Two Japanese scientists and a Tokyo-born American shared the 2008 Nobel Prize for Physics for discoveries in sub-atomic particles, the prize committee said yesterday.

The Nobel committee honoured Yoichiro Nambu, a Tokyo-born American citizen, and Makoto Kobayashi and Toshihide Maskawa of Japan for separate work that dealt with so-called spontaneous broken symmetries.

Their breakthroughs came in the 1960s and 1970s.

The committee said broken symmetries concealed nature's order under an apparently jumbled surface.

Prof. Nambu, of the University of Chicago, was recognised for his discovery of the mechanism of spontaneous broken symmetry in sub-atomic physics.

The committee said his model unified the smallest building blocks of all matter and three of nature's four forces in one single theory.

He receives half of the prestigious €1 million prize, while Prof. Kobayashi of Japan's High Energy Accelerator Research Organisation and Prof. Maskawa of Kyoto University share the other half.

Their work predicted the existence of at least three families of sub-atomic quark particles in nature.

"The fact that our world does not behave perfectly symmetrically is due to deviations from symmetry at the microscopic level," the committee said.

The prize, awarded by the Nobel Committee for Physics at the Royal Swedish Academy of Sciences, was the second of this year's crop of Nobel prizes.

The prizes are handed out annually for achievements in science, peace, literature and economics.

They were first awarded in 1901 in accordance with the will of the Swedish dynamite millionaire Alfred Nobel.