セミナー 2011年

Jun Suzuki, University of Electro-Communications

Radiation from accelerated impurities in a Bose–Einstein condensate (in Japanese)

Seminar room, Kenkyu honkan 3F
We investigate radiation spectra arising from accelerated point-like impurities in the homogeneous Bose– Einstein condensate. A general formula for the radiation spectrum is obtained in the integral form as a function of given impurity trajectory within the Bogoliubov approximation. The Planckian spectrum is obtained for a special accelerated motion, which is shown to be unphysical. Non-Planckian spectrum is found in the case of a uniformly accelerated impurity. We compare our result with similar settings discussed in other quantum systems.

Yoske Sumitomo, Hong Kong University of Science and Technology

Comments on Stability for de Sitter Vacua in String Theory

Meeting room 1, Kenkyu honkan 1F
We analyze a property of mass matrix at positive extrema in type II string theory. In IIA, off-diagonal components are not suppressed, therefore tachyonic directions are likely met in the presence of many moduli. While in a IIB model, such the suppression is achieved due to a hierarchy by non-perturbative effect and an alpha’ correction. Many moduli may help to realize small cosmological constant in the model.

Yuya Sasai, University of Helsinki

Closed string transport coefficients and the membrane paradigm

Meeting room 1, Kenkyu honkan 1F
>I discuss a correspondence between a fictitious fluid in the black hole membrane paradigm and highly excited closed string states according to the black hole correspondence principle. I calculate the membrane transport coefficients of an electric NS-NS 2-charged black hole and transport coefficients of the highly excited closed string states which possess a Kaluza-Klein number and a winding number. Comparing both the transport coefficients at the correspondence point, I show that, except for the bulk viscosity, the membrane transport coefficients are of the same order as the transport coefficients of the closed string states on the stretched horizon. Also, I show that, except for the bulk viscosity, both the dimensionless transport coefficients, which are defined by dividing the transport coefficients by the entropy density, are exactly equal if the central charge is 6.

Xerxes Tata, University of Hawaii


Meeting room 1, Kenkyu honkan 1F
The hypothesis of weak scale supersymmetry ameliorates the gauge hierarchy problem, yields gauge couplings consistent with grand unification, and when augmented by R-parity conservation, provides natural candidates for the observed dark matter (DM). We review strategies for SUSY searches at the LHC, and project its reach in terms of sparticle masses in a relatively model-indendent manner. Assuming that the neutralino is a stable thermal relic from standard Big Bang cosmology, the measured density of cold DM selects out special regions in the parameter space of any underlying SUSY model with concomitant implications for collider physics, dark matter searches and low energy measurements. We examine the thermal neutralino relic density within the mSUGRA model as well as in various one-parameter extensions of mSUGRA (where we relax the underlying untested universality assumption) constructed to yield the measured relic density, and show that these implications, are in general, model-dependent. We nevertheless point out some relatively robust implications of the relic density determination for the LHC. Changing tracks, we describe a new bottom-up strategy for extracting neutralino mass parameters at the LHC and discuss its limitations. We conclude with an outlook for the future.

Daniel K. Brattan, Durham U

Fluid gravity at finite r

Seminar room, Kenkyu honkan 3F
The fluid/gravity correspondence provides a precise link between solutions to a class of Navier-Stokes problems and solving vacuum Einstein’s equations with a negative cosmological constant. In this talk I will attempt to demonstrate that we do not need to be at the boundary of the resultant spacetimes to extract transport coefficients. I will also discuss some tantalising hints of how the membrane paradigm may be embedded as an object in the boundary field theory.

Giacomo Cacciapaglia, IPN Lyon

The Neutrino of the Opera: faster than light, or illusion?

Lecture room 2, 4 go-kan 2F
I will briefly discuss the recent measurement of the speed of neutrinos by the OPERA collaboration, which reported an apparent faster than light propagation. The discussion will focus on some theoretical aspects of the super-luminal interpretation: energy dependence, Cherenkov emission, spectrum of the pion decay. Finally, I will present preliminary results based on a model in 5 dimensions.

Teruaki Suyama, RESCEU, Tokyo University

Dark energy from primordial inflationary quantum fluctuations

Meeting room 1, Kenkyu honkan 1F
We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.

Hikaru Kawai, Kyoto Universtiy


Meeting room, 3 go-kan 1F
宇宙項がプランク質量(の4乗)に比べて100桁以上も小さいことは、宇宙項問題といわれ、古くからの謎である。これを自然に説明する試みの一つに Coleman による baby universe のメカニズムがあるが、残念ながら、Euclid 化された量子重力に特有の問題のため、そもそも何を予言しているのか等、よくわからない点が多い。ここでは、Minkowski の量子重力にもとづいて、multiverse の波動関数を考え、それが baby universe の存在によってどのような影響を受けるかを調べる。その結果、宇宙項の値が非常に小さい値をとる確率が、圧倒的に大きいことがわかり、宇宙項問題が自然に解消していることがわかる。また、同様のメカニズムにより、Higgs mass 等の自然性問題が解決できる可能性についても議論する。

Yuho Sakatani, Kyoto University

Entropic formulation of relativistic continuum mechanics and its applications (in Japanese)

Meeting room 1, Kenkyu honkan 1F
我々が最近行ったエントロピー汎関数を用いた非平衡熱力学の新たな定式化について紹介する。この定式化を用いると、一般的な連続体力学を Onsager の linear regression theory の枠組みから自然に記述することができる。本講演では、この定式化の基本的なアイデアを紹介した後、この枠組みから実際に相対論的流体力学や相対論的粘弾性体力学の基礎方程式が正しく再現できることを確認し、この枠組みの有効性を示す。また、ここで導出した相対論的粘弾性体力学は、弾性的な歪みの効果を取り入れたことで、相対論的流体力学に特有の因果律の破れの問題を緩和し、因果的な流体力学の模型として機能することについても言及する。さらには、これらの研究の応用に関する最近の試みについても紹介する。

Masato Arai, Czech Technical University in Prague

Renormalization effects on the MSSM from a calculable model of a strongly coupled hidden sector

Meeting room 1, Kenkyu honkan 1F
We investigate possible renormalization effects on the low-energy mass spectrum of the minimal supersymmetric standard model (MSSM), using a calculable model of strongly coupled hidden sector. We model the hidden sector by N=2 supersymmetric quantum chromodynamics with gauge group SU(2) x U(1) and N_f=2 matter hypermultiplets, perturbed by a Fayet-Iliopoulos term which breaks the supersymmetry down to N=0 on a metastable vacuum. In the hidden sector the Kahler potential is renormalized. Upon identifying a hidden sector modulus with the renormalization scale, and extrapolating to the strongly coupled regime using the Seiberg-Witten solution, the contribution from the hidden sector to the MSSM renormalization group flows is computed. For concreteness, we consider a model in which the renormalization effects are communicated to the MSSM sector via gauge mediation. In contrast to the perturbative toy examples of hidden sector renormalization studied in the literature, we find that our strongly coupled model exhibits rather intricate effects on the MSSM soft scalar mass spectrum, depending on how the hidden sector fields are coupled to the messenger fields. This model provides a concrete example in which the low-energy spectrum of MSSM particles that are expected to be accessible in collider experiments is obtained using strongly coupled hidden sector dynamics.

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