## December 23, 2007

### Instiki and Rails 2.0

I upgraded Instiki to Rails 2.0.2. There are many, many changes to Rails, from 1.2.5, which is what Instiki, previously, was based on. At least, for the present, I made the bare minimum of changes in Instiki, required. Even so, one gets a whole raft of improvements, “for free.”

## December 13, 2007

### Bricolage

The French term, bricoleur, doesn’t have any real equivalent in English. But perhaps a picture would help.

## December 12, 2007

### MTOS

The Open Source version of MovableType was released today. Or sort-of. What’s available, currently, are nightly builds of the next release, 4.1.

But, now that there’s something to work with, I guess I have no excuse to procrastinate any further about porting my modifications of MovableType to version 4. I hope to migrate the blogs here on Golem from version 3.35 to 4.1, as soon as I feel I have something reasonably stable. There *will* be glitches, though, and I ask, in advance, for everyone’s forbearance.

More broadly, I’d like to refactor as many of my modifications as possible into plugins or modules (that was the original plan, anyway), and hopefully get the modifications, that can’t be so-refactored, committed to the MTOS source tree. That way, people, who want to set up an XHTML+MathML+SVG capable blog, will, *finally*, have a plug-‘n-play Open Source solution.

Anyone, with a modest knowledge of Perl, who’s interested in helping make such a next-generation blogging system a reality, let me know. I could *really* use the help. And making this a group effort will ensure that the end-product reflects the needs and desires of the community.

## December 10, 2007

### AdS/CFT and Exceptional SCFTs

I wrote about Argyres and Seiberg’s paper, incorporating the $E_6$ and $E_7$ “isolated” $\mathcal{N}=2$ SCFTs as ingredients in a proposed S-duality for certain $\mathcal{N}=2$ gauge theories. The proposed dualities, then implied predictions for certain quantities in these, heretofore poorly understood, SCFTs.

Aharony and Tschikawa wrote an interesting paper, in which the endeavoured to check these predictions from AdS/CFT.

## December 9, 2007

### A Little More Group Theory

With a certain reluctance, I wrote a post about Garrett Lisi’s “Theory of Everything,” specifically about Lisi’s claim that he had embedded 3 generations of quarks and leptons in the 248 of $E_8$.

The purported “Theory of Everything” involved embedding
$G = SL(2,\mathbb{C})\times SU(3)\times SU(2)\times U(1)_Y$
in some noncompact form of $E_8$ (as it turns out, the split real form, $E_{8(8)}$), such that the 248 contains 3 copies of
$R = (2, \mathfrak{R}) + (\overline{2}, \overline{\mathfrak{R}})$
where $\mathfrak{R}$ is the $SU(3)\times SU(2)\times U(1)_Y$ representation
$(3,2)_{1/6} + (\overline{3},1)_{-2/3} + (\overline{3},1)_{1/3} + (1,2)_{-1/2} +(1,1)_1$
Note that $\mathfrak{R}$ is a *complex* representation. So $R$, though a real representation of $G$, is *chiral*.

I showed that it is impossible to find an embedding of $G$, which yields 3 copies of $R$, and hence that Lisi’s “Theory of Everything” doesn’t *even* rise to the level of impressive numerology.

And that’s where I left it, *thinking* that this would be enough to settle the matter in the mind of anyone with even a *modicum* of sense. I allowed to slide Lisi’s claim that he “got the first generation right.” After all, what harm could there be, in letting that little bit stand?

Apparently, I was wrong.

So, just so there’s *no ambiguity*, let me go back and point out that Lisi’s proposed embedding of $G$ does not *even* “get the first generation right.”

## December 3, 2007

### QGP on the Lattice

I was chatting with John Harris, the former spokesman for the STAR Collaboration, a few weeks ago, when he mentioned to me some recent lattice calculations of $\eta/s$, the ratio of shear viscosity to entropy density, in pure $SU(3)$ Yang-Mills.

This sounded really interesting.

The claim-to-fame of AdS/QGP is that it allows you to compute transport coefficients in a strongly-coupled gauge theory, something that lattice techniques are supposed to be no good at.

Most famous of all is the calculation of $\eta/s$, which is exactly $\tfrac{1}{4\pi}$ in conformally-invariant AdS/CFT backgrounds, and $\tfrac{1}{4\pi}\left(1+O(1/\lambda)\right)$ in non-conformally-invariant backgrounds (with the leading $1/\lambda$ correction being positive). The quark gluon plasma studied at RHIC is the least viscous fluid known to man. STAR reports $\eta/s \lesssim 0.1$, more than 100 times smaller than that of water.

It would be pretty cool if lattice calculations could reproduce this. So what’s the trick?