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Low-functioning pinhead...
December 31, 2002
Wifi Heaven
Austin is truly Wifi Heaven.
I’m sitting in JP’s Java (a stone’s throw from my office, but much nicer), enjoying the cappuccino and classical music. I’m surrounded by three Dell’s, two Sony Viao’s, two iBooks (counting my own), and a powerbook G4.
UT has Wireless Access in the classroom, libraries, and even on the West Mall. But what’s astounding is the number of free WAPs which have sprung up all over town. Everyone from Schlotzky’s Deli to the Alamo DraftHouse have gotten into the act, as have my favourite Cafés (Triumph and Trianon) near the house.
Of course, Starbucks still wants to charge $50/month for WiFi access, but we all know that they’re evil, don’t we?
December 30, 2002
Sendmail 8.12.7
Sendmail 8.12.7 is out. If you are, as I am, running sendmail, it’s time to update.
Be sure to verify the PGP signature:
gpg -v sendmail.8.12.7.tar.gz.sig tar xzf sendmail.8.12.7.tar.gz
before proceeding with building and installing it.
Whoops! Mine’s finished compiling and installing itself. Gotta run…
Curio
I should have said that Gottfried Curio also has a derivation of the complex Chern-Simons superpotential I discussed previously. I would have said so earlier, but I’m afraid I find his paper nearly impenetrable.
There’s definitely good stuff there, though. Looks like hyperbolic 3-manifolds are rearing their ugly heads in the context of M-theory.
Just when you thought it was safe to go outside again …
Welcome Demian Cho!
Perhaps it’s a bit too early (he hasn’t yet posted any “real” entries to his blog), but here’s a hearty welcome to the latest physics blogger, Demian Cho.
Hey Demian and Aaron! Does Blogger afford you the ability to produce an RSS feed of your blog? If they do, you should flip the relevant switch.
Update: Answered my own question. Guys, just go to voidstar.com or logicerror.com and follow the instructions there.
December 27, 2002
Feeds
I added a few more RSS feeds to this blog (and modified the existing ones a bit). You can now choose from a “plain-Jane” RSS 0.9.1 feed — a basic format, understood by all News Aggregators — or one of the “second generation” RSS feeds (RSS 1.0 or RSS 2.0), which are extensible using XML namespaces.
There’s really not much difference between “1.0” and “2.0”, except for the egos of the developers involved. They look different — open them in your web browser and see — but they are functionally equivalent.
If your News Aggregator supports the additional data supplied by these feeds, you can use whichever one is convenient. Some clients, like NetNewsWire can actually make use of the full-content feed, which includes the full text content of the entries in this blog. You can subscribe to the “Full Content” version and read this blog in NetNewsWire, without ever opening your web browser.
I don’t actually recommend that, as the HTML rendering (especially of math formulae) is pretty lousy. And you can’t view or post comments. Generally, it’s a lot less useful.
There’s also the issue of bandwidth. The 0.91 feed is 5K. The 1.0 and 2.0 feeds are 12K and 10K, respectively. The RSS 2.0 Full Content feed is 36K. So, you see, one pays for the extra information.
I’d be interested in hearing back from subscribers to these feeds, about which format(s) their client software supports, and which features they would like added to the feed(s).
G2 Compactifications
There have been several papers recently on compactifications of M-Theory on “manifolds”, X, of G2 holonomy. I put ‘manifolds’ in quotes because to get nonabelian gauge groups with chiral matter, we need certain types of singularities.
Friedmann and Witten have written about threshold corrections in such theories. At least in the limit that they consider, the threshold corrections are given by the Ray-Singer torsion of the associative 3-manifold, Q, where X can be thought of as a K3 fibration over a base isomorphic to Q, and where the generic K3 fiber has a A4 singularity. In layman’s terms, the threshold corrections are entirely due to massive adjoints of SU(5); there is no contributions (in this limit) from massive fundamentals or other representations.
I’ve been meaning to post some comments on this paper; I guess I’ll get around to that eventually.
More recently, Bobby Acharya has written about the superpotential for models with G-flux. He finds that, in addition to the usual contribution linear in G, there’s also a term in the superpotential proportional to a complex Chern-Simons term on Q.
This ends up fixing the moduli of the compactification, in a manner reminiscent of what happens in some (doubtless related) Type IIA orientifold models. Of course, he ends up with a theory with unbroken N=1 supersymmetry in (3+1)-dimensional anti-de Sitter space. Perhaps (with considerable handwaving) after supersymmetry breaking we might end up with a vanishing or small positive cosmological constant. But understanding the resolution of that question seems as far away as ever.