セミナー・特別講義

GCOE・基研セミナー

title

The equilibrium dynamics of the Dean-Kawasaki model for colloids: the standard MCT and beyond

author

Bongsoo Kim
Changwon National University

date

2013年　3月21日（水）　16:00〜

place

基礎物理学研究所　研究棟・講義室K202

abstract

This talk aims to communicate our recent results on the dynamics of equilibrium density fluctuations of colloids. The Dean-Kawasakiequation, a stochastic model equation for the density fluctuations of colloidal dispersions, poses a theoretical challenge of developing a systematic perturbation theory which preserves the fluctuation-dissipation relation order by order, mainly due to its multiplicative noise nature. A beautiful idea of time-reversal symmetry of the corresponding action offers a solution to the challenge: a loop expansion method applied to the new dynamic action incorporating a new set of auxiliary variables is guaranteed to preserve the fluctuation-dissipation relation (FDR) order by order. Our previous work along this line made an error of overlooking a delta function in one of the FDRs between the response and correlation functions. Restoring this missing contribution cries out for the distinct scenario from that in previous work. Instead of obtaining a single closed equation for the density-density correlation function, we now face with the simultaneous equations of the three independent correlation functions. The standard MCT equation is retrieved from this coupled set of equations after a further approximation to get an equation for the density-density correlation alone. The full one-loop theory is analytically shown to remove the ergodic-nonergodic transition via dynamic coupling to the auxiliary variable, making the dynamics always ergodic.

contact

早川尚男（7024)

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。
*参照 基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51506

GCOE・基研セミナー

title

量子古典対応の情報幾何学的解析

author

松枝 宏明
仙台高等専門学校

date

2013年　3月14日（木）　16:00〜

place

基礎物理学研究所　研究棟・講義室K202

abstract

量子多体系を古典系に変換する方法は，鈴木・トロッター変換等に代表されるように，量子系の数値解析手法において非常に重要である． 一方，超弦理論のAdS/CFT対応のように，基礎物理的に興味のある量子古典変換も発見されて久しい． 更には，エンタングルメントくりこみ仮説（MERA）と呼ばれる最先端の変分理論も，エンタングルメント・エントロピーのスケール性の議論から，量子古典変換の物理を内包していると考えられている． AdS/CFTにおける古典サイドは，双曲（AdS）計量を持っており，それが元々の量子臨界系のスケール不変性を特徴づけている． 古典サイドの幾何学構造の物理的意味を調べることは，一連の物理のより深い理解につながると考えられる． 本研究では，古典サイドを具体的なモデルで表現するのではなく，抽象的な「情報」と捉え，情報がAdS空間に適切に格納できる場合に，その情報の物理的な意味は何か， また元の量子系がどのような性質を持つべきかを情報幾何学的に考察する[1]． 察する対象として，相対Tsallisエントロピーを距離として持つ情報空間を導入する（Tsallisの非加法性を与える因子qは全体の係数としてしか働かないので，基本的には相対vonNeumannエントロピーと同じ意味である）． このとき，最大限エンタングルした量子臨界系のデータは，AdS計量を持つ一次元高い古典情報空間に埋め込まれることが証明できる． 余剰の次元はエネルギー或いは長さスケールに相当する． 少なくとも空間一次元系では，中心電荷cが∞のときに量子系は最大限エンタングルするということが理論的に示せるが，この条件はAdS/CFTのlarge-N極限と同じものになっている． また，元の量子系の密度行列の古典表示は，ホログラフィックな相関関数と見なせるが，それが指数関数的に減衰し，確かに量子臨界的な長距離相関が消えていることが分かる． 物理的には，元の量子系が臨界状態のときには全ての長さスケールの競合を含んでいるので，それをスケールごとに分解すれば量子相関の弱い系としてAdS空間に適切にデータを格納できるということだと考えられる． 関連する研究として文献[2]が挙げられる．ここでは自由ボソン場（c=1）に対する情報空間が議論されている．このときは，c→∞でなくとも情報空間はAdSになる． Brown-Heneaux電荷の意味ではcはTsallisのqに含まれており，large-Nの仮定を緩めても相対エントロピーの構造は不変であることを示唆している．
[1] Hiroaki. Matsueda, arXiv:1208.5103.[2] Masahiro Nozaki, Shinsei Ryu, and Tadashi Takayanagi, arXiv:1208.3469

contact

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。
*参照 基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51501

