Volume 311

iTHEMS Weekly News Letter

Due to errors in the previous article, we are resending the corrected version. We apologize for any inconvenience caused and appreciate your understanding.

Press Release

Shingo Gibo thumbnail
Gen Kurosawa thumbnail

Data and Mathematics toward Understanding the Mysteries of Hibernation

2024-07-11

Body temperature of small mammals during hibernation drops close to the ambient temperature (< 10℃). However, it doesn't stay low throughout hibernation but fluctuates multiple times between this low temperature and their normal body temperature. These significant temperature changes are a crucial part of hibernation, but their physiological significance and control mechanisms are not well understood.

Using high-precision experimental data and mathematical model, an international collaborative research group (including Shingo Gibo and Gen Kurosawa, iTHEMS) has challenged to understand what occurs during these temperature changes. They found a model that simultaneously reproduces data of multiple hibernators.This collaboration includes Yoshifumi Yamaguchi (Hokkaido University), Isao Tokuda (Ritsumeikan University), Elena Gracheva (Yale University), Sviatoslav Bagriantsev (Yale University). Paper was published in npj Biological Timing and Sleep, a new journal from Nature Portfolio.

For more details, please refer to the related link.

Reference

  1. Shingo Gibo, Yoshifumi Yamaguchi, Elena O. Gracheva, Sviatoslav N. Bagriantsev, Isao T. Tokuda, Gen Kurosawa, Frequency-modulated timer regulates torpor–arousal cycles during hibernation in distinct small mammalian hibernators, npj Biological Timing and Sleep 1, 3 (2024), doi: 10.1038/s44323-024-00002-4

Upcoming Events

Seminar

iTHEMS Math Seminar

Topological recursion and twisted Higgs bundles

July 16 (Tue) at 10:30 - 12:00, 2024

Christopher Mahadeo (Research Assistant Professor, Department of Mathematics, The University of Illinois at Chicago (UIC), USA)

Prior works relating meromorphic Higgs bundles to topological recursion have considered non-singular models that allow the recursion to be carried out on a smooth Riemann surface. I will discuss some recent work where we define a "twisted topological recursion" on the spectral curve of a twisted Higgs bundle, and show that the g=0 components of the recursion compute the Taylor expansion of the period matrix of the spectral curve, mirroring a result of for ordinary Higgs bundles and topological recursion. I will also discuss some current work relating topological recursion to a new viewpoint of quantization of Higgs bundles.

Venue: Seminar Room #359, 3F Main Research Building, RIKEN / via Zoom

Event Official Language: English

Seminar

iTHEMS Theoretical Physics Seminar

Mapping the Phase Space of toric Calabi-Yau 3-folds using Explainable Machine Learning

July 16 (Tue) at 13:30 - 14:30, 2024

Rak-Kyeong Seong (Assistant Professor, Department of Mathematical Sciences, Ulsan National Institute of Science and Technology (UNIST), Republic of Korea)

This talk will give a brief introduction on how bipartite graphs on a torus represent 4-dimensional quiver gauge theories and their moduli space which is a toric Calabi-Yau 3-fold - a cone over a Sasaki-Einstein 5-manifold. Under mirror symmetry, the bipartite graph can be identified with the tropical projection of the mirror curve obtained from the Newton polytope associated to the toric Calabi-Yau 3-fold. Changes to the complex structure moduli of the mirror Calabi-Yau determine the overall shape of the bipartite graph on the torus. For certain choices of complex structure moduli, the bipartite graph undergoes a graph mutation which is identified with Seiberg duality of the associated 4-dimensional quiver gauge theory. This talk will discuss recent progress in understanding when such mutations occur from the point of view of Calabi-Yau mirror symmetry with the help of new computational techniques such as machine learning.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359, 3F Main Research Building, RIKEN

Event Official Language: English

Lecture

Differential Topology Seminar: Rigidity and Flexibility of Isometric Embeddings

July 16 (Tue) at 15:00 - 16:30, 2024

Dominik Inauen (Academic Staff, University of Leipzig, Germany)

