ICTP has awarded its 2020 Dirac Medal and Prize to three distinguished physicists – André Neveu of University of Montpellier, Pierre Ramond of University of Florida, and Miguel Virasoro of Universidad Nacional de General Sarmiento – "for their pioneering contributions to the inception and formulation of string theory which introduced new Bosonic and Fermionic symmetries into physics".
String theory is a theoretical framework in fundamental physics that describes matter as composed of one-dimensional microscopic objects, called strings. These strings can be seen as tiny filaments of energy, that vibrate following different patterns. Just like the different vibration patterns of a violin string produce different musical notes, the different vibrational states of strings produce different fundamental particles, such as electrons or neutrinos, by determining their properties, like mass or charge.
String theory is physicists’ latest proposal for a unified theory of physics, attempting to put together Einstein’s general theory of relativity, that describes gravity, and quantum mechanics, that describes the fundamental elements of matter. String theory is of great importance in addressing several questions in fundamental physics, and has been applied in various fields, such as the study of black holes, the early universe, condensed matter, and so on, and has favoured major developments in pure mathematics, thanks to its complex and rigorous formulation.
The first developments of the theory came into being in the late 1960s, when it immediately appeared as a promising candidate for a quantum theory of gravity. Its earliest version was a Bosonic string theory, that is, a formulation that described only the class of particles called bosons. Bosons are particles which have integer spin (0, 1, 2 and so on, measured in units of Planck's constant), such as photons, gravitons or the famous Higgs boson. On the other hand, fermions are particles with half-integer spin (1/2, 3/2, 5/2 and so on, measured in units of Planck's constant), such as electrons, protons and quarks.
In the late 1960s, Miguel Virasoro started working on an ambitious project in the field of theoretical physics, at first with Gabriele Veneziano and then later on his own. This work was mainly focussed on the development of the so-called “Veneziano model”, a mathematical model characterized by specific properties that later made it the first recognized string model. Inspired by the work of Veneziano, that described ‘open strings’, Virasoro developed his own model, later recognized as a ‘closed string’ model. At the time these studies were performed, a theory of strings was not yet fully or clearly developed, and these models were only years later recognized as perfectly describing the physics of strings.
Virasoro continued giving important contributions to the field by studying the mathematical properties of these models, and noticed that they featured some symmetries, characteristic of the model. He identified and formalized these symmetries, that are now known as the “Virasoro algebra”, a complex Lie algebra widely used in two-dimensional conformal field theory and in string theory. This work was of great interest also from the point of view of pure mathematicians, as it is an infinite-dimensional Lie algebra, while until then Lie algebras were normally finite-dimensional.
“This work was very important because it allowed to complete calculations that were not possible before then,” says Professor Giorgio Parisi, President of the Accademia dei Lincei and a member of the Dirac Medal Selection Committee. “Having a model but not knowing its symmetries is an aimless approach; it is like walking in the dark. This is why identifying these symmetry properties was really a turning point.”
André Neveu and Pierre Ramond, on the other hand, are responsible for the inclusion of the Fermionic degrees of freedom in the theory. Much of the work done by Virasoro was in fact dedicated to Bosonic strings, the first ones to be studied in the field of string theory. Neveu and Ramond expanded these works, extending the calculations to include the other portion of matter, made up by fermions.
“What these works have in common, is the fact that they are works of crucial importance in string theory, conducted years before scientists realized these formulations could actually describe strings,” says Parisi. “It was only years later - with the works of Leonard Susskind, Yōichirō Nambu and others - that scientists really started to talk about strings.”
The work done by Andrè Neveu in the early 1970s, together with John Schwarz, and independently by Pierre Ramond, is now known as the RNS formalism, after the initials of its three originators. This was the initial development of superstring theory, generalizing the Virasoro algebra - which is the symmetry algebra that describes boson strings - to an algebra that could also describe fermions, thanks to the property of supersymmetry. This formulation allowed to model all particles and fundamental forces in the Universe as vibrations of tiny supersymmetric strings, thus the name of “superstring” theory, accounting for both fermions and bosons.
