慶應素粒子論セミナー
Keio High Energy Physics Seminars

(2012)

Date: 5/7(Mon.) 16:30 -
Speaker: Dr. Nan Su (Bielefeld Univ.)
Title: QCD thermodynamics at intermediate coupling
Abstract: The weak-coupling expansion of the QCD free energy is known to the order g^6*log[g], however, the resulting series is poorly convergent at phenomenologically relevant temperatures. In the first part of this talk, I will discuss how the gauge invariant hard-thermal-loop perturbation theory (HTLpt) reorganization of the calculation improves the convergence of the successive approximations to the QCD free energy. I will present HTLpt results of QCD thermodynamics to 3-loop order, which are consistent with lattice data down to 2-3T_c. This is a non-trivial result since, in this temperature regime, the QCD coupling constant is neither infinitesimally weak nor infinitely strong with g~2, or equivalently alpha_s~0.3. Therefore, we have a crucial test of the quasiparticle picture in the intermediate coupling regime. Our results suggest that HTLpt provides a systematic framework that could be used to calculate static and dynamic quantities for temperatures relevant at LHC. In the second part of this talk, I will move on to discuss the effect of the gauge fixing ambiguity, i.e. the Gribov copies, on the thermodynamic quantities. I will report the motivation and progress of a 1-loop Yang-Mills thermodynamics calculation with the Gribov copies fixed. The Gribov mass parameter can be solved self-consistently via a non-perturbative horizon condition and the result turns out to be of the order g^2T, i.e. the same order as the magnetic scale. As a consequence, the 1-loop thermodynamic potential already contains contributions from the non-perturbative magnetic scale. In contrast to the conventional Faddeev-Popov gauge fixing case where the vacuum part is discarded in the normalization, there are scale dependent divergences coming from the vacuum part which have to be regularized. As a result, fixing the Gribov copies may provide a perturbative scheme which is able to incorporate (part of) the non-perturbative magnetic contributions.

日時： 2/10(Fri.) 16:30 -
講師： 吉田 健太郎 氏（京大理)
題目： Hybrid integrable structure of deformed sigma models
概要： We show that Yangian x quantum affine symmetries are realized in two-dimensional sigma models with target spaces squashed spheres and warped AdS spaces. These symmetries allow two descriptions to describe its classical dynamics, according to the left and right symmetries. Each of the Lax pairs constructed in both ways leads to the same equations of motion. The two descriptions are related one another through a non-local map. We argue this equivalence also from the point of view of monodromy matrices.

日時： 1/25(Wed.) 13:00 -
講師： 竹内 宏光 氏（広島大)
題目： 2成分ボース・アインシュタイン凝縮体における流体力学的不安定性
概要： お互いに区別できる2種類の希薄ボース気体からなるボース・アインシュタイン凝縮体は、二つの複素秩序変数（巨視的波動関数）で記述され、2成分から成る混相超流体を構成する。この混相超流体は原子間相互作用に依存して、相分離状態と二相混合状態に分類される。本講演では、この二つの状態における基本的な流体力学的安定性とその不安定化ダイナミクスを紹介する。一つ目は、相分離状態におけるドメイン壁を挟んで超流体が相対速度をもつ状況を考え、流体力学におけるケルビン・ヘルムホルツ不安定性との比較を見る。二つ目は、混ざり合った二成分超流体の対向流の不安定性を議論し、２成分量子渦糸タングル状態への遷移ダイナミクスを説明する。

日時： 1/24(Tue.) 16:30 -
講師： 竹内 宏光 氏（広島大)
題目： 2成分ボース・アインシュタイン凝縮体におけるタキオン凝縮
概要： お互いに区別できる2種類の希薄ボース気体からなるボース・アインシュタイン凝縮体は、二つの複素秩序変数（巨視的波動関数）で記述され、2成分から成る混相超流体を構成する。２種類の原子間斥力相互作用が十分大きい場合、２成分凝縮体は相分離を起こしてドメイン壁が安定に存在できる。本講演では、２成分凝縮体におけるドメイン壁と反ドメイン壁の対消滅による不安定性と、超弦理論におけるＤブレーンと反Ｄブレーンのタキオン凝縮との対応を議論する。このタキオン凝縮では、量子渦（基本弦）が生成され、この現象が空間局在した相転移におけるドメイン壁形成の秩序化過程と見なし得ることを説明する。

(2011)

WORKSHOP

日時： 11/14(Mon.) 16:30 -
講師： 花田 政範 氏（Univ. of Washington)
題目： Relationship between QCD and QCD-like theories at finite density
概要： We argue that the whole or the part of the phase diagrams of QCD and QCD-like theories should be universal in the large-N_c limit through the orbifold equivalence. The whole phase diagrams, including the chiral phase transitions and the BEC-BCS crossover regions, are identical between SU(N_c) QCD at finite isospin chemical potential and SO(2N_c) and Sp(2N_c) gauge theories at finite baryon chemical potential. Outside the BEC-BCS crossover region in these theories, the phase diagrams are also identical to that of SU(N_c) QCD at finite baryon chemical potential. We also argue how large finite-N_c correction is expected. Our results strongly suggest that the chiral phase transition and the QCD critical point at finite baryon chemical potential can be studied using sign-free theories, such as QCD at finite isospin chemical potential, in lattice simulations.

