セミナー 2018年

永長直人, 理研・東大

[第八回KEK連携コロキウム] Chirality in dynamics

つくばキャンパス4号館1階セミナーホール/東海キャンパス東海1号館115号室 (TV会議中継) 
When the system lacks both parity and mirror symmetries, it is called “chiral” and can be classified into right-handed and left-handed. Chirality is one of the most fundamental issues in many branches of science [1]. In biology, the chirality of DNA is the same for all the living creatures on earth. In chemistry, to synthesize the molecules of one chirality selectively is an important issue. In physics, the parity violation is a striking feature of weak interaction. Here we focus on the chirality appearing in dynamics. It appears trivial that the flows of particles are different between right and left directions when the system is chiral. However, this is not the case as seen from the simplest problem of a single particle scattering problem by one-dimensional asymmetric potential. Namely, the unitary nature of the quantum mechanical time evolution put the constraint on the S-matrix, and the transmission/reflection probabilities are the same for right and left incident waves. Dissipation breaks the unitary nature of the time evolution, and hence the friction, which brings the classical nature of the dynamics, plays an important role for the directional (nonreciprocal) responses of the system. The time-reversal symmetry of the microscopic Hamiltonian also plays an essential role in the nonreciprocal responses of the system. In this talk, I will discuss that the most fundamental principles in physics manifest themselves in the nonreciprocal responses of chiral systems, i.e., the symmetries, dissipation, quantum-classical crossover/transition, quantal Berry phase and topology, and many-body correlation effects. The concrete examples to discuss include magnetochiral anisotropy of semiconductors [2], Weyl semimetals [3], and superconductors [4], nonlinear spin current generation in Rashba-Dresselhaus systems, and shift currents under photo-excitations [5]. The collaborators of these works are T. Morimoto, K.W. Kim, R. Wakatsuki, K. Hamamoto, M. Ezawa, H. Ishizuka, S. Hoshino, S. Koshikawa, S. Shimizu, Y. Kaneko Y. Saito, T. Ideue, Y. Iwasa, and Y. Tokura.
[1] M. Gardner, The Ambidextrous Universe. Left, Right and the Fall of Parity, Basic Books Inc. (1964)
[2] T. Ideue et al., Nature Physics 13, 578-583 (2017).
[3] T. Morimoto and N. Nagaosa, Phys. Rev. Lett. 117, 146603 (2016).
[4] R. Wakatsuki et al., Science Advances 3, e1602390 (2017)
[5] T. Morimoto and N. Nagaosa, Science Advances 2, e1501524 (2016).

Tomoaki Ishiyama, Chiba University

Supercomputer simulations of dark matter structure formation in the Universe

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
We report the results of ultralarge cosmological N-body simulations of small and large scale structure formation in the Universe. In particular, I focus on the formation and evolution of dark matter halos and subhalos near the free streaming scale, and their impact on the indirect dark matter detection experiments. We also present the implementation of our massively parallel simulation code for modern huge supercomputers.

本間謙輔, 広島大学

Search for weakly-coupling pseudo Nambu-Goldstone bosons by mixing multi-wavelength coherent lights

Room 345, 4 go-kan

Sai Wang, KEK

Probing primordial black hole dark matter with aLIGO using stochastic background of gravitational waves

Meeting room 1, Kenkyu honkan 1F
Advanced LIGO’s discovery of gravitational-wave events is stimulating extensive studies on the origin of binary black holes. Assuming that the gravitational-wave events can be explained by binary primordial black hole mergers, we utilize the upper limits on the stochastic gravitational-wave background given by Advanced LIGO as a new observational window to independently constrain the abundance of primordial black holes in dark matter. We show that Advanced LIGO’s first observation run gives the best constraint on the primordial black hole abundance in the mass range from ~1 to ~100 solar mass, pushing the previous microlensing and dwarf galaxy dynamics constraints tighter by 1 order of magnitude. Moreover, we discuss the possibility to detect the stochastic gravitational-wave background from primordial black holes, in particular from subsolar mass primordial black holes, by Advanced LIGO in the near future.

Sanjaye Ramgoolam, Queen Mary, University of London

Branes, Dominoes and Words.

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Half-BPS and quarter-BPS operators in N=4 super Yang Mills theories with SO(N) gauge group are related to giant graviton branes in an orientifold of AdS5 times S5 string theory. The orientifold projection operation on the half-BPS operators can be calculated using domino tilings of Young diagrams. Through the AdS/CFT correspondence, this reveals a connection between domino combinatorics and branes in orientifolds of AdS5 times S5. The large N limit of counting functions for the quarter BPS operators in U(N) and SO(N) theories reveals a rich structure related to the combinatorics of words. The underlying perspective leading to these results is a permutation approach to gauge invariants, which has proved to be a surprisingly rich source of insights on AdS/CFT.

