Updated on 2024/07/31

写真a

 
Tomizawa Shinya
 
Organization
Graduate School of Engineering Department of Advanced Science and Technology Materials Science and Engineering Mathematical Physics Laboratory Professor   
Degree
博士（理学） （ 東京工業大学 ）
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Contact information
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Research Areas

  • Natural Science / Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics

Main research papers

  • Construction and application of variations on the cylindrical gravitational waves of Weber, Wheeler, and Bonnor

    T. Mishima, S. Tomizawa

    Physical Review D   96 ( 2 )   024023   2017

    Supersymmetric black lenses in five dimensions

    S. Tomizawa, M. Nozawa

    Physical Review D   94 ( 4 )   044037   2016

    New approach to solution generation using SL(2,R)-duality of a dimensionally reduced space in five-dimensional minimal supergravity and new black holes

    S. Mizoguchi, S. Tomizawa

    Physical Review D   84   104009   2011

    Uniqueness theorem for charged rotating black holes in five-dimensional minimal supergravity

    S. Tomizawa, Y. Yasui, A. Ishibashi

    Physical Review D   79   124023   2009

    Topology Change of Coalescing Black Holes on Eguchi-Hanson Space

    H. Ishihara, M. Kimura, S. Tomizawa

    Classical and Quantum Gravity   23   L89   2006

Research History

  • Toyota Technological Institute   Professor

    2020.4

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    Country：Japan

  • Tokyo University of Technology   Associate Professor

    2014.4 - 2020.3

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    Country：Japan

  • Ibaraki University   Associate Professor

    2012.4 - 2014.3

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    Country：Japan

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Education

  • Tokyo Institute of Technology   Graduate School of Science and Engineering

    2002.4 - 2005.3

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    Country： Japan

  • Tokyo Institute of Technology

    2000.4 - 2002.3

  • Tokyo Institute of Technology   School of Science

    1996.4 - 2000.3

Professional Memberships

  • 素粒子論ブループ

    2010.4

  • 理論天文学宇宙物理学懇談会

    2005.4

  • 日本物理学会

    2003.4

  • 一般相対論と重力グループ（JGRG）

    2003.4

Committee Memberships

  • 日本物理学会 大学の物理教育編集委員会   委員  

    2021.4 - 2022.3   

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    Committee type：Academic society

  • 日本物理学会 Jr. セッション   第 1 次審査審査員  

    2021.1 - 2021.3   

  • 日本学術振興会 科学研究費委員会   専門委員 [基盤(C)] (素粒子、原子核、宇宙線および宇宙物理に関連する理論)  

    2020.12 - 2021.11   

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Research theme

  • Quantum black holes

    富沢　真也, 鈴木　良拓（転出・退職）

    2022

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    Outcome：

    2023
    General relativity coupled to nonlinear electrodynamics is known to have nonsingular black hole solutions. We have investigated the existence conditions for such solutions in two-parameter Lagrangian L(F,G). In particular, we have obtained a criterion on the Lagrangian for the existence of nonsingular black hole with a dyonic charge. In addition, we have presented a simple example of two-parameter Lagrangian satisfying the criterion, in which the existence of the dyonic solution is actually confirmed. Moreover, apart from the actual existence of dyonic solutions, we have considered some examples for the Lagrangian satisfying such a criterion.

    2022
    We have investigated the bound orbits of massive/massless, neutral particles and photons moving around regular black holes of Fan and Wang. For massive particles, we have shown the existence of stable/unstable circular orbits and the charge dependence of the radius of the innermost stable circular orbit. Remarkably, we found an unstable circular orbit of photons inside the event horizon. For massless particles and photons, we have shown that both stable and unstable circular orbits can exist in a regular and horizonless spacetime with a slight overcharge. Then, we also discussed the periapsis shift of massive neutral particles orbiting around the black hole, and showed that the charge gives a negative correction to the shift for black holes with small nonlinearity of electrodynamics.

