セミナー

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
A century after their discovery, the astrophysical origins of cosmic rays remain intensely studied. In particular, cosmic rays of the highest energies cannot feasibly be confined in our Galaxy, and is thought to originate from extra-galactic sources. While many source candidates have been proposed, disentangling them is generally complicated by the fact that charged cosmic rays bend in the magnetic universe. However, new observational results on the composition may provide new insights. It has recently been reported that the composition of cosmic rays at the highest energies become increasingly heavy (Fe-like). I will review the composition claims and discuss implications for source candidates. In particular, I will discuss the potential that explosive nucleosynthesis in gamma-ray burst jets can provide a uniquely heavy-nuclei-dominated cosmic ray source.

Carsten Rott, Ohio State University

Closing in on Dark Matter with Neutrino Telescopes

Meeting room 3, Kenkyu honkan 1F
Unraveling the mysterious nature of dark matter is one of the most exciting scientific goals of this decade. While there is overwhelming evidence for its existence, its properties remain literally in the dark. New approaches in the search for dark matter might finally shed light on its properties and distribution in our Galaxy. Neutrino telescopes offer exciting opportunities for the detection of neutrinos produced as part of dark matter self-annihilations or decays. Using data collected during the construction period of the giga-ton sized IceCube detector, I will present a new analysis that searched for a neutrino anisotropy from the Galactic dark matter halo. This search is complementary to searches performed with gamma-ray telescopes and capable to test dark matter models motivated by the observed lepton excess by PAMELA. I will further discuss results from searches looking at the Galactic Center and dwarf spheroidal galaxies, which are expected to be dark matter dominated. Besides these searches that can constrain the dark matter self-annihilation cross section, I will discuss prospect and methods in the search for dark matter captured by the Sun. These Solar WIMP searches offer complementary ways to direct detection experiments to probe the dark matter nucleon scattering cross sections. The talk will also cover a first look at results obtained with the low-energy extension of IceCube, Deep Core, which is taking data since June 2010. Future upgrades that offers exciting opportunities for dark matter searches down to candidate masses in the GeV range, will be discussed as part of an outlook.

Antonio Enea Romano, National Taiwan Univeristy

Corrections to the apparent value of the cosmological constant due to local inhomogeneities

Seminar room, Kenkyu honkan 3F
Supernovae observations strongly support the presence of a cosmological constant, but its value, which we will call apparent, is normally determined assuming that the Universe can be accurately described by a homogeneous model. Even in the presence of a cosmological constant we cannot exclude nevertheless the presence of a small local inhomogeneity which could affect the apparent value of the cosmological constant. Neglecting the presence of the inhomogeneity can in fact introduce a systematic misinterpretation of cosmological data, leading to the distinction between an apparent and true value of the cosmological constant. Modeling the local inhomogeneity with a $¥Lambda LTB$ solution we compute the relation between the apparent and true value of the cosmological constant. Contrary to previous attempts to fit data using large void models our approach is quite general. The correction to the apparent value of the cosmological constant is in fact present for local inhomogeneity of any size, and should always be taken appropriately into account both theoretically and observationally.

Danny Marfatia, Kansas Univeristy

Isospin-Violating Dark Matter

Meeting room 1, Kenkyu honkan 1F
Searches for dark matter scattering off nuclei are typically compared assuming that the dark matter’s spin-independent couplings are identical for protons and neutrons. This assumption is neither without consequence nor well motivated. We consider isospin-violating dark matter with one extra parameter, the ratio of neutron to proton couplings. For a single choice of this ratio, the DAMA and CoGeNT signals are consistent with each other and with XENON constraints, and unambiguously predict a signal at CRESST.

Tsubasa Ichikawa, Kinki U

系統的なエラーに耐性のあるユニタリ操作の設計

Seminar room, Kenkyu honkan 3F
量子情報処理では、系の正確な操作が不可欠である。一方、実際の実験環境ではノイズやエラーの影響により、実際に行った操作が所望の操作からずれてしまうことが一般的である。従って、所望の操作を実装するにあたっては、上手い工夫をして「ずれ」が少なくなるようにすることが望ましい。 本講演では、上述のずれの少ない量子操作をどのように設計すればよいかについて紹介する。近年の進展を概説した後に、二準位系に対する最近の我々のグループの取り組みについて述べる。

1 84 85 86 87 88 89 90

ページ先頭へ戻る