セミナー

Dmitry Khangulyan, JAXA

Shedding light on the pulsar wind

Meeting room 1, Kenkyu honkan 1F
Pulsars are believed to eject ultrarelativistic electron-positron winds that propagate to the large distances leading to the formation of the extended non-thermal sources known as plerions. The wind has been proposed to originate close to the light cylinder, and carry the rotational energy losses of the pulsar. At the beginning the wind is dominated by electromagnetic energy (Poynting flux), but at some later stage the wind is accelerated with most of the Poynting flux being converted to the kinetic energy of bulk motion. Such winds have not been yet observed, therefore the proposed scenario has been deemed inconclusive. The `cold’ winds (in the sense of the low energy of the electrons in the frame of moving plasma) represent a form of “dark substance” since, despite the very high energy of the wind particles, the wind emission is extremely weak. In fact, the pulsar winds are visible only in inverse Compton gamma-rays. Recent observations in high energy (HE) and very high energy (VHE) domains with Fermi Large Area Telescope (Fermi/LAT) and ground based Cherenkov detectors Magic and Veritas allow the key properties of the pulsar winds to be measured in a few important systems. In particular, the recently observed VHE pulsed gamma-rays emitted by the Crab pulsar are best explained as arising from the X-ray photons scattering off the wind’s electrons. This finding supports the presence of an ultrarelativistic wind in the Crab pulsar, and provides unique information about the acceleration site of the wind at R_w ~ 30 light cylinders, and its Lorentz factor, Γ_0 = 5 x 105. In the case of the pulsars located in close binary systems, the dense stellar photon field provided by the companion star can dramatically enhance the interaction rate of wind electrons with target photons, leading to the formation of detectable gamma-ray signal. Interestingly, the bright gamma ray flare of the binary pulsar PSR B1259-63/LS2883 detected by the Fermi/LAT after several weeks of the periastron passage, can be also interpreted as the inverse Compton (IC) emission of the unshocked electron-positron pulsar wind with Lorentz factor Γ_0 ~104.

Aleksey Cherman, University of Cambridge

Sneaking up on dense QCD using large N methods

Meeting room 1, Kenkyu honkan 1F
Finite-density QCD notoriously suffers from the fermion sign problem, which makes lattice Monte Carlo simulations essentially impossible. As a result, we have little non-perturbative information on the behavior of QCD at finite baryon number density. I will discuss a recent proposal to dodge the sign problem by exploiting orbifold equivalence, a property of the large N limit of QCD. The proposal starts with the observation that if the gauge group of QCD is changed from SU(N) to SO(N), the sign problem does not appear at finite baryon number chemical potential, and the resulting theory can be studied on the lattice. Despite this seemingly drastic change, it turns out that there is a large N orbifold equivalence between the SO(N) theory and SU(N) QCD. I will argue that with some extra work, the equivalence can be made to hold at finite chemical potential, while the SO theory does not have a sign problem. This opens up the prospect of learning about QCD at finite baryon number density using lattice studies of the SO(N) theory.

Kunio Kaneta, Osaka University

Parity Violation in SUSY QCD

Meeting room 1, Kenkyu honkan 1F
In SUSY QCD, a mass of left-handed squark is generally not the same as that of right-handed squark. Therefore, parity can be violated in QCD process by quark-squark-gluino vertexes. We focus on this parity violation, and discuss following two topics.
1. A discrimination between SUSY and UED. SUSY and UED are promising candidates beyond the SM. It is important to experimentally distinguish one from the other. We make a proposal to discriminate SUSY from UED at the LHC by focusing on the parity violation without discovering any new particles.
2. A bound for left-right degeneracy between squark masses. Since any parity violations have not been discovered in QCD, non-degeneracy bounds should be obtained between left-and right-handed squarks. We try to estimate the bounds by an investigation of charmonium decay and nucleon interactions.

大川博督, 京都大学基礎物理学研究所

高次元ブラックホール衝突

Meeting room 1, Kenkyu honkan 1F
高次元時空における数値相対論は、高次元ブラックホールの安定性や、高次元重力への検証のような現象を調べる有用な道具の一つとなった。高次元重力理論において、プランクエネルギーがTeVスケール程度としても現時点での重力実験と無矛盾であり、LHCなどの高エネルギー粒子衝突実験において、極小ブラックホールが形成される可能性が指摘された。
プランクスケール以上では本来量子効果を考慮すべきであるが、高エネルギー粒子衝突において、プランクスケールを超える物理過程は生成されるブラックホールの地平面に隠されると信じられている。このスケールでのブラックホール形成の段階は、高次元の一般相対論でよく記述できると考えられているため、形成段階を調べるために高次元高速ブラックホールの衝突を用いる。本発表では、数値相対論について簡単に触れた後、高次元数値相対論を用いた高次元ブラックホール衝突についての結果を発表する。まず、ブラックホール正面衝突からの重力波について述べ、衝突係数を持つブラックホール衝突において、ホライズンに囲まれないプランクスケールを超える領域が生成されることを数値的に示す予定である。

Souvik Banerjee, Institute of Physics, Bhubaneswar

The Holographic Spectral Functions in Non-Equilibrium States

Meeting room 1, Kenkyu honkan 1F
We show how holography gives a framework to reproduce aspects of kinetics in strongly coupled media. We develop a holographic prescription to compute the spectral function of (Bosonic/Fermionic) operators in non-equilibrium states. We apply this prescription to reproduce the expected oscillation of the holographic Fermi surface in states with hydrodynamic fluctuations about equilibrium.

