Wednesday, December 09, 2009

Old News

Since I'm still too busy to write something real, I'll just dump a few links that I stumbled over during the last few days into a list:

  • The world's most energy-efficient computer stands in Germany -- QPACE (QCD Parallel Computing on the Cell) at Jülich leads the Green500 list

  • The Royal Society has brought the back issues of its Philosophical Transactions online -- now you can link to papers from 1665 via their DOI ...

  • The LHC is just being cranked up again, and the ALICE collaboration already have the first paper using LHC collision data accepted for publication

  • A propos unusual papers, this paper has probably most unusual one-line abstract ever seen on the arXiv

Thursday, November 26, 2009

Even the best may need some rest

Being named one of the 50 best physics blogs should probably serve as inspiration for writing a bit more frequently again, I suppose.

Still, you'll have to bear with the current blogging pause a little longer: I have spent each of the past five weekends in a different place, and have two papers to finish, a couple thousand lines of code to rewrite and a bunch of new data to analyse, all before the Christmas break. But you may look forward to a new series of posts on a group of related topics in the spirit of the "lattice quarks" series.

Thursday, October 29, 2009

Silly science policies threaten progress

Suppose you were a politician in charge of shaping your country's science policy. Let's also suppose you are actually interested in promoting the welfare of the nation and humanity at large (hopefully not all politicians are driven by sociopathic greed, and after all, we are talking about you here). Let's also suppose that you are not entirely stupid. What kind of science policy would you make?

Presumably, you would not come up with the kind of ultra-shortsighted policy that the UK has now come up with in determining to weight research proposals' (short-term) 'economic and social impact' by 25% in assessing their merits.

The point with fundamental research, however, is that one just simply cannot make any reliable statement about its likely impact on society. When Dirac postulated the existence of the positron on the basis of his equation, he didn't think of positron emission tomography revolutionising cancer diagnostics. When Einstein described stimulated emission of radiation, he certainly didn't have DVDs in mind. And while Peter Grünberg might have had some applications in mind when he made his discovery of giant magnetoresistance, he probably didn't imagine the iPod (otherwise he'd be very, very rich).

The only research that will fare well under such a short-sighted policy is industrial and quasi-industrial research that has a clear product (i.e. a product that can be readily imagined with current knowledge) in mind. Such applied research is important, sure. But fundamental research is far more important for the overall progress of the human race, because it creates the foundations upon which the applied research of the future is going to rest. Moreover, applied research generates revenue for industry, and therefore it behooves industry to fund it. The government's job in science is the support of fundamental research that will not easily get industry support -- corporations are notoriously short-sighted, rarely looking beyond next year's balance sheet. The government should have more foresight.

Nobel Laureates are leading the fight against this silly policy; you can hear from Chemistry Nobel Laureate Venki Ramakrishnan at nature.com. UK-based readers can sign a petition against the silliness at ucu.org.uk.

Wednesday, October 21, 2009

On Deadlines

Human behaviour being what it is, conference proceedings tend to be written only when the deadline is practically elapsed. This can be seen on hep-lat every year. I remember reading somewhere (in PhysicsWorld, maybe?) that someone had studied the number of proceedings submitted per time period as a function of time until the deadline and had found a power-law behaviour. If that is correct (Google fails me for this, and the paper appears not to be on the arXiv), it would show again that even aggregates of (presumably free-willed) humans can be described well by statistical physics (thankfully, because if the free-will theorem is to be believed, spin-1 particles have free will if humans have). Does anyone know what the reference for the power-law behaviour of conference submissions was?

Wednesday, July 29, 2009

LATTICE 2009 reports open thread

It appears that this blog is not accessible from within the Great Firewall of China (I suppose blogs are inherently subversive, even if they are about as innocuous a topic as Lattice QCD). There is thus little point in having lots of empty comment threads for participants to report their impressions from the Lattice 2009 conference in Beijing, and those threads have accordingly disappeared. This post exists for any comments that people may have about Lattice 2009; comments may also be sent to me by email, and will then be published here (anonymously, if desired).

