NeuroQuantology | September 2011 | Vol 9 | Issue 3 | Page 402‐412 Vitiello G., Hiroomi Umezawa and quantum field theory ISSN 1303 5150 www.neuroquantology.com 402 Article Hiroomi Umezawa and Quantum Field Theory Giuseppe Vitiello Abstract A picture of some aspects of Hiroomi Umezawa’s research activity is sketched. The influences of Rudolf Haag and Werner Heisenberg on Umezawa’s research and intellectual adventure is commented upon by discussing a publication by Susumu Kamefuchi and the author’s direct experience as one of Umezawa’s Ph.D. students and collaborators. Key Words: Umezawa, thermo field dynamics, dissipative quantum model of brain, macroscopic quantum systems, physics of living matter NeuroQuantology 2011; 3: 402‐412 1 The last time I had the opportunity to write about Hiroomi Umezawa was in December 2004 when I was asked to write the foreword for a Japanese translation of a book on quantum mechanics coauthored by Umezawa and myself (Umezawa and Vitiello, 2005). The English edition published in Naples in 1985 (Umezawa and Vitiello, 1985) was translated into Japanese by Mari Jibu and Kunio Yasue. I continue to be grateful to them for the difficult, patient, and skillful work required for the translation, but especially because writing that preface to the Japanese edition of the book brought me back to the feelings and the emotions I had in the years of my PhD studies when I was learning from Umezawa how to do research in physics. I started the foreword (published in Japanese in the book, but unpublished in English) by recalling that in one of his latest papers (Umezawa, 1995) in 1994, Hiroomi Umezawa wrote that he used to joke with his friend Eduardo Caianiello by saying: “Since I was born with quantum physics I will grow with it, but you missed this luck by a couple Corresponding author: Giuseppe Vitiello Address: Giuseppe Vitiello is Science Faculty at the University of Salerno, and INFN, Gruppo Collegato Salerno. e‐mail: vitiello@sa.infn.it Received June 30, 2011. Revised June 30, 2011. Sept 3, 2011. of years.” These words, meant to be a joke, reveal, however, a truth: the life of Hiroomi Umezawa (as well as the one of Eduardo Caianiello) has been fully entangled with the development of modern physics (Vitiello, 1996, p. iii - vi). Umezawa was born in Sapporo, Hokkaido, Japan in 1924. Caianiello was born in Naples, Italy in 1921. Caianiello and Umezawa met for the first time in the middle of the 1950s and a lifelong strong friendship immediately started among them. Caianiello has been an outstanding physicist of the past century, especially known for his contributions to renormalization methods in quantum field theory and for his pioneering works in cybernetics. He introduced me to Umezawa in the spring of 1971. In Naples, under the supervision of Francesco Guerra, in the Caianiello’s group, my undergraduate thesis was on the unstable states in the Lee model. After I had finished the thesis work I was determined to continue my studies in quantum field theory. Guerra taught me how beautiful mathematics can be when it unveils some secret of nature, and from Caianiello I learned how wide the horizon can be for a curious physicist. When I was a first year student, my first teacher of physics was Ettore Pancini. He was universally known for