Yoichiro Nambu was born on January 18, 1921, inTokyo,Empire of Japan.[2][3] In 1923, when Tokyo was devastated by theGreat Kanto Earthquake, the Nambu family relocated toFukui Prefecture, the hometown of his father.[4] Nambu spent the rest of his childhood there and completed his high school education by age 17.
During his youth, he built acrystal radio set by himself. He later recalled being deeply moved when he was able to listen to a livebaseball broadcast through the device, an early moment of fascination with science and technology.[5]
After graduating from high school, Nambu was admitted to the prestigiousFirst Higher School (Ichikō), a preparatory institution for elite universities in Japan. Despite his later achievements intheoretical physics, he struggled with physics during this time. He especially had difficulty understanding the concept ofentropy and failed histhermodynamics course.[6]
He went on to study at theTokyo Imperial University (now the University of Tokyo), whereChushiro Hayashi—later known for his foundational work in astrophysics—was one of his classmates.[7] In his senior year, Nambu expressed interest in studyingelementary particles and approachedHideki Yukawa andShin'ichirō Tomonaga for guidance. However, he was initially turned away, being told, "Only geniuses can understand particle physics."[8]
After receiving his Bachelor of Science in 1942,[1] Nambu was drafted into theImperial Japanese Army in 1942. He served for one year as alieutenant (technical lieutenant 技術中尉), engaged in tasks such as digging trenches and ferrying boats, before being assigned to a research unit focused on shortwaveradar development.[4] During this period, he was ordered by the army to obtain a top-secret naval document written byShin'ichirō Tomonaga on radar theory. Rather than resorting to espionage, Nambu directly approached Tomonaga and obtained the material with his cooperation.[6]
Following the war, from 1945 to 1949, Nambu worked at theUniversity of Tokyo's Faculty of Physics. During this time, he was strongly influenced by Tomonaga's work on quantum electrodynamics andRyogo Kubo's studies in condensed matter physics. He earned his Doctor of Science degree in 1952.[1]
In 1954, Nambu joined theUniversity of Chicago and was promoted to full professor in 1958.[11] From 1974 to 1977, he served as Chair of the Department of Physics. He became a U.S. citizen in 1970 and remained one until his death in 2015.[12]
This concept provided the essential theoretical underpinning for what would eventually become the Higgs mechanism in the Standard Model, influencing the way physicists understand the origin of mass and phase transitions in field theory.
In 1961, Nambu, in two papers co-authored with Italian physicistGiovanni Jona-Lasinio,[15][16] proposed a theoretical model (now known as theNambu–Jona-Lasinio model), in which he attempted to explain the origin of nucleon mass through the mechanism of spontaneouschiral symmetry breaking. Later, this model was reformulated by other researchers within the framework of thequark theory of hadron structure. It turned out to be an effective computational tool for describing low-energy hadron physics, enabling, in particular, the description ofmass spectra and decays of the ground states ofmeson nonets, as well as the study of hadron behavior in hot and dense media (which is relevant, for example, in the study ofquark–gluon plasma).[17]
The NJL model was later adapted by others into the framework of quark-based hadron structure theory. It proved to be a powerful computational tool for describing low-energy hadron physics, including meson mass spectra, decay modes, and behavior in hot and dense media such as the quark–gluon plasma.
In 1964, Nambu provided a general mathematical proof of theGoldstone theorem. The masslessbosons arising in field theories with spontaneous symmetry breaking are sometimes referred to asNambu–Goldstone bosons.[15][16]
This theorem became a central feature of many quantum field theories and models of spontaneous symmetry breaking.
Although later versions of the Standard Model adopted fractional charges, Nambu's proposal of color as a quantum degree of freedom laid the conceptual groundwork for the development of quantum chromodynamics (QCD), the modern theory of strong interactions.
In the early 1970s, Nambu independently discovered that thedual resonance model, originally introduced to describe hadronic scattering amplitudes, could be reinterpreted as a theory of quantized relativistic strings. This insight provided the first theoretical framework in which extended one-dimensional objects, rather than point particles, were used to explain the behavior of fundamental interactions.[25][26] His reformulation laid the groundwork for the development ofbosonic string theory, and he is widely recognized as one of the founding figures of string theory.[27]
One of his key contributions was the introduction of the action principle for strings, now known as theNambu–Goto action, which describes the dynamics of a relativistic string as the area of the worldsheet swept out in spacetime. This formalism became a central component of modern string theory, influencing later developments insuperstring theory,M-theory, and attempts to unifyquantum mechanics with general relativity.
