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

Event Official Language: English

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

Event Official Language: English

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

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

Event Official Language: English

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 (Main Venue) / via Zoom

Event Official Language: English

Discovering Physical Laws with Artificial Intelligence

July 12 (Fri) at 10:00 - 11:30, 2024

Liu Ziming (Ph.D. Student, Department of Physics, Massachusetts Institute of Technology, USA)

Deep neural networks have been extremely successful in language and vision tasks. However, their black-box nature makes them undesirable for scientific tasks. In this talk, I will show how we can make these black-box AI models more interpretable and transparent and use them to discover physical laws, including conservation laws (AI Poincare), symmetries, phase transitions and symbolic relations (Kolmogorov-Arnold Networks). Ziming is a physicist and a machine learning researcher. Ziming received BS in physics from Peking Univeristy in 2020, and is current a fourth-year PhD student at MIT and IAIFI, advised by Max Tegmark. His research interests lie generally in the intersection of artificial intelligence (AI) and physics (science in general).

Venue: via Zoom

Event Official Language: English

Tensionless Strings in a Kalb-Ramond Background

July 10 (Wed) at 16:00 - 17:00, 2024

Ritankar Chatterjee (Ph.D. Student, Indian Institute of Technology Kanpur, India)

We investigate tensionless (or null) bosonic string theory with a constant Kalb-Ramond background turned on. In analogy with the tensile case, we find that the constant Kalb-Ramond field has a non-trivial effect on the spectrum only when the theory is compactified on an S^1 ⊗d background with d ≥ 2. We discuss the effect of this constant background field on the tensionless spectrum constructed on three known consistent null string vacua. We elucidate further on the intriguing fate of duality symmetries in these classes of string theories when the background field is turned on. Based on: https://arxiv.org/abs/2404.01385

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

Event Official Language: English

The role of demographic stochasticity in the evolution of spite and altruism

July 9 (Tue) at 16:00 - 17:00, 2024

Troy Day (Professor, Head of Department, Department of Mathematics and Statistics, Queen's University, Canada)

The evolution of spiteful and altruistic behaviour remains a fascinating and somewhat puzzling phenomenon. In recent years there has been interest in examining how stochasticity arising from a finite population size might affect the evolution of these traits. Some results suggest that such stochasticity can reverse the direction of selection and promote the evolution of traits like altruism and spitefulness that are selected against in very large (deterministic) populations. However, other results seem to call this finding into question. In this talk I will consider a simple but quite general model of spite and of altruistic behaviour and examine how demographic stochasticity affects the evolution of these traits. I will show that stochasticity can indeed affect the direction of evolution but not in the way that previous studies have suggested. The results also help to clarify the broader issue of how and why stochasticity can sometimes reverse the direction of evolution.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

The 26th MACS Colloquium

July 8 (Mon) at 14:45 - 18:00, 2024

Satoshi Taguchi (Professor, Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University)
Michitaka Notaguchi (Professor, Division of Biological Sciences, Graduate School of Science, Kyoto University)

14:45-15:00 Teatime discussion 15:00-16:00 Talk by Prof. Satoshi Taguchi (Professor, Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University) 16:15-17:15 Talk by Prof. Yoshihiro Morishita (Professor, Division of Biological Sciences, Graduate School of Science, Kyoto University) 17:15-18:00 Discussion

Venue: Science Seminar House (Map 9)

Event Official Language: Japanese

Dynamics of the very early universe: towards decoding its signature through primordial black hole abundance, dark matter, and gravitational waves.

July 5 (Fri) at 14:00 - 15:15, 2024

Riajul Haque (Postdoctoral Researcher, Department of Physics, Indian Institute of Technology, India)

I will start my talk with a brief overview of the standard reheating scenario. Then, I will discuss reheating through the evaporation of primordial black holes (PBHs) if one assumes PBHs are formed during the phase of reheating. Depending on their initial mass, abundance, and inflaton coupling with the radiation, I discuss two physically distinct possibilities of reheating the universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs, while inflaton plays the role of the dominant energy component in the entire process. In the other possibility, PBHs dominate the total energy budget of the universe during evolution, and then their subsequent evaporation leads to a radiation-dominated universe. Furthermore, I will discuss the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized. The evaporation of PBHs is also responsible for the production of DM. I will show its parameters in the background of reheating obtained from two chief systems in the early universe: the inflaton and the primordial black holes (PBHs). Then, I will move my discussion towards stable PBHs and discuss the effects of the parameters describing the epoch of reheating on the abundance of PBHs and the fraction of cold dark matter that can be composed of PBHs. If PBHs are produced due to the enhancement of the primordial scalar power spectrum on small scales, such primordial spectra also inevitably lead to strong amplification of the scalar-induced secondary gravitational waves (GWs) at higher frequencies. I will show how the recent detection of the stochastic gravitational wave background (SGWB) by the pulsar timing arrays (PTAs) has opened up the possibility of directly probing the very early universe through the scalar-induced secondary gravitational waves. Finally, I will conclude my talk by elaborating on the effect of quantum correction on the Hawking radiation for ultra-light PBHs and its observational signature through dark matter and gravitational waves.