The problem of embedding abstract Riemannian manifolds isometrically (i.e. preserving the lengths) into Euclidean space stems from the conceptually fundamental question of whether abstract Riemannian manifolds and submanifolds of Euclidean space are the same. As it turns out, such embeddings have a drastically different behaviour at low regularity (i.e. C1) than at high regularity (i.e. C2). For example, by the famous Nash--Kuiper theorem it is possible to find C1 isometric embeddings of the standard 2-sphere into arbitrarily small balls in R3, and yet, in the C2 category there is (up to translation and rotation) just one isometric embedding, namely the standard inclusion. Analoguous to the Onsager conjecture in fluid dynamics, one might ask if there is a sharp regularity threshold in the Holder scale which distinguishes these flexible and rigid behaviours. In my talk I will review some known results and argue why the Holder exponent 1/2 can be seen as a critical exponent in the problem.

Venue: #609, Department of Mathematics, Faculty of Science Bldg. No. 6, , Kyoto University

Event Official Language: English

Seminar

iTHEMS Theoretical Physics Seminar

Quantum Error Transmutation

July 17 (Wed) at 10:30 - 11:30, 2024

Daniel Zhang (Postdoctoral Fellow, University of Oxford, UK)

We introduce a generalisation of quantum error correction, relaxing the requirement that a code should identify and correct a set of physical errors on the Hilbert space of a quantum computer exactly, instead allowing recovery up to a pre-specified admissible set of errors on the code space. We call these quantum error transmuting codes. They are of particular interest for the simulation of noisy quantum systems, and for use in algorithms inherently robust to errors of a particular character. Necessary and sufficient algebraic conditions on the set of physical and admissible errors for error transmutation are derived, generalising the Knill-Laflamme quantum error correction conditions. We demonstrate how some existing codes, including fermionic encodings, have error transmuting properties to interesting classes of admissible errors. Additionally, we report on the existence of some new codes, including low-qubit and translation invariant examples.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359, 3F Main Research Building, RIKEN

Event Official Language: English

Seminar

ABBL-iTHEMS Joint Astro Seminar

Supernovae as Tracers of Massive-Star Evolution

July 17 (Wed) at 14:00 - 15:15, 2024

Daichi Hiramatsu (Post-Doctoral fellow, Harvard University, USA)

Supernovae are the terminal explosions of massive stars with influences on every astrophysical scale. Advanced wide-field and high-cadence transient surveys routinely discover supernovae near the moment of explosion. Coupled with prompt and continuous follow-up facilities, these observations have revealed unprecedented features of dense circumstellar medium in various spatial scales as traced by the expanding supernova ejecta. Such circumstellar medium is thought to originate from mass-loss activities in the final years to decades of stellar evolution; however, their inferred densities exceed the expectations from standard theory by many orders of magnitude. In this talk, I will first introduce standard stellar evolution and supernova explosion mechanisms, and then describe novel observational probes and modeling techniques of supernovae interacting with circumstellar medium to reconstruct their explosion properties and progenitor mass-loss histories. Finally, I will discuss our on-going largest sample study of interacting supernovae and emerging pictures of dramatic dying breaths of massive stars.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building, RIKEN

Event Official Language: English

Seminar

iTHEMS Theoretical Physics Seminar

Surface defect in N=4 SYM and integrability

July 17 (Wed) at 16:00 - 17:00, 2024

Hiroki Kawai (Ph.D. Student, University of California, Santa Barbara, USA)

In the N=4 super Yang-Mills theory, it is well-known that the one-loop anomalous dimension operator for the single trace operators is equivalent to an integrable spin chain. Recent works have extended the application of integrability to scenarios involving a BPS boundary or defects such as 't Hooft line. One can describe the correlators of the single trace operators as an overlap between the Bethe state and the corresponding defect state. This overlap can be exactly calculated if the defect state is a so-called integrable state. We show that the state corresponding to the Gukov-Witten surface defect is integrable. We also calculate the tree-level one-point function of the single trace operators and set up the perturbation calculation in this defect background for one-loop corrections.