Thursday, July 02, 2009

LATTICE 2009 programme online

The programme for the LATTICE 2009 conference in Beijing is up on the Web (here). This gives me the opportunity to remind my readers of the need for guest bloggers to cover the conference, since I will not attend this year.

Sunday, June 14, 2009

我不去 LATTICE 2009 北京

I hope I didn't maltreat the 汉字 above too badly in my ignorance -- in any case, what I'm trying to say is that I am not going to the Lattice conference this year. Yes, that means no conference blog from me.

"But how are we going to survive without the annual conference blog?" I hear a reader exclaim. To which I reply, without so much as batting an eyelid: "You will have to write it yourself." Okay, I admit that imaginary exchange is just silly, but the reality is that I'd still like to cover the Lattice meeting in Beijing, but obviously can't do the reporting myself. So I would like to encourage my readers to volunteer as guest bloggers and cover a session or two from their own point of view. Any conference reports (except for those of a libelous, pornographic or defamatory nature) submitted as comments or by email will be published, with or without attribution as desired by their respective authors.

To make this a more tempting offer I will add a prize for the most productive (by number of sessions covered, by words in case of equal numbers of sessions) guest blogger, who will win my Lattice 2008 Williamsburg baseball cap (autographed or unautographed at the winner's discretion).

Tuesday, May 19, 2009

Austria will not leave CERN

Public pressure has been successful: Austrian chancellor Faymann has decided to veto the pull-out from CERN that his science minister had announced. Over 32,000 people have signed the online petition against the proposed withdrawal, and together with open letters by Nobel laureates and other public figures, this seems to have been enough to convince the Austrian government that leaving CERN would have been bad PR. I suppose that's another example of "yes, we can!"

Sunday, May 17, 2009

Openness >> fraud

In the most recent edition of PhysicsWorld, there are two articles that on the face of it have little to do with each other: one is about Jan Hendrik Schön, the physicist formerly famous for creating the first organic superconductor and the first single-molecule transistor, and now most famous for having simply made up all of those results out of thin air, the greatest kind of scientific fraud in physics. The other article, by Michael Nielsen, is about how the internet is transforming scientific communications, looking at which new means of scientific communication failed (such as Physics Comments and scientists contributing to Wikipedia -- although Scholarpedia is taking off quickly at the moment, probably because its signed and peer-reviewed authorship model is more in line with academic customs than Wikipedia's semi-anarchistic one) and which succeeded (the arXiv, of course) in making the dissemination of scientific results quicker and more transparent.

At first glance these two topics appear to have little to do with each other. At second glance, however, they are closely intertwined.

Schön's deception was only possible because the researchers who tried and failed to replicate his results didn't have access to his primary data. Once doubts had been raised over the appearance of two completely identical graphs supposedly representing two completely different sets of experimental data, Schön's primary data were subjected to close scrutiny and were found to be non-existent -- his labbooks had been destroyed, and his samples were damaged beyond recovery. This raises the question whether it would have been possible to even contemplate such a fraud in an environment where scientists are genuinely expected to hide nothing, and in particular to make their primary data publicly available after publication.

The more radically open schemes, where raw data are being made public before publication, are unlikely to take off largely because of concerns over the enormous plagiarism potential. But once results have been published and priority has thus been established by the original authors, there is no immediately obvious reason not to allow other researchers to perform their own analyses of the primary data, either to confirm (or possibly to refute) the original analysis, or to use their own methods to obtain results from the data that the original authors didn't (either because they weren't interested or because they didn't have the relevant analysis methods at their disposal). Some access controls are needed, of course, in order to ensure that the later researchers will duly acknowledge the use of the original group's datasets.

It is hard to see how a fraud like the Schön case could have occurred under a scheme like this; the groups who wasted years on trying to replicate his results to no avail would likely have realised the fraud if they had had access to Schön's lab books.

