Download ANDRÉ PETERMANN by Antonino Zichichi

ANDRÉ PETERMANN
by Antonino Zichichi
I was in Rome when, for the first time, I heard of André Petermann
during a seminar by Bruno Ferretti on hot topics in Theoretical Physics.
The topic being discussed was the paper by Stueckelberg and Petermann
where the electromagnetic coupling “constant” was loosing its
fundamental property of being “constant”. The audience was literally
shocked to learn that the electric charge had to change with energy.
The origin of this conceptual revolution was the work of E.C.G.
Stueckelberg and A. Petermann [1] who discovered that all quantities
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such as the gauge couplings (i ) and the masses (mj) must “run” with q ,
the invariant quadrimomentum of a process. It took many years to realize
that this “running” allows the existence of a Grand Unification (GUT),
opens the way to Supersymmetry and finally produces the need for a non
point-like description of physics processes – the Relativistic Quantum
String Theory – which should produce the so much needed quantization
of gravity. It is probably interesting to recall the reasons why
Stueckelberg and Petermann paper attracted so much attention [1]. The
radiative corrections to any electromagnetic process were found to be
logarithmically divergent. Fortunately all divergencies could be grouped
into two classes: one had the property of a mass, while the other class had
the property of an electric charge. If these divergent integrals were
substituted with the experimentally measured mass and charge of the
electron, all theoretical predictions could be made to be “finite”. This
procedure was called “mass” and “charge” renormalization.
Stueckelberg and Petermann discovered [1] that if the mass and the
charge are made to be finite, they must run with energy. It remains the
freedom to choose one’s renormalization subtraction points. Petermann
and Stueckelberg proposed that this freedom had to obey the rules of an
Invariance Group, which they called the “Renormalization Group”. This
is the origin of what we now call the Renormalization Group Equations
which, as mentioned above, imply that all gauge coupling and masses
must run with energy. It was remarkable to find that the three gauge
couplings could converge – even if not very well – towards the same
value. This means that all gauge forces could have the same origin: GUT.
We will see that the first fellow, who realized that the convergence of the
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three gauge couplings could be “perfect” if Supersymmetry was
introduced, is Petermann.
The second occasion to know about Petermann came when I was
engaged in measuring the (g–2), anomalous magnetic moment, of the
muon. The most accurate theoretical prediction was due to André
Petermann. There was no high precision measurement of this quantity
due to technical problems which had yet to be solved. For example, the
construction of a magnet able to produce a set of high precision
polinomial magnetic fields along a path as long as possible. This is how
the biggest (6 meters long) “flat magnet” was built at CERN with the
invention of a new technology. André Petermann was working only
during night hours; since he was very interested in the experimental
difficulties, he was spending nights with me in the SC-Experimental Hall.
It was for me a great help to interact with the theorist who was the author
of the most accurate theoretical prediction for the anomalous magnetic
moment of a particle 200 times heavier than the electron.
The muon must show up a difference in such a fundamental
property, its (g–2); otherwise why is its mass 200 times greater than that
of the electron? When the experiment proved that – at the level of (½)‰
– the muon behaves as a perfect electromagnetic object, the problem in
focus was why are there so many muons around? The answer was in the
incredible value of the mass difference between the muon and its father,
the π. Another “heavy electron”, the “3rd lepton” in the Gev-mass-range,
could exist having no father strongly interacting, like a heavy π. Has any
search ever been done for this third “lepton”? The answer was no. Only
strongly interacting particles were studied. This is how the search for a
new heavy lepton, called HL, was implemented at CERN, with the socalled PAPLEP (Proton AntiProton into LEpton Pairs) project: where the
production process was the proton-antiproton annihilation. These topics
were discussed in the CERN Experimental Hall during the night shifts
which André Petermann was spending with me. The results of the
PAPLEP experiment gave the unexpected extremely strong value for the
(Time-like) Electromagnetic Form-Factor of the proton. This is how,
during another series of night discussions with André, it was decided that
the “ideal” production process for a third “lepton” was (e+e)
annihilation. There was no such a collider at CERN. The only one was
being built at Frascati by Bruno Touschek, a good friend of Bruno
Ferretti, and another physicist working preferably at night. I had the great
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privilege of knowing Bruno Touschek when I was in Rome. He also
became a strong supporter of the search for a “3rd lepton” with the new
collider “ADONE”. Unfortunately the top energy of ADONE was 3 Gev
and the only result we could get was a limit of 1 Gev for the mass of the
so much wanted “3rd lepton”.