Venue: Hybrid Format (3F #359 and Zoom), Main Research Building, RIKEN

Event Official Language: English

Seminar

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Quantum Simulation in High Energy Nuclear Physics

July 18 (Thu) at 10:00 - 11:30, 2024

Xingyu Guo (Lecturer, Institute of Quantum Matter, South China Normal University, China)

Quantum simulation is a novel method of simulation physical systems with quantum computers. Compared to conventional methods, quantum algorithms have various advantages in doing non-perturvative calculations and real-time evolutions, which makes it very promising to apply them in high energy nuclear physics. We propose a systematic quantum algorithm, which integrates both the hadronic state preparation and the evaluation of real-time light-front correlators. This algorithm can be applied to the calculation of a wide range of quantities in high energy nuclear physics. As a demonstration, we calculate the parton distribution functions, the light-cone distribution amplitudes and scattering amplitudes in the 1+1 dimensional NJL model. The results are qualitatively consistent with QCD calculations.

Venue: Seminar Room #359, 3F Main Research Building, RIKEN / via Zoom

Event Official Language: English

Seminar

iTHEMS Theoretical Physics Seminar

Thermal radiation exchange in primordial gravitational waves

July 18 (Thu) at 13:30 - 15:00, 2024

Atsuhisa Ota (Postdoctoral Fellow, Institute for Advanced Study, Hong Kong University of Science and Technology, China)

The radiation-dominated universe is a key component of standard Big Bang cosmology. Radiation comprises numerous quantum elementary particles, and its macroscopic behavior is described by taking the quantum thermal average of its constituents. The dynamics of gravitational waves are considered in this smooth fluid. While interactions between individual particles and gravitational waves are often neglected in this context, it raises the question of whether such a hydrodynamical approximation is reasonable. To address this question, we explored the quantum mechanical aspects of gravitational waves in a universe dominated by a massless scalar field, whose averaged energy-momentum tensor serves as background radiation. We computed thermal loop corrections for the gravitational wave power spectrum using the Schwinger-Keldysh formalism. Interestingly, we found that the loop effect enhances the super-horizon primordial gravitational wave spectrum, indicating that the inflationary spectrum is not conserved, contrary to conventional wisdom. These findings have significant implications for our understanding of the early universe. In this talk, I will begin with the basics of cosmology and explain the significance of these results and their relevant observational consequences.

Venue: Seminar Room #359, 3F Main Research Building, RIKEN / via Zoom

Event Official Language: English

Others

iTHEMS NOW & NEXT 2024

July 19 (Fri) at 9:30 - 18:00, 2024

9:30-10:00 Keynote by Lucy Mcneill
10:00-10:30 Keynote by Jose Said Gutierrez Ortega
10:35-11:05 Keynote by Puttarak Jai-akson
11:05-11:35 Keynote by Kannaka Kazuki

11:35-12:30 Lunch Time Session

12:30-13:30 Working Group / Study Group Report

13:30-15:30 Flash Talk & Poster Presentation Part 1

15:30-17:30 Flash Talk & Poster Presentation Part2
17:30 Concluding Remarks by the Director

18:00 reception

Venue: RIKEN Wako Campus, Head Quarter Build., 2F Large Conference Room / via Zoom

Event Official Language: English

Seminar

Quantum Matter Seminar

Probing Majorana excitations in the Kitaev magnet α-RuCl3 through bulk heat capacity measurements

July 22 (Mon) at 10:30 - 11:45, 2024

Kumpei Imamura (Ph.D. Student / JSPS Research Fellow DC, Department of Advanced Materials Science, The University of Tokyo)

Recently, the layered honeycomb material α-RuCl3 exhibits several anomalous features that are consistent with expectations of the Kitaev quantum spin liquid (KQSL) under in-plane magnetic field. Most remarkably, finite planar thermal Hall conductivity has been observed, whose magnitude is close to the half-integer quantization value expected for the chiral edge currents of Majorana fermions[1]. However, it has been reported that the thermal Hall conductivity shows strong sample dependence. Also, there are attempts to offer a different explanation by the bosonic edge excitations due to topological magnons or phonon. A key to distinguishing between fermionic and bosonic origins of unusual features in the high-field state of α-RuCl3 is the difference in the field angle dependence of the excitation gap.