Date: 11/9(Wed.) 16:30 -
Speaker: Prof. York Schroeder (Bielefeld Univ.)
Title: Quark mass effects in QCD thermodynamics
Abstract: Due to asymptotic freedom, QCD is guaranteed to be accessible to perturbative methods at asymptotically high temperatures. However, in 1979 Linde has pointed out the existence of an "infrared wall", beyond which an infinite number of Feynman diagrams contribute. This infrared problem can be overcome in the framework of dimensionally reduced effective theories, combining lattice measurements with lattice and continuum perturbation theory. Within this framework, I will discuss radiative corrections to how quark mass thresholds are crossed, as a function of the temperature, in basic thermodynamic observables - confirming the indication from leading order that the charm quark plays a visible role at surprisingly low temperatures.

日時： 10/17(Mon.) 16:30 -
講師： 佐藤 昌利 氏（東大物性研)
題目： トポロジカル超伝導体とマヨラナフェルミオン
概要： 従来、相構造の研究においては、自発的対称性の破れが重要な役割を果たしてきた。一方、自発的対称性の破れの概念ではとらえきれない量子相の存在も知られており、トポロジカル相と呼ばれている。本講演では、量子ホール状態、トポロジカル絶縁体などに代表されるトポロジカル相について簡単に説明した後、トポロジカル相にある超伝導状態であるトポロジカル超伝導体とその特徴的な励起であるマヨラナフェルミオンについて講演する。

Date: 8/29(Mon.) 16:30 -
Speaker: Prof. Kenichi Konishi (INFN, Pisa & Pisa U.)
開催場所： 慶應義塾大学日吉キャンパス第2校舎224番教室 (普段と異なるので注意!)
Title: The monopole-vortex complex: dual gauge symmetry from flavor
Abstract: The idea that the dual gauge symmetry of nontrivial type (i.e., non-Abelian) is a new manifestation of the global flavor symmetry, seems to be gaining familiarity, if not yet properly understood. The main issue is the subtle interplay between the strong gauge dynamics involving various soliton-like excitations and the global symmetry. We discuss, in an attempt to go into the heart of the problem, monopole-vortex complex solitonlike configurations arising in hierarchically broken gauge systems, G → H → 1, taking as a concrete model the softly-broken N=2 supersymmetric Quantum Chromodynamics. Our consideration involves also the rich results on the non-Abelian-vortex moduli obtained in the last few years, as well as some old and more recent results about non-Abelian monopoles. There is in fact a clear indication how the dual gauge symmetry arises from flavor in the r-vacua of the softly-broken N=2 susy QCD. If realized in the real world QCD, this kind of mechanism would explain why the chiral symmetry breaking and confinement appear to be interlocked.

Date: 7/20(Wed.) 13:30 -
Speaker: Dr. Marco Ruggieri (YITP)
Title: Exploring QCD with a chiral chemical potential
Abstract: I discuss the phase structure of QCD with a chiral chemical potential, which represents a sign-free theory whose interest is related both to the phenomenology of heavy ion collisions (mainly to the chiral magnetic effect) and to the theory (mainly, to the possibility of performing simulations of grand canonical ensembles).

日時： 6/20(Mon.) 16:30 -
講師： 大河内 豊 氏（IPMU)
題目： Constraints on Direct Gauge Mediation Models
概要： 近年注目されている超対称性の破れのモデルをもとに、宇宙論的な観測からくる 制限をついて議論する。特にISSモデルをもとに構成したダイレクト型のゲージ メディエーションモデルについてコスミックストリングからくる制限を紹介する。

日時： 5/30(Mon.) 16:30 -
講師： 今村 洋介 氏（東京工業大学)
題目： Exact results in 3d gauge theories and M-theory
概要： 近年、局所化と呼ばれる方法を用いることで、超対称ゲージ理論の分配関数やインデックスが厳密に計算された。このセミナーでは、３次元ゲージ理論のインデックスの公式の導出方法を紹介する。また、いくつかの3次元超対称Chern-Simons理論のインデックスをlarge N 極限において計算した結果をAdS_4/CFT_3の予言と比較することで、AdS_4/CFT_3の非自明なチェックを行う。

