The 2016 Yukawa-Kimura Prize:
Dr. Atsushi Taruya for his research on exploration of precision nonlinear perturbation theory for gravitational evolution of structures in the universe

The measurements of the cosmic microwave background (CMB) has been one of the main pillars of the observational cosmology. The standard cosmological model has been established and precisely tested through the CMB observations such as the WMAP and the Planck experiments. With the advent of automated telescopes and improvements in spectroscopes, the large scale structure (LSS) of the universe is gaining more importance as the test place of the modern cosmology. It is the time to open up a new frontier in physics, by clarifying the problems within the standard cosmology with the measurements of LSS.

Dr. Atsushi Taruya has, in his work with Dr. Takashi Hiramatsu, formulated an analytical method in the cosmological perturbation theory. With his method, it became possible to make precise predictions on the non-linear gravitational clustering. Furthermore, he has contributed to the improvement of the computing speed, model buildings with the observational effects, and the development of modified gravity. He has completed a theoretical template which is highly practical for the observational cosmology based on the observations of LSS. He made his template open to the public, and the code is already used in various galaxy survey projects.

In addition, Dr. Taruya has, in his work with Dr. Takahiro Nishimichi and Dr. Shun Saito, successfully derived a new analytic expression for the redshift-space distortions from the data of the galaxy redshift survey. He has applied this result for obtaining a new constraint for dark energy and modified gravity. In his work with Dr. Shun Saito and Dr. Masahiro Takada, he has obtained a constraint on the total neutrino mass by taking account of the effect of the neutrino mass for LSS. These works are quite fundamental and essential for the progress in high-precision cosmology, especially in the age where many observational projects are planned or on going.

These achievements mentioned above are appropriate for the Yukawa-Kimura prize, especially in the sense that they improve the perturbation theory of LSS based on the field-theoretic treatment. The perturbative method has been used in cosmology before LSS has been discovered, but it is his work that makes the perturbation theory practically useful and has completed a high-precision theoretical template including nonlinear systematics. The papers are published with the names of his collaborators. Most of them, however, are his students or postdoctoral researchers, and Dr. Taruya has played a central role among them.

At present, many projects of the galaxy survey are planned or on going in the world. In Japan, the SuMIRe Project, which uses the Subaru telescope, is on going. The research of Dr. Taruya provides an essential theoretical tool for extracting cosmological information from the statistical properties of LSS, and its application should widely contribute to the development of the precision cosmology in the future. Besides the subjects mentioned above, he has also made many brilliant achievements over a wide range of themes of the relativistic cosmology. He is one of the leading physicist in Japan, and his further success is greatly anticipated.