  • Analog black holes

    富沢　真也, 鈴木　良拓（転出・退職）

    2022

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    Outcome：

    2023
    We proposed a new simple model of acoustic black hole in a thin tube, where the difference in the gravitational potential is used to create a transonic flow. The main merit of our transonic flow model is that the Euler equations can be solved analytically. In fact, we obtained an exact solution to the equation in terms of a height function in the monatomic case. For a more general case, we found that it takes a simple form by the near-sonic approximation. Moreover, we obtained two analytic solutions describing a backward wave and a forward wave, from which we confirmed the existence of sonic horizons.

  • Theoretical studies on black holes using large D limit method in Einstein-Gauss-Bonnet theory

    富沢　真也, 鈴木　良拓（転出・退職）

    2021

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    Outcome：

    2023
    We have investigated the nonlinear dynamics of D=2N+3 Myers-Perry black holes with almost equal angular momenta, which have N equal spins out of possible N+1 spins. In particular, we have studied the ultraspinning instability and the fate of its nonlinear evolution using the large D effective theory approach. We have found that every stationary phase can be mapped to the counterpart in the singly rotating phase within the leading order effective theory. From the known results of singly rotating solutions, we have obtained the phase diagram of almost equally rotating black holes. We have also obtained a certain implication for the possible topology changing transition.

    2022
    The phase and stability of black strings in the Einstein-Gauss-Bonnet (EGB) theory are investigated by using the large D effective theory approach. The spacetime metric and thermodynamics are derived up to the next-to-leading order (NLO) in the 1/D expansion. We found that the entropy current defined by the Iyer-Wald formula follows the second law. As in the Einstein theory, the entropy difference from the total mass produces an entropy functional for the effective theory. Including the NLO correction, we found that for the large Gauss-Bonnet coupling constant, the Gregory-Laflamme instability of uniform black strings needs longer wavelength. Moreover, we showed that the critical dimension, beyond which non-uiform black strings becomes more stable than uniform ones, increases as α becomes large, and approaches to a finite value for α→∞.

  • Motion of particles and photons around black holes and microstate geometry

    富沢　真也, 鈴木　良拓（転出・退職）

    2021

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    Outcome：

    2023
    Using the exact solution that describes multi-centered rotating black holes, recently discovered by Teo and Wan, we have investigated the innermost stable circular orbit (ISCO) for massive particles and the circular orbit for massless particles moving around a spinning black hole binary. We assume equal masses M1 = M2 = m and equal spin angular momenta |J1| = |J2| for both black holes. Firstly, we have examined the case where two black holes are spinning in the same direction (J1 = J2). We have clarified that that for particles rotating in the same direction as (opposite directions to) black holes’ spin, the greater the spin angular momenta of the black holes, the more the radii of the ISCO for massive particles and the circular orbit for massless particles decrease (increase). We have shown that distinct ISCO transitions occur for particles rotating in the same direction as the black holes in three ranges of spin angular momenta: 0 < J1/m^2 = J2/m^2 < 0.395..., 0.395... < J1/m^2 = J2/m^2 < 0.483..., and 0.483 . . . < J1/m^2 = J2/m^2 < 0.5. Conversely, particles rotating in the opposite direction to the black holes exhibit a consistent transition pattern for the case 0 < J1/m^2 = J2/m^2 < 0.5. Secondly, we study the situation where binary black holes are spinning in opposite directions (J1 = −J2). We have clarified that for large (small) separations between black holes, the ISCO appears near the black hole that is spinning in the same (opposite) direction as particles’ rotation. Additionally, we have shown that different ISCO transitions occur in the three angular momentum ranges: 0 < J1/m^2 = −J2/m^2 < 0.160..., 0.160... < J1/m^2 = −J2/m^2 < 0.467..., and 0.467... < J1/m^2 = −J2/m^2 < 0.5.

