Through research on elementary particle phenomena over a wide energy range from 1 GeV to 1019 GeV, we are developing new particle theory models which go beyond the present Standard Model. We also investigate the dynamics of field theories as a framework describing properties of elementary particles. Current topics include dynamical symmetry breaking models (composite Higgs models), supersymmetric/extra-dimensional theories and related elementary particle phenomena, grand unified theory, superstring theory, ultra-high precision calculation of QED, and lattice gauge theory. In addition, we are studying mathematical aspects of field theories.
Quark-Hadron Theory Group [H Lab]
Masayasu HARADA (Professor)
We aim to theoretically understand diverse phenomena of quarks/gluons and their many-body systems, or hadrons, in the fundamental theory of strong interaction, QCD. Research subjects include hadron properties and phase transition phenomena in QCD at high temperatures and high densities, phenomenology of heavy-ion collision experiments, and hadron structure. With an eye to experiments as well as theoretical aspects, we are developing new theories in an effective theory framework, phenomenological models, and fundamental aspects of QCD using lattice QCD, as well as novel analytical approaches based on these theories.
In our laboratory, we are investigating gravitational physics including higher dimensional theories like superstring. We try to solve the problems of the inflation epoch in the early universe, and accelerating expansion of the present universe, and the phenomena under the strong gravity as in the black hole. We aim to find any constraint and/or any clue for the understanding of the nature of the gravity theory from the cosmological observations etc. We are mainly working in the following themes of recent researches.
Dark energy: Now it is believed that there should be something unknown, whose density should be about 70% of the critical density, in the present universe. We call this substance as "dark energy". The dark energy is generating the accelerating expansion of the universe. We are now investigating, various models of the dark energy and we aim to obtain any clue of the theory coming from higher dimensions, like superstring theory, and we are considering how we could verify this kind of theory by the experiments and/or observations.
Space-time and quantum theory: Various phenomena in physics occurs in the container called "space-time", whose shape is deformed by the gravity. It is believed that the quantum theory of the gravity could be obtained by summing up the shapes of the space-time. By using the formulation where the summation is obtained by discretizing the space-time into a set of simplices as in Figure, we try to clarify the nature of the gravity as a quantum theory.
Other topics: We are also studying the primordial fluctuations via quantum effects by considering the quantum entanglement. Black hole physics, like the Hawking radiation by using the fluid, the high energy phenomena, which could be generated by an extremely large black hole in the nucleus of active galaxies, etc., are also investigated.
Plasmas in laboratories and space involve a variety of nonlinear phenomena in the non-equilibrium states. Turbulence and shocks are the typical examples. We are theoretically studying the nonlinear plasma physics by utilizing numerical methods and high performance computing. Current research topics cover kinetic plasma turbulence and transport, shock formation and particle acceleration in space, self-excitation of auroras etc. We are also developing numerical methods for fluid and kinetic plasma simulations as well as nonlinear plasma theories.
We are theoretically studying the origin and evolution of structures in the universe. We are mostly working on the field of Observational Cosmology. With recent breakthroughs in space observation techniques, unexpected features of the universe have been successively revealed. This situation highlights the role of theoretical research toward understanding phenomena in the universe. In our laboratory, we strive to theoretically understand the hierarchy of the universe from celestial bodies such as stars and galaxies to the universe itself, through physics and multifaceted approaches, including analytic theory, numerical simulation, and theoretical analysis of observational data.
Laboratory of Theoretical Astronomy & Astrophysics [TA Lab]
We investigate the origins of astrophysical objects in the universe. Although our current focus is mainly on the formation of stars and planets, we are also investigating various astrophysical processes such as cosmic ray acceleration, gas accretion and energy dissipation around compact objects, etc. using analytical and numerical methods for Newtonian or relativistic (magneto-)hydrodynamics and kinematics.
Laboratory of Galaxy Evolution [Ω Lab]
Tsutomu T. TAKEUCHI (Associate Professor)
A galaxy is a large agglomeration of stars, gas, and dark matter, and is a fundamental unit on the cosmological scale. Galaxies appear to be very different in various wavelengths or energy regions, hence multiwavelength observations are fundamentally important. In the context of cosmic evolution over the last 13.7 billion years, we are examining the formation and evolution of galaxies, with an emphasis of their star formation activities. As a multi-wavelength approach, we study galaxy evolution from two standpoints: data analysis from ground-based instruments, space telescopes, and astronomical satellites, and modeling of the emission from galaxies which reproduce observations.
