坂口貴男, Brookhaven National Laboratory
電磁プローブによる重イオン衝突の研究
Seminar room, Kenkyu honkan 3F
２０００年よりＲＨＩＣで始まった重イオン衝突の実験においては、これまで生成量が小さかったために困難であった、ハード過程を利用した研究が可能となった。衝突でできた高温高密度物質と、ハード過程で散乱されたパートンの相互作用によって起きた、高横運動量ハドロンの収量の抑制は、この研究手法における大きな成果の一つであるが、その解釈を決定的にしたのが、衝突初期の情報をそのまま持ち出す単光子の測定である。 単光子は衝突初期から、系がハドロン化するまでに、連続的に放射されるため、重イオン衝突を系統的に研究する、最適のプローブである。 本講演では、重イオン衝突における単光子測定の歴史と、その測定手法、そしてRHICにおける最新の測定結果を紹介する。
Handhika Satrio Ramadhan, LIPI
Exotic Transitions in 6d Flux Compactifications
Room 345, 4 go-kan
“We present two profound tunneling phenomena in 6d Toy Model of Flux compactification. The first is a non-perturbative instability of the flux vacua, where the tunneling is achieved by dropping all the flux altogether and tunnel to no-flux state. We found that this state is a state with no (classical) space-time. It is a tunneling to Nothing, i.e., a bubble of nothing (reminiscent to the Wittens bubble of nothing). The second is the reverse-process, i.e., that the flux vacua can be spontaneously created from Nothing. We dubbed it Bubble from Nothing. Finally we show that a bubble from nothing is stable against nucleation of bubble of nothing, and in fact there is a smooth transition between the two.”
Mitsuru Kakizaki, Toyama University
Dark matter in UED : the role of the second KK level
Room 345, 4 go-kan
We perform a complete calculation of the relic abundance of the KK-photon LKP in the universal extra dimension model including all coannihilation channels and all resonances. We show that the production of level 2 particles which decay dominantly into SM particles contribute significantly to coannihilation processes involving level 1 KK-leptons. As a result the preferred dark matter scale is increased to R^{-1}=1.3 TeV. A dark matter candidate at or below the TeV scale can only be found in the non-minimal model by reducing the mass splittings between the KK-particles and the LKP. The LKP nucleon scattering cross section is typically small, ¥sigma <10^{-10} pb, unless the KK-quarks are nearly degenerate with the LKP.
Shuichiro Yokoyama, Nagoya University
初期揺らぎの非ガウス性と構造形成
Meeting room 1, Kenkyu honkan 1F
近年の宇宙論的観測の進歩により、現在の宇宙の構成要素だけでなく、初期宇宙の物理にも迫る研究が盛んに行われている。特に初期揺らぎの情報から、初期宇宙の重要なパラダイムの一つであるインフレーション理論に対してより詳細な議論が可能となることが期待されている。そのような現状において、初期揺らぎの非ガウス性が注目を集めている。線形摂動論＋量子ゆらぎ起源という仮定のもとでは、初期揺らぎはガウス統計に従うと考えられるが、一般に揺らぎの発展が従うアインシュタイン方程式は非線形方程式であるし、場の相互作用を通じて、非ガウス性は生じる。精密観測により、この非ガウス性を精査することで、初期宇宙の新たな物理が見えてくることが期待される。例えば、宇宙背景輻射の観測では、温度揺らぎの三点相関が有力な観測量となる。また大規模構造形成のシナリオにも様々な影響を与える。本セミナーでは、この初期揺らぎの非ガウス性について、簡単なレビューをし構造形成にどのような影響を与えるかを議論する。
Takashi Shimomura, Niigata University
Constraining the Higgs masses from false vacua in the NMSSM.
Meeting room 1, Kenkyu honkan 1F
We analyze a vacuum structure of the Higgs sector in the Next-to Minimal Supersymmetric Standard Model (NMSSM). We show that some minima, which can be identified as false vacua, can be found analytically along specific directions. These minima can become deeper than the true vacuum or the electroweak symmetry breaking vacuum. Such minima should be avoided to ensure the stability of the true vacuum, resulting in constraints on the parameters of the NMSSM. The masses of the Higgses can be restricted using the constraints. We show that the Higgs masses can not be heavy so much in some parameter regions even in the NMSSM.