日時： 5/16(Mon.) 16:30 -
講師： 疋田 泰章（慶應義塾大学)
題目： The FZZ duality with boundary -- D1-branes in 2d black hole and their dual
概要： The Fateev-Zamolodchikov-Zamolodchikov (FZZ) duality relates Witten's 2d black hole and sine-Liouville theory. Sine-Liouville theory describes the condensation of closed string tachyon winding over a cylinder. The FZZ duality states that the tachyon condensation deforms the cylinder geometry to the cigar (Euclidean 2d black hole) geometry. In our previous work, we have proven the duality for sphere amplitudes and generalized to the case with closed Riemann surface of arbitrary genus. In this talk, we extend the duality to disk amplitudes. More specifically, we relate D1-branes in the cigar model to D2-branes in the sine-Liouville theory.
参考文献：arXiv:1012.4731 [hep-th]

Date : 2/28(Mon.) 16:30 -
Speaker： Dr. Walter Vinci（Univ. of Minnesota）
Title： Non-Abelian Monopoles in the Higgs Phase
Abstract： We use the moduli matrix approach to study the moduli space of 1/4 BPS kinks supported by vortices in the Higgs phase of N = 2 supersymmetric U(N) gauge theories when non-zero masses for the matter hypermultiplets are introduced. We focus on the case of degenerate masses. In these special cases vortices acquire new orientational degrees of freedom, and become "non-Abelian". Kinks acquire new degrees of freedom too, and we will refer to them as "non-Abelian". As already noticed for the Abelian case, non-Abelian kinks must correspond to non-Abelian monopoles of the unbroken phase of SU(N) Yang-Mills. We show, in some special cases, that the moduli spaces of the two objects are in one-to-one correspondence. We argue that the corre- spondence holds in the most general case. The consequence of our result is two-fold. First, it gives an alternative way to construct non-Abelian monopoles, in addition to other well- known techniques (Nahm transform, spectral curves, rational maps). Second, it opens the way to the study of the quantum physics of non- Abelian monopoles, by considering the simpler non-Abelian kinks.
Reference：arXiv:1012.4057 [hep-th]

Date : 1/24(Mon.) 16:30 -
Speaker： Dr. Antonino Flachi（YITP）
Title： Four-fermion effective theories in curved space at finite temperature and density
Abstract： The aim of this talk is to present a new formalism that allows to deal with four-fermion effective field theories at finite temperature and density in curved and flat space. The formalism is based on the use of the effective action and zeta function regularization, and supports the inclusion of inhomogeneous and anisotropic phases. One of the key points of the method is the use of a non-perturbative ansatz for the heat-kernel that returns the effective action in partially resummed form, providing a way to go beyond the approximations based on the Ginzburg-Landau expansion for the partition function. The effective action for the case of ultra-static Riemannian spacetimes is discussed in general. A series representation, valid when the chemical potential satisfies a certain condition, and a more general expression for the effective action, valid for arbitrary values of the chemical potential, are presented. We finally present a sample application, and show how the formalism can be used to discuss the formation of inhomogeneous phases in the case of static Einstein spaces and illustrate how numerical implementations of the method can be done.

(2010)

日時： 11/29(Mon.) 16:30 -
講師： 太田 和俊 氏（明治学院大学）
題目： Volume of Moduli Space of Vortices and Localization Formula
概要： We evaluate volume of moduli space of BPS vortices on a compact Riemann surface by using topological field theory and localization formula developed by Moore, Nekrasov and Shatashvili. We apply this technique to Abelian (ANO) vortex and show that the volume of moduli completely agrees with the previous results by Manton et al. We extend our evaluation to non-Abelian gauge group and multi flavors. We also compare our result with a volume of the Hanany-Tong moduli space.

日時: 11/15(Mon.) 16:30 -
講師： 岡澤 晋 氏（高エネルギー加速器研究機構）
題目： Black Holes and the Fluctuation Theorem
概要： We investigate non-equilibrium nature of fluctuations of black hole horizons by applying the fluctuation theorem developed in the non-equilibrium statistical physics. The theorem applied to space-times with black hole horizons reveals a violation of the generalized second law of thermodynamics. In this talk, after introducing the fluctuation theorem, we show that some characteristics of the Fokker-Planck equation which describes non-equilibrium dynamics of black hole horizons and matters.
参考文献：arXiv:1008.1184 [gr-qc]

日時：: 10/25(Mon.) 16:30 -
講師： 酒井 一博 氏 (慶應義塾大学)
題目： Gluon scattering amplitudes and thermodynamic Bethe ansatz equations
概要： Alday and Maldacena proposed a method of computing gluon scattering amplitudes in N=4 super Yang-Mills at strong coupling by using the AdS/CFT correspondence. The amplitude is given by the area of a minimal surface in AdS_5 with a null polygonal boundary. Recently, it turned out that minimal surfaces corresponding to the general n-point amplitudes are characterized in terms of a sort of Thermodynamic Bethe Ansatz (TBA) equations. After reviewing the general TBA description, we focus on the case of n=6 and analyze the solution in detail. We explain how to solve the TBA equations perturbatively and compute the amplitude by making use of the underlying integrable model.
参考文献： arXiv:0911.4708 [hep-th], arXiv:1002.2459 [hep-th], arXiv:1002.2941 [hep-th] arXiv:1005.4487 [hep-th]