Kyohei Mukaida, Tokyo U
Boltzmann equation for non-equilibrium particles and its application to non-thermal dark matter production
Meeting room 1, Kenkyu honkan 1F
We consider a scalar field which is very weakly interacting with the thermal bath, and study thermal effects on the evolution of its number density. We use the Boltzmann equation derived from the Kadanoff-Baym equation, assuming that the degrees of freedom in the thermal bath are well described as “quasi-particles” with thermally modified dispersion relations. The obtained Boltzmann equation differs from the conventional one since the collision term is thermally modified through “quasi-particles.” Then, we apply this equation to the Freeze-In dark matter production scenario. We show that thermal effects can change the resultant dark matter abundance by ${cal O} (10-100) %$ compared to the result without taking account of thermal effects.
Corneliu Sochichiu, Sung KyunKwan U
Dirac Lattice or Down to High Energy
Meeting room 1, Kenkyu honkan 1F
I consider the conditions for the emergence of Dirac/Weyl/Majorana fermions from a (nonrelativistic) Fermi system.
Soichiro Goda, Kyoto U
Chiral condensate in nuclear matter beyond linear density using chiral Ward identity
Seminar room, Kenkyu honkan 3F In low-energy Quantum ChromoDynamics, spontaneous breaking of chiral symmetry is one of the most important phenomenon because this is responsible for the generation of the constituent quark mass. We focus on partial restoration of chiral symmetry in a finite density environment such as inside of atomic nucleus. Partial restoration of chiral symmetry can be observed by investigating the modification of hadron properties in nuclear matter. To examine partial restoration of chiral symmetry in nucleus experimentally, binding energy and width of 1s state of deeply bound pionic atom are measured precisely [1]. This experiment suggests that the chiral condensate which is an order parameter of the chiral symmetry breaking is reduced by about 30 % at the nuclear density. In our work [2], we analyze density corrections of the chiral condensate up to Next to leading order (NLO) using the chiral Ward identity [3] and in-medium chiral perturbation theory [4,5]. The in-medium chiral condensate is calculated by a correlation function of the axial current and pseudoscalar density in nuclear matter as a consequence of the chiral Ward identity. The correlation function is evaluated using in-medium chiral perturbation theory with the hadronic quantities of pion and nucleon dynamics. We assume that all of the in-vacuum interaction vertices are known and in-vacuum loop corrections are supposed to be done by using the experimental values of the couplings in the calculation of the condensate. This procedure leads to a density (fermi momentum) expansion. Based on this density expansion approach, we analyze diagrammatic structure of the current Green function which gives density effects to the condensate. This analysis shows that medium effects to the chiral condensate beyond linear density come from interactions between pions and nuclear matter such as pion-exchange process. As a result, we find that NLO contribution is small.
In low-energy Quantum ChromoDynamics, spontaneous breaking of chiral symmetry is one of the most important phenomenon because this is responsible for the generation of the constituent quark mass. We focus on partial restoration of chiral symmetry in a finite density environment such as inside of atomic nucleus. Partial restoration of chiral symmetry can be observed by investigating the modification of hadron properties in nuclear matter. To examine partial restoration of chiral symmetry in nucleus experimentally, binding energy and width of 1s state of deeply bound pionic atom are measured precisely [1]. This experiment suggests that the chiral condensate which is an order parameter of the chiral symmetry breaking is reduced by about 30 % at the nuclear density. In our work [2], we analyze density corrections of the chiral condensate up to Next to leading order (NLO) using the chiral Ward identity [3] and in-medium chiral perturbation theory [4,5]. The in-medium chiral condensate is calculated by a correlation function of the axial current and pseudoscalar density in nuclear matter as a consequence of the chiral Ward identity. The correlation function is evaluated using in-medium chiral perturbation theory with the hadronic quantities of pion and nucleon dynamics. We assume that all of the in-vacuum interaction vertices are known and in-vacuum loop corrections are supposed to be done by using the experimental values of the couplings in the calculation of the condensate. This procedure leads to a density (fermi momentum) expansion. Based on this density expansion approach, we analyze diagrammatic structure of the current Green function which gives density effects to the condensate. This analysis shows that medium effects to the chiral condensate beyond linear density come from interactions between pions and nuclear matter such as pion-exchange process. As a result, we find that NLO contribution is small.
[1] K. Suzuki et al., Phys. Rev. Lett. 92, 072302 (2004).
[2] S. Goda and D. Jido, in preparation. ; D. Jido, S. Goda, arXiv:1108.6144 [nucl-th].
[3] D. Jido, T. Hatsuda and T. Kunihiro, Phys. Lett. B 670,109 (2008).
[4] J. A. Oller, Phys. Rev. C 65, 025204 (2002).
