For a given system, the structure of the minimal subspace where the state unfolds determines the static and dynamical properties of the state. The Krylov subspace method is a mathematical framework for constructing the space systematically and has been applied to a wide variety of problems. The method was applicable only for systems with time-indepedent generators. As applications to quantum dynamics with time-dependent Hamiltonians, we discuss the constrution of the adiabatic gauge potential and the generalization of the Krylov algorithm to time-dependent generators.

Light hypothetical particles with masses up to O(100) MeV can be produced in the core of supernovae. Their subsequent decays to neutrinos can produce a flux component with higher energies than the standard flux. We study the impact of heavy neutral leptons, Z′ bosons, in particular U(1)Lμ−Lτ and U(1)B−L gauge bosons, and majorons coupled to neutrinos flavor-dependently. We obtain new strong limits on these particles from no events of high-energy SN 1987A neutrinos and their future sensitivities from observations of galactic supernova neutrinos.

PROGRAMME
Visit of students enrolled in the ASCENT Program at Chiba University
Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS):
RIKEN Wako Campus (Wako City, Saitama)
Event date: Monday, January 13th, 2025

ASCENT-6E Program:
iTHEMS members:

Schedule
10:30-10:40 (10 min):
Arriving procedure

10:40-11:00 (20 min) at meeting room on the 4th floor, Main Research Building
Introduction of students (to hear their names and scientific fields of interest). We will provide colour-coded badges to write their names and the colour would represent their field of interest (e.g., blue for biology, green for math, red for physics).

11:00-11:10 (10 min) Bathroom break

11:10-12:00 (50 min) at meeting room on the 4th floor, Main Research Building
First set of talks by iTHEMS members (10 min each)
Tetsuo Hatsuda (Physics, mathematics)
Catherine Beauchemin (Physics, biology)
Tsukasa Tada (Physics, mathematics)
Gen Kurosawa (Biology)
Misako Tatsuuma (Physics)

12:00-12:50 (50 min) at Common Space in the 4th floor of Main Research Building (tentative)
Discussion Lunch with students

12:50-13:40 (50 min) at meeting room on the 4th floor, Main Research Building
Second set of talks by iTHEMS members (10 min each)
Akihisa Yamamoto (Physics, biology)
Ryo Namba (Physics)
Christy Kelly (Mathematics, physics)
Rumi Hasegawa (Physics)
Jose Gutierrez (Biology)

13:40-13:50 (10 min) at meeting room on the 4th floor, Main Research Building
Brief overview of iTHEMS and RIKEN programmes (T.Hatsuda, C.Beauchemin, or T. Tada)
(e.g., JRA, IPA, SPDR, RS/SRS)

13:50-14:00 (10 min) Bathroom break

14:00-14:15 (15 min) at meeting room on the 4th floor, Main Research Building (tentative)
Short statements by Prof. Jun Nomura and ASCENT program coordinators Qian Wang and Hina Morishige

14:15-16:00 (105 min) at Common Space in the 4th floor of Main Research Building (tentative)
Informal discussions among ASCENT program students and iTHEMS members over some snacks and coffee. iTHEMS members will spread at different areas in the common space of 3rd floor and will display posters or conduct activities that can facilitate discussion. If posters are used, they may be the ones used in the Now & Next or new ones.

Anthropologists have long noted structural similarities among geographically distant societies. To investigate the origins of these patterns, I develop simple models of human interactions based on field observations, simulating the emergence of social structures. This talk focuses on two key topics. The first examines the evolution of kinship structures in clan societies [1, 2, 3]. By modeling kin and in-law cooperation alongside mating competition, I show how cultural groups with specific marriage rules spontaneously emerge. The second explores the transition of social organizations through competitive gift-giving [4, 5]. By modeling how gifts deliver material goods to recipients and confer social reputation upon donors, I demonstrate transitions across four phases—band, tribe, chiefdom, and kingdom—each characterized by distinct social networks and distributions of wealth and reputation. In both cases, I highlight the alignment between theoretical predictions and empirical observations, offering quantitative criteria and empirically measurable explanatory parameters for classifying social structures.