GCOE・基研セミナー

title

重力波望遠鏡が拓く新しい天文学

author

安東正樹
国立天文台

date

2013年　3月8日（金）　16:00〜

place

基礎物理学研究所　研究棟・講義室K202

abstract

重力波の存在は、一般相対性理論によって理論的に存在が予言され、連星パルサーの軌道周期変化の観測から間接的に証明されている。 その一方、非常に微弱な信号であるため、直接検出は未だなされていない。 しかし、重力波を観測することができれば、連星合体や超新星爆発などの極限天体現象の中心部やブラックホールに関連する現象、晴れ上がり以前の初期宇宙など、これまでの電磁波による観測では得られない情報をもたらしてくれることが期待できる。 「かぐら」 (KAGRA)は日本が中心となって建設を進めている大型干渉計型重力波望遠鏡である。 KAGRAは、約200Mpc遠方の連星中性子星を観測できるだけの性能を持つ計画であり、実現されれば重力波の直接検出と、それによる新い天文学の創成を成し遂げることが期待できる。 本講演では、重力波天文学の可能性とその創成に向けたこれまでの取り組み、KAGRA計画の概要と建設の現状、さらに、将来の展望を紹介する。

contact

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。
*参照 基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51494

GCOE・基研セミナー(物性）

title

水面を浮遊する粉体の動的不均一性

author

齊藤 国靖
University of Twente, the Netherlands

date

2013年　2月25日（月）　16:00〜

place

基礎物理学研究所　研究棟・講義室K202

abstract

湖沼に発生したアオコや海を浮かぶ廃棄物など、水面を漂う浮遊物は時に厄介であり、その集団運動を理解することは環境を守るという観点からも重要である。 そこで、本実験では、浮遊物の集団的な振舞いを理解するため、水面に浮かぶ粉体の動的不均一性と被覆率との関係を調べた。 まず、水面に多数の粉体を浮かべ、水の入った容器を加振することで粉体を駆動する。 加振の強さは固定するため、粉体の被覆率が唯一のパラメータである。 この時、粉体同士は毛管力（capillary　force）を介して複雑に相互作用し、水面に生じる対流によって運ばれる。 個々の粉体の変位の内訳は、対流による輸送分がほとんどだが、その輸送分を差し引いた「ゆらぎ」に注目すると、驚くほど空間的に不均一であることが解った。 そこで、浮遊する粉体の易動度及びその分散を調べることで動的不均一性の時間スケールを見積もり、４点相関関数から動的相関長を測定した結果、ジャミング転移点の近傍で冪的な発散を示すことが解った。 また、本実験で得られた動的臨界指数の値は、異なる駆動力を用いた先行研究の結果とほぼ一致している。 本実験の重要な結論は、流れがある中にも動的不均一性を見出した点と、動的臨界指数が駆動力に依らない普遍性を持つことを示唆した点である [1]。 [1] C. Sanli, K. Saitoh, S. Luding, and D. van der Meer, “Denseheterogeneous flow of cohesive floaters on capillary ripples: A comparativestudy on morphological and conventional approaches to understand dynamicheterogeneities”, in preparation

contact

基礎物理学研究所 教授 早川尚男（内線：7024）

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。 *参照 基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51485

GCOE・基研セミナー(素粒子）

title

Matrix models for irregular conformal blocks

author

Chaiho Rim
Sogang University

date

2013年　2月15日（金曜日）　16:00

place

基礎物理学研究所　湯川記念館・会議室Y306

abstract

Irregular conformal block is a new tool to study Argyres-Douglas theory, whose irregular vector is represented as a simultaneous eigenstate of a set of positive Virasoro generators. We describe how to find the irregular conformal block using the partition function of the beta-ensemble of hermitian matrix model.

contact

基礎物理学研究所 細道和夫（内線７０７７）

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。 *参照 基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51483

