiberg and Shih’s paper on gauge mediation. But Patrick Meade was visting this week, so perhaps I can make amends.
There is a huge literature on models of gauge mediated supersymmetry-breaking. And there are a variety of characteristic predictions that emerge from particular classes of models. What these guys do is provide a model-independent characterization of gauge-mediation and try to isolate what features are generic to all models versus those which are special to particular subclasses of models of gauge mediation.
April 13, 2008
Corruption
I must just be unlucky. Here’s how I managed to waste my afternoon.
I committed an update to the Instiki BZR repository, and then did a
bzr log -v
which yielded an ominous
⋮ KnitCorrupt: Knit <bzrlib.knit._KnitAccess object at 0x24b6170> corrupt: While reading {distler@golem.ph.utexas.edu-20080108060135-7ujf0nen62ge328t} got IOError(CRC check failed 3032481332 2792320114)
Yikes!
The .bzr directory is a labyrinth of plain text and gzip-compressed files. Evidently one of the latter was corrupted. But which?
April 12, 2008
Dinosaur
The big news this week, depending on your point of view, is either the progress in Bagger-Lambert theory, or that MathML and SVG have been added to the HTML5 Specification.
As anyone who’s been following this weblog is doubtless bored to tears to hear, serving XHTML is a complicated, finicky, business, requiring jumping through elaborate hoops to ensure well-formedness. It would be so much easier to serve this content as text/html, and rely on the liberal parsing of the HTML parser. Hence it’s very cool that future browsers will support precisely that. As far as I can tell, the only change that would be required, here, is to send the SVG unprefixed. But, since the prefixing is done programmatically (to keep the MTValidate plugin happy), this would be a very easy change. Instiki already emits unprefixed SVG.
I say “as far as I can tell,” because there are no implementations of this days-old addition to the Specification to test against. Eventually, there will be, though I wonder how MathPlayer would handle a change to text/html. There would be a grim irony if IE+MathPlayer became the only browser which needed to be sent application/xhtml+xml.
I look forward to the day when this blog becomes a dinosaur. And, now that MathML is part of the the HTML Spec, I look forward to some more browser implementations.
1 Sam, in his blog post, points out that