[5] U. G. Meissner, J. A. Oller and A. Wirzba, Annals Phys. 297, 27(2002).
Makoto Oka, Tokyo Institute of Technology
[Particle and Nuclear Physics Seminar at J-PARC] Spectroscopy and Interaction of Heavy Hadrons
Tokai 1st building 115, KEK Tokai campus
I discuss topics on the heavy-baryon spectroscopy and its implication to QCD. I also look for possibilities of finding charmed hypernuclei.
Tatsuo Kobayashi, Kyoto
TeV scale mirage mediation in NMSSM
Meeting room 1, Kenkyu honkan 1F
We study the next-to-minimal supersymmetric standard model. We consider soft supersymmetry breaking parameters, which are induced by the mirage mediation mechanism. We concentrate on the mirage mediation, where the so-called mirage scale is the TeV scale. In this scenario, we can realize the up-type Higgs soft mass of O(200) GeV, while other masses like gaugino and stop masses are heavy such as 1 TeV. Cancellation between the effective mu-term and the down-type Higgs soft mass ameliorates the fine-tuning in the electroweak symmetry breaking. The lightest Higgs mass can be 115-130 GeV. The higgsino and singlino are light and their linear combination is the lightest superparticle.
Toru Fuda, Hokkaido U
連続的な観測を受ける量子系の数学的研究
Seminar room, Kenkyu honkan 3F
量子系に対する観測により, 量子系の状態は非因果的に変化する. では, その観測を連続的に行った場合, 量子系はどのような挙動をみせるだろうか？ 1977年にB.MisraとE.C.G.Sudarshanはこのような問いを立て, それに対して直感とは相容れない結果を得た. 彼らの得た結果は, 端的に言って, 「量子系を連続的に観測するとその状態が凍結される」という奇妙ものであった. この効果は, 「飛んでいる矢は止まっている」と主張する有名なゼノンのパラドックスとの類似から, 量子ゼノン効果と呼ばれる. 本発表では, 量子ゼノン効果の数学的な取り扱いについて示し, そのいくつかの新たな側面を紹介する. 特に, 連続的な観測によって, 状態ベクトルを状態空間上の曲線に乗せて移動させることが出来ることを詳しくみていく. これは量子ゼノン効果のある種の一般化にもなっている. なお, 本発表の内容は新井朝雄教授（北海道大学）との共同研究に基づく.
Joe Sato, Saitama U
レプトンのCP位相、特にディラック位相、を考える
Meeting room 1, Kenkyu honkan 1F
最後の混合角がはかられた現在、次の興味は「ニュートリノ振動でCPの破れを測れるか」に移っている。この講演ではこの測定が持つ意味について考えるための土台になりそうな事柄について議論する。
Yuhma Asano, Kyoto University
Factorization of the Effective Action in the IIB Matrix Model
Meeting room 1, Kenkyu honkan 1F IIB matrix model is one of the candidates for nonperturbative formulation of the string theory.
IIB matrix model is one of the candidates for nonperturbative formulation of the string theory.
While the coordinates are represented by matrices in the original interpretation, the matrices are interpreted as a covariant derivative in the “derivative interpretation.” The advantage of the representation is the manifest diffeomorphism invariance.
We calculate the low-energy effective action in the derivative interpretation and find that it is expressed as a sum of terms, each of which is factorized into a product of diffeomorphism invariant action functionals. This form of the action can be interpreted as describing a multiverse where the universes are connected by wormholes. I will also discuss the locality and the relation to realistic models.
Marco Panero, University of Helsinki
Strongly coupled gauge theories in a spacetime with a compact extra dimension
Meeting room 3, Kenkyu honkan 1F
The idea that the physical spacetime might have more than four dimensions dates back to almost a century ago, but during the last few decades it has received renewed attention, due to its connections to String Theory, and to potential applications for New Physics at energies within reach of the LHC experiments. In particular, gauge theories defined in a spacetime with compact extra dimensions are a theoretically appealing setup for models of Grand Unification and electroweak symmetry breaking, for the fermion hierarchy problem, and for the strong-CP problem. While a gauge theory in a spacetime with more than four dimensions is generally non-renormalizable, and thus cannot be considered as a fundamental theory, it can be interpreted as a low-energy effective description of an underlying, more fundamental theory. In this talk, after reviewing the general properties of models defined in extra dimensions, I shall discuss the construction and the non-perturbative lattice investigation of a strongly coupled SU(2) gauge model in a five-dimensional spacetime with a compact extra dimension. In particular, I shall present the phase diagram of the model, and discuss how various four-dimensional theories can emerge in different low-energy limits.
Hajime Sotani, NAOJ
Constraint on equation of state of Nuclear matter via neutron star asteroseismology
Meeting room, 3 go-kan