GCOEセミナー

title

New features of broken time reversal symmetry in unconventional superconductors

author

Professor Manfred Sigrist
（ETH Zurich）

date

2013年　2月15日（金曜日）　10:00-11:30

place

理5号館（物理学教室）第４講義室（5階525号室）

abstract

Spontaneously broken time reversal symmetry (TRS) has been a fascinating feature of unconventional superconductivity every its discovery. In this talk I will discuss two phenomena in unconventional superconductors, one motived by recent experiments on the 3-Kelvin phase of Sr2RuO4 and the other representing a prediction of a novel state in non-centrosymmetric superconductors.
(1) The Josephson effect coupling Pb to Sr2RuO4 through Ru-metal inclusions shows a pronounced anomaly in the Josephson critical current at the transition to bulk superconductivity in Sr2RuO4. We will argue that this behavior may result from the TRS breaking chiral p-wave phase introducing topologically frustrated Josephson junction with a new limiting effect on the Josephson current.
(2) It was shown a few years ago that non-centrosymmetric superconductors could produce a TRS breaking phase locally at twin boundaries. However, this phase does not produce any magnetic features unlike other TRS breaking superconducting phases. We will show that in combination with spin magnetism the twin boundary state can undergo a secondary transition to a phase producing spin and orbital magnetism. This phase may be considered as spontaneous spin Hall effect.

contact

Y. Maeno（3783）

note

GCOE・基研セミナー（物性）

title

Nonequilibrium thermodynamics theory describing heat working at maxmum power

author

泉田 勇輝
お茶の水女子大学 シミュレーション科学教育研究センター

date

2013年　2月6日（水曜日）　16:00

place

基礎物理学研究所　研究棟・講義室K202

abstract

In recent years, there have been renewed interests in the efficiency at the maximum power (EMP) of heat engines among theoretical physicists since the so-called Curzon-Ahlborn (CA) efficiency [1] has been generally proved to be the upper bound of EMP for the linear irreversible systems in 2005 [2]. In this talk, I would like to introduce some recent theoretical advances on this new and old problem, especially focusing on our work. First I study a molecular kinetic model of a finite-time Carnot cycle working in the linear irreversible regime in detail [3, 4]. I show that the model satisfies a special condition to attain the bound (CA efficiency) by analyzing its transport coefficients explicitly. Then I propose a minimal model of general nonlinear irreversible heat engines [5], extending the results of the linear irreversible systems [2]. I derive an upper bound of EMP for these systems, which turns out be higher than the CA efficiency. If time permitted, I would also like to discuss physical significance of the size dependence of EMP by a molecular dynamics computer simulation of a heat engine model [6].

[1] F. Curzon and B. Ahlborn, Am. J. Phys. 43, 22 (1975).
[2] C. Van den Broeck, Phys. Rev. Lett. 95, 190602 (2005).
[3] Y. Izumida and K. Okuda, EPL. 83, 60003 (2008).
[4] Y. Izumida and K. Okuda, Phys. Rev. E 80, 021121 (2009).
[5] Y. Izumida and K. Okuda, EPL. 97, 10004 (2012).
[6] Y. Izumida and N. Ito, submitted

contact

基礎物理学研究所 教授 早川尚男（内線：7024）

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。 *参照 基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51478

GCOE・基研セミナー（物性）

title

Nonequilibrium Equation of States for a Confined Quantum Gas: Effects due to a Moving Piston

author

中村 勝弘　
(ウズベキスタン国立大学(タシケント))

date

2013年　2月4日（月曜日）　16:00

place

基礎物理学研究所　研究棟・講義室K202

abstract

We study a nonequilibrium equation of states for an ideal quantum gas confined in the cavity under a moving piston with a small but finite velocity [1], [2]. Confining to the thermally-isolated process, the quantum nonadiabatic (QNA) contribution to Poisson’s adiabatic equation and to Bernoulli’s formula which bridges the pressure and internal energy is elucidated. We carry out a statistical mean of the pressure operator in both the low-temperature quantum-mechanical and high temperature quasi-classical regimes. The QNA contributions are quadratic in the piston’s velocity and therefore time-reversal symmetric, in marked contrast to the conventional belief, and they are positive, which means that the moving piston gives rise to the apparently repulsive interaction among non-interacting Fermi particles, for both expansion and contraction of the cavity. The QNA contributions are inversely proportional to the longitudinal size of the cavity, and thereby play a nontrivial role in nano-scale heat engines based on quantum dots. The investigation is done for a unidirectionally-expanding 3-d rectangular parallelepiped cavity as well as its 1-d version. Its relevance in a realistic nano-scale heat engine is discussed.
[1] K. Nakamura, et al: Phys. Rev. E 83, 041133 (2011);
[2] K. Nakamura, et al: Phys. Rev. E 86, 061128 (2012).

