Professor Hitoshi Murayama
May 22, 2025
Hitoshi Murayama, professor at the University of California, Berkeley and the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), has been awarded the 2025 Particle Physics Medal by the Japan Particle and Nuclear Theory Forum.
He is being recognized for his work on the "Unified Description of the Nambu-Goldstone Theorem", developed with then-Berkeley graduate student Haruki Watanabe (now Associate Professor at the University of Tokyo). Their 2012 paper, “Unified Description of Nambu–Goldstone Bosons without Lorentz Invariance,” published in Physical Review Letters, provided a general framework for understanding Nambu-Goldstone bosons in systems lacking Lorentz invariance.
Kyoto University professor Yoshimasa Hidaka will also receive the medal for his independent 2013 paper, “Counting Rule for Nambu-Goldstone Modes in Nonrelativistic Systems,” which reached the same conclusion using a different approach.
“Explaining all natural phenomena with a unified theory is the ultimate goal of physics,” said Murayama. “This work spans systems from fridge magnets to neutron stars. Haruki’s deep knowledge of condensed matter physics combined with my background in field theory and geometry made this possible. Collaboration with mathematicians at UC Berkeley and Kavli IPMU, especially in symplectic geometry and representation theory, was also crucial. This project has been a highlight of my career, and I’m deeply honored by the award.”
Murayama’s contribution advances our understanding of symmetry and spontaneous symmetry breaking, key concepts across physics. The classic Nambu-Goldstone theorem states that in relativistic systems, every spontaneously broken continuous symmetry yields a Nambu-Goldstone boson. However, in non-relativistic systems, this relationship is more complex.
Murayama and Watanabe, and independently Hidaka, showed that symmetry generators can be classified into commutative and noncommutative pairs, based on their commutation relations. The number of Nambu-Goldstone bosons is then determined by the number of commutative generators plus the number of noncommutative pairs. The modes associated with commutative generators have linear dispersion, while those from noncommutative pairs show quadratic dispersion.
Murayama and Watanabe used the effective Lagrangian method from quantum field theory, while Hidaka employed the Mori projection operator method. Their complementary approaches produced a unified theory of Nambu-Goldstone bosons in nonrelativistic systems—a significant advance in theoretical physics.
The Nambu-Goldstone theorem, named after Nobel Laureate Yoichiro Nambu, originally applied only to systems at absolute zero and in vacuum. The work by Murayama, Watanabe, and Hidaka extended its applicability to finite temperature and density, allowing for a universal treatment across physical systems.
The Particle Physics Medal, awarded annually since 2000 by the Japan Physical Society’s Particle Theory Committee, honors major contributions to particle and nuclear theory. Past recipients include neutrino oscillation theorist Jiro Maki and quantum electrodynamics pioneer Toichiro Kinoshita.
The 2025 award ceremony will take place at the 80th Annual Meeting of the Japan Physical Society, hosted at Hiroshima University, September 16–19.