Just like with the arXiv (which after all started out as a specialised High Energy Physics preprint server and now has revolutionised publishing in most of physics and mathematics, plus assorted other areas), particle physicists are pushing ahead with schemes to open access to raw data, and lattice QCD is right at the forefront of the movement: since the most expensive step in unquenched simulations is the actual generation of the gauge configurations, using those just once for whatever analysis or analyses interests one specific group would be an irresponsible waste of computer resources, postdocs' lifetime and taxpayers' money.

It has therefore been common for a long time now for lattice theorists to form larger collaborations that pool their resources to generate their configurations and then perform different analyses on them (policies differ: some collaborations publish all of their papers as a collaboration, some break up into smaller groups for most analyses). But with the huge effort needed for unquenched simulations on large ultrafine lattices with very light quarks, even that becomes inefficient; in particular, groups that don't belong to any of the major collaborations would be left out in the quenched darkness. Therefore, it is becoming an increasingly common policy to make gauge configurations available to the larger lattice community after performing some initial analyses that the collaboration generating the ensemble is particularly keen on doing (generally, that includes the hadron spectrum, plus some other stuff).

Configurations have been available for a while at NERSC's Gauge Connection, and are now quickly beginning to be available on the International Lattice Data Grid (ILDG). This way the many CPU cycles that have been invested in generating these ensembles are put to even better use by enabling other groups to run their analyses on them.

Just like in the case of the arXiv, it may take a while for other disciplines to follow suit, but it appears likely that if and when more and more scientists choose to make their raw data public after publication (and those that don't therefore become increasingly subject to suspicion by their peers), a fraud case like that of Jan Hendrik Schön will become quite impossible at some point in the future.

Tuesday, May 12, 2009

Austria to leave CERN?

Austria's Science Minister Johannes Hahn has announced that Austria is to pull out of CERN. The reason given is that the 20 M$/year that Austria contributes to CERN is too much in these economically difficult times. Given the amounts handed out to bankrupt banks these days, that seems like an odd argument against participating in the greatest international endeavour of our time, an endeavour whose spinoffs include among others the WWW, no less. Maybe the crackpots convinced Mr Hahn that the LHC was going to end the world? Or maybe the Austrian government just wants to reap the global benefits of international research without contributing anything to it? You can sign a petition against this piece of political silliness here.

Thursday, April 09, 2009

arXiv goes Facebook

Remember my slightly tongue-in-cheek question when we'd see a "My arXiv papers" application for Facebook? Well, it has happened, and apparently not on April Fool's Day. In fact, it is a part of the new author identifiers system introduced by the arXiv, which will help identify papers by the same author (since not everyone has the advantage of having a name that is unique within his field).

Saturday, April 04, 2009

MAMI and beyond, Day Five

Today's first talk was by Savely G. Karshenboim (Garching and St Petersburg) who spoke about hadron physics' impact on precision in atomic physics. Atomic physics is famously precise in its measurements, with relative precisions of order 10-12 now being achieved for some quantities. The largest uncertainty in theoretical predictions there now comes from uncertainty about the effects of nuclear and proton structure.

The second speaker was Wolfgang Gradl (Mainz) with a talk on hadronic uncertainties in flavour physics. Flavour physics is about quark-level quantities (CKM matrix elements), but only hadronic decay and oscillation processes are experimentally accessible; thus one needs good control of QCD effects contained in form factors, decay constants and the B meson bag parameter. Lattice QCD is an important ingredient here, in particular when coupled with effective field theories such as HQET.

This was followed by discussion sessions about the prospects for MAMI, about the prospects for an electron-nucleon collider, and about the impact of hadronic physics on high-energy physics. The good news for lattice theorists is that there is a high demand for precise lattice predictions by experimentalists. The not so good news is that most of that demand is in areas where the lattice is not in a position to make accurate predictions in the near future, such as resonances, hadronic scattering lengths or hadronic light-by-light scattering amplitudes.