contact

基礎物理学研究所 教授 早川尚男（内線：7024）

note

このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。
基研HP：http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51477

GCOE セミナー

title

High Field NMR in Cuprates and Quantum Spin Systems

author

Prof. Claude Berthier　
（LNCMI, CNRS (UPR 3228) UJF, UPS, INSA,
CNRS, BP 166, 38042 Grenoble Cedex, France）

date

2012年　11月8日（木曜日）　16:00−17:00

place

物理学教室　(理学部5号館)　401号室

abstract

After a short presentation of the Grenoble High Field magnetic facility, I’ll first describe recent experimental results on detwinned ultra-pure single crystals of underdoped YBaCuO6+x. In the ortho II and the ortho VIII phases, it is shown that above threshold field and below some threshold temperature, the magnetic field H induces a charge ordering which is compatible with stripe order of period 4a [1], providing a natural explanation for a reconstruction of the Fermi surface and the quantum oscillations observed in these sample. I’ll also discuss the particular case of YBaCuO6.45 on which neutron experiments have shown an increase “magnetic ordering” with the magnetic field [2]. NMR experiments show that this corresponds to a progressive freezing of AF fluctuations, with a huge increase of their average amplitude of the with H. The underdoped part of the phase diagram of the cuprate is re-discussed on this basis [3].
In the second part, I’ll illustrate the physics of weakly coupled dimers by NMR experiments in two quasi 2D systems, SrCu2(BO3) [4] and BaCuSi2O6 [5] . The first one is a frustrated system which is the archetype of the physics of magnetization plateaus. The second one undergoes a Bose Einstein Condensation triplet of excitations[6], but presents very unconventional properties[7] , namely an apparent 2D BEC due to the frustration between adjacent planes and different spin-gaps every second plane [5].
[1] T. Wu et al., Nature 477 191 (2011)
[2] D. Haug et al., Phys. Rev. Lett. 103 017001 (2009) ; New. J. Phys. 12 105006 (2010)
[3] T. Wu et al., submitted to PRL.
[4] K. Kodama et al., Science 202 (2000) ; M. Takigawa et al, arXiv : 1209.0069
[5] S. Kramer et al., Phys. Rev. B 76 100406 (2007) and unpublished
[6] M. Jaime et al., Phys. Rev. Lett. 93 087203 (2004)
[7] S.E. Sebastian et al., Nature 441 617 (2006)

contact

石田　憲二(kishida＠scphys.kyoto-u.ac.jp), 内線3752

note

GCOE Lecture

title

Quantum Spin Systems under high magnetic field

author

Prof. Claude Berthier　
（LNCMI, CNRS (UPR 3228) UJF, UPS, INSA,
CNRS, BP 166, 38042 Grenoble Cedex, France）

date

I: 2012年 10月　26日（金曜日）　16:00−17:30
II: 2012年 11月　2日（金曜日）　10:00−12:30

place

I: 物理学教室　理学部5号館北館　363号室
II: 物理学教室　理学部5号館　525号室

abstract

Lecture 1
・Introduction to general concepts
1. Quasi-1D systems:
Introduction to Jordan Wigner transformation, and Tomonaga-Luttinger Liquid
・The XXZ spin chain
・Alternated spin chains, J1-J2 Frustrated spin chains, spin-Peierls case.
・Spin-ladders
・Others

Lecture 2
2. Quasi-2D systems
・Bipartite systems
(square lattice, J1-J2 frustrated square lattice and geometrically)
・Frustrated systems (Triangular, Kagome lattice)
・Weakly coupled dimers
・Bose Einstein Condensation
・Magnetization plateaus

