Aharon Casher 1941–2018
Aharon (Rony) Casher was born in Haifa, Israel, and graduated from the Technion where he performed his thesis work on condensed bosonic systems under Micha Revzen. He then went to Yeshiva University in New York, where he wrote a well-known paper with Joel Lebowitz on heat flow in random harmonic chains. This is also where his longstanding collaborations with Yakir Aharonov and Lenny Susskind began.
The Aharonov–Casher effect, which is dual to the Aharonov–Bohm effect, is textbook material and also led to a beautiful result on the number of zero modes in 2D magnetic fields. With Lev Vaidman, Casher and Aharonov developed the mathematics underpinning weak measurements; and in a separate work with Shimon Yankielowicz they introduced the mechanism of magnetic vacuum condensation for confinement in QCD. The early suggestion by Aharon, Susskind and John Kogut that a vacuum polarisation mechanism can account for quark confinement was extremely influential. Additional, important joint papers on strong interactions, partons and spontaneous chiral symmetry breaking appeared in the early 1970s. The collaboration with Susskind also led to Aharons’ familiarity with string theories and to the early paper with Aharonov of a dual string model for spinning particles.
In the high-energy physics community, Aharon is best known for his work on spontaneous chiral symmetry breaking in QCD. In a singly authored paper he provided a beautiful insight into this subject, followed by a famous paper with Tom Banks that related such breaking to the enhanced density of the low eigenvalues of the Dirac operator. These topics dominated Aharon’s interest throughout the 1970s and early 1980s. His deep knowledge of topological field theory and understanding of non-perturbative effects enabled him to make key and long-lasting contributions.
Aharon often visited Brussels, where he worked with François Englert and others on supergravity, quantum gravity and studies of the early universe. Englert, in turn, became a frequent visitor at Tel Aviv University, and non-perturbative effects in quantum gravity and possible connections to the physics of black holes became a shared passion of both. Although Aharon gave a series of influential lectures on string theory at Tel Aviv shortly after the 1984 “string revolution”, and published with Englert, Nicolai and Taormina a paper showing that all superstring theories are contained in the bosonic string, he was critical of strings as the ultimate theory of nature. He was an independent thinker, uncompromisingly honest when analysing novel ideas in theoretical physics.
Aharon stayed at Tel Aviv for almost 50 years, his knowledge and remarkable talents enabling him to teach any subject in theoretical physics from memory alone. He was accessible to students and attracted many who subsequently had independent academic careers, including Neuberger, Nissan Itzhaki and Yigal Shamir. Aharon was an avid reader, interested in literature, history, science fiction, sports and politics. One could have an interesting conversation with him on any topic.
Aharon was highly negligent as a self- promoter and was in science for the sheer pleasure of doing it. He rarely gave talks about his work, preferring to think and calculate at his desk, and his collaborators and many others had the deepest respect for him. His ability to keep challenging us and to relentlessly pursue the subtleties that could harbour fatal flaws helped maintain our own scientific integrity. Aharon will be deeply missed.
• Yakir Aharonov, François Englert, Herbert Neuberger and Shmuel Nussinov.
Adalberto Giazotto 1940–2017
On 17 August 2017 the Virgo and LIGO interferometers recorded the first gravitational-wave signal from the merger of two neutron stars. Their combined data, promptly indicating the direction of the source, made it possible for ground- and space-based telescopes to observe a newly born “kilonova” and for the first time follow its evolution. The data allowed spectroscopic identification of r-process nucleosynthesis, which can explain the abundance of heavy elements such as gold or uranium.
Italian physicist Adalberto Giazotto, who passed away in November, had been a convinced advocate of using gravitational-wave detectors spread around the world as a “single machine” and worked hard to have this vision become reality. Born in 1940 in Genoa, Giazotto graduated in Rome with a thesis in theoretical physics and then joined the experimental physics group at the electron synchrotron in Frascati led by Edoardo Amaldi studying π+ production with an 800 MeV electron beam.
The availability of a higher energy accelerator and the troubled times of 1968 were to prompt his move to Daresbury in the UK with a few colleagues. The NINA electron synchrotron was providing 5 GeV beams, allowing precision studies of the π+ axial form factor. Subsequently, Giazotto participated at CERN in the NA1 experiment for the photoproduction of charmed particles and lifetime measurements. With the same spectrometer, by scattering π– off electrons in a liquid hydrogen target, he worked at the NA7 experiment at CERN to measure the π– and K– space-like form factor, yielding precise values for their radiuses.
Since the early 1980s, forced to give up travel to Geneva for health reasons, Giazotto turned to general relativity, realising that new experimental techniques for the detection of gravitational waves had to be developed. Although pulsars or binary neutron stars could be quite numerous and intense sources, they would produce signals in the range of tens of Hz, where instruments are overwhelmed by microseismic noise. Twenty years of development were necessary for Giazotto and his group to develop an instrument capable of recording those low-frequency oscillations. In the meantime, after joining with Alain Brillet and collaborators, came the proposal to CNRS and INFN to build the Virgo interferometer. In 2002 the infrastructure was delivered, but another 15 years had to pass before the results were seen.
With interests in many fields, Giazotto was also a passionate collector of crystals. He always expressed his wonder at the beauty that can emerge through nature and time, as well as the work of humanity, in particular music. Guided by long-term goals, he was practically impervious to the daily mechanisms of the workings of scientific research and driven only by the search for perfection necessary to undertake “a thing of enormous difficulty”.
Adalberto gave us an extraordinary example of how scientific ideas can be carried forward, without compromise, but always respecting nature, to reach unthinkable objectives. His vision and energy will be missed.
• Francesco Fidecaro, Fulvio Ricci and Federico Ferrini.
Sandibek Nurushev 1932–2018
Prominent Russian scientist Sandibek Baitemirovich Nurushev passed away on 16 February after a long disease. Nurushev was born on 25 December 1932 and graduated in physics from Moscow Engineering Physics Institute (MEPhI) in 1955, after which he started to work at JINR in Dubna. From the first days he took an active part in the creation of the first polarised proton beam at the JINR synchrocyclotron and in the earliest studies of spin effects in the interaction of protons with atomic nuclei. Nurushev defended his PhD in 1963.
From 1964 up until the last days of his life, he worked at the Institute of High Energy Physics (IHEP) in Protvino.
Nurushev was the father of experimental spin-physics in Russia. With the use of his ideas and under his leadership, many spin experiments were carried out both in Russia and abroad. He was the spokesperson of the first Russian–French polarisation experiment, HERA, at the U-70 accelerator in Protvino in the early 1970s and also of several other spin experiments there.
He was an exceptionally bright figure in the E581 and E704 experiments in Fermilab during the 1980s and 1990s, using polarised proton and antiproton beams with energies near 200 GeV in spin studies, as well as in the spin programme at STAR and the E925 polarisation experiment at Brookhaven National Laboratory. Nurushev left more than 550 scientific papers to his colleagues and followers, many of which added to our understanding of the structure of matter. Those who worked with him, who knew and loved him, will continue his work and develop his ideas.
For many years Nurushev was engaged in teaching activities at MEPhI, and he encouraged many students to deal with polarisation effects and spin physics. He is the author of a textbook on polarisation phenomena and in 1990 was awarded the title of professor in high-energy physics. He also actively participated in the work of the international spin community.
Nurushev died peacefully at home in Protvino, leaving his wife, three children, several grandchildren and great-grandchildren. His last words to his granddaughter a few minutes before his death were: “I fulfilled my programme. I leave, I am satisfied”. Sandibek Nurushev will forever live in our memories.
• His numerous colleagues and students at IHEP and MEPhI.