Luigi Radicati, one of the eminent Italian theoretical physicists of the past century, passed away on 23 August 2019 in his home in Pisa, about 50 days before his 100th birthday.
Born in Milan, Radicati received his laurea in physics from the University of Torino under the supervision of Enrico Persico in 1943, and became the assistant professor of Eligio Perucca at Torino Polytechnic in 1948. In between this, during the Second World War he was also a member of a partisan division ﬁghting against German occupation.
The years 1951–1953, which Radicati spent as a research fellow at the University of Birmingham in the group of Rudolf Peierls, had a major impact on his training. Then, in 1953 Radicati became a professor of theoretical physics, first at the University of Naples and two years later at the University of Pisa. In 1962 Radicati was ﬁnally called to the Scuola Normale Superiore (SNS) in Pisa as one of two professors in the “Classe di scienze”, the other being the great mathematician Ennio De Giorgi. Radicati remained at SNS until 1996, acting as vice-director between 1962 and 1964, and director between 1987 and 1991.
Luigi Radicati can be remembered for two main reasons: the special role that he attributed to symmetries; and the broadness of his interests in physics, as in the relations between physics and other disciplines. His most important and well known physics results stem from the early 1960s. After working with Paolo Franzini to show evidence for SU(4) symmetry in the classiﬁcation of nuclear states, introduced by Wigner in 1937, in 1964 Radicati proposed, together with Feza Gürsey, the enlargement of SU(4) to SU(6) as a useful symmetry of hadrons. Gell-Mann had introduced the SU(3) symmetry in 1962 and at the beginning of 1964 had proposed, simultaneously with George Zweig, the notion of quarks. The SU(6)-subgroup SU(3) × SU(2) puts together Gell-Mann’s SU(3) with the spin SU(2) symmetry, thus unifying in single multiplets the pseudo-scalar together with the vector mesons and the J = 1/2 together with the J = 3/2 baryons. At a deeper level, SU(6) gave momentum to view the quarks as real entities obeying peculiar statistics, preliminary to the introduction of colour.
In the latter part of the 1960s Radicati began turning his attention to astrophysics, gravity, plasma physics and statistical physics. Here it is worth mentioning the long-lasting collaboration with Emilio Picasso, which started in 1977 during a discussion in the CERN cafeteria: the use of a gravitational-wave detector consisting of a system of two radio-frequency cavities, coupled to create a two-level system with a tunable diﬀerence between their oscillation frequencies.
Radicati’s collaborations brought frequent visits of eminent physicists to Pisa, among them Freeman Dyson, Feza Gürsey, T D Lee, Louis Michel, Rudolf Peierls, David Speiser and John Wheeler. Most of all, Radicati played a prominent role in bringing from CERN to the SNS Gilberto Bernardini, who acted as SNS director from 1964 to 1977, and Emilio Picasso, who was SNS director from 1992 to 1996.
Radicati was a member of the Accademia Nazionale dei Lincei from 1966, named Chevalier de la Légion d’Honneur and Doctor Honoris Causa at the École Normale in Paris in 1994, and was awarded the honour of Cavaliere di Gran Croce of the Italian Republic in 2004. During his career, he also translated and introduced important physics books into Italy, including The Meaning of Relativity by Albert Einstein, A History of Science by William Dampier and Quantum Mechanics by Leonard Schiﬀ.
Luigi Radicati is survived by his wife and four of his sons.