"It is an honor and pleasure for me, as the new director of ICTP, to announce the 2020 Dirac Medal," says ICTP's Director Atish Dabholkar. "Dirac has been an inspiring figure in theoretical physics and especially so for ICTP. The three pioneers in the field of string theory selected for the medal this year by a very distinguished selection committee are in some ways the intellectual inheritors of Dirac’s way of thinking and doing physics."
About the medallists
André Neveu, born in Paris, France, is a theoretical physicist working in the fields of string theory and quantum field theory. He is considered a pioneer in string theory for having developed the first string theory that also described fermions, thus initiating the idea of supersymmetry, developed independently by several groups at the time.
Neveu studied in Paris at the École Normale Supérieure and is since 1989 at the Institute for Theoretical Physics of the University of Montpellier II (now L2C, Laboratory Charles Coulomb). Before moving to Montpellier, he was at Princeton University (1969-1971), at the Institute for Advanced Study in Princeton (1972-1977), at the Ecole Normale Supérieure in Paris (1977-1983) and at CERN (1983-1989). He was a visiting professor in the University of California, Berkeley. He has been awarded several prizes for his contributions to theoretical physics, including the Paul Langevin Prize of the Société Française de Physique in 1973 and the Gentner-Kastler Prize in 1988.
Pierre Ramond, born in Neuilly-sur-Seine, Hauts-de-Seine, France, is considered the initiator of the development of superstring theory. He completed the Bosonic string theories available in the early 1970s with Fermionic strings, generalizing the Virasoro algebra to a superconformal algebra, called the Super Virasoro algebra. He is distinguished professor of physics at University of Florida in Gainesville, Florida.
He was a postdoctoral fellow at FermiLab and then became instructor and later assistant professor at Yale University. He spent some time as an R. A. Millikan Senior Fellow in Caltech. Ramond received several awards for his contributions to theoretical physics, including the 1992 Boris Pregel award from the New York Academy of Sciences and the prestigious Dannie Heineman Prize for Mathematical Physics in 2015. He is a Fellow of the American Physical Society.
Miguel Virasoro, born in Buenos Aires, Argentina, is well-known for his research in theoretical physics and mathematical physics. He graduated at Universidad de Buenos Aires in 1962 and left Argentina after la Noche de los Bastones Largos in 1966, when students and teachers were forcibly dislodged from five academic faculties of the University of Buenos Aires by the Federal Argentine Police. He obtained a post-doctoral position at the Weizmann Institute of Science in Rehovot, Israel, and then later spent a few years in international institutions, such as University of Wisconsin, University of California, Berkeley, the Institute for Advanced Study, Princeton and the École normale supérieure in Paris, France, with two short visits back to Argentina in between. He moved to Italy in 1977, first to Turin and then in 1981 to Università di Roma "La Sapienza", where he remained for thirty years as a Professor, teaching physical-mathematical models for economy and electromagnetism. He is currently Honorary Professor at the Instituto de Ciencias, Universidad Nacional de General Sarmiento, Argentina.
Virasoro is well-known for the discovery of the Virasoro Model (which is a closed string model) and for his great contributions to the development of infinite-dimensional Lie algebras, i.e. the introduction of the Virasoro algebra, a crucial tool in string theory. Together with Giorgio Parisi and Marc Mézard, Virasoro gave great contributions to the field of statistical mechanics, and in particular to the study of spin glass states in infinite dimensions.
From 1995 to 2002 he served as Director of ICTP in Trieste.
About the ICTP Dirac Medal
First awarded in 1985, ICTP's Dirac Medal is given in honour of P.A.M. Dirac, one of the greatest physicists of the 20th century and a staunch friend of the Centre. It is awarded every year on Dirac's birthday, 8 August, to scientists who have made significant contributions to theoretical physics. Recipients of ICTP’s Dirac Medal join a list of Medallists comprising the world’s top physicists, many of whom have proceeded to win Nobel Prizes, Fields Medals or Wolf Prizes. An international committee of distinguished scientists selects the winners from a list of nominated candidates. An award ceremony, during which the three winners will present lectures on their work, will take place in 2021. For more details about the prize and a list of past winners, visit the web page.
---- Marina Menga