Therefore, we distinguish these origins from combined low-temperature measurements of high-resolution specific heat and thermal Hall conductivity with rotating magnetic fields within the honeycomb plane. A distinct closure of the low-energy bulk gap is observed for the fields in the Ru-Ru bond direction, and the gap opens rapidly when the field is tilted. Notably, this change occurs concomitantly with the sign reversal of the Hall effect. General discussions of topological bands show that this is the hallmark of an angle rotation–induced topological transition of fermions, providing conclusive evidence for the Majorana-fermion origin of the thermal Hall effect in α-RuCl3[2].

Furthermore, to understand the nature of the high-field state, it is crucial to elucidate the effects of disorder, which inevitably exists in real materials. We artificially introduce point defects by electron irradiation and compare the low-energy excitations in the pristine and irradiated sample by high-resolution specific heat measurements. We observed an additional in-gap T-linear term in C/T, whose coefficient shows distinct field-sensitive behaviors suggestive of Majorana physics in the KSL. This can be interpreted by the weak localization of Majorana fermions, which is induced by the disorder[3]. Moreover, recently, we succeed in synthesizing very high-quality crystals of α-RuCl3[4].

References

  1. Y. Kasahara et al., Nature (London) 559, 227 (2018)
  2. K. Imamura et al., Sci. Adv. 10, eadk3539 (2024)
  3. K. Imamura et al., Phys. Rev. X 14, 011045 (2024)
  4. R. Namba, K. Imamura et al., arXiv: 2402.03986

Venue: via Zoom / Hybrid Format (3F #359 and Zoom), Seminar Room #359, 3F Main Research Building, RIKEN

Event Official Language: English

Seminar

DEEP-IN Seminar

Symmetries and Generalization for Machine Learning on a Lattice

July 23 (Tue) at 15:00 - 16:30, 2024

Andreas Ipp (Senior Scientist, Institute for Theoretical Physics, TU Wien, Austria)

Symmetries such as translations and rotations are crucial in physics and machine learning. The global symmetry of translations leads to convolutional neural networks (CNNs), while the much larger space of local gauge symmetry has driven us to develop lattice gauge equivariant convolutional neural networks (L-CNNs). This talk will discuss how the challenges of simulating the earliest stage of heavy ion collisions led us to use machine learning and how these innovations could improve lattice simulations in the future.

Andreas Ipp is a Senior Scientist at the Institute for Theoretical Physics at TU Wien. He received his PhD in 2003 and held postdoctoral positions at ECT* in Trento and the Max-Planck-Institute in Heidelberg before returning to TU Wien in 2009. He completed his habilitation on "Yoctosecond dynamics of the quark-gluon plasma" in 2014. His current research focuses on symmetries in machine learning for applications in lattice gauge theory and heavy ion collisions.

References

  1. Srinath Bulusu, Matteo Favoni, Andreas Ipp, David I. Müller, Daniel Schuh, Generalization capabilities of translationally equivariant neural networks, Phys.Rev.D 104 (2021) 7, 074504 (2021), doi: 10.1103/PhysRevD.104.074504, arXiv: 2103.14686
  2. Matteo Favoni, Andreas Ipp, David I. Müller, Daniel Schuh, Lattice Gauge Equivariant Convolutional Neural Networks, Phys.Rev.Lett. 128 (2022) 3, 3 (2022), doi: 10.1103/PhysRevLett.128.032003, arXiv: 2012.12901
  3. Kieran Holland, Andreas Ipp, David I. Müller, Urs Wenger, Machine learning a fixed point action for SU(3) gauge theory with a gauge equivariant convolutional neural network, arXiv: 2401.06481

Venue: Seminar Room #359, 3F Main Research Building, RIKEN / via Zoom

Event Official Language: English

Seminar

iTHEMS Biology Seminar

Multi-Agent Reinforcement Learning for Exploring Collective Behavior

July 25 (Thu) at 16:00 - 17:00, 2024

Kazushi Tsutsui (Assistant Professor, Graduate School of Arts and Sciences, The University of Tokyo)

Humans and other organisms develop collective behaviors through interactions with diverse environments and various species. These behaviors are significant topics across multiple research fields, including evolutionary biology, behavioral ecology, and animal sociology. Unraveling the decision-making mechanisms of individuals in groups within cooperative and competitive contexts has captured the attention of many researchers but remains a complex challenge. This seminar will present research cases that employ multi-agent reinforcement learning, a machine learning technique, to investigate the decision-making processes underlying collective behavior. Through this approach, we aim to provide deeper insights into the dynamics and mechanisms that drive group behaviors in various biological systems.

