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Note:These pages make extensive use of the latest XHTML and CSS Standards. They ought to look great in any standards-compliant modern browser. Unfortunately, they will probably look horrible in older browsers, like Netscape 4.x and IE 4.x. Moreover, many posts use MathML, which is, currently only supported in Mozilla. My best suggestion (and you will thank me when surfing an ever-increasing number of sites on the web which have been crafted to use the new standards) is to upgrade to the latest version of your browser. If that's not possible, consider moving to the Standards-compliant and open-source Mozilla browser.

October 30, 2005


Pumkpin carving, chéz nous, involves a certain amount of thought and planning. The results are often striking, even when the real world disappoints.

But then there are the times when events intervene, derailing the best-laid plans, …

Posted by distler at 2:14 PM | Permalink | Followups (1)

October 28, 2005

Patience is a Virtue

Scooter Libby mug shot

Gawd, how I’ve been waiting for this.

Waiting as Randy “Duke” Cunningham sailed off into the sunset. Waiting, as Jack Abramoff and David Safavian were indicted and the latter pled guilty in that ever-widening scandal. Waiting, as Michael Brown resigned in disgrace — another little bit of Bush cronyism, gone badly awry. Waiting, as Bill Frist is investigated by the SEC for insider trading.

Finally, Tom Delay was indicted for money laundering and funnelling illegal corporate contributions to Texas State political campaigns (yes, pretty minor stuff, on the scale of his machinations but, then, they nabbed Al Capone for tax-evasion).

And now … this.

Scooter Libby indicted on 5 counts of Obstruction of Justice and Perjury, in connection with the Valerie Plame investigation. The Prosecutor has made it clear that this is but the first round. His investigation of Karl Rove (and, perhaps others) continues…

Posted by distler at 2:38 PM | Permalink | Followups (1)

October 26, 2005

CDO and Pure Spinors

One of the drawback of having other things to do besides blogging is the long list of half-completed posts sitting on my computer. One of them was adiscussion of the work of Witten and Kapustin on chiral differential operators. The basic idea is to recast the nontrivial aspects of 2D (supersymmetric) nonlinear σ\sigma-models. One works with an open covering of the target space. On each patch, one can replace the nontrivial σ\sigma-model action by a free theory, with a first-order action

S=η i¯X i+ S = \int \eta_i \overline{\partial} X^i +\dots

On patch overlaps, one has nontrivial transition functions for the algebra of observables. All of the nontrivial aspects (the β\beta-function, anomalies, etc.) of the σ\sigma-model are encoded in how the local observables patch together. The usual global observables (whatever they are) are obtained as global sections of the sheaf of local observables.

I have written some observations on Berkovits’s pure-spinor approach to the superstring. In that approach, the (bosonic) ghosts, λ α\lambda^\alpha, (which contribute c=+22c=+22 to the total central charge) are a Majorana-Weyl spinor of Spin(9,1)Spin(9,1) (Spin(10)Spin(10), if you’re not too particular about reality conditions) satisfying the constraint λ αγ αβ mλ β=0 \lambda^\alpha \gamma^m_{\alpha\beta}\lambda^\beta=0 The ghosts, λ α\lambda^\alpha, and the anti-ghosts, w αw_\alpha, have a free-field action. But, because of the constraints, rather than really being free fields, we have a nontrivial σ\sigma-model.

Berkovits and Nekrasov realize the space of (Euclidean) pure spinors as a cone over SO(10)/U(5)SO(10)/U(5). Since the action is already of the “free”, first-order form, (1) one can adopt the same CDO technique to study it. Urs has posted a nice summary of a talk by Nikita on the subject.

Of course, even adopting this CDO approach, there’s a big difference with the examples studied by Kapustin and Witten. Here, the cone is not a smooth manifold. I’m not sure how that impacts the analysis. But, evidently, there’s some progress in understanding the composite operators which are the analogues of the bb-antighosts, in the bosonic string, as Čech cohomology classes. This, as you’ll recall, was the point on which my understanding of the pure-spinor approach fell apart.