The KdV equation and the Toda lattice are two central and widely studied examples of classical integrable systems, and many of their variations have been introduced to the present. In particular, the box-ball system (BBS) is a basic example of a discrete integrable system, which has been revealed to be an ultra-discrete version of the KdV equation and the Toda lattice. The BBS has been studied from various viewpoints such as tropical geometry, combinatorics, and cellular-automaton. As a new perspective, research on probabilistic approaches to this system has been rapidly expanding in recent years, including the application of the Pitman transform, analysis of invariant measures and its generalized hydrodynamics. More recently, we find that the application of the Pitman transform and the study of invariant measures of i.i.d.-type also work in the same manner for the discrete KdV equation and the discrete Toda lattice. Further research has begun on the relationship between the Yang-baxter maps and the existence of i.i.d.-type invariant measures for the discrete integrable systems. In this talk, I will introduce these new research topics that have been spreading over the past several years from the basics. This talk is based on several joint works with David Croydon, Tsuyoshi Kato, Satoshi Tsujimoto, Ryosuke Uozumi, Matteo Mucciconi, Tomohiro Sasamoto, Hayate Suda and Stefano Olla.

Note for registration [2024-12:24]:
We are sorry that the number of registration has reached the capacity of the lecture room. Thank you for your understanding.

Note for participants [2024-12:18]:
For participants, please register from the above form. We may limit the number of participants due to the capacity of the lecture room.
For participants in RIKEN who have already answered a questionnaire on this lecture, you do not have to register.

Program:
Day 1 (Jan. 28th)
10:30-12:00 Lecture 1
12:00-13:30 Lunch time
13:30-15:00 Lecture 2
15:00-15:30 Coffee break
15:30-17:00 Lecture 3

Day 2 (Jan. 29th)
10:30-12:00 Lecture 4
12:00-13:30 Lunch time
13:30-15:00 Lecture 5
15:00-15:30 Coffee break
15:30-17:00 Lecture 6

Abstract:
Quantum Error Mitigation (QEM) offers a practical approach to reducing errors in noisy intermediate-scale quantum (NISQ) devices without requiring the encoding of qubits. In this seminar, I will begin by discussing the fundamentals of noise modeling in quantum systems, followed by an overview of QEM techniques, including extrapolation, probabilistic error cancellation (PEC), virtual distillation, quantum subspace expansion, and Clifford data regression. Next, I will present advanced QEM methods, such as the stochastic PEC approach, which mitigates the effects of Lindblad terms in Lindblad master equations and the generalized quantum subspace expansion, which is a unified framework of QEM. I will also explore recent research on the information-theoretic analysis of QEM, shedding light on its fundamental limits and connections to non-Markovian dynamics. Furthermore, I will discuss studies combining QEM with quantum error correction to enhance the reliability of computations in the early fault-tolerant quantum computing era. Lastly, I will highlight the relevance of hybrid tensor networks, particularly their connections to quantum subspace expansion techniques.

Research on planet formation involves various approaches, including explorations of small solar system bodies, observations of protoplanetary disks, dust experiments, simulations, and theoretical studies. One of the primary objectives in this field is to develop a comprehensive theory that explains how kilometer-sized planetesimals form from micrometer-sized dust grains, drawing upon findings from these diverse research methods.

This workshop will focus on the concept of pebbles, which play a crucial role in the planet formation process. Pebbles — typically defined as solids ranging from millimeter to centimeter in size — are intermediate building blocks in planet formation, though their definition varies depending on the context. Assuming pebbles has led to theoretical advances in mechanisms such as streaming instability and pebble accretion, which promote the formation and growth of planetesimals. Additionally, pebbles have been linked to barriers against dust growth, such as the bouncing barrier. Furthermore, observations of protoplanetary disks have revealed the size distribution and porosity of solids, while the strength and thermal conductivity of comets obtained by the Rosetta mission suggest the accumulation of pebbles due to disk instabilities. However, inconsistencies have been pointed out between pebble formation and theories of dust growth.

This workshop aims to revisit and refine our understanding of solid materials implicated in planet formation, particularly in light of findings from solar system explorations and protoplanetary disk observations. We aim to reevaluate the definition and role of pebbles in the broader context of planet formation, with a special focus on the current challenges and open questions in the field. The workshop will include discussions of experiments and simulations of dust growth and collisions, and planetesimal formation mechanisms such as streaming instability. The workshop features keynote talks from the perspectives of explorations, observations, experiments, simulations, and theories, and we also call for presentations on related topics.

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.