We develop a multiscale approach to estimate high-dimensional probability distributions. Our approach applies to cases in which the energy function (or Hamiltonian) is not known from the start. Using data acquired from experiments or simulations we can estimate the underlying probability distribution and the associated energy function. Our method—the wavelet-conditional renormalization group (WCRG)—proceeds scale by scale, estimating models for the conditional probabilities of “fast degrees of freedom” conditioned by coarse-grained fields, which allows for fast sampling of many-body systems in various domains, from statistical physics to cosmology. Our method completely avoids the “critical slowing-down” of direct estimation and sampling algorithms. This is explained theoretically by combining results from RG and wavelet theories, and verified numerically for the Gaussian and φ4-field theories, as well as weak-gravitational-lensing fields in cosmology.

Misaki Ozawa obtained his Ph.D. in 2015 from the University of Tsukuba. He did his first postdoc at the University of Montpellier in France. He then moved to Ecole Normale Supérieure (ENS) Paris as the second postdoc. Currently, he is a CNRS permanent researcher at Grenoble Alpes Univeristy in France. His background is in the physics of disordered systems such as glasses and spin glasses. He is also working on interdisciplinary studies between statistical physics and machine learning.

iTHEMS Cosmology Forum Workshop is a series of short workshops, each focused on an emerging topics in cosmology. The targeted audience is cosmologists, high-energy physicists and astronomers interested in learning about the subject, not just those who have already worked on the topic. The goal of the workshop is to provide working knowledge of the topic and leave dedicated time for discussions to encourage mutual interactions among participants.

The second workshop is devoted to explanations of the stochastic gravitational wave background (SGWB). The SGWB is a significant detection of GW from pulsar timing arrays. The origin of this background could be either supermassive black holes or primordial. Surprisingly, both of these early Universe mechanisms are not well understood. This one-day workshop gathers both the observational and theoretical aspects of this growing topic.

The workshop will be in English. The workshop venue will be either at Main Research Building #435-437 or at Okochi Hall, and we will decide and announce which one will be actually used after the registration is closed.

The workshops are organised by the iTHEMS Cosmology Forum working group, which is the successor of the Dark Matter Working Group at RIKEN iTHEMS.

Invited Speakers:
Keitaro Takahashi (Kumamoto University)
TBA

Kazuyuki Sugimura (Hokkaido University)
Supermassive black hole formation

Ryusuke Jinno (Kobe University)
First-order phase transitions and gravitational wave production in the early Univers

Yuichiro Tada (Nagoya University)
Scalar-induced gravitational waves as a cosmological phonograph

Time table:
09:00-09:30 -- Opening remarks and coffee
09:30-10:45 -- Takahashi (keynote)
10:45-11:45 -- Sugimura
11:45-13:30 -- Lunch time
13:30-14:30 -- Jinno
14:30-15:30 -- Discussion and coffee
15:30-16:30 -- Tada
16:30-17:30 -- Panel Discussion

Organisers:
Kohei Hayashi, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Ryo Namba

We will have the 5th workshop on "Medicine and Math" in Kobe (hybrid style) on Sep. 29-30, 2024.
For more information and registration, please visit the related links.

Organizers:
Akihisa Yamamoto (RIKEN iTHEMS)
Tetsuo Hatsuda (RIKEN iTHEMS)
Motomu Tanaka (Heidelberg Univ. / Kyoto Univ.)
Hiroshi Suito (Tohoku Univ. / RIKEN iTHEMS)
Eiryo Kawakami (Chiba Univ. / RIKEN R-IH)
Takashi Sakajo (Kyoto Univ. / RIKEN iTHEMS)

The density functional theory (DFT) is one of the powerful methods to solve quantum many-body problems, which, in principle, gives the exact energy and density of the ground state. The accuracy of DFT is, in practice, determined by the accuracy of an energy density functional (EDF) since the exact EDF is still unknown. Currently, DFT has been used in many communities, including nuclear physics, quantum chemistry, and condensed matter physics, while the fundamental study of DFT, such as the first principle derivations of an accurate EDF and methods to calculate many observables from obtained densities and excited states, is still ongoing. However, there has been little opportunity to have interdisciplinary communication.

On December 2022, we had the first workshop on this series (DFT2022) at Yukawa Institute for Theoretical Physics, Kyoto University, and several interdisciplinary discussions and collaborations were started. On February 2024, we had the second workshop on this series (DFT2024) at RIKEN Kobe Campus, and more stimulated discussion occured. To keep and extend collaborations, we organize the third workshop. Since the third workshop, we extend the scope of the workshop to the development and application of DFT as well. In this workshop, the current status and issues of each discipline will be shared towards solving these problems by meeting together among researchers in mathematics, nuclear physics, quantum chemistry, and condensed matter physics.

This workshop mainly comprises lectures/seminars on cutting-edge topics and discussion, while sessions composed of contributed talks are also planned.