We have also just started to explore the physics of the very early Universe with radio data taken with ground based and space facilities by applying our knowledge and experience on galaxy evolution.
Science of Complexity Theory Laboratory [ΣT Lab]
Masanori NUNAMI (Visiting Associate Professor)
We investigate complexity as it appears in high energy-density physics and, in particular, in laser plasmas, via computer simulations. Current research topics include particle acceleration by short pulse lasers, which is expected to have medial applications. We are also interested in the generation of highly-energetic electrons by ultra-high intensity lasers, since this is one of the crucial issues in fast ignition of laser fusion. Another topic under investigation is the inevitable hydrodynamic instability in implosion of laser fusion. In order to carry out these studies, we are developing new techniques for high-performance computing and highly accurate simulations. These techniques will allow unparalleled level of insight into a variety of scientific problems.
The interaction between an ultra-high intensity laser and overdense plasma for fast ignition research.
Identifying dark matter, which remains a mystery, is the ultimate challenge in elementary particle physics. Neutrino mass, if it exists, may partly solve this mystery. Although observations of cosmic rays and solar neutrinos suggest neutrino oscillation, neutrinos resulting from an oscillation have yet to be captured. However, nuclear emulsion technology as along with an international collaboration with research groups in Europe has enabled the OPERA experiment, which aims to capture emerging tau-neutrinos. This nuclear emulsion technology focuses on a very powerful method of searching for supersymmetric particles, or WIMPs, and a project using this technology is in the planning stages. The nuclear emulsion technology, which our laboratory has been developing for more than thirty years, is employed not only in elementary particle research,
but is also finding applications in the research of hadrons containing charm quarks and γ-ray astronomy as well as the diagnosis of the interior of reinforced columns and blast furnaces, which X-rays cannot penetrate.
We use frontier high-energy particle accelerators to study elementary particles, which constitute matter, and their interactions. In the B-factory experiment, we use an electron-positron collider with the world's highest luminosity, and study the violation of particle-antiparticle symmetry (CP violation) in B-meson decays and searching for tau-lepton decays induced by new physics beyond the standard model. In Europe, the LHC experiment, which is a proton-proton collision experiment with the world's highest energy, has been launched. In this experiment, we try to discover the Higgs particle, which is predicted by theory to explain the origin of mass, and also new particles beyond the standard model.
Furthermore, we are actively conducting research and development on the TOP counter and aerogel RICH, which are particle detectors originating from our own ideas.
We study the properties of elementary particles and physics laws behind them through precision measurements. We start our researches with the slow neutrons: the chargeless massive particle with the lifetime as long as 15 minutes.
We apply advanced neutron optics to control the instantaneously most intense slow neutrons in the energy range of 100 neV to 1 eV from the spallation neutron source of the J-PARC (Japan Proton Accelerator Research Complex) to overcome the present experimental limitations to discover new physics in the breaking of discrete symmetries, short-range gravity, etc.
Understanding how stars, galaxies and supermassive black holes formed and have been evolved across the Hubble time is one of the biggest challenges in modern astrophysics. We are trying to address those big questions by exploiting millimeter/submillimeter-wave observations of interstellar gas and dust---origins of every astronomical objects---in the Milky Way, nearby and high redshift galaxies. We use not only NANTEN2, a 4-m radio telescope that we are operating in Chile, to study molecular clouds in the Milky Way and the Magellanic Clouds, but ASTE and ALMA to unveil forming galaxies in the remote Universe. We also develop instruments for these existing and future radio telescopes which allow for cutting-edge sciences.
Space Astronomy Laboratory (Infrared Astronomy Group) [UIR Lab]
The main purpose of our research is to understand the properties of interstellar dust and gas under various environments in our Galaxy and nearby galaxies through near- to far-infrared observations using satellites and balloons. We have developed a far-infrared imaging spectrometer for AKARI, the first Japanese infrared astronomical satellite, which was launched in February 2006. We are analyzing AKARI data extensively to pursue the above scientific researches. We are also developing cryogenic optics and far-infrared detectors for future space missions such as SPICA. We are deeply involved in the JAXA-led project of SPICA, which will be the 2nd Japanese infrared astronomical satellite to be launched in 2017.
