Diego Cruces, Tomotaka Kuroda, “A consistent formulation of stochastic inflation I: Non-Markovian effects and issues beyond linear perturbations” arXiv:2605.00476 (submitted to JCAP)
Masahiro Kawasaki, Tomotaka Kuroda, “Numerical simulation of the stochastic formalism including non-Markovianity” arXiv:2602.11652 (submitted to JCAP)
Tomotaka Kuroda, Atsushi Naruko, Vincent Vennin, Masahide Yamaguchi, “Primordial black holes from a curvaton: the role of bimodal distributions”, arXiv:2504.09548, JCAP 07 (2025) 052
“A consistent formulation of stochastic inflation I: Non-Markovian effects and issues beyond linear perturbations” arXiv:2605.00476
To the best of my current understanding, stochastic inflation applied to the inflatons themself — rather than the stochastic formalism for spectator fields — still involves several ambiguities. These include the treatment of gravitational sectors with constraints and the validity of the formalism in non-perturbative regimes. As a step toward resolving these issues, we investigate the internal consistency of the formulation by focusing on non-Markovian effects. In this paper, we indicate that, in order to reproduce the “correct” quantum-theoretical results, such as those obtained from in-in computations, both IR and UV contributions must be treated consistently, at least in a perturbative sense with respect to the amplitude.
“Numerical simulation of the stochastic formalism including non-Markovianity” arXiv:2602.11652
In this work, I became seriously involved in numerical simulations for the first time in my life, which was quite challenging for me. I developed a code to study the stochastic dynamics of IR modes by solving the IR Langevin equations together with the equations of motion for all UV modes. Applying this code to MSSM setups, we were able to correctly describe the dynamics of flat directions coupled to non-flat directions in MSSM scenarios, correcting a mistake made in previous works. In addition, within a general mathematical setup, we observed several non-Markovian effects. Note, however, that higher-order correction terms should be included when going beyond the linear order in self-interactions, which are neglected here for simplicity.
“Primordial black holes from a curvaton: the role of bimodal distributions”, arXiv:2504.09548
This is my first paper. Through this work, I learned many fundamentals of early-universe cosmology. The main message of the paper is quite simple: non-adiabatic perturbations can generate large non-Gaussianity. In our case, this arises from the curvaton distribution determined by the stochastic formalism and is described non-perturbatively using the (classical) δN formalism. From a phenomenological perspective, this setup yields bimodal distributions whose peaks correspond to different curvaton reheating scenarios. This leads to interesting PBH phenomenology compared with the standard case of single-peaked distributions.
“Several examples of stochastic(-delta N) formalism”, Non-perturbative methods in inflation, Dec. 2025, Barcelona, Spain
“Non-Markovianity in stochastic inflation”, Contemporary Perspectives on Cosmology and Gravity, Nov. 2025, Paris, France
“Stochastic formalism in the perturbative regime”, Prague Spring 2025: CAS - IBS CTPU-CGA - ISCT Workshop in Cosmology, Gravitation and Particle Physics, Apr. 2025, Prague, Czech Republic
“Insights of non-Markovianity in the stochastic formalism”, Gravity2026, Apr. 2026, Daejeon, Korea
“Non-Markovianity in the stochastic formalism”, Intensive lecture course on inflation by Prof. Misao Sasaki, Feb. 2026, Chiba, Japan
“Insights of non-Markovianity in the stochastic formalism”, JGRG34, Jan. 2026, Kyoto, Japan
“Cosmological perturbations in stochastic inflation”, RIKEN-IBS Joint Workshop on Mathematical Approaches to Nature: from High-energy Physics to Biology, Dec. 2025, Daejeon, Korea
“Bimodal distributions in the stochastic delta N formalism”, CosKASI Conference 2025, Sep. 2025, Daejeon, Korea
“Bimodal distributions in the stochastic delta N formalism”, GWEU2025, Sep. 2025, Ningbo, China
“Cosmological aspect of stochastic formalism”, IBS CTPU-CGA 2025 Summer School and Workshop for High Energy Physics and Cosmology in Korea, Jul. 2025, Jeonju, Korea
“Bimodal distributions in the stochastic delta N formalism”, CosPA 2025, Jul. 2025, Daejeon, Korea
“Stochastic formalism in the presence of a curvaton”, High1 Workshop on Particle, String and Cosmology, Jan. 2025, Gangwon, Korea
“Stochastic formalism in the presence of a curvaton”, JGRG 33, Dec. 2024, Osaka, Japan
[poster] “The stochastic formalism in the presence of a curvaton”, COSMO’24, Oct. 2024, Kyoto, Japan
“カーバトンシナリオにおけるストキャスティクス形式”, 日本物理学会 第79回年次大会（2024年）, Sep. 2024, Hokkaido, Japan (talk in Japanese)
“The stochastic formalism with a curvaton”, IBS CTPU-CGA, Tokyo Tech, USTC 2024 Summer School and Workshop on Cosmology, Gravity, and Particle Physics, Sep. 2024, Chiba, Japan
“The stochastic formalism in the presence of a curvaton”, IBS CTPU-CGA 2024 Summer School and Workshop for Particle Physics and Cosmology in Korea, Jul. 2024, Muju, Korea
“The stochastic formalism in a curvaton scenario”, PASCOS 2024, Jul. 2024, Quy Nhon, Vietnam
“Stochastic-δN formalism with a curvaton”, Joint Workshop on General Relativity and Cosmology (JGRC 2024), Mar. 2024, Chiba, Japan
Institute for the Physics and Mathematics of the Universe (IPMU), Prof. Misao Sasaki and Prof. Masahiro Takada, Feb. 2026, Chiba, Japan
Institute of Cosmic Ray Research (ICRR), Prof. Masahiro Kawasaki, Feb. 2026, Chiba, Japan (talk in Japanese)
University of Portsmouth, Institute of Cosmology and Gravitation (ICG), Prof. Kazuya Koyama, Nov. 2025, Portsmouth, UK
Universidad Autónoma de Madrid, Instituto de Física Teórica (IFT), Prof. Guillermo Ballesteros, Apr. 2025, Madrid, Spain
Laboratoire de Physique de l’École normale supérieure (LPENS), Prof. Vincent Vennin, Nov. 2024, Paris, France
University of Helsinki, Cosmology Seminar of the Helsinki Institute of Physics, Prof. Syksy Räsänen, Nov. 2024, Helsinki, Finland
Chulalongkorn University, Prof. Vicharit Yingcharoenrat, Jul. 2024, Bangkok, Thailand