Antonio Bianconi
From Maiorana theory of "Incomplete P' triplets" to Feshbach resonances
There is in these years a high interest on Feshbach resonances in ultracold gases and condesed matter to control the pairing interaction driving the system to a superfluid phase. It is therefore time to recognize that the paper of 1931 by Ettore Majorana published on Nuove Cimento 8, 107 (1931) is one of the first quantum theoretical approach to multielectron excitations degenerate with the continuum. After the paper by Wensel (Z. Phys. 43, 524 (1927)) discussing the non radiative recombination (L. Meitner Z Phys.11, 35, 1922;P. Auger Comptes Rendus 180, 65(1925); Ann de Phys. 6, 229, 1926) by multi-electron excitations, the paper of Majorana plays a key step to describe the probability amplitude of the autoionization levels observed by Sawyers 1926 and Lawrence 1931. This work therefore plays a key step towardthe theory of Fano for the autoinization lines of Helium involving the configuration interaction between discrete and continuum ionization channels that is at the basis of Feshbach resonances.
David Brink
Exchange forces in nuclei
Soon after the discovery of the neutron Heisenberg published a theory of the structure of nuclei based on exchange forces between nucleons. This theory had some nice features but it required a strongly repulsive core in the nuclear force to avoid nuclear collapse. In January 1933 Majorana came to Leipzig with a fellowship to spend several months in Heisenberg's Institute. On arrival he prepared a paper on a new kind of exchange force which avoided the difficulties of Heisenberg's theory. It was published at the beginning of March and was so satisfying aesthetically that the theory was accepted immediately. The lecture in Catania will analyse the origin, motivation and impact of Majorana's theory and give some information about his stay in Leipzig.
Nicola Cabibbo
Neutrino Oscillations
Roberto Casalbuoni
Ettore Majorana and the infinite component wave equations
In 1932 Majorana trying to avoid the problem of negative energy solutions of the Dirac equation realized that this was possible by using unitary representations of the Lorentz group. Since this group is not compact these representations are infinite-dimensional. Majorana formulated his equation both for spin integer and half-integer spin obtaining as a result a theory with a mass spectrum spin dependent. This paper (in italian) went practically unknown, but it is interesting to notice that the mathematical theory of the unitary representations of the Lorentz group was formulated only in 1948 by Gelfand and Yaglom. We will discuss the paper of Majorana and we will try to illustrate some of the strange properties of the infinite component wave equations based on unitary representations of the Lorentz group.
Salvatore Esposito
Ettore Majorana researcher and teacher: the last achievements
In this talk we present the results of an accurate historical and scientific research conducted upon unpublished study and research notebooks (1927-1932) and on the Moreno Paper (corresponding to the lecture notes delivered by Majorana at the University of Naples), recently retrieved. An analysis of other important documents, previously unknown, has been performed as well. Such a study, though confirming the exceptional abilities of Majorana as a physicist, puts new light on his peculiar personality, only partially emerged from the accounts of friends and colleagues.
Ettore Fiorini
Neutrinos: Dirac or Majorana
The recent impressive results on neutrino oscillations have strongly enhanced interest in neutrinoless double beta decay. This process, where the nucleus acts as a "microlaboratory", is the most powerful tool to investigate the conservation of the lepton number. It can clarify therefore if neutrino is a Majorana particle, as presently suggested by many theoretical considerations including hints on the origin of the Universe. If neutrinos are Majorana particles neutrinoless double beta decay would also allows to determine with unprecedented accuracy the absolute value of the neutrino mass. The present results of past and running double beta decay experiments will be reported and discussed. Second generation experiments on double beta decay, being designed and in some case under direct R&D study, aiming to reach the sensitivity indicated by neutrino oscillation experiments will be reviewed and compared.
Roman Jackiw
Topological Mass Generation in Four Dimensions
These days fundamental physics still needs an answer to the question: How is mass generated? In dimensions lower than the physical four, well known topological mechanisms can give rise to masses. I describe a topological mechanism that does a similar job in four dimensions.