Space Astronomy Laboratory (High-energy Astronomy Group) [Uxg Lab]
By observing the universe with high-energy photons (X-rays) or even gravitational waves (GW), we can investigate the high-energy phenomena in the universe. We are developing new GW detection schemes such as space antenna, DECIGO, for low-frequency GWs from the inflation period in the early universe. We are also developing next generation X-ray mirrors, its multilayer reflectors, and high-throughput thermal shields, and observing energetic objects, such as clusters of galaxies and super massive black holes. We are the member of X-ray observatories to be launched soon, such as XRISM for spectroscopy and IXPE for X-ray polarimetry and proposing more. Observational research on the misterious MeV gamma-rays of thunder-cloud are also on-going.
Science of Complexity Experiment Laboratory [ΣE Lab]
Kenichi NAGAOKA (Visiting Professor)
A remarkable characteristic of plasma as a nonlinear medium is the "self-organization" of spatiotemporal structures through the interplay of instability and nonlinearity. This phenomenon is widely observed in space, solar atmosphere, ionosphere and in laboratory devices. In our research group, linear and nonlinear phenomena in plasmas are experimentally studied by exploring a variety of laboratory plasmas.
Our experiments are mainly performed at the Large Helical Device and "HYPER-I" at the National Institute for Fusion Science.
We study physical and mathematical theories of nonlinear phenomena by means of analytical and numerical methods. Present subjects of investigation include the following:
(1) Chaos in Hamiltonian systems : phase space structure, invariant sets and their relation to flow in the phase space; slow dynamics such as Arnold diffusion, Nekhoroshev theorem and Boltzmann-Jeans theory; motion of charged particle in non-uniform magnetic field; dynamics of multiple pendulum and its phase space structure
(2) Dynamics of nonlinear spatial structures such as solitons, vortices and patterns
(3) Development and application of singular perturbation methods
(4) Computational geomorphology : understanding geomorphology by physical modeling and computation
(5) Dynamics of chain-type systems : active motion of chain-end particles
Solid State Theory Laboratory (Condensed Matter Theory Group) [Sc Lab] Solid State Theory Laboratory (Quantum Transport Theory Group) [St Lab]
We examine theoretically the fundamental problems in condensed matter physics and statistical physics.
(1) In the high density quantum systems such as high-Tc superconductors, strong electron-electron correlations are considered to play a crucial role in the appearance of superconductivity. Starting with this assumption, we are currently developing a new theory of superconductivity beyond the BCS theory.
(2) We probe quantum fluctuations inherent to superconducting states, charge density wave states, and spin-density wave states of low-dimensional organic conductors.
(3) We are also investigating the dynamical phenomena related to crystal growth and non-equilibrium pattern formation at interfaces.
Biological complexes, structured ensembles of proteins and nucleic acids, perform many vital cellular functions and dysfunctions of those result in severe diseases. In order to understand diseases and develop treatments, the functional mechanisms of these biological complexes need to be elucidated. A crucial step in this process is the characterization of the structure and dynamics of these complexes. Our goal is to develop computational methods to obtain atomic level description of the functional states of biological complexes. Such methods will rely on the integration of computational simulations with various experimental data such as high resolution X-ray crystallography, lower resolution cryo-EM and X-ray Free Electron Lasers.
The research in the lab is interdisciplinary. We use physics, chemistry, and computational science to study biological systems. More specifically, to describe the dynamics and energetics of biological molecules, we use empirical force fields based on the physico-chemical properties of atoms or, to reduce complexity, we also use coarse-grained models.
Then methods such as molecular dynamics simulations/normal mode analysis are used to obtain structural models by incorporating experimental data into the modeling procedure, where numerical optimizations techniques, such as Monte Carlo and gradient following techniques, need to be implemented in programs.
Our research group specializes in nuclear magnetic resonance (NMR) spectroscopy, which is a powerful probe for studying microscopically magnetic and electronic properties of solids. Recently our activities have focused on strongly correlated electron systems in transition metal oxides and low-dimensional quantum spin systems. The goal of our research is to understand a variety of exotic quantum phenomena that the spin, charge, and orbital degrees of freedom of the electrons yield in novel solids. In particular, our current efforts are directed towards understanding the metal-insulator and spin-state transitions, as well as charge and orbital ordering in transition metal oxides. The superconducting mechanism in iron-based superconductors is also investigated by the NMR technique.