Reference

  1. Kazushi Tsutsui, Ryoya Tanaka, Kazuya Takeda, and Keisuke Fujii, Collaborative hunting in artificial agents with deep reinforcement learning, eLife 13, e85694 (2024), doi: 10.7554/eLife.85694

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359, 3F Main Research Building, RIKEN

Event Official Language: English

Seminar

iTHEMS Seminar

Stringy Nonlocality: Operator Formalism and Implications

July 26 (Fri) at 14:00 - 15:30, 2024

Wei-Hsiang Shao (Ph.D. Student, Department of Physics, National Taiwan University, Taiwan)

Nonlocality is a fundamental property of string theory, where point-like particles are replaced by extended strings. This feature is especially evident in string field theories, where field components interact through form factors containing spacetime derivatives of infinite order. The usual approach to canonical quantization is no longer applicable, and thus a non-perturbative treatment of nonlocal effects at the quantum level remains unclear. In this seminar, I will discuss a recent attempt to construct an operator formalism for stringy nonlocal field theories, and explore the potential implications for black hole radiation and primordial fluctuations in the early universe.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359, 3F Main Research Building, RIKEN

Event Official Language: English

Special Lecture

RIKEN iTHEMS & AIPmath Special Lecture: Contact geometry in 3-dimensional space and higher

July 29 (Mon) at 15:30 - 16:30, 2024

Emmy Murphy (Professor, Princeton University, USA)

In mathematics, contact geometry is a type of geometry describing a variety of dynamical systems. They are the phase spaces of systems arising in geometric optics, semi-classical quantum systems, classical dynamics, and control theory. On the mathematical side, contact geometry relates to a variety of other geometric structures, such as Kahler geometry, smooth topology, and foliation theory. It can be especially interesting to look at contact geometry in 3-dimensional space, because we can explicitly visualize the spaces. Additionally, by connecting contact geometry with our understanding of 3-D topology, mathematicians have the ability to understand the large-scale structure of these spaces like never before.
The talk will introduce the basics of contact geometry and its applications. We'll particularly focus on the 3-dimensional case, while also mentioning some of the unique properties of higher-dimensional spaces which are recently being explored.

Registration required: Register before Wednesday, July 24, 15:00.

Venue: RIKEN Tokyo Liaison Office (Nihonbashi) / via Zoom

Event Official Language: English

Seminar

iTHEMS Biology Seminar

Social behavior and social engineering in bacteria

August 1 (Thu) at 16:00 - 17:00, 2024

Ashleigh Griffin (Professor, Department of Biology, University of Oxford, UK)

This year is the 60th anniversary of WD Hamilton’s seminal paper in which he outlined his theory of inclusive fitness and showed how it could be used to understand altruism in the social insects. In this talk, I will describe efforts made to use his theory to understand social behavior in bacteria. And I’ll go on to explore the potential of using these insights to tackle problems of antibiotic resistance in infections.

Venue: Seminar Room #359, 3F Main Research Building, RIKEN / via Zoom

Event Official Language: English

Others

What will Happen to iTHEMS⊗Masason Foundation Members?

August 2 (Fri) at 13:30 - 17:30, 2024

Venue: Seminar Room #359, 3F Main Research Building, RIKEN

Event Official Language: English

Upcoming Visitors

July 16 (Tue) - 20 (Sat), 2024

Hiroki Kawai

Ph.D. Student, University of California, Santa Barbara, USA

Visiting Place: RIKEN Wako Campus

July 16 (Tue) - 31 (Wed), 2024

Samuel Crew

Postdoctoral Fellow, Imperial College London, UK

Visiting Place: RIKEN Wako Campus

Paper of the Week

Week 2, July 2024

2024-07-11

Title: Krylov fractality and complexity in generic random matrix ensembles
Author: Budhaditya Bhattacharjee, Pratik Nandy
arXiv: http://arxiv.org/abs/2407.07399v1

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