Kwang-Chang Lai, Chang Gung University

Astrophysical High Energy Neutrinos

Large meeting room, 2 go-kan 1F
The construction of neutrino telescopes such as IceCube, ARA, KM3Net, etc. makes important progress toward the neutrino astronomy. With the capability of observing astrophysical high energy neutrinos (AHENs) and of identifying their flavors, neutrino telescopes open a new window on both astrophysics and particle physics. In this report, I will first review briefly different sources of AHENs, in terms of their flavor compositions. The difficulty in resolving the source type is analyzed by combining the accuracies in neutrino telescope observations and the knowledge of neutrino mixing angles. Second, a new parametrization of flavor transition matrix will be introduced, with which I discuss classification of flavor transition mechanisms, including decay models, and probes for transition matrix elements. Finally, neutrino signals in the telescope and discrimination of their flavors will be addressed.

Seiji Zenitani, National Astronomical Observatory of Japan

Numerical modeling of relativistic magnetic reconnection (in Japanese)

Meeting room 3, Kenkyu honkan 1F
There is a growing attention to magnetic reconnection in relativistic astrophysics, but basic mechanisms of relativistic reconnection have been poorly understood.  In this talk I will overview our numerical investigations on magnetic reconnection in relativistic pair plasmas.  Kinetic particle-in-cell (PIC) simulations demonstrate that reconnection is a powerful particle accelerator and that various kinetic instabilities take place.  Relativistic two-fluid and resistive relativistic magnetohydrodynamic (RRMHD) simulations show larger-scale pictures including various new shocks.  General features in these results as well as the relevance to the theoretical models will be presented.

佐野崇, 東京大学

有限密度QCDにおけるランダム行列模型の応用と複素ランジュバンシュミュレーション

Seminar room, Kennkyu honkan 3F
有限密度QCDの模型としてのカイラルランダム行列(ChRM)模型に対し、我々は二通りの応用を行った。
第一に、カイラル凝縮とダイクォーク凝縮を秩序変数としたChRM模型を構築し、有限温度密度相構造を研究した。QCD相互作用のもつ対称性から、クォーク・反クォーク、クォーク・クォーク相互作用の結合定数の比は一意に定まり、相構造も一意に得られる。3つのクォークフレーバの質量が同じ時には、低密度側でカイラル対称性の敗れた相(ChSB)が、高密度側でcolor-flavor locked(CFL) 相が基底状態として得られる。また、udクォークとsクォークの間に質量の非対称性がある(2+1フレーバ)場合には、udクォークによるダイクォーク凝縮のみの存在する2SC相が、ChSB相とCFL相との中間密度領域に現れる。
第二に、格子QCDシミュレーションの方法として提案されている、複素ランジュバン方程式を用いた方法を、ChRM模型を用いて試行した。複素ランジュバンシミュレーションは、有限密度QCDにおける符号問題を回避しうる方法として提案されているが、数学的基礎付けが不十分で、シミュレーションが正当化できるかどうか明らかではない。発表では、複素ランジュバンシミュレーションに対する現状の理解をまとめてレビューし、その後、ChRM模型の厳密解と数値解 を比較する。複素ランジュバンシミュレーションは、一部の領域で解析解を再現できないことが発見され、その理由を、符号問題とあわせて考察する。

Takehiro Nabeshima, Toyama University

TeV-Scale Seesaw with Loop-Induced Dirac Mass Term and Dark Matter from U(1)_{B-L} Gauge Symmetry Breaking

Meeting room 3, Kenkyu honkan 1F
show a TeV-scale seesaw model where Majorana neutrino masses, the dark matter mass, and stability of the dark matter can be all originated from the U(1)_{B-L} gauge symmetry. Dirac mass terms for neutrinos are forbidden at the tree level by U(1)_{B-L}, and they are induced at the one-loop level by spontaneous U(1)_{B-L} breaking. The right-handed neutrinos can be naturally at the TeV-scale or below because of the induced Dirac mass terms with loop suppression. Such right- handed neutrinos would be discovered at the CERN Large Hadron Collider (LHC). On the other hand, stability of the dark matter is guaranteed without introducing an additional Z_2 symmetry by a remaining global U(1) symmetry after the U(1)_{B-L} breaking. A Dirac fermion Psi_1 or a complex neutral scalar s^0_1 is the dark matter candidate in this model. Since the dark matter (Psi_1 or s^0_ 1 ) has its own B-L charge, the invisible decay of the U(1)_{B-L} gauge boson Z′ is enhanced. Experimental constraints on the model are considered, and the collider phenomenology at the LHC as well as future linear colliders is discussed briefly.

Jun Suzuki, University of Electro-Communications

Radiation from accelerated impurities in a Bose–Einstein condensate (in Japanese)

Seminar room, Kenkyu honkan 3F
We investigate radiation spectra arising from accelerated point-like impurities in the homogeneous Bose– Einstein condensate. A general formula for the radiation spectrum is obtained in the integral form as a function of given impurity trajectory within the Bogoliubov approximation. The Planckian spectrum is obtained for a special accelerated motion, which is shown to be unphysical. Non-Planckian spectrum is found in the case of a uniformly accelerated impurity. We compare our result with similar settings discussed in other quantum systems.

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