Purpose of The Lectures
Although a spin is by essence a quantum object, the denomination quantum spin system is usually dedicated to low-dimensional systems including localized electronic spins of small values (1/2, 1..), dominantly coupled by anti-ferromagnetic (AF) exchange interaction. These conditions enhance thermal and quantum fluctuations, and can destabilize the “semi-classical” long range order ground states, of Neel type. The interest for quantum spin systems has appeared very early from the theoretical point of view with the introduction of the Ising model, the Heisenberg model, the Jordan Wigner transformation, and the Bethe ansatz for spin 1/2 chains, all of them between 1925 and 1931. The excitations of the Heisenberg spin 1/2 chains were calculated in 1962, and notions like fractional excitations (the spinons), predictions in the framework of the Luttinger-Tomonaga paradigm, the Haldane conjecture that spin chains of integer spin should have gaped excitations have appeared well before any experimental support. For example, the first experimental evidence of spinons came only in 1995.
The purpose of these two lectures is not to review that enormous field, but simply to present an experimentalist point of view the general concepts used in the study of quantum spin systems, the development of this area in the last few decade, as well as unanswered questions. I’ll focus on the important role the magnetic field in the physics of quantum systems which has the capability to induce quantum critical points and new exotic ground states, like for example Bose-Einstein condensate or Wigner crystals of triplet excitations. This will be illustrated by examples based on experiments using NMR technique, which is presently (with EPR) the only technique allowing microscopic investigation above 17 T.

contact

Kenji Ishida (kishida＠scphys.kyoto-u.ac.jp), 内線3752

note

GCOE seminar

title

Stochastic differential equations and a review of their applications

author

Professor Petr Lansky　
（Academy of Sciences of the Czech Republic）

date

2012年 11月　1日（木曜日）　13:30−14:30

place

物理学教室　413号室

abstract

Differential equations played a unique role in physics over centuries and later on this also held for other branches of research as engineering, biology, chemistry and recently economics. In the first part of this lecture, the concept of stochastic differential equations will be introduced and illustrated on the simplest stochastic functions, namely Poisson and Wiener stochastic processes. In the next part, several applications to the real world problems will be mentioned, including population modeling and mathematical finance applications. Further, questions about the identification of the parameters of the stochastic differential equations will be shortly reviewed. Finally, a summary of our own results, including numerical techniques and search for the first passage time as a functional of random functions will be given. These results will be presented together with their implications for neuronal coding.

contact

篠本 滋, shinomoto＠scphys.kyoto-u.ac.jp

note

GCOEセミナー

title

Fate of long wavelength fluctuations and initial states of inflationary universe

author

Dr. Yuko Urakawa　
（University of Barcelona）

date

2012年　10月26日（金曜日）　17:30−18:30

place

基礎物理学研究所研究棟K206

abstract

The infrared(IR) behavior of fluctuations in (a quasi) de Sitter spacetime has been an issue of debate for more than decade. A key to the IR issue is to remove influences from an unobservable region in the universe, which can be interpreted also as gauge artifacts in the local observable universe. In this talk, we will adress the regularity of IR contributions in a general single field mode of inflation without employing the slow-roll approximation. We will show that the IR regularity of primordial perturbations strictly constrains the allowed quantum state. We will also reveal the connection between the IR regularity and the gauge invariance in the local universe.

contact

Takahiro Tanaka, tanaka＠yukawa.kyoto-u.ac.jp・宇治 7018）

note

GCOEセミナー

title

Trapped Anti-hydrogen : A new frontier in fundamental physics・
トラップされた反水素：基礎物理の新たな最先端

author

Prof. Dr. Niels Madsen氏　
（Swansea University, Department of Physics）
（京都大学招へい外国人学者 受入先：化学研究所）

date

2012年10月4日（木曜日）　15:00−16:30

place

物理学教室　北館　第2講義室

abstract

Detailed comparisons of anti-hydrogen with hydrogen promise to be a fruitful test bed of fundamental symmetries such as the CPT Theorem for quantum field theory or　studies of gravitational influence on antimatter. With a string of recent successes, starting with the first trapped anti-hydrogen and recently resulting in the first measurement of a quantum transition in anti-hydrogen, the ALPHA collaboration is well on its way to perform such precision comparisons. The presentation will discuss the key innovative steps that has made these feats possible and in particular focus on the detailed work on positron and antiproton preparation to achieve anti-hydrogen cold enough to trap as well as the unique features of the ALPHA apparatus that has allowed the first quantum transitions in anti-hydrogen to be measured with only a single trapped anti-hydrogen atom per experiment. We will also look at how ALPHA plans to step from here towards more precise comparisons of matter and antimatter and what we could possibly learn from such comparisons.