Thursday, April 02, 2009

MAMI and beyond, Day Four

Today's first talk was Fabio Ambrosino (INFN Napoli) speaking about flavour physics at the 1 GeV scale. Of course, flavour physics here does not mean charm or B-physics -- the topic was instead the accurate determination of |Vud| and |Vus| from nuclear transitions and Kaon decays. The very accurate results obtained there confirm the unitarity of the first row of the CKM matrix to great accuracy, as well as confirming universality (via a comparison of Gμ and GF).

The next talk was by Christoph Hanhart (Forschungszentrum Jülich), who spoke about QCD exotics such as hybrids, glueballs, tetraquarks and hadronic molecules. Here I learned what the physical difference between a tetraquark and a mesonic molecule (who after all both consist of two quarks and two antiquarks) is: since hadrons (as opposed to quarks) can go on-shell, the S-matrix elements for a hadronic molecule (but not a tetraquark state) would contain non-analyticities.

The remainder of the day had talks mostly about hypernuclear physics (hypernuclei are nuclei with a nucleon replaced by a strange baryon), which I feel unable to summarise (I only remember that hypernuclei are smaller and more tightly bound than normal nuclei), and accelerator physics, which I skipped in order to look after my email and a couple of papers that are in the final pre-arXiv stages of the pipeline.

MAMI and beyond, Day Three

Today's morning session was filled with experimental talks making the case for an electron-nucleon collider to study the structure of the nucleon.

The short afternoon session had a talk by Akaki Rusetsky (Bonn) about the determination of resonance properties from finite-volume spectroscopy using a combination of Lüscher's formula and heavy-baryon chiral perturbation theory applied to lattice simulations near (or ideally at) the physical quark masses.

After that there was an excursion to Kloster Eberbach, a nearby former Cistercian monastery, where a guided tour was combined with a wine tasting. After that, the conference dinner took place in a castle hotel on the Rhine.

MAMI and beyond, Day Two

Hello again from Mainz, where I am at the conference "MAMI and beyond".

Today's first talk was by Barry Holstein (UMass Amherst), who spoke on "Hadronic physics and MAMI: past an future". The hadronic physics was cast mainly in the language of Chiral Perturbation Theory and its extensions. An interesting detail was the magnetic polarisability of the nucleon, which suggest that the nucleon in 10,000 times "stiffer" electromagnetically than a typical atom; this is in spite of the fact that the ability of the nucleon to transition to a Δ resonance ought to give it strongly paramagnetic properties from the quark spins; heutistically this is countered by the diamagnetism of the nucleon's pion cloud. Another feature that I found interesting was that the experimental determination of hadronic scattering lengths seems to be rather involved (possibilities mentioned involved the decay of pionium, or an analysis of the cusp structure in the energy dependence of K->3π or η->3π decays), and that the best way to determine them from theory is apparently from the lattice via Lüscher's formula for the volume-dependence of two-particle state energies.

The next speaker was Rory Miskimen (also UMass Amherst) talking about the measurement of nucleon polarisabilities in real and virtual Compton scattering. Real Compton scattering is, well, Compton scattering, virtual Compton scattering is the production of a photon in the scattering of an charged particle by a proton: γ*p -> pγ. Apparently the results from MAMI lie on a different curve from those from other experiments at other energies, which might suggest that there is something interesting happening around energies of Q2=0.3 GeV2.

The next two talks were by Bernard Pire (CPHT/Polytechnique) and Diego Bettoni (INFN Ferrara), who both talked about timelike processes. Due to my limited understanding of the relevant physics, I feel unable to give a summary of those talks, except that apparently it is quite difficult to disentangle the different form factors experimentally.

After that Fred Jegerlehner (Katowice and DESY Zeuthen) spoke about the running of the fine structure constant α. The running of α, which at zero energy is known to astounding precision, is of particular interest around the muon mass (where it enters the determination of the muon anomalous magnetic moment) and around the Z boson mass. The difficult part is to determine the contributions to the running of α coming from hadronic loops, the uncertainty about which causes a loss of five significant figures when evolving α from 0 to MZ. Using a method based on the Adler function (essentially a derivative of the self-energy with respect to the momentum squared), it should be possible to get a much more precise running of α by improving the understanding of low-energy hadronic contributions. Since most of the information needed in this approach would come from the Euclidean momentum region, the lattice might be able to help here.

