Gubser flow is an evolution with cylindrical and boost symmetries, which can be best studied by mapping the future wedge of Minkowski space ℝ^{(3,1)} to dS_3 × ℝ in a conformal relativistic theory. Here, we sharpen the analytic results of Banerjee, Mitra, Mukhopadhyay Soloviev, EPJC (2024) and validate them via the first numerical exploration of the Gubser flow in a holographic conformal field theory. Remarkably, the leading generic behavior at large de Sitter time is free-streaming in transverse directions and the sub-leading behavior is that of a color glass condensate. We also show that Gubser flow can be smoothly glued to the vacuum outside the future Minkowski wedge generically given that the energy density vanishes faster than any power when extrapolated to early proper time or to large distances from the central axis. We find that at intermediate times the ratio of both the transverse and longitudinal pressures to the energy density converge approximately to a fixed point which is hydrodynamic only for large initial energy densities. We argue that our results suggest that the Gubser flow is better applied to collective behavior in jets rather than the full medium in the phenomenology of heavy ion collisions and can reveal new clues to the mechanism of confinement. The talk will be based on Mitra, Mondkar, Mukhopadhyay, Soloviev, arxiv:2408.04001/hep-th (accepted for publication in JHEP).

The 'Knitting Day' event is a one-day gathering that brings together students and researchers from diverse fields to explore the fascinating connections between the topology and mechanics of knitting. It aims to foster interdisciplinary discussions on how knitting techniques can be understood through mathematical, physical, and engineering lenses and their potential applications in industry.

This event is organized with the Interdisciplinary Math Study Group.

Schedule:

10:00 – 10:30: Welcome coffee

10:30 – 11:00: Samuel Poincloux

11:10 – 11:30: Kotone Tajiri

11:30 – 12:00: Discussion

12:00 – 13:00: Lunch

13:00 – 13:30: Daisuke Shimamoto

13:40 – 14:00: Taiki Goto

14:00 – 14:30: Discussion

14:30 – 15:10: Sonia Mahmoudi

15:10 – 16:00: Discussion & Coffee Break

16:00-18:00: Internal Discussion

From 18:00: Dinner

Titles:

Taiki Goto: Twist deformation in trefoil knot
Sonia Mahmoudi: A new topological model of knitting
Samuel Poincloux: Knit mechanics and frictional troubles
Daisuke Shimamoto: TBA
Kotone Tajiri: Curling morphology of knitted fabrics: structure and mechanics

The RIKEN conducts a wide variety of research. In this session, four researchers working at the Kobe Campus in the fields of mathematical science, information science, and biology will present their work. From iTHEMS, Research Scientist Kyosuke Adachi will introduce his research, which aims to uncover the mechanisms of collective motion using physics and computers.

For those interested in participating, please check the event website via the related link for instructions on how to attend.

This year's meeting on "Outreach of RIKEN iTHEMS 2024@Sendai&Zoom" will be held from FRI November 15 to SUN November 17, as a face-to-face meeting at TOKYO ELECTRON House of Creativity of Tohoku Forum for Creativity in cooperation with iTHEMS SUURI-COOL (Sendai) using ZOOM for the necessary part as well.

9:30-10:30: Toky Andriamanalina

Title: Untangling 3-periodic entanglements of filaments and nets

Abstract: Entanglements of curves and nets can used to describe various biological and chemical structures, such as coordination polymers, liquid crystals, or DNA origami crystals. We recently developed new diagrammatic descriptions of 3-periodic entanglements. These new diagrams are drawn out of a projection along one axis of a unit cell of a 3-periodic structure. By using these diagrams, we define the notion of untangling number for 3-periodic structures, which is a measure of complexity of the entanglement.
Thanks to this, it is now possible to characterise the least tangled structures that we call ground states, and in particular we show that the rod packings are the generic ground states of entanglements of curves.

10:30-11:00: coffee break

11:00 - 12:00: Stephen Hyde

Title: Tangles... and untangles

Abstract: Knots, braids, links, self-entangled nets, multiple catenated infinite nets... are examples of what we call, simply, “tangles”. They are relevant to molecular-scale (bio)materials, from duplexed ssRNA to metal-organic frameworks.

We are interested in understanding:
1.Which tangles are “simple”?
2.How tangled is a tangle!?

Our tangle toolkit is a simple one: we assemble helices into networks, allowing a broad spectrum of tangles to be built, from knots to tangled nets. Interesting “simple” tangles are entanglements of the edges of Platonic polyhedra [1] and entangled 2-periodic nets [2].
A proposed answer to point 2. above will be discussed. if there is time.
The ideas are at present largely unpublished, and being working into a book to be published, we hope, in late 2025 [3].

13:00 - 14:00: Myfanwy Evans

Title: Can solvents tie knots? Helical folds of biopolymers in liquid environments.

Abstract: Using a simulation technique based on the morphometric approach to solvation, we performed computer experiments which fold a short open flexible tube, modelling a biopolymer in aqueous environments, according to the interaction of the tube with the solvent alone. We find an array of helical geometries that self-assemble depending on the solvent conditions, including symmetric double helices where the strand folds back on itself and overhand knot motifs. Interestingly these shapes—in all their variety—are energetically favoured over the optimal helix. By differentiating the role of solvation in self–assembly our study helps illuminate the energetic background scenery in which all soluble biomolecules live.

This event is organized with the Interdisciplinary Math Study Group.

Inverse problems are widely studied in various scientific fields, including mathematics, physics, and medical imaging (such as CT and MRI reconstructions). In this talk, I will present a novel method for solving inverse problems using the diffusion model, with an application to CT reconstruction. The diffusion model, which is a core component of recent image-generative AI, such as Stable Diffusion and DALL-E3, is capable of producing high-quality images with rich diversity. The imaging process in CT (i.e., CT reconstruction) is mathematically an inverse problem. When the radiation dose is reduced to minimize a patient's exposure, image quality deteriorates due to information loss, making the CT reconstruction problem highly ill-posed. In the proposed method, the diffusion model, trained with a large dataset of high-quality images, serves as a regularization technique to address the ill-posedness. Consequently, the proposed method reconstructs high-quality images from sparse (low-dose) CT data while preserving the patient's anatomical structures. We also compare the performance of the proposed method with those of other existing methods, and find that the proposed method outperforms the existing methods in terms of quantitative indices.

14:45-15:00 Teatime discussion
15:00-16:00 Talk by Dr. Ryusuke Hamazaki (RIKEN Hakubi Team Leader, Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team)
16:15-17:15 Talk by Dr. Teruaki Enoto (Associate Professor, Department of Physics, Division of Physics and Astronomy, Graduate School of Science, Kyoto University)
17:15-18:00 Discussion

The quantisation of gravity is widely believed to result in gravitons - particles of discrete energy that form gravitational waves. But their detection has so far been considered impossible. Here we show that signatures of single gravitons can be observed in laboratory experiments. We show that stimulated and spontaneous single graviton processes can become relevant for massive quantum acoustic resonators and that stimulated absorption can be resolved through optomechanical read-out of single phonons of a multi-mode bar resonator. We analyse the feasibility of observing a signal from the inspiral, merger and post-merger phase of a compact binary inspiral. Our results show that single graviton signatures are within reach of experiments. In analogy to the discovery of the photoelectric effect for photons, such signatures can provide the first experimental evidence of the quantisation of gravity.

[1] G. Tobar, S. K. Manikandan, T. Beitel, and I. Pikovski, Nature Communications 15, 7229.
[2] G. Tobar, Igor Pikovski ,Michael E. Tobar, arXiv:2406.16898 (2024).

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.