# Outline of Project C03

## Gravitation and cosmology: principles and applications based on quantum information (21H05189)

General Relativity proposed by A. Einstein is the most convincing classical theory of gravity describing the dynamical fluctuations of space and time. Cosmological models based on General Relativity have successfully explained a bunch of phenomena observed in the Universe. Nevertheless, some fundamental issues remain long-standing puzzles. Of most prominence is the origin of the two phases of the accelerated expansion of the early and late universe, a.k.a. inflation and dark energy. This exposes a lack of our profound understanding of gravity and spacetime. In this project, we therefore aim to clarify the whole consistent picture of gravity and spacetime, which would make progress toward resolution of the beginning and the accelerated expansion of the Universe.

The research proposal of our group (C3) is two-fold: one is to incorporate the aspects of quantum information—which has been substantially developed during the past decade by the Ryu-Takayanagi formula in the gauge/gravity correspondence—into “braneworld.” A braneworld describes our 4-dimensional universe as a thin membrane corresponding to the boundary of higher dimensional anti-de Sitter spacetime. This model has been motivated by and consistently derived from particle physics. We try to reframe the braneworld model from the perspective of quantum information theory. It is our hope that this new braneworld perspective would be a powerful tool and provide a clue to get deeper insight into problems of universe.

Another blueprint of our research proposals is to identify the direct signature of quantum gravity by exploring a broad range of topics on gravitational physics. The recent experimental activities including the detection of gravitational wave signals and the image of supermassive black holes have reached a sensitivity where the deviation from General Relativity is testable. Stimulated by this new exciting window of opportunity in cosmology/astrophysics, we address phenomena that lead to the robust predictions of quantum aspects of gravity.

### Members in C03

**[Principal Investigator]**

Tetsuya Shiromizu Graduate School of Mathematics, Nagoya University

**[Co-Investigator]**

Keisuke Izumi Kobayashi-Maskawa Institute, Nagoya University

Tsutomu Kobayashi Department of Physics, Rikkyo University

Masato Nozawa Faculty of Engineering, Osaka Institute of Technology

Norihiro Tanahashi Faculty of Science and Engineering, Chuo University

Hirotaka Yoshino Graduate School of Science, Osaka Metropolitan University

**[ExU Postdoctoral Fellows(Research Collaborators)]
**Daisuke Yoshida Graduate School of Mathematics, Nagoya University

Norichika Sago Kyoto University / Osaka Metropolitan University

**[Research Collaborators]**

Sumio Yamada Faculty of Science, Gakushuin University

**[Graduate Students]**

Diego Soligon Graduate School of Mathematics, Nagoya University

Takamasa Kanai Graduate School of Mathematics, Nagoya University

Lee Kangjae Graduate School of Mathematics, Nagoya University

Lei Fu Graduate School of Mathematics, Nagoya University

Masaya Amo Yukawa Institute for Theoretical Physics, Kyoto University

Kensuke Sueto Graduate School of Science, Osaka Metropolitan University