After the lunch break, I skipped a couple of experimental talks to go over to the IWHSS workshop held next door and listen to a talk by Chris Michael about hadronic physics on the lattice. Chris presented approaches that can enable the determination of the nature of resonances and even the description of ρ -> ππ decays on the lattice.

After the coffee break, the lattice session of the MAMI conference took place: Meinulf Göckeler gave a summary of recent work towards the determination of generalised parton distributions on the lattice; Dru Renner at DESY Zeuthen works on this kind of thing, so I have heard about it a few times; it seems very hard each time I hear it, but I suppose saying "let's wait a few more years before starting on something like this" is not really an option.

Mike Peardon spoke about hadron spectroscopy on the lattice, giving a great introduction to lattice spectroscopy for the non-latticists in the audience. The highlight for lattice theorists was his mention of a new method that might replace noisy estimators for all-to-all propagators: a redefinition of quark smearing as a projection on the subspace spanned by the low modes of the Laplacian on a timeslice, enabling one to then exactly calculate all elements of the quark propagator out of this (relevant) subspace. The results shown looked rather promising, and the cost for diagonalising the Laplacian on a timeslice is of course much lower than that for diagonalising the Dirac operator as needed for the Dublin method of all-to-all correlators with low-modes.

Andreas Jüttner gave a talk about ongoing work to study mesonic form factors and (g-2). Using twisted boundary conditions to induce a momentum, he obtained very nice pion and K->π form factors. The (g-2) work is still in progress, but looks promising.

Silvia Necco gave an introduction to the links between Lattice QCD and Chiral Perturbation Theory, covering the extraction of SU(2) and SU(3) low-energy constants from Nf=2 and Nf=2+1 lattice simulations, and of the leading-order couplings Σ and F from simulations in the ε-regime.

Finally, Johann Kühn (Karlsruhe) spoke about precision physics in e+e- interactions, where the perturbative determination of the hadron-to-muon ratio R(s) has made it possible to precisely determine αs, mc and mb from experimental data (and the former two also from lattice simulations via the moments of current-current correlators).

In the evening, there was a social event: A string quartet played for us at the university's faculty of music in Mainz. The program was Mozart (Divertimento No. 1, KV 135), Schubert (String quartet No. 13 "Rosamunde) and Shostakovich (String quartet No 8 op. 110), the first two pieces quite pleasant, the last rather harrowing.

MAMI and beyond, Day One

Hello from Schloss Waldthausen near Mainz, where I am attending the conference "MAMI and beyond".

The meeting started this morning with welcome speeches by the VP for research of Mainz University, the VP of physics of the German Research Foundation, and the acting director of the Mainz nuclear physics institute. This was followed by the first talk, given by Ulf G. Meissner (Bonn University), who spoke about "Hadron physics at the 1 GeV scale and its impact". He paid particular attention to isospin violating effects, which can come from both QED and QCD sources, since the up and down quarks differ in both mass and charge. MAMI experiments could measure isospin violating effects in πN scattering, η -> 3π and η' -> ηππ decays, and in Kaon photoproduction on the proton, for all of which there are higher-order predictions from some versions of chiral perturbation theory. Beyond MAMI, interesting isospin violating effects are the mass splittings of heavy baryon mutliplets, where the mass of the cdd Σc0 is greater that that of the cud Σc+, even though md>mu, but the ordering of the Σs baryons is the normal one, an effect that may be explained by the presence of a new operator appearing in the O(p2) χPT effective Lagrangian for heavy quarks, which has a different sign for c and b quarks because of their different electrical charge.