Massimo Inguscio
Majorana spin-flip" and ultralow temperature atomic physics. The impact in modern atomic physics of the Majorana's 1932 seminal work on oriented atoms in a magnetic field (1) will be highlighted. We shall start recalling the intriguing Majorana-Brossel lineshapes observed in double resonance experiments and very recently re-interpreted by Claude Cohen-Tannoudji in terms of quantum interference. We shall then illustrate the crucial role now assumed by the "Majorana spin-flip" in the physics of the magnetic confinement of atomic gases and their cooling to nanokelvin temperatures for the achievement of Bose Einstein condensation (BEC. Nowadays, seventy-four years after its development, Majorana's treatment is again exploited to outcouple coherent matter waves and create a novel "atom laser". (1) Ettore Majorana "Atomi orientati in campo magnetico variabile" Nuovo Cimento 9, 43 (1932)
Luciano Maiani
The Majorana neutrino, 70 years later
The possibility that there may be fermions which are completely neutral, that is that coincide with their antiparticles, is a great discovery. It gave a new view on the Dirac theory, originally made for charged particles like the electron. The possibility that Neutrinos are indeed Majorana particles has given rise to many interesting investigations, both theoretical and experimental. After an illustration of Majorana's work, I shall follow the story of the Majorana Neutrino up to our times and describe briefly the most advanced experiments that try to clarify this fundamental issue.
Rosario Nunzio Mantegna Majorana’s article on “The value of statistical laws in physics and social sciences”
This article was found by Majorana’s brother among Ettore Majorana’s files and was published in 1942 after Majorana’s disappearance in the international Italian journal Scientia. The article is a rather special article in several respects. It was intended to present the point of view of a physicist about the value of statistical laws in physics and social sciences to scholars of a broad spectrum of different disciplines. It also considers philosophical aspects related to the nature and value of deterministic and statistical laws in science. In his article, Majorana considers quantum mechanics as an irreducible statistical theory because the theory is not able to describe the time evolution of a single particle or atom in a controlled environment at a deterministic level. In his article, he concludes that quantum mechanics suggests that there is an “essential analogy between physics and the social sciences, between which an identity of value and method has turned out”. By analyzing the messages of this paper we conclude that Majorana deserves a great tribute not only for his exceptional achievements in theoretical physics but also for his fresh and original views on the importance and role of statistical laws in physics and in other disciplines such as the social sciences.
Emilio Migneco High energy neutrino astronomy Roberto Petronzio Neutrinos by INFN Bruno Preziosi Majorana in Naples The relevance of his lectio magistralis, the hystory of the notes he left to his pupil Gilda Senatore and his relations with the city of Naples will be briefly discussed
Renato Pucci
Majorana: From atomic and molecular to nuclear physics
In the centennial of Ettore Majorana's birth (1906-1938?), we re-examine some aspects of his fundamental scientific production in atomic and molecular physics, including a not well known short communication. There, Majorana critically discusses Fermi's solution of the celebrated Thomas-Fermi equation for electron screening in atoms and positive ions. We argue that some of Majorana's seminal contributions in molecular physics already prelude to the idea of exchange interactions (or Heisenberg-Majorana forces) in his later workson theoretical nuclear physics. In all his papers, he tended to emphasize the symmetries at the basis of a physical problem, as well as the limitations, rather than the advantages, of the approximations of the method employed.
Erasmo Recami
Ettore Majorana:his human and scientific personality
Ettore Majorana, probably the most brilliant Italian theoretical physicist of the last century (as well-knowm, Enrico Fermi compared him to Galileo and Newton), disapeared misteriously from Naples in 1938, when he was 31 yeras old: and this year, 2006, we celebrate the centennial of his birth. We shall present his human and scientific personality (on the basis of documents, letters, depositions collected by us during almost thirty years), with sketchy mention of the significance of some parts of his publications.
Antonino Zichichi
Ettore Majorana: genius and mistery
The geniality of Ettore Majorana is discussed in the framework of the crucial problems being investigated at the time of his activity. These problems are projected to our present days, where the number of space-time dimensions is no longer four and where the unification of the fundamental forces needs the Majorana particle: neutral, with spin ½ and identical to its antiparticle. The mystery of the way Majorana disappeared is restricted to few testimonies, while his geniality is open to all eminent physicists of the XXth century, who had the privilege of knowing him, directly or indirectly.