Gradient flow exact renormalization group 1

July 5 (Tue) at 13:30 - 17:00, 2022

Prof. Hiroshi Suzuki (Professor, Graduate School of Science, Kyushu University)

Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has however been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Here, we propose a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. I explain the basic idea and properties of GFERG. If time permits, I want to present a possible application of GFERG to the consideration of the axial anomaly.

Venue: via Zoom

Event Official Language: English

Gradient flow exact renormalization group 2

July 6 (Wed) at 13:30 - 17:00, 2022

Prof. Hiroshi Suzuki (Professor, Graduate School of Science, Kyushu University)

Wilson’s exact renormalization group (ERG), which tells how a system changes under the scale transformation, provides a fundamental framework to define quantum field theory even beyond the perturbation theory. It has however been known that it is difficult to preserve a manifest gauge symmetry in ERG because of the usage of the momentum cutoff in ERG. Here, we propose a possible modification of ERG, the gradient flow exact renormalization (GFERG), which preserves a manifest gauge symmetry being based on a gauge-covariant diffusion equation. I explain the basic idea and properties of GFERG. If time permits, I want to present a possible application of GFERG to the consideration of the axial anomaly.

Venue: via Zoom

Event Official Language: English

Virus vs. Bacteria: Art of the war in the microbial world

July 7 (Thu) at 16:00 - 17:00, 2022

Dr. Namiko Mitarai (Associate Professor, Niels Bohr Institute, University of Copenhagen, Denmark)

A virulent phage (virus that infects bacteria) infection to a host bacterial cell results in lysis of the cell, where possibly hundreds of phage particles are released after a latency time. The phage pressure is believed to be an important factor to shape the microbial communities and a driving force of their evolution, and yet we are far from having a full picture of their warfare. In this talk, I highlight a few factors that play significant roles in phage-bacteria interactions and their coexistence, such as the effect of herd immunity and the importance of the spatial structure in a few cells scale to the colony scale. *Her talk will be accessible to physicists, mathematicians, and also biologists.

Venue: via Zoom

Event Official Language: English

The 20th MACS Colloquium

July 8 (Fri) at 15:00 - 18:00, 2022

Dr. Akira Mori (Associate Professor, Division of Biological Sciences, Graduate School of Science, Kyoto University)
Dr. Namiko Mitarai (Associate Professor, Niels Bohr Institute, University of Copenhagen, Denmark)

15:00-16:00 Talk by Dr. Akira Mori "Defense with prey toxins: A snake that has both venomous and poisonous glands" 16:15-17:15 Talk by Dr. Namiko Mitarai "Who "sleeps" and when? Bacterial growth and dormancy" 17:15-18:00 Discussion

Venue: via Zoom

Event Official Language: Japanese

Stem cells determine complexity of hematopoiesis and immunity: A key in maintenance of homeostasis and fighting disease

July 11 (Mon) at 10:00 - 11:30, 2022

Dr. Fumihiko Ishikawa (Team Leader, Laboratory for Human Disease Models, RIKEN Center for Integrative Medical Sciences (IMS))

The hematopoietic system, is a complex organ in which all cells, including white blood cells (also known as leukocytes), red blood cells and platelets originate from the hematopoietic stem cells. White blood cells/leukocytes are critical effectors of immunity. At baseline, we have about 5000-10000/microL circulating white blood cells/leukocytes, composed of more than ten distinct subsets. Among them, the most abundant (50-60%) is the neutrophil, which are capable of preventing bacterial and fungal infection. Others include T lymphocytes which attack tumors and virus-infected cells and B lymphocytes that produce immunoglobulins. Each of the leukocyte subsets have different roles in protecting us from diseases. Defects in white blood cell number or function expose us to risks of infections and tumors. Maintenance of normal homeostasis of these white blood cells is governed by expression levels of approximately 20,000 genes in hematopoietic stem cells. In this presentation, first, I will discuss current understanding of a hierarchical system of stem cells generating many different kinds of leukocytes. Second, I will talk about leukemia, a cancer of white blood cells, in which critical genes are hit by mutations, resulting in a loss or gain of function of those genes in stem cells. Third, I would like to discuss with the iTHEMS scientists potential approaches by which we can collaborate to understand the normal and diseased human blood/immune systems.

Venue: Hybrid Format (Common Room 246-248 and Zoom)

Event Official Language: English

Adiabatic pumps in quantum spin systems

July 12 (Tue) at 16:00 - 17:15, 2022

Dr. Ken Shiozaki (Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)

The Thouless pump is a one-parameter cycle of 1-dimensional gapped quantum systems with U(1) symmetry, which is classified by integers. In this talk, I introduce a generalization of the Thouless pump to quantum spin systems in any dimension with any finite group onsite symmetry. I show a simple model with Z_2 onsite symmetry, and how it is nontrivial via boundary degrees of freedom. Using the framework of the injective matrix product state, one can construct the topological invariant in a way similar to the Berry phase. If time allows, I will briefly introduce a group cohomology model by Roy and Harper for generic space dimensions and discuss its properties.

