Thursday, December 29, 2005

UK Annual Theory Meeting

The semester has ended, there are no weekly seminars to write about, I have had my yearly winter cold (but that was not interesting enough to say much about) and now Christmas has come and gone, but just before it began (I mean December 25th rather than the retail definition of mid-October) I started to write up the following...

For the last few days I have been getting up much earlier than normal, meeting many more friends, listening to more lectures and eating larger meals than normal. This is not some new life plan undertaken on my part but rather I have been to Durham to attend the annual Christmas UK theory meeting. The meeting takes place every year near Christmas and has a prestigous history of speakers. It is also a meeting that attempts to present an overview of the current state of the art in theory ranging from phenomenology and the construction of particle accelerators to string theory and tries to find a balance between them (which is very hard, and invariably different talks were appreciated to different degrees by disparate groups, save the final one).

I arrived at Grey College, where we were housed, at quarter-to-one on Monday, a feat which required a near superhuman effort to awaken at six-thirty that morning. It was my first benefit of daylight saving time, there was pristine blue sky and it was actually pleasurable to see the light reflected from all the unfamiliar angles of the buildings near my home. Despite the lack of sleep, the three hour train journey at a cost of £88.00(!) was very pleasant. However the rest of the afternoon was not so nice for me, since the talks were dedicated to experimental particle physics. While string theorists must not decouple from experiment, it is very easy for a PhD student in strings, who has specialised in group theory, differential geometry and gravitational physics to never have come into contact with much QCD or lattice simulations and certainly not at the level of the talks that first afternoon, alas. Of course the same is true within any large subject area, and from this blog you will know how often I have had trouble even following stringy seminars. From the number of sleepers in the various talks I feel there was a similar disappointment for some of the phenomenologists and others during some of the stringier talks. Ho-hum.

The first talk was "Results from the B factories" by Steve Playfer, where we heard about the latest data cuts and fittings comng out of the Belle and BaBar experiments. What are Belle and BaBar? Well they're the B meson factories and they look to see whether charge (particle-antiparticle) and parity (physical mirror) symmetries are violated in the decay of the B and the anti-B, or B-bar. Belle is located at KEK in Japan and BaBar is at the Stanford Linear Accelerator in California. The two experiments have confirmed (BaBar 2002) that the B-mesons do violate CP-symmetry. Steve is part of the BaBar team and his talk describing recent results, hinting at future results and improvements in error ranges displayed a healthy amount of competitive spirit with the Belle experiment.

The rest of the afternoon was filled with talks possessing a phenomenological nature, and again outside your humble blogger's limited range of semi-enlightenment. The roll-call reads: "Heavy Flavour Physics" by Matthias Neubert and "Lattice QCD and results from CLEO" by Paul MacKenzie. The evening was spent in the pub and then subsequently the "trendy" wine-bar Jimmy Allen's where all the cocktails had decidedly dismal names, but nevertheless a good time was had.

The tuesday began much earlier than most tuesdays, perhaps this was the effect of the drink the night before or perhaps it was due to the hour. The first talk, "Twistors and Perturbative Gravity" was given by Dave Dunbar from Swansea University and was of a similar format to many of the twistor talks I have seen this year in that there was a long review of the material for the skeptics in the audience who, like me, have so far shied away from twistors and MHV amplitudes. As ever the simplification of loop calculations coming from twistors seemed nothing short of miraculous, and, as ever, I have made a solemn pledge to myself to read Witten's twistor paper and work through some of the calculations myself.