Venue: via Zoom

Event Official Language: English

Recent progress of microscopic equation of state for hyperon-mixed nuclear matter

July 4 (Thu) at 14:00 - 15:00, 2024

Togashi Hajime (Specially Appointed Assistant Professor, Research Center for Nuclear Physics, Osaka University)

The presence of hyperons in the neutron star interior have been investigated by many researchers using both phenomenological and microscopic approaches for the equation of state (EOS) of neutron star matter with hyperons. However, hyperon fractions in nuclear matter are still far from being understood, since there are relatively large uncertainties in hyperon interactions due to the small amount of the experimental data. Furthermore, recently observed masses of massive pulsars impose severe constraints on the hyperon EOS. In this seminar, I will review the recent results of microscopic nuclear EOS including hyperons and its applications to astrophysical compact objects to discuss the possible signatures of the presence of hyperons in compact star interiors. In particular, I will discuss the effect of three-body forces including hyperons on the structure and particle composition of (proto) neutron stars.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

SLMath Summer Graduate School "h-principle"

July 1 (Mon) - 12 (Fri), 2024

Venue: TOKYO ELECTRON House of Creativity, Katahira Campus, Tohoku University

Event Official Language: English

Worldline Path Integrals for the Graviton and 1-Loop Divergences in Quantum Gravity

June 28 (Fri) at 16:00 - 17:20, 2024

Fiorenzo Bastianelli (Professor, University of Bologna, Italy)

In this talk, I will discuss perturbative quantum gravity at the 1-loop level by reviewing and systematizing old results on UV divergences and presenting new findings along with new methods for their calculation. The traditional approach to this problem employs the Schwinger-DeWitt heat kernel method. We extend this approach by incorporating worldline path integrals to compute the perturbative expansion at small proper time. In addition, we explore a more principled approach that utilizes the BRST path integral quantization of the N=4 spinning particle, which describes the graviton in first quantization. Using these methods, we calculate the one-loop divergences in quantum gravity with a cosmological constant in arbitrary dimensions. When evaluated on-shell, these calculations yield a set of gauge-invariant coefficients that characterize pure quantum gravity with a cosmological constant. These coefficients may serve as benchmarks for comparing various approaches to quantum gravity.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Challenging conventional wisdom in binary evolution

June 28 (Fri) at 14:00 - 15:15, 2024

Ryosuke Hirai (Special Postdoctoral Researcher, Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research (CPR))

The majority of massive stars, stars with more than 8 times the mass of the Sun, are known to be born in binary or higher-order multiple systems. During the course of their evolution, the stars can interact in many different ways and cause interesting astrophysical phenomena such as eruptions and explosions or create objects like X-ray binaries, gravitational wave sources, etc. Many studies have been conducted over the last few decades to tie our latest models to these observables in order to refine our understanding of massive binary evolution. However, in some cases "refining" a model is not enough and a paradigm shift is required to explain all the observables in a coherent way. In this talk, I will introduce some topics from my past work where I challenge conventional wisdom to resolve long-standing problems. The topics are as follows: 1. impact of supernova ejecta on companion star evolution, 2. wind accretion onto black holes, 3. common-envelope evolution, 4. neutron star kicks. I will also discuss how these new views impact the overall landscape of binary evolution theory.

Venue: via Zoom

Event Official Language: English

Y-chromosome turnover in Drosophila – Escaping from an evolutionary dead-end?

June 28 (Fri) at 14:00 - 16:00, 2024

Masafumi Nozawa (Associate Professor, Tokyo Metropolitan University)

The Y chromosome (Y, hereafter) is degenerated in many organisms but cannot be lost due to their important functions in sex determination and/or male fertility. This is true for Drosophila and an individual without Y become a sterile male. Therefore, the Y has been considered as indispensable in Drosophila as in the case of mammals. However, we recently discovered that Drosophila lacteicornis, endemic to Ryukyu islands, is polymorphic in terms of the presence or absence of the Y; i.e., XY and XO males coexist within species. Unlike other Drosophila species, the XO males of this species are fertile. In this seminar, I will introduce how the Y becomes dispensable in this species. To our surprise, our genome and transcriptome analyses revealed that a novel Y is likely emerging in this species rather than an old Y is being lost. In other words, a turnover of the Y is ongoing in this species. Our results indicate that the Y is not necessarily a static entity in an evolutionary dead-end but can be a dynamic entity, sometimes going back to an autosome or even disappearing. Therefore, I would like to emphasize that we should understand the evolution of sex chromosomes not by a one-way path to dead-end but by a circular process, i.e., “sex-chromosome cycle.”

