Koki TOKESHI

I am working on theoretical cosmology of the early universe, in particular stochastic methods in inflationary cosmology dubbed as stochastic inflation, primordial fluctuations and their non-perturbative aspects, and formation of primordial black holes.

Apr. 2021 - present: Doctor of Philosophy (PhD) in Physics, Department of Physics, Faculty of Science, the University of Tokyo, Tokyo, Japan (Supervisor: Prof. Jun'ichi Yokoyama)

Apr. 2019 - Mar. 2021: Masters of Science (MSc) in Physics, Department of Physics, Graduate School of Science, the University of Tokyo, Tokyo, Japan (Supervisor: Prof. Jun'ichi Yokoyama)

Apr. 2017 - Mar. 2019: Bachelor of Science in Physics, Department of Physics, Faculty of Science, the University of Tokyo, Tokyo, Japan

Apr. 2015 - Mar. 2017: College of Arts and Science, the University of Tokyo, Tokyo, Japan

Apr. 2023 - Jul. 2023: Département de Physique, École Normale Supérieure, Paris, France (Working with Prof. Vincent Vennin)

1. K. Tokeshi and V. Vennin, Why does inflation look single field to us? [arXiv]
2. M. Honda, R. Jinno, L. Pinol, and K. Tokeshi, Borel resummation for secular divergences in stochastic inflation, Journal of High Energy Physics 08 (2023) 038. [JHEP] [arXiv]
3. J. Usami, K. Tokeshi, T. Matsui, and H. Fukuyama, Superconducting Niobium Calorimeter for Studies of Adsorbed Helium Monolayers, Journal of Low Temperature Physics 203 (2021) 1–10. [JLTP] [arXiv]
4. K. Tokeshi, K. Inomata, and J. Yokoyama, Window function dependence of the novel mass function of primordial black holes, Journal of Cosmology and Astroparticle Physics 12 (2020) 038. [JCAP] [arXiv]

1. Constrained Langevin equation in stochastic inflation, 2023/9/16-19, JPS Annual Meeting 2023, Tohoku University, Miyagi, Japan. [Oral, Japanese]
2. Borel resummation for secular divergences in stochastic inflation, 2023/8/9-12, RESCEU Summer School 2023, Shinshu University, Nagano, Japan. [Oral, English]
3. Borel resummation in stochastic inflation, 2023/7/13-28, YITP International Molecule-type Workshop, 2023, Yukawa Institute for Theoretical Physics, Kyoto, Japan. [Oral, English]
4. Borel resummation for secular divergences in stochastic inflation, 2023/5/22-26, Planck 2023, Warsaw University, Warsaw, Poland. [Oral, English]
5. Use of Borel resummation method in stochastic inflationary model, 2023/3/22-25, JPS Spring Meeting 2023, Online. [Oral, Japanese]
6. Systematic biases of primordial black hole mass function, 2022/12/21-23, 35th Rironkon Symposium, Corasse Fukushima, Fukushima, Japan. [Poster, Japanese]
7. Correction to primordial black hole mass function from two-point correlation, 2022/9/6-8, JPS Autumn Meeting 2022, Okayama University of Science, Okayama, Japan. [Oral, Japanese]
8. Primordial black hole abundance from joint formation criteria, 2022/08/21-26, APPC15, Online. [Oral, English]
9. Two-point correlation in primordial black hole formation, 2022/8/18, RESCEU Summer School 2022, Online. [Oral, English]
10. Abundance of primordial black holes from joint formulation, 2022/3/17, JPS Annual Meeting 2022, Online. [Oral, Japanese]
11. Primordial black hole abundance from joint formation criteria}, 2021/12/6-10, The Online Workshop on General Relativity and Gravitation in Japan (Online JGRG/JGRG 30), Online. [Poster, English]
12. Systematic biases on primordial black hole mass function, 2021/8/18, RESCEU Summer School 2021, Online. [Oral, English]
13. Spherically symmetric perturbations in peak counting theory and its physical consequences, 2021/3/14, 76th JPS Annual Meeting, Online. [Oral, Japanese]
14. Primordial black holes, improved mass function, and its window function dependence, 2020/11/23, The Online Workshop on General Relativity and Gravitation in Japan (Online JGRG), Online. [Oral, English]
15. Primordial black holes and uncertainty of the mass function: window function dependence, 2020/11/11, AAPPS-DACG Workshop on Astrophysics, Cosmology and Gravitation, Online. [Oral, English]
16. A novel mass function of primordial black holes and its window function dependence due to coarse-graining density perturbations, 2020/9/15, JPS Autumn Meeting 2020, Online. [Oral, Japanese]
17. Primordial black hole mass spectrum and window function dependence, 2020/8/19, RESCEU Summer School 2020, Online. [Oral, English]
18. Spacetime Thermodynamics: to the Entropic Gravity, 2019/7/30-8/2, 49th Summer School for Young Students on Astronomy and Astrophysics, Aichi, Japan. [Poster, English, Review]

1. [to be] TBA, 7/12/2023, Tohoku University, Japan
2. [to be] Constrained random processes in stochastic inflation, 7/11/2023, Rikkyo University, Japan

• 2021/4/1-2024/3/1, JSPS DC1 Fellowship Grant No. JP21J20818 (Research Fellowship for Young Scientist; JPY 2,200,000), The University of Tokyo.

• 2023/3/13-14, Organisation of Joint Workshop on General Relativity and Cosmology (JGRC), Tokyo, Japan
• 2023/3/7, Outreaching in Seibu Junior High School, Saitama, Japan. This has been conducted as a STEM education.
• 2023/1-2023/3, Seminar Organizer at RESCEU, The University of Tokyo.
• 2022/4-2023/3, Seminar Organizer at RESCEU and UTAP, The University of Tokyo.
• 2020/9-2020/12, Teaching Assistant in Exercises for Physics (Lecturer: Kohei Kamada) associated with a class on Quantum Mechanics III, The University of Tokyo, Tokyo, Japan.
• 2019/9-2020/1, Teaching Assistant in General Relativity (Lecturer: Jun'ichi Yokoyama), The University of Tokyo, Tokyo, Japan.

Koki Tokeshi
Research Center for the Early Universe (RESCEU)
The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo, 113-0033, Japan
Email: tokeshi [at] resceu.s.u-tokyo.ac.jp