Posted by distler at 4:30 PM | Permalink | Followups (4)

October 21, 2005

Shih on OSV

David Shih visited with us this week, which gives me an excuse to talk about the checks he and collaborators have been able to carry out on the Ooguri-Strominger-Vafa conjecture. I’ve written about the work of Dabholkar et al, which focusses on “small” BPS blackholes which, in their examples, have heterotic duals, the Dabholhar-Harvey states (whose degeneracies are, therefore, exactly-known). In the end, that wasn’t a very satisfactory test, because — even in the large-charge limit — the volumes of some cycles on XX turned out to be small. There wasn’t an a-priori reason to expect agreement with OSV.

Shih, Strominger and Yin computed the degeneracy of 1/4 BPS blackholes in N=4N=4 string theory (IIA compactified on K3×T 2K3\times T^2 with nonzero D0, D2, D4 and D6-brane charge, or one of its duals), and 1/8 BPS blackholes in N=8N=8 string theory. These blackholes are “large,” already at the classical level.

Shih and Yin then went on to compare these degeneracy formulæ with OSV.

Posted by distler at 3:21 AM | Permalink | Followups (10)

October 20, 2005


I’ve been playing around with implementing OpenID here on Musings. PGP-signed Comments, which we’ve been offering for a year and a half, offer two distinct advantages.

  1. They provide proof that the person who left a comment is the same person who owns the web site in the URL link.
  2. They provide proof that the comment has not been altered in any way, either by the blog owner, or by some third party.

But they have two distinct disadvantages.

  1. They require that the computer you’re posting from have PGP or GnuPG installed.
  2. You must also have a copy of your secret keyring on hand.

This precludes posting signed comments from a public terminal, an internet café, or wherever.

OpenID offers a way to prove that you own a certain web site, without requiring any special software or a secret key installed on your computer. That’s the more interesting of the two features offered by PGP-signed comments. Since the requirements are lower, it might be something more people would actually use.

I tried Mark Paschal’s MT plugin, but really didn’t like it, either from the point of view of the code (which I had real problems with) or for the way it displays the commenter’s information. I’m not looking for a substitute for the traditional name/email/URL information; I’m looking for a supplement to it: an attestation that the URL actually belongs to the commenter.

I ended up shelving, for the moment, the idea of implementing OpenID here. The one positive outcome of the little experiment is that I have a working OpenID server (a hacked-up version of Mark Paschal’s server). If you’re an author at the String Coffee Table, you can use it to authenticate using OpenID on other blogs. Either list your SCT profile page (e.g., Robert Helling’s) as your URL, or, if you prefer, add

<link rel="openid.server" href="" />
<link rel="openid.delegate" href="">

(where the URL in the second line is your SCT profile page) to the <head> element of your homepage. Anytime you want to make an OpenID-authenticated comment, you just need to log into MovableType, here (and stay logged in as long as you need).

Try out the OpenID demo.

Posted by distler at 11:58 PM | Permalink | Followups (6)

October 14, 2005

Expectations and Reality

Yesterday was Yom Kippur and, by coincidence, the 3-year anniversary of Musing. A time, therefore, for a bit of reflection on (if not atonement for) having started this blog.

What I set out to do, three years ago, was test the idea that weblogs could provide a useful medium for exchanging ideas in physics, less formal than research papers, but still archived, searchable, and hyperlinked. I also hoped that whatever software modifications were required to enable mathematical blogging would be easily adopted by the hordes of fellow physicists who would, surely, flock to the medium.

One of the things I feared was that the comments section would be overwhelmed by the noise that long ago made USENET and most Web Forums (cosmoCoffee being a notable exception) hopeless sinkholes.

How did the reality measure up?

Posted by distler at 10:50 AM | Permalink | Followups (9)

October 12, 2005


We have Jesse Thaler visiting us from Harvard. The first thing I got him to do when he arrived was to guide me in installing the software for the LHC Olympics. If Golem ever seems slow, in the next few months, it may be because I’m mucking about with the Pythia event generator.

His seminar was a more detailed version of one of points expounded in Nima Arkani-Hamed’s talk at Strings 2005. The problem of extracting new Physics from the LHC will be a tricky one. The map from “parameter space” to “signal space” is many-to-one, with radically dissimilar “bins” in parameter space mapping to the same “bin” in signal space.

What they’ve been doing is exploring this systematically in a class of MSSM models. They allow the gluinos and squarks to range in mass from 600 GeV to 1 TeV, the other gauginos, the higgsino and the sleptons to range in mass from 100 GeV to 1 TeV, and tanβ\tan\beta to range between 2 and 50. They then generated 1 year (10 fb 1\text{fb}^{-1}) of “LHC data” for each of 39137 MSSMs and study all the LHC signals they could think of for these models.