Nobuya Nishimura, YITP, Kyoto University

Synthesis of the Trans-Iron Elements in Stars

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Stellar nucleosynthesis beyond iron-group nuclei provides additional problems that we do not encounter when studying nucleosynthesis processes for light nuclei. Besides ambiguity in the determination of astrophysical sites/conditions, uncertainties in nuclear physics inputs have signifiant impacts on the theoretical nucleosynthesis predictions. In this talk, I present recent results of comprehensive nucleosynthesis studies, focusing on the uncertainties of relevant nuclear reactions and decays. The evaluated uncertainty range for the several nucleosynthesis processes, e.g., s- and r-processes, gamma-process and nup-process, are discussed. I also show the lists of “key reactions”, which have strong impacts on the nucleosynthesis yields, based on our Monte-Carlo based analysis.

Alessandro Sfondrini, ETH Zürich - Institute of Theoretical Physics

Integrability, correlation functions, and stringy WZW models

Meeting room 1, Kenkyu honkan 1F
Integrability techniques have been crucial to compute non-protected observables in AdS/CFT, starting from the planar spectrum (two-point functions) of the theory. Recently it was understood that planar three- and higher-point functions, as well as non-planar observables, can be computed by integrability techniques. I will discuss these advances in relation to one recently-discovered integrability setup: the AdS3xS3xT4 stringy Wess-Zumino-Witten model.
Based on: 1611.05436, 1710.10212, 1804.01998, 1806.00422.

宮武宇也, KEK和光原子核科学センター


つくばキャンパス研究本館/小林ホール東海キャンパス東海1号館116号室 (TV会議中継)
物質の起源と銀河の進化を探求する宇宙核物理と呼ばれる研究領域は、宇宙物理、天文観測、原子核物理などの研究者が連携して急速に進化を遂げている領域です。原子核物理のセクターでは、短寿命原子核などが介在する元素合成過程を地上の加速器実験で再現し、起源天体の解明・特定を目指しています。2016年度より共同利用を始めた和光原子核科学センター(WNSC)の元素選択型質量分離器(KEK Isotope SeparationSystem;KISS)も、宇宙核物理に寄与するために設置された装置です。この装置によるおもな研究課題は、天体における重元素合成過程、特に金や白金を生み出した速い中性子捕獲(r-)過程の研究を通じて、爆発的天体現象の解明を行う点にあります。このコロキウムでは、最近の中性子星合体天文観測からのインパクトも含めて、KISSプロジェクトの一端をご紹介したいと思います。  

Chinami Kato, Waseda University

The evolutions of massive stars and the importance of neutrino observations

Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
Massive stars with more than 8 solar mass initially are supposed to be progenitors of core-collapse supernovae, however, there still remain many problems about the understanding of their evolutions and deaths, especially the interior profile of cores and the explosion mechanism. In order to solve these problems, some observations are necessary. Then we focus on the observations of “neutrinos”, which are emitted inside the stellar core or proto-neutron stars and decide their evolutionary paths. In this talk, I want to talk about what we can learn about the stellar evolutions from the observations of pre-SN and SN neutrinos and what we should do theoretically for the next galactic supernovae which will occur in the near future. In detail, we calculate the realistic neutrino luminosities and spectra for all flavors and estimate the number of events at the terrestrial neutrino detectors.

Debasish Borah, IIT Guwahati, India

When Freeze-out Precedes Freeze-in: Sub-TeV Dark Matter with Radiative Neutrino Mass

Seminar room, Kenkyu honkan 3F
We discuss a minimal predictive scenario for dark matter and radiative neutrino mass where the relic abundance of dark matter is generated from a hybrid setup comprising of both thermal freeze-out as well as non-thermal freeze-in mechanisms. Considering three copies of fermion triplets and one scalar doublet, odd under an unbroken reflection symmetry Z2, to be responsible for radiative origin of neutrino mass, we consider the lightest fermion triplet as a dark matter candidate which remains under-abundant in the sub-TeV regime from usual thermal freeze-out. Late decay of the Z2-odd scalar doublet into dark matter serves as the non-thermal (freeze-in) contribution which not only fills the thermal dark matter deficit, but also constrains the mother particle’s parameter space so that the correct relic abundance of dark matter is generated. Apart from showing interesting differences from the purely freeze-out and purely freeze-in dark matter scenarios, the model remains testable through disappearing charge track signatures at colliders, observable direct and indirect detection rates for dark matter and prediction of almost vanishing lightest neutrino mass.

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