セミナー 2014年

George T. Fleming, Yale U

Non-perturbative quantum field theory on curved manifolds

Meeting Room 1, Kenkyu Honkan 1F
A challenging problem in quantum field theory is the study of conformal (or nearly-conformal) fixed points occurring in the non-perturbative regime of a quantum field theory. Using radial quantization, computation on curved manifolds is essential. We propose a new approach called Quantum Finite Elements (QFE), an extension of the usual Finite Element Method (FEM) to solving classical PDEs, where renormalization of couplings can play a key role in the restoration of rotational invariance. Some aspects of our approach can be found in earlier work related to Regge calculus and lattice quantum gravity, as well as the random lattice approach of Christ, Friedberg and Lee. 

Dian-Yong Chen, Institute of Modern Physics, Chinese Academy of Sciences

Meson Loop Contributions to Heavy Quarkonium Decay

Seminar room, Kenkyu honkan 3F
As a phenomenological description of the non-perturbative property of QCD, meson loop mechanism plays a crucial role in understanding some particular decay behaviors of heavy quarkonia. In this talk, I will present our estimations of meson loop contributions to some strong decay process, such as $\Upsilon(5S) \to \omega \chi_{bJ}$, $\psi(4160)/\psi(4040) \to \eta J/\psi$ and $\chi_{c1} \to VV$. In addition, the meson loop contributions to the radiative transition processes are also discussed.

Kyohei Kawaguchi, Yukawa Institute, Kyoto University

Black hole-neutron star binary merger: dependence on black hole spin orientation and equations of state

Meeting room 1, Kenkyu honkan 1F
Black hole-neutron star binary mergers are the one of most promising sources of gravitational waves for next generation ground-based gravitational-wave detectors such as Advanced LIGO, Advanced VIRGO, and KAGRA, and gravitational waves from black hole-neutron star binary are expected to be detected in a next decade. Black hole-neutron star binary mergers have also been proposed as the progenitor of short gamma-ray-bursts in the so-called merger scenario. Moreover, some part of neutron-rich material of the neutron star is ejected dynamically during the merger, and the emission powered by decay of radioactive nuclei would occur (Kilonova/Macronova), which reflect the property of the binary. In this talk, I will discuss dependence of the gravitational waveform, the disk formation and the mass ejection from black hole-neutron star binary merger on the mass ratio of the binary, the equation of state of the neutron star and the black hole spin, which have been clarified by the numerical relativity simulations. In particular, I will focus on the case that the black hole spin is misaligned with the orbital angular momentum of the binary, and discuss the effects of the spin misalignment on the merger process.

Jnanadeva Maharana

Dimensional Reduction and T-duality

Seminar room, Kenkyu honkan 3F
String theory is rich in symmetry contents. When the string effective action is dimensionally reduced to lower spacetime dimensions new symmetries manifest. T-duality is one of them. Of particular interest is the emergence of O(d,d) symmetry. I shall bring out the essential features of this symmetry. I shall also very briefly mention about the recent paper of Lechtenfeld, Sen and Zweibach.

Martin Stoll, The University of Tokyo

High-pT top tagging

Meeting room 1, Kenkyu honkan 1F
For highly boosted top quarks (pT above ~TeV), its decay products become collimated. Due to limited detector resolution commonly used jet substructure methods fail to work, whereas charged tracks still offer the possibility for efficient top tagging. I briefly review some standard top taggers and present recent development of the high-pT Top Tagger (HPTTopTagger). This algorithm is based on the charged tracks inside a large-radius jet and allows to probe new resonances in the multi-TeV range.

Astushi Tanaka, Tokyo metropolitan university


Seminar Room, Kenkyu Honkan 3F
断熱準静過程によるサイクル上を物理系が一周しても何の変化も起きないように思われます。しかし、孤立した量子系で始状態を固有状態に準備した場合、断熱サイクルは幾何学的な位相因子(ベリーの位相因子)と呼ばれる非自明な変化を状態ベクトルにもたらします。これはファイバー束のホロノミーとの対応 (Simon 1983)から(位相の)量子ホロノミーとも呼ばれます。Aharonov と Anandan (1997) はサイクルを記述する空間として射影ヒルベルト空間を用いることで、量子ホロノミーの非断熱拡張を与えました。 近年、断熱サイクルは固有エネルギーや固有空間に対しても非自明な変化をもたらすことが報告されてきました。これらを新奇な量子ホロノミーと呼びます (例えば、Yonezawa et al., PRA 87 (2013) 062113 とその引用文献参照)。ここでは、断熱サイクルが複数の固有エネルギーや固有空間達の置換を引きおこします。この現象はパラメーターを持つ量子系の解析全般、例えば、分子のボルン・オッペンハイマー近似、あるいは、固体中の電子のバンド理論と関連するように思われます。 本講演では、新奇な量子ホロノミーを示す物理系をいくつか紹介した後で、新奇な量子ホロノミーの位相幾何学的な背景について報告します。そこで現れる被覆空間の構造と断熱サイクルのホモトピーによる分類の役割を中心にお話しします。これは、幾何学的位相における Simon の定式化や Aharonov-Anandan の非断熱拡張に対応するものです (文献は AT and T. Cheon, arXiv:1409.5211)。