Changing the parameters continuously, it is easy to distinguish nearby models. Change, say, the wino mass by a few 10s of GeV, and it is easy to distinguish that model from the original one. However, changing the parameters by a lot, one runs into pairs of models with nearly identical (statistically indistinguishable) signatures, but which occupy radically different positions in parameter space.

While they were looking at a particular class of MSSM models, the phenomenon seems to be true more generally, whenever the dominant signatures involve missing transverse energy (as is true in SUSY models with R-parity, large-extra dimension models, …), so that you don’t completely reconstruct all the decay chains.

Unless someone get very clever, we may turn on the LHC, see that there’s new physics, and have no way to pin down any of the details of what’s going on for several decades, until the ILC turns on. And, since that’s only a 500 GeV COM machine — at least initially — we will, likely still have trouble even after it turns on.

Anyway, though I have no illusions about being the one clever enough to crack this nut, I do want to play around and really get a feel for the tough interpretational issues we’re gonna face in 3 years time.

I’d love to expound more on this, but I have a lecture to write for our Geometric Langlands seminar, tomorrow, and I still have some calculations to finish for that…

Posted by distler at 12:15 AM | Permalink | Followups (1)

October 11, 2005


If you look at the surveys, some huge percentage of American Protestants and a smaller, but still significant percentage of Catholics, don’t believe in Evolution. I’ve always found the hold of anti-Evolution sentiment, in religious circles, rather puzzling. Aligning your Theology against Science is, surely, a long-run losing strategy — a lesson you’d think the Catholic Church learned after they condemned Galileo.

By contrast, surveys of Jewish opinion strongly favour Evolution1. Even among the Orthodox, Evolution is broadly accepted2. Of course, it helps that biblical literalism was never accorded much respect in Rabbinic circles:

He described those profound truths, which His Divine Wisdom found it necessary to communicate to us, in allegorical, figurative, and metaphorical language. Our Sages have said (Yemen Midrash on Gen. i. 1), “It is impossible to give a full account of the Creation to man. Therefore Scripture simply tells us, In the beginning God created the heavens and the earth” (Gen. i. 1). Thus they have suggested that this subject is a deep mystery, and in the words of Solomon, “Far off and exceedingly deep, who can find it out?” (Eccles. vii. 24). It has been treated in metaphors in order that the uneducated may comprehend it according to the measure of their faculties and the feebleness of their apprehension, while educated persons may take it in a different sense.

Rather than viewing Science as some foreign sphere, at best irrelevant, at worst opposed, to theological discussions, Rabbinic tradition has generally taken scientific knowledge as simply another source of insight into theological questions. From the Talmud to the writings of Maimonides (from which the above passage is drawn), they are filled with discussions of what passed for the best scientific knowledge of the day.

These laws, however, presuppose an advanced state of intellectual culture. We must first form a conception of the Existence of the Creator according to our capabilities; that is, we must have a knowledge of Metaphysics. But this discipline can only be approached after the study of Physics; for the science of Physics borders on Metaphysics, and must even precede it in the course of our studies.

Which brings us to the strange case of Nossom Slifkin, an Orthodox rabbinical scholar and self-taught zoologist. A year ago, on the eve of Yom Kippur, three of his books were declared heretical by a group of 23 prominent ultra-Orthodox rabbis, for their citation of modern Biology, Evolution, and Cosmology.

A bitter controversy erupted with the Orthodox community

But if the ban was intended to draw interest away from Slifkin’s ideas, it had the opposite effect. Within a few days, his out-of-print book was selling at used book stores for four times its original price of $24.95. Unprompted by the author, an international group calling itself Jews For A Re-Evaluation Of The Rabbi Nosson Slifkin Ban wrote a counter-petition, urging the 23 signatories to change their minds. Hundreds of outraged students protested the ban in long Internet postings, and numerous ultra-Orthodox rabbis, including Rabbi Aryeh Carmell of the Jerusalem Academy, penned scholarly essays in Slifkin’s defense. Rabbi Tzvi Hersch Weinreb, executive vice president of the Orthodox Union, threw his support behind Slifkin, telling The Forward that Slifkin had used “impeccable traditional Jewish sources to back up his views.”