Venue: via Zoom

Event Official Language: English

Speed limits for macroscopic transitions

July 13 (Wed) at 13:30 - 15:00, 2022

Dr. Ryusuke Hamazaki (RIKEN Hakubi Team Leader, Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team, RIKEN Cluster for Pioneering Research (CPR))

Speed of state transitions in macroscopic systems is a crucial concept for foundations of nonequilibrium statistical mechanics as well as various applications in quantum technology represented by optimal quantum control. While extensive studies have made efforts to obtain rigorous constraints on dynamical processes since Mandelstam and Tamm, speed limits that provide tight bounds for macroscopic transitions have remained elusive. Here, by employing the local conservation law of probability, the fundamental principle in physics, we develop a general framework for deriving qualitatively tighter speed limits for macroscopic systems than many conventional ones. We show for the first time that the speed of the expectation value of an observable defined on an arbitrary graph, which can describe general many-body systems, is bounded by the “gradient” of the observable, in contrast with conventional speed limits depending on the entire range of the observable. This framework enables us to derive novel quantum speed limits for macroscopic unitary dynamics. Unlike previous bounds, the speed limit decreases when the expectation value of the transition Hamiltonian increases; this intuitively describes a new trade-off relation between time and the quantum phase difference. Our bound is dependent on instantaneous quantum states and thus can achieve the equality condition, which is conceptually distinct from the Lieb-Robinson bound. We also find that, beyond expectation values of macroscopic observables, the speed of macroscopic quantum coherence can be bounded from above by our general approach. The newly obtained bounds are verified in transport phenomena in particle systems and nonequilibrium dynamics in many-body spin systems. We also demonstrate that our strategy can be applied for finding new speed limits for macroscopic transitions in stochastic systems, including quantum ones, where the bounds are expressed by the entropy production rate. Our work elucidates novel speed limits on the basis of local conservation law, providing fundamental limits to various types of nonequilibrium quantum macroscopic phenomena.

Venue: Hybrid Format (Common Room 246-248 and Zoom) (Main Venue) / via Zoom

Event Official Language: English

Superconducting-like heat current: Effective cancellation of current-dissipation trade-off by quantum coherence

July 25 (Mon) at 13:30 - 15:00, 2022

Dr. Tajima Hiroyasu (Assistant Professor, Graduate School of Informatics and Engineering, The University of Electro-Communications)

Recent developments in statistical mechanics have revealed a tradeoff between heat current and dissipation [1,2]. In various situations, this current-dissipation tradeoff represents a relationship between thermal energy flow and entropy increase, similar to Joule’s law W=RI^2. On the other hand, the coherence effect on the current-dissipation tradeoff has not been thoroughly analyzed. Here, we systematically analyze how coherence affects the current-dissipation tradeoff [3]. The results can be summarized in the following three rules:

Venue: via Zoom

Event Official Language: English

From the Black Hole Conundrum to the Structure of Quantum Gravity

July 26 (Tue) at 15:30 - 17:00, 2022

Prof. Yasunori Nomura (Director, Berkeley Center for Theoretical Physics, University of California, Berkeley, USA)

Having a complete quantum theory of gravity has long been a major goal of theoretical physics. This is because a naive merger of quantum mechanics and general relativity — though it works in certain limited regimes — suffers from major theoretical problems. A particularly acute one arises when one considers the quantum mechanics of black holes: two fundamental principles of modern physics — the conservation of probability in quantum mechanics and the equivalence principle of general relativity — seem to be incompatible with each other. I will explain how recent theoretical progress begins to address this problem and portray the emerging picture of how spacetime and gravity behave at the level of full quantum gravity.

Venue: 2F Large Meeting Room, RIBF Building, RIKEN Wako Campus / via Zoom

Event Official Language: English

iTHEMS Science Outreach Workshop 2022

July 29 (Fri) - 31 (Sun), 2022

This year’s meeting on “Outreach of RIKEN iTHEMS 2022@Kobe&Zoom” will be held from FRI July 29 to SUN July 31, as a face-to-face meeting as much as possible at iTHEMS SUURI-COOL Kobe using ZOOM for the necessary part as well. This is a meeting where members of iTHEMS and science journalists, science writers, etc meet together. iTHEMS researchers explain their research to journalists etc. and science journalists and writers talk about their experiences.

Venue: SUURI-COOL (Kobe) / via Zoom

Event Official Language: Japanese

DM3 - Deep insights and Multiple strategies for Deciphering the Mystery of Dark Matter

September 15 (Thu) - 17 (Sat), 2022

Venue: SUURI-COOL (Kobe) / via Zoom

Event Official Language: English