The 2019 Yukawa-Kimura Prize:
Dr. Teruaki Suyama and Dr. Masahide Yamaguchi for their research on "Non-Gaussianity in primordial fluctuations of the universe"

With the progress of cosmological observations, inflationary cosmology is being established as a standard scenario to prepare the seed of structure formation of the universe. The accuracy of the observation of the initial fluctuation through the cosmic microwave background radiation has been improved, aiming at identifying the inflation model and elucidating the physics of the early universe. In the near future, information about three-dimensional density fluctuations is also expected to be obtained with high accuracy over a large volume.

Dr. Teruaki Suyama and Dr. Masahide Yamaguchi have found that an inequality between the three-point correlation and the four-point correlation of the initial fluctuation generated during inflation, which holds independently of the details of the inflation model. In particular, the equality is saturated for simple models where initial fluctuations are caused only by a single inflaton field. Therefore, focusing on this inequality allows us to clearly distinguish whether the initial fluctuation originates from a single field or from multiple fields. Also, if this inequality turns out to be violated, it will overturn the paradigm of the inflationary cosmology. In this sense, one can say that this inequality is a relation that serves as a test stone for the inflation paradigm. Therefore, the test of this inequality is listed as one of the main goals of ongoing projects of cosmological observations. Dr. Suyama and Dr. Yamaguchi have further extended the generality of this inequality in collaboration with Satoshi Takahashi and Shuichiro Yokoyama.

This relation named ¡ÈSuyama-Yamaguchi inequality¡É is an essential relation that should not be neglected when we talk about observational verification of inflationary cosmology. Although it turned out that the non-Gaussian three-point correlation and the four-point correlation of initial fluctuations are not so large as to be observed in the cosmic microwave background radiation, it is certain that we will obtain high- precision map of three-dimensional density fluctuation in the near future. Then, more fluctuation modes can be observed, which is expected to dramatically increase the accuracy of measurement of three and four-point correlations. In such a coming era the importance of this inequality for sure will increase further.

In addition to the research mentioned above, both Dr. Suyama and Dr. Yamaguchi have made various outstanding achievements in the field of studying the early universe, and have been leading the field so far. Therefore, their future success is fully expected. For these reasons, we judged it appropriate to send the 13th Yukawa-Kimura Prize to Dr. Suyama and Dr. Yamaguchi.


  1. T. Suyama and Masahide Yamaguchi:
    Non-Gaussianity in the modulated reheating scenario,
    Physical Review D77, 023505, 1-8 (2008).
  2. Teruaki Suyama, Tomo Takahashi, Masahide Yamaguchi, and Shuichiro Yokoyama:
    On classification of models of large local-type non-Gaussianity,
    Journal of Cosmology and Astroparticle Physics 1012, 030, 0-59 (2010).