One New York rabbi who has inside knowledge of the Slifkin ban tells me that it represents a major “breaking point” within ultra-Orthodox society. “Over the past 15 years, the rabbis of Bnai Brak and the more open American ultra-Orthodox rabbis have been split on a number of important policy decisions,” says the rabbi, who asks to remain unnamed. “The Slifkin ban is a huge break. It’s a kind of power struggle, and those who didn’t sign the ban are outraged right now. I’m talking about rabbis with long white beards who are furious about it.” Slifkin’s views, according to this rabbi, are shared by countless figures within the ultra-Orthodox community. “He’s saying out loud what a lot of people have been talking about quietly all along. To those people, he’s a kind of figurehead.”

Googling around, you’ll find zillions of blog posts and forum discussions of the ban and its aftermath. There’s much hand-wringing about how this has undermined the religious authority of the Rabbis who promulgated the ban (though opinion is divided as to whether to blame the proponents for having acted foolishly, or the opponents for openly challenging their decision).

Arguably, though, this short term loss-of-face pales as a threat to rabbinical authority beside the folly of insisting that the world is 6000 years old, and modern Physics be damned!

There is, after all, not likely to be much of a market for a Haredi Dino Theme Park.

1 The HCDI survey is of MDs. You might hope for something better, but, in fact, their opinions end up closely mirroring those of the population at large.

2 The Haredi may hold other objectionable views; they’re just not reflexively anti-Science, in the manner of your average Evangelical.

Posted by distler at 9:46 AM | Permalink | Followups (7)

Helling Wades In

Robert Helling has taken upon himself to live-blog Loops 2005. From the first two days reports (Day I, Day II), it sounds like he’s not having an easy time of it. It’s hard to sustain one’s energy to blog through a week of really good talks. But, when you’re annoyed by many of the proceedings

The careful reader will have noticed that yesterday, my blogging got sparser and sparser. This was probably due to increasing boreodom/annoyance on my part. Often, I thought the organisers should have applied the charta of sci.physics.research that forbits contributions that are so vague and speculative that they are not even wrong. I could not stand it anymore and had to leave the room when the speaker (I am not going to say who it was) claimed that “the big bang is just a phase transition”.

it must be much, much harder.

Bon courage, mon ami! I hope that things improve and, that you make it through the week.

Posted by distler at 8:30 AM | Permalink | Followups (1)

October 3, 2005


לשנה טובה ומתוקה תכתבו.

Posted by distler at 6:33 PM | Permalink | Followups (2)

October 1, 2005

4 Steps

Though I’m a Mac user, viewing MathML on a Mac has been an unsatisfactory experience, as long as I’ve had this blog. Mostly, this is the result of a long-standing bug in Mac/Mozilla. Fortunately, the bug has recently been fixed.

So, herewith, are the steps to better viewing of MathML on the Mac.

  1. Get yourself a recent version of Mozilla or Firefox (Camino is not MathML-enabled).
  2. Install the Mathematica fonts and the Code2001 font on your system.
  3. Edit the
    ~/Library/Mozilla/Profiles/default/XXXXXX.slt/user.js [Mozilla]
    ~/Library/Application\ Support/Firefox/Profiles/default/XXXXXX.slt/user.js [Firefox].
    XXXXXX” is some random string unique to your installation. Add the lines
    user_pref("font.mathfont-family", "Math1,Math2,Math4");
    user_pref("font.mathfont-family.\u2212.base", "Times");
    to the user.js file.
  4. Now the tricky part. The bug was caused by a missing file. Eventually, the missing file will find its way into the distributed version of Mozilla/Firefox. In the meantime, download it and install it inside the application by typing
    cp /Applications/
    cp /Applications/
    or whatever.
    The patch has landed in CVS, so grab the latest nightly build of Mozilla or Firefox.

Now, if you have even a smidgen of appreciation for good typography, you will scream in pain at the ugly, ugly fonts I told you to install at step 2. Unfortunately, the release of the Stix fonts has been delayed yet again (not till mid-2006 at the earliest; but don’t hold your breath). And there remain various rendering problems, some of which are clearly related to the crappy, mismatched fonts, some of which may be actual bugs in Mozilla.

Still, what you’ll see, if you follow the above steps, will be legible, if not pretty. Which is a big improvement over the previous situation.

Update (11/21/2005):

Recent bugfixes make some of these steps obsolete. See this post for details.
Posted by distler at 2:31 AM | Permalink | Followups (7)