The second talk was a report from the front line on the construction of the LHC at Cern given by Jos Engelen. We saw pictures of heavily-laden lorries shipping extraordinarily large structures back and forth, heard tales about the pitfalls of purchasing specially made detector crystals from a Russian manufacturer who "forgot to pay their electricity bills" and subsequently upped the price for the consignment, and we marvelled at the design ingenuity of the engineers having to form these perfectly symmetric detectors at such a large scale and underground too, in prticular Jos told us about one detector whose perfect circular cross-section was designed only to be achieved once the final segment was installed and its weight would bring about the perfect circle. We heard abut the 27km track (how perhaps only the rate of intallation of the 50m magnets needs to speed up), Altlas, CMS, LHCb and
Alice. In short all is well, Jos paraphrased this:
"We are going to do the first new physics in Summer 2007. This sentence does not define new physics, it defines Summer 2007."
Vijay Balasubramanian spoke about his approach to "Gravitational Thermodynamics" which was quite different to all other talks on this subject that I have ever heard, for example there was almost no mention of charge ensembles (at least not until the questions at the end, when it was asked how his work relates to the more usual stringy appraoch to degrees of freedom). Before he began there was an advertisement for a postdoc position and a faculty position at the University of Plymouth, details to be found here. He spoke with great enthusiasm and volume about horizons and Unruh radiation and very large states. In gravitational thermodynamics the information loss paradox is side-stepped if black holes do theoretically contain all the degrees of freedom of the states that fall into them and that information could theoretically re-emerge from the black-hole, eventually. Pure states remain pure. Vijay was addressing the question of just what is a pure state and what would it take to be able to probe it. His arguments can be found in his paper with Vishnu Jejjala and Joan Simon, "The Library of Babel". But the main argument is that while states do remain pure and information is not lost, "almost no probes are able to differentiate the microstates of a black-hole". To find out what almost means you'll have to read the paper (7 pages), and I heartily encourage you to read the short story that the paper borrows its name from by Borges.

In the afternoon we had a very nice, pedagogical talk from Hans Peter Nilles, who amongst other things explained to us in detail exactly what an orbifold is. His title was "Grand Unification in Strings" and he said was based on work found here, here and href="">here.

Finally we ended the day with a talk by Keith Ellis, provocatively entitled "Marching Orders for QCD" which he said could be found online here, so I left. That evening also found me making further investigations into beverages of Jimmy Allen's.

The final morning began with Herman Verlinde building bridges between string theory and experimental particle physics. His title was "Geometry and the Standard Model" and his proposition was to decouple the landscape. He described the landscape as 10^500 doors with locks on, and suggested that we should start with the only key we have: the standard model. His aim was to start with the minimally supersymmetric standard model, to use this to find a moduli space for the SuSy vacua and to use this to find a configuration space of Calabi-Yau manifold singularities. The devil is in the detail, and he led us on a path that took in fractional branes, quiver gauge theory, Del Pezzo surfaces and how to draw a Moose. During the question session the attempt to build bridges between theory and experiment was welcomed, but only after the rivalry between string theorists and those hoping for a more readily tangible explanation of high-energy physics had once again flared up. A member of the audience had been willing to bet against string theory being the correct unifying theory, and Hermann Verlinde had steadfastly opposed his negative opinions by saying he was willing to take such a bet. This is the first time, beyond the internet, where I have witnessed any kind of head-on confrontation about the nature of string theory. I expect it will not be the last.

The final talk of the meeting was of a much more gentle nature and was enjoyed by a broad spectrum of the audience, regardless of their predisposition towards string theory. It was entitled "How did Einstein get the Nobel Prize?" given by the very entertaining Cecilia Jarlskog. She gave us a colourful review of the life of Alfred Nobel and the early history of the Nobel prize and we got to see all the nominations in the years leading up to Einstein's prize, and even to see some of the photocopies of handwritten letters of recommendation for the prize. All of which was very nice, and made for a fitting end to the meeting and also, for me, to the year of physics celebrating the centenary of Albert's miraculous year.

Wednesday, December 07, 2005


Two noteworthy events occured at King's College last Friday. One of which involved "one-hundred drunk LSE students" rioting in the lower levels of our Strand campus and the other did not. The rioters flooded our building and caused havoc, some attempted to invade the maths classrooms no doubt eager to benefit from the wisdom of our faculty, and others began ripping ceiling tiles from the English department in an attempt to seemingly tear a building to bits whilst still inside it, causing £30,000 worth of damage. The second event of note last Friday was our mathematics department colloquium which was given by the impressive Don Zagier under the title "Dilogarithms and the Bloch group: from algebraic K-theory to modular forms to conformal field theory". The rioters caused our colloquium to start late, a fact that was noted by Professor Zagier when nearly out of time he suggested that perhaps he himself could riot in order to circumvent the need to vacate the lecture thatre at the prescribed time so he could get to the end of his talk.