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

Event Official Language: English

Inferring collective behavior from social interactions to population coding

June 27 (Thu) at 16:00 - 17:30, 2024

Chen Xiaowen (Postdoctoral Researcher, Laboratoire de Physique de l’École normale supérieure, CNRS, France)

(This is a joint iTHEMS Biology Seminar) From social animals to neuronal networks, collective behavior is ubiquitous in living systems. How are these behaviors encoded in interactions, and how do they drive biological functions? Recent insights from statistical physics applied to biological data have offer exciting new perspectives. However, previous research has mostly focused on the statics, i.e. the steady-state distributions of the collective behavior, without taking into consideration of time. In this talk, I will present two recent progresses tapping into the temporal domain. First, I will present a study of collective behavior in social mice from their co-localization patterns. To capture both static and dynamic features of the data, we developed a novel inference method termed the generalized Glauber dynamics (GGD) that can tune the dynamics while keeping the steady state distribution fixed. I will first outline the explanation power of the GGD dynamics, then explain how to infer the dynamics from data. The inferred interactions characterize sociability for different mice strains. In the second example, we studied information flow among neurons in the larval zebrafish hindbrain. By adapting the method of Granger causality to single cell calcium transient data, we were able to detect both a global information flow among neurons, as well as identifying brain regions that are key in locomotion.

Venue: via Zoom

Event Official Language: English

Obstructions to Lagrangian surgery

June 27 (Thu) at 15:00 - 17:00, 2024

Emmy Murphy (Professor, Princeton University, USA)

Given a Lagrangian immersion with a transverse double point, we can surger this point to obtain an embedded Lagrangian with more complicated topology. As a classical example, both the Clifford and Chekanov tori in C² are obtained via Lagrangian surgery on a immersed sphere called the Whitney sphere. In the talk we'll discuss a Floer-theoretic obstruction to this: that is, showing that a Lagrangian cannot be realized as a surgery. An interesting dilemma is that PH invariants of an immersed Lagrangian itself cannot detect the fact that it is immersed. Instead, we have to consider families of Floer invariants coming from all possible surgeries, and use properties specific to SFT Lagrangian cobordism maps.

Venue: Room 201 in Building No.15, RIMS, Kyoto University

Event Official Language: English

Liouville symmetry groups and pseudo-isotopies

June 25 (Tue) at 17:00 - 18:30, 2024

Emmy Murphy (Professor, Princeton University, USA)

Even though Cⁿ is the most basic symplectic manifold, when n>2 its compactly supported symplectomorphism group remains mysterious. For instance, we do not know if it is connected. To understand it better, one can define various subgroups of the symplectomorphism group, and a number of Serre fibrations between them. This leads us to the Liouville pseudo-isotopy group of a contact manifold, important for relating (for instance) compactly supported symplectomorphisms of Cⁿ, and contacomorphisms of the sphere at infinity. After explaining this background, the talk will focus on a new result: that the pseudo-isotopy group is connected, under a Liouville-vs-Weinstein hypothesis.

Venue: Room 056, Graduate School of Mathematical Sciences, The University of Tokyo (Main Venue) / via Zoom

Event Official Language: English

Magnonic spin current and shot noise in an itinerant Fermi gas

June 25 (Tue) at 13:30 - 15:00, 2024

Tingyu Zhang (Ph.D. Student, Department of Physics, Graduate School of Science, The University of Tokyo)

Spin transport phenomena at strongly-correlated interfaces play central roles in fundamental physics as well as spintronic applications. Although the spin-flip tunneling process, a key mechanism of spin transport, has been extensively studied in solid-state systems, its behavior in itinerant Fermi gases remains elusive. In this regard we study the spin tunneling in a repulsively interacting ultracold Fermi gas based on the conventional quasiparticle tunneling process. we investigate the spin current induced by quasiparticle and spin-flip tunneling processes to see their bias dependence and interaction dependence. To anatomize spin carriers, we propose the detection of the spin current noise in the system. The Fano factor, which is defined as the ratio between the spin current and its noise can serve as a probe of elementary carriers of spin transport. The change of the Fano factor microscopically evinces a crossover from the quasiparticle transport to magnon transport in itinerant fermionic systems.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Grassmann Tensor Renormalization Group for two-flavor Schwinger model with a theta term

June 24 (Mon) at 16:00 - 17:00, 2024

Hayato Kanno (Special Postdoctoral Researcher, Theory Group, RIKEN BNL Research Center, RIKEN Nishina Center for Accelerator-Based Science (RNC))

QCD has been understood through numerical calculations by the Monte Carlo method. However, this method does not work for some parameter regions because of the sign problem. For example, QCD with a theta term has a sign problem, so the nature of QCD with a finite theta parameter is unknown. The theta dependence is also important to axion physics. To reveal such systems, tensor network methods are powerful tools. Tensor network methods have been developed by condensed matter theorists. Furthermore, recently there have been some attempts to apply them to high energy physics. In particular, the tensor renormalization group (TRG) method is remarkable for its applicability to higher dimensions. The Schwinger model is known as a two-dimensional toy model of QCD. It has the chiral symmetry and theta term as the same as QCD. In this study, the free energy of the two-flavor Schwinger model is calculated in a broad range of mass and theta parameters. We use TRG to calculate it, with obvious 2pi periodicity of theta parameter. We check the consistency with analytical values in large and small mass limits.

Venue: via Zoom / Seminar Room #359

Event Official Language: English