Spectrum of two color QCD


In a preceding post (see here) I have shown how SU(2) QCD can be reduced to a theory easily amenable to perturbation treatment. This case is quite easy as, due to the gauge group, algebra is not too much involved. At the leading order one gets the following set of equations

i\gamma^0\partial_\tau q_0+\frac{1}{2\sqrt{2}}\phi_0\Sigma q_0=0


that are very easy to solve and so, we can get an understanding of the mass spectrum both for \phi and the quark field. At a first glance we easily recognize that, at this order, is clear that QCD has a chiral symmetry and this symmetry arises naturally from the strength of the coupling g.

At this stage we want just to write down the mass spectra. For the gluon field we have


exactly as for SU(3). The only change here should be the value of the string tension \sigma.Indeed, the folowing relation should hold \sigma_{SU(2)}=\sqrt{2/3}\sigma_{SU(3)} and so, if \sigma_{SU(3)}=(440MeV)^2 one will have \sigma_{SU(2)}\approx (398MeV)^2. This is in perfect agreement with lattice evidence (see here). This lattice evidence is quite old and should be pursued further. For a quark we have the spectrum


and as for the glueball spectrum we have n=0,1,2,\ldots and K(i) an elliptic integral. From this we say that the lowest state in the spectrum will have zero mass, the pion, and this is just a manifestation of the above approximate chiral symmetry.

The next step will be to go to higher orders and correct these results. But we see that, already at leading order, we conclude that the glueball spectrum must manifest itself at an experimental level exactly as happens to hadronic spectrum. Any other correction to it is just higher order.


LHC will stop for at least eight months


The damages following LHC accident, occurred last month, are more serious than expected. Some design errors have been identified into the valves that should regulate the quantity of helium flowing in such cases. Helium entered inside the ring and the valves were underdimensioned for the aims. Bad news is that repairing damages will require at least eight months. Optimistically one can hope starting of operation on May or June 2009. An article can be read in Nature about (see here). Dynamics of the accident is given by CERN here.

LHC and media


I cannot avoid to write down this post as a lot of friends and colleagues are asking me about the next doomsday on September 10th. Indeed, our newspapers in Italy are now plenty of horrible misinformation about claiming the possibility that in that day a black hole will be produced and World will be finally eaten up.

As for us physicists we know that nothing of this is really possible even if a story about a PhD student producing our universe for her thesis is recurring. We are aware that the injected beams on that date will be at very low energy, 0.45 TeV, but anyhow I have found a beautiful article by Matthew Chalmers in Physics World (see here) explaining all the matter. The interested reader should go through it.

Finally, I am pleased to think that Hawking would be in the verge of receiveing a Nobel prize wherever we see an evaporating black hole. As this theory is really fascinating, it would be also a big hit if it would be proved true in such a controlled way.

Thanks Telecom Italia!


Doing blogging implies one has a reliable internet connection. But thanks to these guys working at Telecom Italia I am without such a connection since a week now due to presumed improvements on my line. They did such an improvement that I now miss the service!

I will report on QCD 08 on monday. Sorry for the delay in my answers and further posting.

QCD 08


The next week I will be in Montpellier to attend QCD 08. So, I will stop blogging till friday. I will put a link to my talk I will give there.

Happy July 4th for US readers.

A World of Physics and a lot more


This is the start-up post of this new physics blog. I will talk about a lot of questions I care about, mostly current research open problems that need some tribune to be heard. But I will also discuss some other arguments that could be of interest to a larger audience.

Most of the questions on physics that pass to the media are about string theory, unification, quantum gravity and all other aspects of fundamental research that can hit the interest of common people. But one should consider that most of the breakthroughs that happened in science have come from unexpected directions.  And last but not least, there is generally an average time, that is not short, before an important finding becomes a recognized and acquired truth. This means that is important to make knowledge to flow as fastly as possible and blogs are an excellent way to achieve such a goal.

I am working mostly on QCD and for this particular field there are different alleys that are currently pursued and just now something is going to converge for experiments, lattice and theory and is worthwhile to let everybody know the work of these people that someday could impact in a more generally way to all the community. The reason to expect this relies on the fact that QCD is a theory eminently not perturbative and a lot of innovative views should be expected here.

Indeed, one of the most serious problems to face in physics is the treatment of problems where a large parameter enters that makes the problem non perturbative, that is, impossible to manage with perturbation theory. Till now, perturbation theory appears as the only serious approach to get analytical solutions to equations and needs a small parameter to work. Despite several important attempts as the renormalization group and a few of exact solutions, in the end of the day one has to rely on this venerable approach to extract physically meaningful results from equations.

This approach has become such a part of physics that a lot of prejudices invaded some fields where it applies. A clear example of this is quantum field theory. Quantum field theory works only through small perturbation theory and so, renormalization that was born with it is believed to be inherent to any quantum field theory independently on the method one use to treat it. But this latter point of view is to be proved!

So, let us begin. Happy blogging!

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