Kenji Ogawa, National Chiao-Tung University/KEK-NCTS exchange program visitor
The lattice study of many flavor QCD with twisted boundary condition
Meeting room 1, Kenkyu honkan 1F
Incorporated with twisted boundary condition, Polyakov loop correlators can give a definition of renormalized coupling. We employ this scheme for step scaling function in the search of conformal fixed point. Staggered fermion and plaquette gauge action are used in the lattice simulation with six different lattice sizes L = 20, 16, 12, 10, 8 and 6. For the largest lattice size L = 20, we used a large number of GPU’s and accumulated 3,000,000 trajectories in total. We found that the step scaling function sigma(u) is consistent with u in the low beta region. It strongly suggests the existence of conformal fixed point. Some details of our analysis and simulations will also be presented.
Ardian Nata Atmaja, Indonesian Institute of Sciences (LIPI)
Anisotropic Drag Force from 4D Kerr-AdS Black Holes
Meeting room 1, Kenkyu honkan 1F
Using AdS/CFT we investigate the effect of angular-momentum-induced anisotropy on the instantaneous drag force of a heavy quark. The dual description is that of a string moving in the background of a Kerr-AdS black holes. The system exhibits the expected focussing of jets towards the impact parameter plane. We put forward that we can use the connection between this focussing behavior and the angular momentum induced pressure gradient to extrapolate the pressure gradient correction to the drag force that can be used for transverse elliptic flow in realistic RHIC. The result is recognizable as a relativistic pressure gradient force.
Zdzislaw Burda, Jagellonian University
Spectrum of the Product of Independent Random Gaussian Matrices
Meeting room 1, Kenkyu honkan 1F
We show that the eigenvalue density of a product $¥X=¥X_1 ¥X_2 ¥cdots ¥X_M$ of $M$ independent $N¥times N$ Gaussian random matrices in the limit $N¥rightarrow ¥infty$ is rotationally symmetric in the complex plane and is given by a simple expression $¥rho(z,¥bar{z}) = ¥frac{1}{M¥pi} ¥sigma^{-¥frac{2}{M}} |z|^{-2+¥frac{2}{M}}$ for $|z|¥le ¥sigma$, and is zero for $|z|> ¥sigma$. The parameter $¥sigma$ corresponds to the radius of the circular support and is related to the amplitude of the Gaussian fluctuations. This form of the eigenvalue density is highly universal. It is identical for products of Gaussian Hermitian, non-Hermitian, real or complex random matrices. It does not change even if the matrices in the product are taken from different Gaussian ensembles. We present a self-contained derivation of this result using a planar diagrammatic technique. Additionally, we conjecture that this distribution also holds for any matrices whose elements are independent, centered random variables with a finite variance or even more generally for matrices which fulfill Pastur-Lindeberg’s condition. We provide a numerical evidence supporting this conjecture.
Tomohiro Takahashi, Kyoto University
Lovelock Black Holeの安定性解析
Meeting room 2, Kenkyu honkan 1F
時空が高次元の場合、加速器でblack holeが生成される可能性が指摘されている。そのため、高次元のblack hole解や解の持つ性質が調べられている。それらの研究のほとんどはEinstein理論に基づいて行われている。本発表においては、重力理論の高次元への“自然な”拡張であるLovelock理論に基づき、解の性質の一つである線形安定性について議論する。まず、Lovelock理論とその理論の厳密解である球対称静的なblack hole解について述べる。その後に、その解の周りの線形摂動が従う方程式を紹介し、摂動が時間的に増大する条件について述べる。最後に、その判定条件を用いて十分massの小さいblack holeは不安定であることを述べる。
Shunsaku Horiuchi, Ohio State Univeristy
The possible origins of heavy nuclei ultra-high energy cosmic rays
Meeting room 1, Kenkyu honkan 1F
