Superstring theory is a leading candidate for the unified theory including gravity. It predicts that our world is not really four-dimensional, but ten- or eleven-dimensional. Consequently the implications of such higher dimensional theories to gravity and cosmology in four dimensions have been actively studied in recent years. In this situation, Dr. Jiro Soda has made many outstanding achievements on higher-dimensional black holes and on brane cosmology based on higher-dimensional gravity theories. In particular, he has made substantial contribution in (1) the formulation of cosmological perturbation theory for the brane universe, (2) the derivation of effective theories of gravity on the brane by systematic use of the gradient expansion method, and (3) the perturbation theory for higher-dimensional rotating black holes. In fact, we consider that even just one of these achievements would deserve a Yukawa-Kimura prize.
In a series of joint works with Sugumi Kanno, he succeeded in deriving low energy effective theories of gravity on the brane in a systematic manner by applying the method of gradient expansion. This technique of deriving low energy effective theories is highly generic in the sense that it does not depend much on details of a model. Consequently it played a central role in studying universal properties of brane models.
Much attention has been paid to black holes in higher-dimensional spacetime both from the cosmology and particle physics communities in recent years. In this area, Dr. Soda has made pioneering contribution on the perturbation theory of rotating higher-dimensional black holes. In particular, with Keiju Murata, using the fact that the symmetry of the system is enhanced when two angular momenta of a five-dimensional rotating black hole are equal, he succeeded in deriving a master equation for the gravitational perturbations of the system for the first time. We also mention that he succeeded in interpreting the Hawking radiation from rotating black holes in terms of the gravitational anomaly.
In view of these achievements, we concluded that this year's Yukawa-Kimura prize should go to Dr. Jiro Soda.