Japan's Makoto Kobayashi and Toshihide Maskawa, and Yoichiro Nambu of the United States have won the Nobel Physics Prize for pioneering work on fundamental particles of matter called quarks.
Nambu won half the prize for developing a "standard model of elementary particle physics (which) unifies the smallest building blocks of all matter and three of nature's four forces in one single theory", the Nobel jury said.
The Japanese duo were honoured for their discovery "of the origin of the broken symmetry which predicts the existence of at least three families of quarks in nature".
"Spontaneous broken symmetry conceals nature's order under an apparently jumbled surface," the Royal Swedish Academy of Sciences said in its citation. "Nambu's theories permeate the standard model of elementary particle physics. The model unifies the smallest building blocks of all matter and three of nature's four forces in one single theory."
Kobayashi and Maskawa "explained broken symmetry within the framework of the standard model but required that the model be extended to three families of quarks".
The trio will share the 10 million kronor ($A1.97 million) purse, a diploma and an invitation to the prize ceremonies in Stockholm on December 10.