In 1973, Nambu proposed a generalization ofHamiltonian mechanics now known asNambu mechanics.[28] This formulation extended classical dynamics by introducing multiple Hamiltonian functions and a higher-order structure called the Nambu bracket. Unlike traditional Hamiltonian systems that use a single Hamiltonian and aPoisson bracket, Nambu mechanics allows the evolution of physical systems to be described using ternary (or higher) brackets with multiple conserved quantities.
Though initially overlooked, Nambu mechanics later gained attention in the study of non-linear systems,fluid dynamics, and higher-dimensional theoretical frameworks. It has influenced areas such asquantum Nambu brackets, generalized integrable systems, and has been discussed in the context of string theory andM-theory as a potential mathematical structure underlying extended objects like membranes.
Nambu's early work laid essential groundwork for his later breakthroughs:
In 1951, he independently proposed the concept of associative production of strange particles, explaining their appearance in high-energy collisions.
In 1957, he predicted the existence of the vectoromega meson, and derived a fundamental relation known as crossing symmetry, which became a key tool in analyzing particle interactions.[29]
In 1994, Yoichiro Nambu was appointed as a visiting professor atRitsumeikan University and an academic advisor atRitsumeikan Asia Pacific University. That same year, the two institutions established the Yoichiro Nambu Research Encouragement Fund. In 1996, he received the first honorary doctorate awarded byOsaka University (UOsaka), and in 2006, he became a specially appointed professor there. He held a research office on the UOsaka Toyonaka Campus.[30]
In 2011, Nambu returned to Japan and settled permanently inToyonaka, Osaka Prefecture. He continued his affiliation with Osaka University. TheNambu Hall was opened on the second floor of the J Building, Graduate School of Science, in 2017.[32]
Nambu also held the titles of Honorary Professor and Special Distinguished Professor atOsaka City University (nowOsaka Metropolitan University). The university later established theNambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP) on November 1, 2018.[33]
Yoichiro's father, Kichiro Nambu (南部 吉郎,Nanbu Kichirō), was originally from Fukui and attendedRitsumeikan Middle School before going on to study literature atWaseda University. His graduation thesis focused onWilliam Blake, the English poet, painter, and printmaker. The following year, in 1921, Yoichiro was born in Tokyo. However, after theGreat Kanto Earthquake struck in 1923, the family of three returned to Fukui, where Kichiro took up a position as an English teacher atFukui Girls' High School.
The name of Dr. Kozaburo Nambu (南部 考三郎,Nanbu Kōzaburō), one of the main characters in the famous Japanese animeScience Ninja Team Gatchaman, was inspired by Yoichiro Nambu.[34]
Nambu died ofheart failure at the hospital in Osaka on 5 July 2015, at the age of 94, and his death was announced 12 days later.[35][36][37][38] His funeral and memorial services were held among close relatives.[36]
Nambu was survived by his wife, Chieko, and his son, John.[36]
In 2008, although awarded theNobel Prize in Physics, Nambu did not travel toStockholm to attend the award ceremony. At his request, his former colleagueGiovanni Jona-Lasinio traveled in his place and graciously delivered the Nobel Lecture on his behalf.[39]
"He was always ten years ahead of us, so I tried to understand his work in order to contribute to a field that would flourish a decade later. But contrary to my expectation, it took me ten years just to understand what he had done."[40]
"Professor Nambu is the greatest physicist Japan has ever produced. I believe he stands even aboveHideki Yukawa andShin'ichirō Tomonaga."[41] "Japan's Nobel-winning physicists are all brilliant, and I know them well—but if I had to name a true 'genius,' it would be Yoichiro Nambu."[42]
^Nambu, Y. (1970). "Quark model and the factorization of the Veneziano amplitude." In R. Chand (ed.),Symmetries and quark models (pp. 269–277). Singapore: World Scientific.
^"名誉市民の南部陽一郎先生が逝去されました。 福井市ホームページ". Archived from the original on 23 September 2015. Retrieved30 May 2024.{{cite web}}: CS1 maint: bot: original URL status unknown (link)2015年8月11日 閲覧(in Japanese)
