• JRG

    Junior Research Groups (JRG)

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    Black Holes, Quantum Gravity and String Theory

    Black hole is a theoretical testing ground for understanding quantum gravity. The fact discovered by J.Bekenstein and S. Hawking that black holes are thermodynamic objects having temperature, entropy, and emitting thermal radiation provides us a strong guide for studying the black holes and their microscopic quantum structure. 

    Our group aims at studying the quantum nature of thermodynamics of the black holes arising in string theory. We analyze the problems from both macroscopic and microscopic directions, which are respectively via supergravities and corresponding dual supersymmetric gauge theories given by AdS/CFT correspondence. We develop ways of treating quantum aspects of back hole entropy. Some of the approaches allow us to exactly capture the quantum effects on black hole entropy in a systematic way, by which we provide precise tests for string theory as a candidate for a theory of quantum gravity. We further study various thermodynamic properties of black holes or extended objects in different ensembles. 


    String Theory and Quantum Chromodynamics

    Solving the theory of strong interactions, quantum chromodynamics (QCD), is one of the major remaining problems in theoretical physics. Recent advances in gauge/gravity duality may help to shed light on the dynamics of the theory. This research group studies various topics at the interface of string theory, QCD, and other strongly interacting theories. Special focus is on QCD matter at finite density, where theoretical analysis is particularly hard. Gauge/gravity duality, supported by input from nuclear physics, lattice simulations, and perturbation theory, can provide answers to open questions in this regime, which is relevant for core-collapse supernova explosions and binary neutron star mergers. 

    Dualities in String/M-theory and Quantum Gravity

    String/M-theory is a strong candidate for quantum gravity and provides a theoretical framework for unifying various interactions in nature. In this research group, we study the structure of classical and quantum gravity via various fascinating ideas in string/M-theory, especially dualities, and exploit them to various interesting problems. It encompasses scattering amplitudes, black hole physics, gauge/gravity duality, double copy, and the mathematical structure of stringy geometry.  

    Observational Cosmology

    The observational cosmology group extracts statistical information from combinations of large scale structure, Cosmic Microwave Background temperature fluctuations and astrophysical distance measurements, then uses the data to place constraints on the evolution, initial conditions and energy contents of the Universe. Current state-of-the-art cosmological data are increasingly pointing towards tension in the standard cosmological model -- local and cosmological distance measurements are discrepant, violations of statistical isotropy have been detected in the matter fluctuations. These trends suggest that the standard model may require significant modification. The observational cosmology group are applying innovative statistical techniques to the latest galaxy catalogs, and testing both the standard model and the underlying assumptions that are made during the process of cosmological data reduction.

    In tandem, the group is studying spherically symmetric spacetime metrics for scalar-tensor dark energy models, the intrinsic alignment of galaxies at high redshift, the topology of random fields, statistical violations of isotropy of finite volume random fields and the matter distribution in the local Universe. Our research lies at the intersection of theoretical, observational and numerical cosmology and we are continually seeking to apply our methodologies to other branches of physics.  

    Physics of matter at non-equilibrium

    We aim at revealing universal structures or governing principles behind complex physical phenomena in a variety of systems including QCD matter, fractonic systems, chemical reaction networks, and so on.  

    Physics beyond the Standard Model and its Phenomenology

    We focus on model buildings of neutrino(quark) physics, dark matter candidates, and their related phenomenologies such as lepton flavor violations(LFVs), muon anomalous magnetic moment(muon g-2), Z boson decays, and collider physics that can be tested by Large Hadron Collider. Through the model buildings, we try to construct all the phenomenologies can be explained by as a minimal way as possible.  

    Interfaces and Defects in Strongly Coupled Matter

    Our group studies the physics of strongly coupled matter when space-time symmetries are broken by interfaces, boundaries and other defects. Our primary tools are holography and string theory motivated techniques, though this research synthesizes ideas from both high energy and condensed matter theory. Our focus is on discovering and exploring new and non-trivial phases of matter, from RG interfaces to topological insulators.  

    Holography and Black holes

    Holography, which is duality between QFT and gravity, is a fruitful arena for testing our understanding of quantum gravity, QFT and quantum information theory. The black hole information problem is also deeply involved in fundamental questions in the quantum nature of our spacetime. Our group aims at deep understanding of quantum field theory, quantum information, quantum gravity and black hole via holography. We will focus on strongly correlated systems and holographic duals thereof; quantum chaos and the application of random matrix theory; black hole physics; finite temperature QFTs and open quantum system; quantum gravity and higher spin AdS/CFT correspondence; irrelevant deformation of QFTs.  

    Magnetized Plasma Physics and Astrophysics

    Magnetized plasmas are ubiquitous in the Universe, with examples being astrophysical jets and accretion disks, the solar corona, the solar wind, planetary magnetospheres, and the interstellar medium. Our research group focuses on three distinct processes that characterize the lifetime of a magnetized plasma: generation of magnetic fields, relaxation of plasma systems, and explosion resulting from magnetic to wave/kinetic energy conversion. The resultant fundamental aspects are relevant to next-generation laboratory plasma systems such as nuclear fusion devices and particle accelerators.

    Theoretical frameworks that describe magnetized plasmas can be divided into four main branches, in order of increasing accuracy and decreasing simplicity: (i) magneto-hydrodynamics (MHD), (ii) multi-fluid description, (iii) Vlasov-Maxwell or Boltzmann description, and (iv) single-particle description. We use all four frameworks as needed, choosing the most appropriate model for the system in question. We perform numerical simulations to verify our models, and compare them to observations and/or experiments if possible.  

    Thermodynamics of microscopic nonequilibrium systems

    Thermodynamics is an essential tool for understanding how to make an energy transformation more efficient and effective. Conventional thermodynamics, in particular, has provided us with a comprehensive understanding of thermodynamic phenomena of macroscopic systems at equilibrium. 

    This research group aims to study the thermodynamics of microscopic nonequilibrium systems through the extension of thermodynamic concepts to fluctuating systems. By using statistical formalism for stochastic processes, we investigate a broad range of issues in microscopic systems including active matters and quantum systems, for example, universal trade-off relations, fundamental efficiency bounds, inference of the experimentally infeasible entropy production, etc.