Another argument being discussed with André has its roots in the
famous work with Stueckelberg: the running with energy of the
fundamental coupling of the three interactions: electromagnetic, weak
and strong. The crucial point here was at the EPS conference in York
(1978) and at the EPS conference in Geneva (1979). In my closing lecture
at the EPS-Geneva I stated: “Unification of all forces needs first a
Supersymmetry. This can be broken later, thus generating the sequence of
the various forces of nature as we observe them”. This statement was
based on a work with André where the renormalization group running of
the couplings, introducing a new degree of freedom due to
Supersymmetry, was studied: the convergence of the three couplings
improved a lot. This work was not published, but known to a few. The
Erice Schools «Superworld I», «Superworld II» and «Superworld III»
sparked off from this work.
This is how we arrived at 1991 when it was announced that the
search for Supersymmetry had to wait until the multiTev energy
threshold could be available. A group of 50 young physicists was
engaged at LEP with me to search for the lightest supersymmetric particle
in the L3 experiment. If these new theoretical “predictions” were true
there was no point in spending so much efforts to look for
Supersymmetry breaking at LEP energy. Reading these papers, we
realized that no one had ever considered the Evolution of Gaugino Mass
(EGM). During many nights of work we improved the 1979 unpublished
result mentioned above: the EGM effect was to bring down the energy
threshold for Supersymmetry breaking by nearly three orders of
magnitude. Thanks to this series of works I could assure my collaborators
that the “theoretical” predictions on the Energy level where SUSY
breaking could occur was perfectly compatible with LEP energy (and
now with LHC).
Finally, in the field of Scientific Culture, I would like to pay tribute
to André Petermann for having been a strong supporter for the
establishment of the Ettore Majorana Centre for Scientific Culture in
Erice. In the old days, when no one knew Ettore Majorana, André
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Petermann was one of the very few fellows who knew about the
Majorana neutrinos and about the fact that relativistic invariance does not
give any privilege to (spin ½) particles such as the privilege of having
antiparticles, all spin values being with the same privilege. In all my
projects André has been of great help, encouraging me to go on, no
matter what the opposition could present in terms of arguments which
often he found to be far from being of rigorous validity.
REFERENCES
[1]
The Normalization Group in Quantum Theory
E.C.G. Stueckelberg and A. Petermann, Helv. Phys. Acta 24, 317 (1951);
La Normalisation des Constantes dans la Théorie des Quanta
E.C.G. Stueckelberg and A. Petermann, Helv. Phys. Acta 26, 499 (1953);
Quantum Electrodynamics at Small Distances
M. Gell-Mann and F.E. Low, Phys. Rev. 95, 1300 (1954);
Introduction to the Teory of Quantized Fields
N.N. Bogoliubov and D.V. Shirkov, Interscience Publishers, New York
(1959);
For an excellent description of the subject see "Renormalization and
Symmetry: a review for Non-Specialists", S. Coleman, in "Properties of the
Fundamental Interactions", Erice 1971, A. Zichichi (ed), Editrice
Compositori, Bologna, 605 (1973);
Renormalization Group and the Deep Structure of the Proton
A. Petermann, Phys. Reports 53, 157 (1979);
Renormalization
J.C. Collins, Cambridge University Press, (1984).
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