## The XV Workshop on Statistical Mechanics and nonperturbative Field Theory

25/09/2011

This week I was in Bari as the physics department of that university organized a major event: SM&FT 2011. This is a biennial conference having the aims to discuss recent achievements in fields as statistical mechanics and quantum field theory that have a lot of commonalities. The organizers are well-known physicists and so it was a pleasure for me to see my contribution accepted. Leonardo Cosmai wrote to me confirming my partecipation. Leonardo, together with Paolo Cea, Alessandro Papa and Massimo d’Elia produced a lot of significant works in quantum field theory and a recent paper by Cosmai and Cea arose some fuzz also in the blogosphere (see here). Their forecast for the Higgs boson agrees quite well with my view about this matter. They were also part of the organizing committee. Of course, I was in Bari with my friend Marco Ruggieri that lived there for more than twelve years gaining a PhD in that university.

The scientific content was really interesting an I have had the chance to learn something more about lattice field theory. You can find all the talks here. About this, it should be said that people work with small lattices yet. While this has been a natural way to manage the QCD on the lattice due to missing computational resources, things are rapidly changing due to CUDA as I discussed a lot in my blog and was presented in some talks at this conference. Small groups will be able, with very few bucks of their budgets, to reach a significant ability to analyze increasingly lattice volumes. Besides, also large scale projects in this direction, mostly due to INFN and extending the APE project originated by Nicola Cabibbo and Giorgio Parisi, were presented (see talks by Francesco di Renzo e Piero Vicini). A typical situation in this kind of lattice analysis, improved using CUDA,  was also pointed out by Massimo D’Elia in his talk.  Thanks to this new technology they are increasing significantly the volumes. You can compare the content of his talk with that of his collaborator Francesco Negro, discussing a really interesting problem on the lattice (and a promise for the future with CUDA), with smaller volumes due to reduced computational resources. The interest for the activity of this group and Francesco’s work is strongly linked to a paper that I and Marco Ruggieri wrote together about the QCD vacuum in presence of a magnetic field (see here). The work by Francesco, even if for small volumes, provides interesting conclusions. It should be said that the Nambu-Jona-Lasinio model is there well alive and kicking.

Petruzzelli Theater

From a strictly theoretical side, I would like to point out the talks by Giuseppe Mussardo, with which I have had a nice mail exchange and is author of some beautiful books (e.g. see here), and the ones by Adriano Di Giacomo and Valentin Zakharov that seem to have some relevant contact points with my work. There was also a talk by Edward Shuryak, one of the proponents of the instantons liquid for the QCD vacuum that is strongly supported by lattice simulations and theoretical works like mine.

At the end of the social dinner, we have had some interesting discussions with Di Giacomo and Cosmai. There was some excitation about the announced seminar about neutrinos by CERN and INFN. In a pub after the dinner, I have had some interesting discussions about a proposal by Michele Pepe and others (see his talk) that holds the promises to improve significantly lattice computations removing artifacts. It was also the chance to hear the point of view of Owe Philipsen (see his talk) about the current situation on lattice simulations on QCD at finite temperature. As I have discussed in some posts in this blog, this kind of simulations are plagued by the infamous sign problem and most of the work turns back to try to get rid of it. My friend Marco expressed the somewhat pessimistic view that a critical endpoint will never be seen on lattice computations. Indeed, he is the proponent of the use of a chiral chemical potential that does not display this stumbling block on the lattice (see his talk). This approach holds the promises to reach the goal as he showed in a recent paper. His proposal is under scrutiny by the lattice community. The QCD critical endpoint is a Holy Grail for all of us working in this area as QCD displays a quite rich phase diagram and we have also a lot of experimental data in heavy ion collisions to understand. You should take a look both at the talks of Marco and Alessandro Papa.

I would like to have cited all the talks and I apologize for omissions. If my readers have some time to spend usefully just read it all, as the conference was well organized and with very interesting contents in a really nice atmosphere somehow excited by neutrino news in the last two days.