After the coffee break, Jens Erler (UNAM, Mexico) talked about "Low-energy tests of the Standard Model and beyond". Low-energy probes, such as leptonic decays, flavour-changing neutral current contributions to Kaon decays, first row CKM matrix unitarity tests, tests of CP violation, search of nucleon and lepton electric dipole moments, atomic parity violation, (g-2) measurements and many more from particle, nuclear and atomic physics, can surprisingly probe very high energies by placing extremely stringent limits on various kinds of beyond-the-Standard-Model physics, excluding in many cases BSM contributions from scales below a few 100 TeV or so. This makes them a very useful complement to high-energy collider experiments that search for BSM particles and processes in a more direct manner.

The next talk was an overview of form factors given by Carl Carlson (College of William and Mary). The point that stuck to my mind most prominently was that measurements of hydrogen hyperfine splitting when combined with proton structure measurements and calculations are accurately predicted to more than 1 p.p.m. and show now evidence of new physics to such accuracy.

After the lunch break, Constantia Alexandrou (Cyprus University) gave an overview of nucleon structure on the lattice, concentrating on Nf=2 studies using dynamical twisted mass, Wilson clover or overlap fermions. Special attention was drawn to the fact that it is now becoming possible to simulate at the physical pion mass, and that the first such simulations have recently been done by the Wuppertal group.

This was followed by another experimental talk by Volker Burkert (Jefferson Lab). What I took home from this talk was that there is experimental support for the notion that the Roper resonance is a radial excitation of the nucleon, and that there is such a thing as femtotomography, where an image of the charge distribution inside a hadron is created from the Fourier transform of its structure functions.

After this, Mauro Anselmino (INFN Torino) spoke about the spin structure of the nucleon from a mostly theoretical point of view, followed after the coffee break by Klaus Rith (Erlangen-Nürnberg University) speaking about the same from a mostly experimental point of view. The "spin crisis" caused by the discovery that the quark spins only contribute about 33% of the nucleon's spin still appears somewhat unresolved. The gluons appear to contribute very little, and the contributions of the angular momenta of up and down quarks, which must make up the remainder, interestingly have opposite sign. A lot of research still seems to be ongoing in this very complex area, and I honestly don't understand enough of it to be able to give a decent summary of the enormous amount of information contained in these talks.

The same is true (and to an even larger extent) of the experimental talks that followed, and to which I didn't pay the necessary attention in any case, since I had to deal with several pressing matters by email.

Friday, March 13, 2009

The World Wide Polymath

20 years ago today, the World Wide Web was first invented by (now Sir) Tim Berners-Lee. The most successful "spin-off" to come from particle physics in recent times, the WWW has transformed one after another the way we inform ourselves, do our shopping, and (with social networking sites becoming the great wave) keep in contact with (or even find) friends.

The reason the web was invented was of course the large-scale collaborative nature of experimental particle physics research, which created a need to connect the various bits and pieces of information that were created by different collaborators into a coherent whole. Other areas of science have become more and more collaborative as well, and researchers in those areas have also profited from the existence of the web, as have countless groups of people inside and outside academia who are connected by some common interest, but separated by geography.

One discipline which so far has withstood the tendency towards large-scale collaboration has been pure mathematics, which is still dominated by single-author papers and sometimes two-person teams. Fields Medalist Tim Gowers has now set out to use the web in order to transform the way mathematical research is (or at least may be) done: on his blog, he has started a series of discussion threads aiming for a new proof of the density Hales-Jewett theorem for k=3 (which apparently is of genuine interest to combinatorialists) by a large-scale collaboration of mathematicians connecting their ideas through the web. This project appears to have succeeded. Whether this is the beginning of a new era of massively-collaborative mathematics remains to be seen, but it is fair to say that the World Wide Web's power to transform many and diverse areas of human endeavor by bringing people and information together in new ways still hasn't found its limits.

Friday, March 06, 2009

Hey, that guest post should be here!

There's a guest post at Shores of the Dirac Sea about exact lattice supersymmetry. It's good to see that physicists in other areas are interested in what lattice field theory has to say.

Brief sign of life

There hasn't been much going on on this blog recently since I've been busy with other stuff and am still busy with still more other stuff, which I'm afraid has to take precedence over blogging. Guest posts, however, would be more than welcome!