Highlights

The latest article by A. Naruko and M. Sasaki chosen for "IOP Select"
2011. 7. 15

The recent article by Mr. Atsushi Naruko, a fifth year graduate student and JSPS research fellow, and Prof. Misao Sasaki in Yukawa institute for Theoretical Physics with the title "Conservation of the nonlinear curvature perturbation in generic single-field inflation" has been added to "IOP Select" from IOP Publishing's research journals by Institute of Physics (IOP) publishing, which is a special collection of articles showing important breakthroughs or having significant impacts on future research. The articles will be accessible via the Select service free of charge for 365 days. (See this URL for more.)

It is believed that our universe was born about 14 billion years ago. 400 thousand years after its birth、electrons and protons decouple from photons and photons start to propagate freely. This is called the recombination of the universe and these freely propagating photons are called the Cosmic Microwave Background (CMB) radiation. In 1964, these photons were observed for the first time which have a black-body spectrum at 3K.

There are inhomogeneous structures on large scales in the universe such as galaxies or clusters of galaxies which were formed from the primordial fluctuations in the matter density through gravitational interactions. Because of these primordial fluctuations, CMB acquires fluctuations in its temperature. From observation of these temperature fluctuations, we know that the universe at the recombination was basically homogeneous and had tiny fluctuations (~0.001%)

Inflation naturally explains the origin of these tiny fluctuations of the universe. Inflation is a period of accelerated expansion in the very early universe. Because of this accelerated expansion, a homogeneous universe is realized and quantum fluctuations on microscopic scales are stretched to extremely macroscopic scales which eventually form the structure of the present universe such as galaxies and clusters of galaxies. One of the important issues in cosmology is to understand in depth the generation and evolution of these fluctuations.

Mr. Naruko and Prof. Sasaki proved a conservation law which plays an important role in predicting the amplitude of these fluctuations. The proof is a great help for us to understand the nature of fluctuations from inflation. This study may cause various applications in near future.