P. Cea, & L. Cosmai (2011). The trivial Higgs boson: first evidences from LHC arXiv arXiv: 1106.4178v1

Marco Frasca, & Marco Ruggieri (2011). Magnetic Susceptibility of the Quark Condensate and Polarization from Chiral Models Phys.Rev.D83:094024,2011 arXiv: 1103.1194v1

Marco Ruggieri (2011). The Critical End Point of Quantum Chromodynamics Detected by Chirally
Imbalanced Quark Matter Phys.Rev.D84:014011,2011 arXiv: 1103.6186v2

## Back from Paris

13/06/2011

It is several days that I have no more posted on the blog but for a very good reason: I was in Paris for the Eleventh Workshop on Non-Perturbative Quantum Chromodynamics (see here). It has been a beautiful chance to see Paris with the eyes of a tourist and being immersed in a lot of physics in the area I am currently contributing. The conference was held at the Institut d’Astrophyisique de Paris. This week was indeed plenty of information for people in high-energy physics due to the release by D0 of their measurements on the Wjj data, showing that the almost 5 sigma bump of CDF was not there (see here, here and here). In the conference there has been room for talks by experimentalists too and it was the most shocking part as I will explain below.

The talks were somehow interesting with a couple of days mostly dedicated to AdS/CFT approach for QCD. So, string theory got a lot of space even if I should say that more promising approaches seem to exist. The first day there have been a couple of talks that were very near my interest by Dario Zappalà and Marco Ruggieri. They were reporting on their very recent papers (here and here). With Marco, I spent all the week together while with Dario we have had a nice dinner near Latin Quartier. The question Dario presented was about the existence of massive excitations (let me say “persistence”) also beyond the critical temperature for Yang-Mills theory. We discussed together with Marco this result and Marco claimed that massive excitations should have melted beyond the critical temperature while my view is that the residual of mass should be due to temperature corrections to the mass spectrum of the theory. Marco in his talk presented the idea of measuring the chiral chemical potential on the lattice as this could give plain evidence of existence for the critical endpoint without the annoying sign problem. A proof of existence of the critical endpoint is somehow the Holy Grail of finite temperature QCD and something under a lot of studies both theoretically and on the lattice. So, Marco’s proposal can turn out a significant shortcut toward the reaching of this goal.

The second day Carl Bender gave a very beautiful talk telling us about PT invariant quantum mechanics. PT stays for Parity and Time reversal. The point to start from is the Dirac postulate about the Hamiltonian being Hermitian self-adjoint. Differently from the other postualates of quantum mechanics, this one is too much a mathematical requirement and one could ask if can be made somewhat looser. The paradigm Hamiltonian has the from $H=p^2+ix^3$. The answer is yes of course and we were left with the doubt that maybe this is the proper formulation of quantum mechanics rather the standard one. I suspect that this could represent a possible technique useful in quantum gravity studies.

I have already said of the two days on string theory. I have just noticed the talk by Luca Mazzucato showing how, with his approach, my scaling with $\lambda^\frac{1}{4}$ for the energy spectrum could be recovered in a strong coupling expansion being $\lambda$ the ‘t Hooft coupling. Unfortunately, Gabriele Veneziano could not partecipate.

On Wednesday there was the most shocking declaration from an experimentalist: “We do not understand the proton”. The reason for this arises from the results presented by people from CERN working at LHC. They showed a systematic deviation of their Montecarlo simulations from experimental data. This means for us, working in this area, that their modeling of low-energy QCD is bad and their possible estimation of the background unsure. There is no way currently to get an exact evaluation of the proton scattering section. I am somewhat surprised by this as so far, as I have always pointed out in this blog, at least the structure of the gluon propagator at low energies should be known exactly from the lattice. So, modeling the proton in such Montecarlo models should be a mitigated issue. This does not seem to be so and these different communities do not seem to talk each other at all. After these shocking news, the evening we took an excellent social dinner and I have had some fine discussions with foreigners colleagues that were well aware of the books from Umberto Eco. One of these, Karl Landsteiner, suggested us to visit the Pantheon to look at the Foucault pendulum. I, Marco Ruggieri and Orlando Oliveira took this initiative the next day and it was a very nice place to visit. If you are a physicist you can understand the emotion of being there seeing that sphere moving like Newton’s equations demand and inexorably proving the rotation of the Earth. Karl gave an interesting talk that day where AdS/CFT is used to obtain transport coefficients in heavy ion collisions.

In the same day, Orlando Oliveira gave his talk. Orlando is a friend of mine and gave relevant contribution to our understanding of the behavior of low-energy gluon propagator. He has been the author of one of the papers that, at Regensburg on 2007, started the end of the so called “scaling solution” for the gluon propagator (see here). Orlando is going ahead, starting from the acquired form of the gluon propagator, to understand low-energy phenomenology of nuclear forces. In this work, he and his colleagues introduce an octect of scalar fields having the aim to produce the gluon mass through a non-zero vacuum expectation value (see here) producing chiral symmetry breaking. My work and that of Orlando are somewhat overlapped in the initial part where we have an identical understanding of the low-energy behavior of  Yang-Mills theory.