The group's research focus is on nanoscale magnetism and spin related effects, aiming at discovering novel concepts in condensed matter physics. Research study in nanostructures allows us to address the challenging questions in the field of spin-related phenomena by artificially designing and fabricating nanostructures. A number of remarkable new physical effects associated with the conservation law of angular momentum and energy have been already discovered designing artificial interfaces, where strong electron-phonon-spin coupling emerges at nanoscale. Quite the opposite, revealing the physics underlying provides a fundamental basis and means for manipulating the physical phenomena. The group's current research topics include cross-correlations in multiferroic heterostructures, quasi-particle transmission and tunneling, magnon-phonon coupling and thermal transport, and correlation of spin current and magnetic orders, etc.
Artificial control of nanomagnetism and spin properties
Laboratory of Condensed-Matter Physics of Functional Materials [V Lab]
V-laboratory is interested in the physical properties of "interesting and useful materials" in strongly correlated systems. In a strongly correlated system, conduction electrons affect with each other through the strong Coulomb repulsion, and move together in a "correlated" manner. As a result, a conventional band picture is seriously broken down, and new phenomena can arise beyond the prediction of a band theory. In this respect, such materials are prime examples for "More is different". We are mainly studying on large thermopower in Co oxides and nonlinear conduction in organic conductors at present.
The schematic picture of the layered cobalt oxide NaxCoO2. This material can convert heat into electricity with a performance as high as other thermoelectric materials.
Proteins are inherently dynamic molecules that undergo structural changes and interactions with other molecules over a wide timescale range, from nanoseconds to milliseconds or longer. Furthermore, protein motions play an important biological role in the assembly into protein complexes, ligand binding and enzymatic reactions. Therefore, understanding the dynamic behaviour of a protein is a requisite for gaining insight into their function mechanisms. We develop novel methods for directly observing protein's dynamics based on high-speed atomic force microscopy (AFM), which is one of scanning probe microscopy, and exploit new paradigm of dynamic structural biology. Also we analyze structural dynamics of rhodopsin at atomic resolution using X-ray crystallographic technics for understanding the molecular mechanism and creating new functional GPCRs.
Photosynthesis performed by plants and cyanobacteria is a highly elaborate natural system of light energy conversion, in which carbon dioxide and water are converted into sugars and molecular oxygen. We are studying the molecular mechanism of photosynthesis, especially that of water oxidation (oxygen evolution), proton-coupled electron transfer, and excitation energy transfer, using various physicochemical methods such as Fourier transform infrared spectroscopy (FTIR), electron spin resonance (ESR), ultrafast time-resolved spectroscopy, thermoluminescence (TL) and delayed luminescence (DL), and quantum chemical calculations. Understanding the photosynthesis mechanism provides important basis for solving the energy and environment problems that confront the human race today.
The structure of photosystem II (left) and its electron transfer pathway (right). Photosystem II, which is embedded in thylakoid membranes of plants and cyanobacteria, is a multisubunit protein complex that has a function of light-driven water oxidation to evolve molecular oxygen.
Laboratory of Cellular Signaling Biophysics [K Lab]
Our research is aimed at understanding the mechanisms of information transfer in biological systems. Our interests include the investigation of protein folding at the molecular level. We focus primarily on characterizing events which occur during folding reactions by means of experimental techniques such as spectroscopy, kinetic methods and protein engineering, with the goal of understanding the molecular mechanisms of protein folding. Another area of interest is the mechanisms of intracellular signaling at the cellular level. We study various presynaptic processes of synaptic transmission, especially modulation of transmitter release and dynamics of divalent cations, by means of electrophysiological and fluorescence imaging techniques.
Heliospheric and Geospace Physics (Institute for Space-Earth Environmental Research)
We are studying the global atmospheric environment, which is closely related to our life. Our goal is to understand the mechanism of global and local environmental changes, including ozone depletion and global warming, in order to help to solve environmental problems. To this end, we are conducting research on the following topics. Based on the latest technologies for radio waves (millimeter/submillimeter waves), we are developing new, highly sensitive instruments to measure trace constituents in the atmosphere. Using these instruments, we are examining changes and reaction processes of substances related to ozone depletion and global warming. In addition, we are employing ground-based instruments to observe atmospheres on planets other than Earth.