contact

野田　章（Akira Noda、noda＠kyticr.kuicr.kyoto-u.ac.jp・宇治(17)内線3281）

note

GCOEセミナー

title

Dissipation through dispersion

author

Professor Avraham Soffer　
（Rutgers University）

date

2012年6月27日（木曜日）　16:30−

place

物理学教室　5号館北棟第一講義室（265号室）

abstract

We consider systems coupled to a dispersive medium, in particular, Hamiltonian systems, both linear and nonlinear. The prime examples are the Nonlinear Klein-Gordon equation, the NLS with multibound state linear part, and the resonance problem in Quantum Mechanics. We show how the coupled modulation equations to the internal degrees of freedom of the localized system, leads to dissipation, through the dispersion of waves to infinity, and to, in general, non linear Master quations. In particular, this approach was used to derive rigorously the phenomena of “Selection of the Ground State” for NLS, which was later observed experimentally.

contact

太田隆夫（Takao Ohta,　ext 3740）

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GCOEセミナー

title

Asymptotic Stability of Solutions-Modulation Equations

author

Professor Avraham Soffer　
（Rutgers University）

date

2012年6月20日（木曜日）　16:30−

place

物理学教室　5号館北棟第一講義室（265号室）

abstract

I will describe a general theory to study the dynamics of soliton type solutions of Dispersive equations, under small perturbations. The solution equations are nonintegrebale in general, and the dynamics for large times of such systems is very rich and complicated. The approach I will use allows the control of the dynamics for all times, the scattering theory included, for small perturbations of such solitons.

contact

太田隆夫（Takao Ohta,　ext 3740）

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GCOE・基研セミナー

title

Particle Acceleration in Relativistic Shocks

author

Dr. Donald Ellison　
（North Carolina State University）

date

2012年4月26日（木曜日）　15:00−

place

京都大学基礎物理学研究所　研究棟・会議室K206

abstract

The first-order Fermi mechanism for particle acceleration in collisionless shocks has been studied extensively for over 30 years. Nevertheless, important problems remain, particularly when the shock speed approaches the speed of light. Nonrelativistic shock acceleration has been applied in many astrophysical environments, and relativistic shocks may be important for pulsar winds and for gamma-ray bursts, two of the most exotic of all phenomena. I will discuss the Fermi mechanism in general, and show new Monte Carlo results for relativistic shocks both in the test-particle limit and when accelerated particles make up a sizable fraction of the total energy. I will emphasize trans-relativistic shocks, a regime that is particularly difficult to address analytically but one that may be important for gamma-ray burst afterglows.

contact

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このセミナーは京都大学基礎物理学研究所と京都大学理学研究科グローバルCOEプログラム「普遍性と創発性から紡ぐ次世代物理学」の共催で行われます。

GCOEセミナー

title

The Surprising Story of Collisionless Shocks in Astrophysics

author

Dr. Donald Ellison　
（North Carolina State University）

date

2012年4月12日（木曜日）　11:00−

place

京都大学基礎物理学研究所　研究棟・会議室K206

abstract

For more than 30 years, first-order Fermi particle acceleration in collisionless shocks (i.e., diffusive shock acceleration, DSA) has remained the mechanism of choice for producing cosmic rays and other superthermal particle populations in various astrophysical environments. The nonlinear nature of the mechanism, a result of the intrinsic high acceleration efficiency, has presented challenges and surprises for modelers over the years. I will briefly describe some of the surprising aspects of DSA and, in particular, focus on magnetic field amplification and particle escape; two phenomena that highlight the difficult plasma physics involved and which are undergoing active current research. While collisionless shocks, with associated particle acceleration, are believed to exist on scales from the Earth bow shock to galaxy clusters, supernova remnants (SNRs) offer our best chance to study the mechanism.
This is the case because SNRs occur in varying environments including dense molecular clouds and several SNRs show extremely broadband continuum emission from radio to TeV gamma rays, sometimes accompanied with thermal X-ray emission. Other aspects, such as the morphology of some young remnants, offer unique clues to fundamental properties of the underlying plasma physics of both the remnant and the coupled acceleration mechanism.

contact

長瀧 重博
( nagataki@yukawa.kyoto-u.ac.jp)

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