    2023
    Recently, various types of the regular black hole model are reintroduced as the solution of the Einstein equations coupled with nonlinear electrodynamics (NED). In NED, it is known that photons do not propagate along the null geodesics of the spacetime geometry, but of so-called effective geometry, which suggests the possibility of so-called “faster/slower than light” photons. We have studied the relation between the causality of photons and the dominant energy condition (DEC) in some static and spherically symmetric black hole spacetimes in NED. We have shown that if photon trajectories with a nonzero angular momentum are timelike in the spacetime geometry, DEC is always satisfied in static and spherically symmetric spacetimes in any NED that admits the Maxwell limit, and vice versa, at least, in the weak field limit. Thus, this implies that in such NED, the violation of DEC admits the existence of faster than light photons.

    2022
    We showed the existence of stable bound orbits for the massive and massless particles moving in the simplest microstate geometry spacetime in the bosonic sector of the five-dimensional minimal supergravity. In our analysis, reducing the motion of particles to a two-dimensional potential problem, we numerically investigated whether the potential has a negative local minimum.

  • Nonlinear gravitational waves in Einstein-Maxwell theory

    富沢　真也

    2020

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    Outcome：

    2023
    Using the ``composite harmonic mapping method," we haveconstructed exact solutions for cylindrically symmetric gravitational and electromagnetic waves within the Einstein-Maxwell system, focusing on the conversion dynamics between these types of waves. In this approach, we have employed two types of geodesic surfaces in H^2_c : (a) the complex line and (b) the totally real Lagrangian plane, applied to two different vacuum seed solutions: (i) a vacuum solution previously utilized in our studies and (ii) the solitonic vacuum solution constructed previously by Economou and Tsoubelis. We have studied three scenarios: case (a) with seeds (i) and (ii), and case (b) with seed (ii). In all cases (a) and (b), solutions demonstrate notable mode conversions near the symmetric axis. In case (a) with seed (i) or seed (ii), we have shown that any change in the occupancy of the gravitational or electromagnetic mode relative to the C-energy near the axis always reverts to its initial state once the wave moves away from the axis. Particularly in case (b) with seed (ii), nontrivial conversions occur even when the wave moves away from the axis. In this case, the amplification factors of electromagnetic modes range from an upper limit of approximately 2.4 to a lower limit of about  0.4, when comparing the contributions of electromagnetic mode to C-energy at past and future null infinities.

    2022
    Applying a simple harmonic map method to the cylindrically symmetric Einstein-Maxwell system, we obtained exact solutions representing strong nonlinear interaction between gravitational waves and electromagnetic waves in the case without any background field. As an interesting fact, we showed that with adjusted parameters the solution represents occurrences of large conversion phenomena in the intense region of fields near the cylindrically symmetric axis.

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Papers

  • New black ring with all independent conserved charges in five-dimensional minimal supergravity Reviewed

    Ryotaku Suzuki, Shinya Tomizawa

    Physical Review D, arXive:2407.18142 [hep-th]   2024.7

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    Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

  • New construction of a vacuum doubly rotating black ring by the Ehlers transformation Reviewed

    Ryotaku Suzuki, Shinya Tomizawa

    Physical Review D, arXive: 2406.11804 [hep-th]   2024.6

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    Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

  • Nonlinear dynamics driving the conversion of gravitational and electromagnetic waves in cylindrically symmetric spacetime Reviewed

    Takashi Mishima, Shinya Tomizawa

    Physical Review D   110 ( 2 )   024038   2024.5

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    Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1103/PhysRevD.110.024038

  • Innermost stable circular orbits around a spinning black hole binary Reviewed

    Eiki Kagohashi, Ryotaku Suzuki, Shinya Tomizawa

    Physical Review D   110 ( 2 )   024013   2024.3

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    Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

    DOI： 10.1103/PhysRevD.110.024013

  • Solution Generation of a Capped Black Hole Reviewed

    Ryotaku Suzuki, Shinya Tomizawa

    Physical Review D   110 ( 2 )   024026   2024.3

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    Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

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MISC

  • 26pSL-1 Novel properties of the new cylindrically symmetric solitonic gravitational waves

    Mishima T., Tomizawa S.