The plasma and energy carried to the Earth and the other planets by the solar wind exert physical effects on the magnetosphere and ionosphere, which are called "Geospace" including the upper atmosphere (above 70 km altitude) in the case of the Earth. We are investigating these effects and associated phenomena, primarily through observational approaches. In addition, we strive to understand elementary processes of physical phenomena occurring in the Geospace and various planetary space environment. Topics of interest currently include the interaction and the energy transfer mechanisms among the solar wind and the terrestrial/planetary atmospheres and intrinsic magnetic fields especially in their boundaries in the near-planetary space, the polar regions, and the mid-low latitudes. Through international cooperation, we are using equipment, including EISCAT radars, a Sodium LIDAR, a Fabry Perot Interferometer (FPI), an MF radar, meteor radars, high-sensitivity cameras, a photometer, and magnetometers, installed in the northern polar region to observe the Geospace. The in-situ measurements based on the instruments onboard satellites/spacecraft, which are innovated/developed in our laboratory, are also powerful methods to elucidate the space dynamics. The remotely sensed data could also be combined with the data in space directly obtained by rockets and satellites/spacecraft to study dynamical phenomena in the Gospace such as auroras, magnetic (space) storms, ionospheric currents, and atmospheric waves (planetary, tidal and gravity waves). With respect to the mid-low latitude, we are using HF radars, high-sensitivity cameras, GPS multipoint observation networks, VHF radars, and magnetometers to remotely sense the ionosphere and upper atmosphere in the mid-low latitude and equatorial region. These data are then used to study the interactions between the space plasma and the Earth's atmosphere at the space-atmosphere interface as well as couplings between the high-latitude and mid-latitude regions, including auroras observed even in Japan and atmospheric waves from the polar regions.
Through integrated data analysis, we are studying the transport of energy and particles from the Sun to the Earth. Our research is primarily based on analysis of data obtained from satellites and ground-based observations, and computer-based numerical simulation/modeling. Specifically, we are focusing on the dynamics in solar and space plasmas (such as solar cycle, solar flares, coronal mass ejections, magnetic storms, and auroras), which result from nonlinear processes in multiple-layer and multiple-scale interactions in space. Recently, disturbances in space may cause failures in our infrastructures, including power-grids, communication systems, and satellites. This has been recognized as a serious problem in our economy and community, and the importance of "space weather" research to elucidate and predict events in the Sun and the "geo-space", that is space near the Earth, has increased. In our group, we are investigating space weather as well as "space climate", which is long-term influence of the solar activity upon the environment of the Earth.
Cosmic Rays -- high-energy particles from space -- bring us new knowledge of nature; new species of elementary particles including dark matters, high-energy phenomena of the universe and signatures of past solar activities are notable examples. Through cosmic-ray observations we pursue a variety of interdisciplinary research topics between particle physics and astrophysics as follows:
a) The LHCf and RHICf experiment: a study of hadron interactions of ultra high-energy cosmic rays by using zero degree electro-magnetic calorimeters at the CERN Large Hadron Collider (LHC) and BNL Relativistic Heavy Ion Collider (RHIC).
b) Neutrino and dark matter experiments: neutrino observations with Super-Kamiokande and Hyper-Kamiokande. Dark matter searches with the XENONnT liquid xenon experiment in Italy.
c) Solar neutron observations; the fully-active solar-neutron telescope SciCRT in Mexico and a small satellite dedicated for solar neutron measurement in the space.
d) Measurement of radiocarbon (14C) contained in tree rings to probe variations of the cosmic-ray flux due to solar activities and astronomical burst events in the past.
e) Gamma-ray observations: Investigation of origin and propagation of cosmic rays and search for dark matters with the Fermi gamma-ray satellite and Cherenkov Telescope Array.
The Sun continuously emits a supersonic plasma flow called the solar wind, and all planets of the solar system are engulfed by this stream. A huge space called the heliosphere is created by the solar wind in the interstellar gas. The solar wind ceaselessly changes on a various time scales, and imposes some significant influences on the space environment and the upper atmosphere condition around the Earth. Strong interaction between the solar wind and the interstellar gas takes place in the boundary region of the heliosphere. Many fundamental properties of the solar wind such as the generation mechanism, 3D structure of the heliosphere, and the cause of variability have never been yet fully understood. Our SW group aims at elucidating these unsettled questions of the solar wind from ground-based observations of interplanetary scintillation (IPS) using large radio-telescopes, which have been developed at our lab. The IPS method we use here is unique in the world, and enables to investigate hidden aspects of the solar wind.
Department of Physics
Graduate School of Science / School of Science
