报告人：张同杰，北京师范大学
时间： 7月14日（周五）10:00
单位：中科院高能物理研究所
地点：化学楼C305
Constraining neutrino mass remains an elusive challenge in current physics and astronomy. Precision measurements are expected from several upcoming cosmological probes of large-scale structure. Achieving this goal relies on an equal level of precision from theoretical predictions of neutrino clustering. Numerical simulations of the non-linear evolution of cold dark matter and neutrinos play a pivotal role in this process. We run the world’s largest cosmological N-body simulation, named TianNu, which coevolved just under 3 trillion CDM and neutrino particles on Tianhe-2(Galaxy-2) supercomputer. Based on TianNu data, we discover the differential neutrino condensation effect and the dipole in real space using the simulation density and velocity fields. In addition, we also provide details of our production run, which uses 86% of the machine (13,824 compute nodes), and a discussion of the unanticipated computational challenges that were encountered during the TianNu runtime.
2Dynamic scaling in 2D Ising spin glasses
报告人：Anders W. Sandvik，Boston University
时间：7月12日（周三）10:00
单位：北京师范大学物理系
地点：物理楼106
Spin glasses are characterized by complex energy landscapes and slow relaxation dynamics. In two dimensions, the glass transition temperature of the classical Ising spin glass is exactly T=0. In this talk I will discuss how simulated annealing with Metropolis dynamics relaxes the system toward the glass state as the temperature is lowered to zero in different ways. The dynamic exponent z governing the relaxation is very large, z~10 (meaning that the simulation time needed to reach the lowest energy scales with the system length as t~L^z). Moreover, there is a qualitative difference between systems with bimodal and continuous coupling distributions, which can be explained by degenerate or unique ground states for the two cases. In addition to giving information on the nature of the spin-glass transition, the insights can also be useful in the context of optimization theory.
3Axions: Current Bounds and Discovery opportunities
报告人：Alessandro Mirizzi，INFN, Bari and Bari U.
时间：7月12日（周三）10:00
单位：中科院高能物理研究所
地点：Seminar Room 312, Library Building
Very light axion-like particles (ALPs) with a two-photon vertex are predicted in many extensions of the Standard Model of particle physics. Depending on the actual value of their mass, ALPs can play an important role in cosmology, acting as cold dark matter. The coupling with photons allows for ALP-photon mixing in external electromagnetic fields. This effect is exploited for direct searches of ALPs in laboratory experiments. The two-photon vertex would also induce the mixing with ALPs for photons emitted by distant astrophysical sources, and propagating in the large-scale cosmic magnetic fields. This mixing could produce signatures in astrophysical observations, ranging from the cosmic microwave background to the high-energy gamma-rays. In this talk the speaker will present an overview of current bounds on ALPs and discovery opportunities in the planned laboratory and astrophysical experiments.
4Unconventional magnetism and spontaneous spin-orbit ordering
报告人：Congjun Wu，University of California
时间：7月12日（周三）15:00
单位：北京师范大学物理系
地点：物理楼106
报告人：姚秋玲，中科院高能研所
时间：7月12日（周三）15:00
单位：中科院高能物理研究所
地点：计算中心二楼会议室
CASTOR是一套由CERN开发的分级存储管理系统，用于存储海量物理数据，实现在磁盘和磁带不同级别的存储介质之间进行文件的迁移。CASTOR中的文件可通过RFIO（远程文件输入/输出）协议采用命令行或函数调用的方式进行访问。CASTOR在CERN和IHEP中已经应用很长时间。
6Engineering and probing topological properties of Dirac semimetal films by asymmetric charge transfer
报告人：Kyungwha Park，VirgininaTech
时间： 7月13日（周四）14:00
单位：中科院高能物理研究所
地点：M楼830
Dirac and Weyl semimetals have been under intense investigation due to topologically protected Weyl nodes and Fermi arc states connecting the node projections at a surface. Recently, Na3Bi, Cd3As2, PtSe2, and PtTe2 have been experimentally confirmed to be Dirac semimetals (DSMs), where the Dirac nodes are stabilized by crystal rotational symmetries. In the presence of an external magnetic field, the DSMs become Weyl semimetals. In heterostructures involving DSMs, charge transfer may occur at the interfaces, which can be used to probe and control their bulk and surface topological properties through surface-bulk connectivity. Here we demonstrate that despite a band gap in thin DSM films, asymmetric charge transfer at the surface enables one to accurately identify locations of the Dirac-node projections from gapless band crossings and to examine and engineer properties of the topological Fermi-arc surface states connecting the projections, by simulating adatom-adsorbed DSM films using a first-principles method and by comparing with the effective model. We show that as the amount of charge transfer varies, unique spin textures near the projections and a separation between the Fermi-arc states change. Our results can be observed by top or bottom gating without adatoms.
7Topological Band Theory for Non-Hermitian Hamiltonians
报告人：沈汇涛，MIT
时间：7月13日（周四）15:30
单位：中科院物理研究所
地点：M楼830
Recently, there have been many experimental realizations of the non-Hermitian Hamiltonians in both open quantum systems and classical wave systems with gain or loss. I will show that the non-Hermitian Hamiltonians host topological classification very differently from the Hermitian ones. There are non-trivial generalizations of the Chern number in two dimensions, and a new classification in one dimension, which is based on the energy dispersion rather than the Bloch state.
I will first start talking about the basics of the non-Hermitian Hamiltonians, and then introduce the topological band theory, by explicitly showing the topological invariants. I will also talk about the non-Hermitian bulk-edge correspondence as well as the phase diagram for topological phase transitions, if there is time.