    Meeting Abstracts of the Physical Society of Japan   70.2   370   2015 （     eISSN:2189-0803 ）

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    Language：Japanese   Publisher：The Physical Society of Japan  

    DOI： 10.11316/jpsgaiyo.70.2.0_370

  • New solution-generation-techniques using SL(2, R)-duality and general black holes

    Shinya Tomizawa, Shun’ya Mizoguchi

    The 13th Marcel Grossmann Meeting: On Recent Developments in Theoretical and Experimental General Relativity, Astrophysics and Relativistic Field Theories - Proceedings of the MG13 Meeting on General Relativity, 2012   ( 210699 )   1327 - 1329   2015

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    Language：English   Publishing type：Article, review, commentary, editorial, etc. (international conference proceedings)   Publisher：World Scientific  

    The dimensional reduction of (the bosonic sector of) five-dimensional minimal supergravity to four dimensions leads to a theory with a massless axion and a dilaton coupled to gravity and two U(1) gauge fields (one of which has Chern-Simons coupling), whose field equations have SL(2, R) invariance. Utilizing this SL(2, R)-duality in the dimensionally reduced spacetime, we provide a new formalism for solution generation. Using the SL(2, R)-duality, we construct general Kaluza-Klein black hole solutions which carry six independent charges, its mass, angular momentum along four dimensions, electric and magnetic charges of the Maxwell fields in addition to Kaluza-Klein electric and magnetic monopole charges.

    DOI： 10.1142/9789814623995_0162

  • 24aZW-11 Rotating Squashed Multi-Black Holes with Godel Parameter

    Matsuno Ken, Ishihara Hideki, Tomizawa Shinya, Nakagawa Toshiharu

    Meeting Abstracts of the Physical Society of Japan   63.1.1   109   2008 （     eISSN:2189-0803 ）

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    Language：Japanese   Publisher：The Physical Society of Japan  

    DOI： 10.11316/jpsgaiyo.63.1.1.0_109_4

  • 23pZH-2 Coalescence of Rotating Black Holes on Eguchi-Hanson space

    Matsuno Ken, Ishihara Hideki, Tomizawa Shinya, Kimura Masashi

    Meeting Abstracts of the Physical Society of Japan   62.2.1   112   2007 （     eISSN:2189-0803 ）

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    Language：Japanese   Publisher：The Physical Society of Japan  

    DOI： 10.11316/jpsgaiyo.62.2.1.0_112_4

  • 21pSG-2 Masses of Kaluza-Klein black holes

    Matsuno Ken, Ishihara Hideki, Tomizawa Shinya, Kimura Masashi

    Meeting Abstracts of the Physical Society of Japan   61.2.1   63   2006 （     eISSN:2189-0803 ）

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    Language：Japanese   Publisher：The Physical Society of Japan  

    DOI： 10.11316/jpsgaiyo.61.2.1.0_63_2

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Presentations

  • 位相検閲定理とブラックホールの非一意性 Invited

    富沢真也, 鈴木良拓

    茨大素粒子Mini Workshop  ( 茨城大学 )   2024.3 

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    Presentation type：Oral presentation (invited, special)  

  • 重力波・電磁波が伝播する円筒対称時空中の試験粒子の挙動

    三島隆*, 富沢真也

    日本物理学会　２０２４年春季大会  ( オンライン )   2024.3 

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    Presentation type：Oral presentation (general)  

  • A capped black hole I : Solution generation of spherical black holes

    富沢真也, 鈴木良拓

    日本物理学会　２０２４年春季大会  ( オンライン )   2024.3 

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    Presentation type：Oral presentation (general)  

  • A capped black hole II : Non-uniqueness of spherical black holes

    鈴木良拓, 富沢真也

    日本物理学会　２０２４年春季大会  ( オンライン )   2024.3 

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    Presentation type：Oral presentation (general)  

  • 厳密解を用いた重力的波動現象における非線形効果の探求 Invited

    三島隆*、富沢真也

    ブラックホール研究会  ( 日本大学 )   2024.3 

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    Presentation type：Oral presentation (invited, special)  

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Awards

  • Research highlights of 2006/2007,

    2007   Classical and Quantum Gravity,   Topology change of coalescing black holes on Eguchi-Hanson space,

Grant-in-Aid for Scientific Research