Permit me to pass on some brief comments from the beginning of Zagier's talk about the dilogarithm with the caveat that most of this remains beyond my ken. Nevertheless the dilogarithm has been studied by some truly great mathematicians including Euler, Leibnitz, Abel, Lobachevsky, Borel, Ramanujan, and others so if only for historical interest it is nice to look at some of the properties of the dilogarithm in passing.

We are all on first name terms with the logarithm function (that's log to you and me):
But perhaps not so well known is it's relation the dilogarithm: There are plenty of others, which are specific values, s, of the polylogarithm, or Jonquiére's function, Zagier told us that there are only 8 closed forms for the dilogarithm, some of which include the golden ratio, The only irrationals on the left hand side are powers of the golden ratio. We might look for properties of the dilogarithm that are similar to those we know of the logarithm, for example we know that, Zagier told us that there was no simple equivalent of this for the dilogarithm, but that we did have a formula, named for Abel even though it had been discovered by others before him (Spence, 1809) and after him (Lobachevsky), Zagier told those of us taking notes in the audience to just write "junk" instead of the right-hand-side of the above, however, he stressed that the order of the left-hand-side terms was important. I think practitioners of this art tend to normalise their dilogarithm functions into the Rogers L-function, which gets rid of the junk. There are a number of useful identities for the dilogarithm two of which are,These lead to equivalent forms of the five-term equation via X ~ 1/X ~ 1-X ~ 1/(1-X) ~ 1-(1/X) ~ X/(X-1). Furthermore if you define a junk-removing functional equation: Then this equation has a modulo 5 symmetry,Try it and see!

Zagier went on to look at the Bloch-Wigner dilogarithm, whose five-term equation is equal to zero and to give an argument in terms of the volume of tetrahedra in a hyperbolic 3-space modulo PSL_2(C) about why it should be zero. It sounded very nice, but I can't say I understood. For those interested the argument is given in section four of sixth set of notes by Matilde Lalin from classes given by Fernando Rodriguez Villegas called "Topics in K-Theory and L-functions". Those interested in seeing many more five-term functional equations should look through Kirillov's Dilogarithm Identities. For an introduction to dilogarithms Maximon's article seems a good place to commence.

Zagier talked fluently, rapidly and energetically about many more topics, such as the Bloch group (if you google Bloch group you may not find much helpful information but you will come across Dr. Bloch's group page), the five-term equation related to the Schrodinger equation for a cubic potential, K-theory (in particular K_3) and also rational conformal field theory, where he spoke with great enthusiasm of the recent conjectures of Werner Nahm. He never once, to my knowledge, resorted to rioting to extend his talk.

Thursday, December 01, 2005

Beyond Einstein

Here's some very short (actually it's already started) notice of the physics equivalent of Live 8. To celebrate the world year of physics physicists, internet pioneers and others will be participating in a marathon 12-hour broadcast performing covers of classic pop songs to raise awareness of physics live on the web and will discuss Einstein's theory of special relativity and more. In the words of the BBC article,
Alongside E=mc², there will be discussion of gravitational waves, the search for the Higgs Boson and the mysteries that still linger behind Einstein's work.
So get the popcorn in, get broadband installed and go and watch (or put on in the background) the webcast at Beyond Einstein. Just so you know there are some well known names who will be participating later on today. Included, amongst others, on the list is (broadcast times are in brackets and are Central European Times):

  • Albert Einstein (1200-0000)
  • David Gross(1700)
  • Gerard't Hooft (1700)
  • Murray Gell-Mann(1700)
  • Paul Davies (2230)
  • Stephen Hawking (TBC)

    Quite a list eh? Although there must be some code for the yellow and green stripes on the particpator list I presume they are all taking part. The full programme is available here.

    Given that this is obviously a very-well prepared event it is amazing not to know anything about it until after it has begun! Clifford at cosmicvariance also found about it today, and I only heard about it thanks to the Emperor of our office, Peter McKeag - he's not Emperor for nothing!