Thursday, 27 November 2008

Airport musings

"You have very little chance of getting at the truth, if you know in advance what the truth ought to be." -- Spencer (Robert. B. Parker).

Advice which many in the field need not. They massage their results until they arrive where they expected to, and they get cited for it.

So here I am sat in an airport waiting lounge. Was somewhat disappointed to find that either the arXiv hadn't updated on time, or that this place was refusing to refresh its cache, so I can't read the new abstracts. Meh.

Selling your physics.

It is important to market yourself, and your material, properly. Especially if you're a PhD student or Postdoc. You want people to read your abstract and think "wow", so that then hopefully they'll at least get through your introduction and conclusion before putting your paper to one side, rather than just letting it scroll off the top of the page as they persue the arXiv.

Of course, there is selling yourself, and then there is writing blatant crap. This morning I read this in a paper of a few years back. It isn't a direct quote -- I've cut out a few words to disguise its origin, but the statements are faithful representations of the original.

"There is no obstacle to formulating the theory for non-constant
F(x), but we shall concentrate on the case of constant F for simplicity.
Up to terms involving derivatives of F(x), our leading order results
are therefore also valid for varying F(x)."

Wow. Way to go dudes.

Wednesday, 26 November 2008

Talk on the LHC.

The incoming director general of Cern, Rolf-Dieter Heuer, gave a talk on the LHC, this week, in Dublin. You can now stream it from here.

I was told I couldn't attend, because by the time I tried to book a seat, 750 places had already been reserved and there was a waiting list of 400.

Well, a shame, I thought, but great that the public are obviously so interested.

Yeah, bull. Take a look at 2 mins 51 seconds of the above video, and you'll notice that the hall is half empty.

So, well done the RDS for shafting that one.

Friday, 14 November 2008

Try new "Group Theory"!

I'm not sure what it is about this place, but every seminar I go to involves some god awful group like PSL(2,4) and the word `irrep' scattered liberally all over the place. Even the Masters and PhD students can't give a 20 minute seminar without something transforming in an irrep of something else. (Aside: the Russian Masters student has papers already. Wowzer.)

Now, before anyone blows a gasket, yes, we all know what irreps are and we all know that they're important. But don't you wish, sometimes, that the speaker would just write down the relevant field and the way it transforms? Don't you get the feeling that they're telling you "3*3=5+1+3" and then running out of the room with nothing else because, well, they can't be bothered to actually construct the fields of the theory they're talking about?

Example: anyone who's ever taken a course on string theory will be familiar with this phenomenon.

Lecture 1: you spend the obligatory hours trawling through the commutators of the modes, constructing the Hamiltonian and the spectra, identifing the tachyon and the photon, etc. It's not super exciting, but hey it's your first course in string theory and it's still pretty cool, because you can do everything explicitly and really its just like your QFT course. Importantly, you can see what's going on. Now, time to get fermions in the game.

Lecture 2:
Superstrings: 3+3=8+1. Sniff.

Lecture 3: N=4 SYM and the AdS-CFT correspondence in all its gory glory -- WOAHHH.

Wait. What happened there? What happened to all the supersymmetric stuff? Well, you've been told what representation it's in, what more do you want? You haven't written down a string, a single commutator, you haven't seen the spectrum, you're just told that there's a 2bar, a 4+1 bla bla bla, and now you should be able to understand all the gumph about conifolds and G2 and holography that the papers are full of.

Didn't it annoy you? It annoyed me. So, while group theory is important and funky and here to stay, don't you just feel sometimes that physics once saw an advert and thought `yup, that's for me', and that advert said:

"Group Theory: for when you just can't be arsed to do it by hand."

Saturday, 8 November 2008

Gribov copies.

There's an interesting discussion on BRST going on over at Not Even Wrong. Someone mentioned Gribov copies, in which I have an interest, and I put my two pence worth in.

I think I inadvertently caused the discussion to split into two groups -- BRST and copies, and it ended with people apologising on the comments board. Rolls eys. Physicists apologizing for their views on physics -- if only the string theorists would go for that idea in a big way.

Anyway, I'll summarise my thoughts here.

Gribov copies have physical effects -- they do have something to do with confinement. This is really very easy to show -- see work by Bagan, McMullan and Lavelle. What they have shown is that although you can write down the wavefunction for a physical quark (so not simply the fermion in the Lagrangian, as that isn't anything physical) in perturbation theory, you cannot do so non-perturbatively. If you could, there would exist a globally well defined gauge fixing for Yang Mills, and there isn't, because we know there are copies.

Seeing this from a slightly different angle, your supposedly gauge invariant quark picks up a non--perturbative gauge dependence (and hence becomes unphysical) precisely through the action of the Gribov copies. In other words, you can have physical quarks in perturbation theory (weak coupling, which makes perfect sense since we have asymptotic freedom), but not non--perturbatively (strong coupling, when we expect the flux tube to form). Non-perturbatively, you can't have single quarks, but the above argument doesn't go through for multiquark states, so you can have mesons and hadrons -- well great, this is exactly what we see!

However, this doesn't give you the confinement scale or anything like it. For that you need dynamical, quantum, arguments, and probably non--perturbative arguments at that. So, just like every other approach to confinement, it doesn't go all the way, but it's a very simple, very physical argument.

The way most people are introduced to Gribov copies is, probably, as an overcounting in the path integral. That's not the fundamental origin of the copies, it's just a symptom of their existence. If there is some other, operator, picture in which the copies don't appear --as mentioned in the discussion linked above-- then either there is something amiss with that picture (it isn't capturing all the physics, in particular non-pert. physics) or there is something wrong with our understanding of that picture (which is probably easier to accept).

But then, I'm going up against Nakanishi -- and he invented the Nakanishi Lautrup field, compare: what have I done?, so you should probably take what I say with a pinch of salt.