On Friday, there have been a couple of significant events. The first one was my talk. This is a report on my recent paper. I will not discuss this point further leaving this material to your judgement. The second relevant event was given in the talks by Thierry Grandou and our Chairman and Organizer Herbert Fried. The relevant paper is here. While Grandou made a more mathematical introduction with a true important result: the resummation of all gluon exchange diagrams realizing some dream of having completely solved QCD, Fried provided a more concrete result giving the binding potential between quarks analytically obtained from the preceding theorem. We were somehow astonished by this that seems just a small step away from the Millenium prize. Berndt Mueller, one of the Organizers, suggested to Fried to determine the mass gap and wait a couple of years to get the prize. Indeed, this appears a true striking exact result in the realm of QCD.

All in all, an interesting conference in a special place: Paris. For me, it has been a very nice period of full immersion in physics with the company of very nice friends.

Update: Mary Ann Rotondo put online the slides of the talks (see here).

P. Castorina, V. Greco, D. Jaccarino, & D. Zappalà (2011). A reanalysis of Finite Temperature SU(N) Gauge Theory arXiv arXiv: 1105.5902v1

Marco Ruggieri (2011). The Critical End Point of Quantum Chromodynamics Detected by Chirally
Imbalanced Quark Matter arXiv arXiv: 1103.6186v1

Irene Amado, Karl Landsteiner, & Francisco Pena-Benitez (2011). Anomalous transport coefficients from Kubo formulas in Holography JHEP 05 (2011) 081 arXiv: 1102.4577v3

O. Oliveira, W. de Paula, & T. Frederico (2011). Linking Dynamical Gluon Mass to Chiral Symmetry Breaking via a QCD Low
Energy Effective Field Theory arXiv arXiv: 1105.4899v1

Marco Frasca (2011). Chiral symmetry in the low-energy limit of QCD at finite temperature arXiv arXiv: 1105.5274v2

H. M. Fried, Y. Gabellini, T. Grandou, & Y. -M. Sheu (2009). Gauge Invariant Summation of All QCD Virtual Gluon Exchanges Eur.Phys.J.C65:395-411,2010 arXiv: 0903.2644v2

## A great intuition

11/08/2008

In the fall of August 2001 I was in Gargnano on Garda Lake in Italy to participate at the Conference “Mysteries, Puzzles and Paradoxes in Quantum Mechanics”. This was one of a series of Conferences with the same title organized by Rodolfo Bonifacio, a former full professor at University of Milan and now retired (latest news say that he is taking sun in Brasil). These Conferences were very successful as the participants were generally the most representative in the field of quantum optics and fundamental physics. I have had also the luck to meet interesting people that are still in touch with me like Federico Casagrande, an associate professor at University of Milan currently carrying on relevant research in quantum optics and laser physics. That year there was also Vittorio Giovannetti. Vittorio took a PhD in Physics at University of Camerino with Paolo Tombesi and David Vitali that are behind an international renowned group of quantum optics and gave also to the community a number of high quality researchers. At that time Vittorio was a post-doc at MIT and was working together with Seth Lloyd and another brilliant Italian post-doc Lorenzo Maccone. This collaboration produced a lot of relevant papers, mostly in applications of quantum mechanics, that appeared on Nature, PRL and several other high impact archival journals.

Bonifacio was involved with an original idea about intrinsic decoherence. He got a paper published on Nuovo Cimento B and another, with the collaboration of Camerino’s group, on PRA. After we listened at his talk about this interesting matter I exit the room where talks were taken place and exchanged some words with Vittorio and another person. In a while I averted my attention from Vittorio and the other person and started to mumbling thinking about decoherence. Than, looking at Vittorio I said loudly: “Yes, thermodynamic limit! Classical limit can be obtained from quantum mechanics much in the same way thermodynamics is obtained from statistical mechanics!”. Vittorio stared at me and repeated “Yes, thermodynamic limit.” than kept on talking with the other person. This was the start of a lot of papers I have got published on this matter and some interesting experimental work has also been done. The question is still open. The proceedings of the Conference are here.

Today there is a lot of confusion in physics about classical limit and interpretation of quantum mechanics. Indeed, there is a lot of people accepting without critics many-world interpretation without realizing that are out of the realm of physics in this case. If a theory has no criteria to undergo an experimental check is not a theory and we have to forget about this. I have seen a lot of unprepared people talking about many-worlds without elementary cognitions of physics. This is bad and this is why we are living this times today. Mathematics is not enough to be a physicist.