Yukinao Akamatsu, KMI, Nagoya U

Chiral plasma instabilities for Abelian and non-Abelian gauge fields

Meeting room 345, 4 go-kan 3F
Recently, kinetic theory of chiral fermions has been developed. Spin of chiral fermions introduces an interesting nontrivial structure in the phase space: Berry connection in the momentum space in the monopole configuration. This new kinetic theory can describe the axial U(1) anomaly and the so-called chiral magnetic effect. In this talk, we consider QED and QCD plasmas with massless fermions and apply the new kinetic theory to the dynamics of gauge fields. When there is an imbalance between left-handed and right-handed fermions (chirality imbalance), we find that the gauge field becomes unstable. We call this instability chiral plasma instability. The unstable mode grows so as to reduce the chiral imbalance, which is the source of the instability. The effect of collisions is relevant for the instability of the QCD plasma while it is not for the QED plasma. We also develop an effective chiral Langevin theory for non-Abelian gauge fields in QCD plasma that describes both the chiral plasma instability and soft collisions.

Tatsuma Nishioka, The Univ. of Tokyo

Entanglement Entropy in Gapped System

Meeting room 3, Kenkyu honkan 1F
Entanglement entropy is a useful order parameter charactering phases in quantum field theories in various dimensions. For example, it can capture confinement/deconfinement and quantum phase transitions. The analytic computations, however, are limited to special cases such as conformal and free field theories. In this talk, I would like to elucidate various properties of entanglement entropy in gapped systems by using both field theoretic and holographic approaches. I will also discuss how entanglement entropy behaves under a perturbation of CFT by a relevant operator and point out that the perturbative calculation may fail depending on the conformal dimension.

Toshifumi Yamada, NCU, Taiwan

T-odd asymmetry in W+jet events at the LHC

Meeting room 3, Kenkyu Honkan 1F
W bosons produced at high transverse momentum in hadron collisions can
have polarization along the direction perpendicular to the production
plane, which is odd under naive-T-reversal where both the
three-momenta and angular momenta are reversed. Perturbative QCD
predicts non-zero polarization at the one-loop level, which can be
measured as parity-odd components in the angular distribution of
charged leptons from the decay of W bosons. We perform a
detector-level simulation with the generator aMC@NLO, and demonstrate
that the asymmetry can be observed at the 8 TeV LHC with 20 fb^-1 of
data. If confirmed, it will be the first experimental measurement of
the sign of the imaginary part of one-loop QCD amplitudes.

Khaiming Wong, Universiti Sains Malaysia(USM) MALAYSIA School of Physics

Half-Integer Magnetic Monopole and Dyon Solutions in the SU(2) Yang-Mills-Higgs Theory

Seminar room, Kenkyu honkan 3F
We review magnetic monopoles and dyons of one-half topological charge with finite energy in the SU(2) Yang-Mills-Higgs theory.
The half-monopole can exist individually, where it is located at the origin of the coordinate axes r = 0. It can also coexist with a ‘t Hooft-Polyakov monopole, with the one-monopole with charge +1 at the positive z-axis and a half-monopole with charge – ½ at the origin.
Both of these axially symmetric configurations possess finite total energy and magnetic dipole moment. The total energy is found to increase with the strength of the Higgs field self-coupling constant λ. The magnetic dipole moment and the dipole separation (one plus half-monopole) decrease with λ. Both the two configurations are non-BPS solutions even in the BPS limit when the Higgs self-coupling constant vanishes. By switching on the time component of the Yang-Mills potential, electric charge is introduced into the system, where we now have half-dyon and one plus half-dyon.
Besides possessing electric charge which varies with λ and electric charge parameter η, the configurations also exhibit critical behaviour in total energy, electric charge, and dipole moment, when η→1.

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