Seminars in academic year 2024

"In recent years, AI-based image generation technology has been gaining attention. Behind AI that creates photorealistic images and artistic illustrations lies a technique known as the 'diffusion model.' This technique works by gradually adding noise to an image, effectively blurring it, and then reconstructing a clear image by reversing this process.

In this seminar, we will first explain the fundamental principles of diffusion models. Furthermore, as a recent research achievement, we will introduce a novel approach to formulating and analyzing diffusion models using 'path integrals,' a formalism from quantum mechanics, offering a new perspective on this technology."

The first half of the presentation will introduce the fundamentals of quantum computation with the goal of understanding how quantum teleportation circuits work. The second half will introduce recent research using quantum computation [1]. We will mainly introduce the Hayden-Preskill thought experiment on a quantum computer, which applies the principle of quantum teleportation, and discuss the future prospects of quantum computation on larger scales.

[1] Kazuhiro Seki, Yuta Kikuchi, Tomoya Hayata, Seiji Yunoki, arXiv:2405.07613 [quant-ph]

Dark matter is essential to explaining what this universe is now. Mankind has not yet succeeded in seeing dark matter itself. However, through observations of visible objects in the universe, such as galaxies, we can draw hints about their properties.

In this talk, I will focus on the physics of dark matter halos, which follow nature from the known properties of dark matter, I will introduce a method to approach the true nature of dark matter through its growth in the history of the universe.

The high penetrating power of cosmic ray muons to matter has been used to develop “cosmic ray muon imaging,” which visualizes the distribution of integrated density inside objects up to several kilometers thick. 2015 saw the launch of the ScanPyramids project, which used this technology to explore the unknown interior of Egypt's King Khufu We have been exploring the unknown interior structure of the pyramid; in 2016 we discovered a passage-like space behind the pyramid's north face, and in 2017 we discovered a huge space in the center of the pyramid. Subsequently, additional observations using cosmic ray muon imaging allowed us to estimate the detailed location and shape of the passage-like space, and in 2023, we succeeded for the first time in photographing the passage-like space using a fiberscope, preserving its 4,500 year-old state. In this talk, I will introduce the method of cosmic ray muon imaging and how the space was discovered using it, and also discuss future developments.

Of the four forces that exist in nature, the electromagnetic and weak forces are unified at temperatures above about 100 gigaelectron volts and are thought to be differentiated by the electroweak phase transition. If the electroweak phase transition were a first-order phase transition, very interesting phenomena such as the generation of gravitational waves could occur. It is known that the order of the electroweak phase transition is not first order in the Standard Model of elementary particles, but it may be first order in the Extended Model with multiple Higgs bosons. In this talk, I will discuss the electroweak phase transition in such an extended Higgs model.

Heisenberg's uncertainty principle (or uncertainty relation), which forms the basis of quantum theory, has become one of the most popular physical terms, along with Einstein's principle of relativity. The uncertainty relation is a broad term that describes incompatibility or complementary properties in the quantum world as a trade-off relation. Historically, various trade-off relations have been found and many formulations have been proposed, including the “quantum fluctuation” relation widely treated in textbooks, the “observer effect” relation known from the gamma-ray microscope thought experiment, and the “quantum measurement accuracy” relation.

In this seminar, we will give an overview of a part of the 100-year history of the development of uncertainty relations, with these three typical relations as the warp and woof. We will then introduce our universal formulation as an example of a recent proposal, and in particular, we will give an overview of how this formulation unifies the description of multiple compensatory relations that have been treated individually and separately in the past. Finally, we will review the significance of the uncertainty principle as an impossibility theorem in quantum theory through this new and broad perspective.

When the U(1) symmetry is spontaneously broken in quantum field theory, it is known that a soliton called a cosmic string appears. In particular, cosmic strings often appear in models that explain the existence of dark matter and neutrino masses, which are unsolved problems in the Standard Model, and play an important role in the early universe. 

In this talk, I will show the existence of new soliton solutions called knot solitons consisting of two types of cosmic strings in models that yield QCD axion and gauge B-L symmetry, which are often discussed as physics beyond the Standard Model. Their implications for the early universe and their testability by gravitational waves are discussed.

The magnetic field is a fundamental component of our universe, and understanding the magnetic field is essential to elucidate the history of the formation and evolution of the structure of the universe.

Radio wave observation is one of the few methods to study the cosmic magnetic field, and there are high expectations for magnetic field research with next-generation radio telescopes such as the Square Kilometer Array (SKA), which is currently under construction. In this talk, I will explain the observation of the cosmic magnetic field and introduce the latest research.

In the universe, matter and galaxies are known to have a characteristic way of distribution, which is called the cosmic large-scale structure. In this talk, I will explain how the cosmic large-scale structure can be used to explore dark matter and dark energy, which are components of the universe, or the initial state of the universe. I will also introduce recent studies of the large-scale structure of the universe using numerical simulations and observational data analysis using data science methods.

With a mass of eV (about 10^6th of an electron), dark matter has one of the longest histories of dark matter. In this talk, I will explain why the existence of dark matter is evidence of a new physical law and discuss how it can be investigated now and in the future, focusing on eV dark matter.

 Particle physics is the study of identifying the smallest constituents of matter and explaining the laws of physics in terms of their interactions. The four currently known forces are gravity, electromagnetic force, weak force, and strong force, and the discovery of the Higgs boson confirmed the particle standard theory describing the three forces other than gravity.

 The purpose of particle physics is to explain unknown physical laws, including dark matter, etc., from the interaction of the smallest constituents of matter. In this seminar, I will introduce what particle physics and dark matter are and how they are related. I will also present excerpts from my recent work on dark matter, baryon number production, and cosmic inflation, and discuss recent approaches to high-energy theory and its relevance to particle experiments and observations.

　We will discuss the Lμ-Lτ symmetry as a theoretical framework to explain phenomena that cannot be explained by the Standard Model of elementary particles. The Standard Model is a well-developed framework that explains most ground-based particle experiments. However, there are still some things that remain a mystery. These include neutrino masses, the anomalous magnetic moment of muons, the spectrum of cosmic neutrinos observed by IceCube, and the phenomenon known as the Hubble tension. As a framework to solve these problems simultaneously, I will explain the model that extends the Standard Model to have Lμ-Lτ symmetry.

Protons and neutrons, the fundamental elements of matter, are composed of quarks and gluons. The physics of quarks and gluons is described by a quantum field theory model known as Quantum Chromodynamics (QCD). The theoretical understanding of QCD still harbors many fundamental mysteries, exemplified by the problem of quark confinement: "Why can quarks not be isolated and are only observed as part of protons or neutrons?" This seminar will explore the difficulties and fascinations of the low-energy physics and vacuum structure of QCD. Additionally, it will introduce recent research on the semiclassical analysis of the QCD vacuum through T^2 compactification.