セミナー

Xerxes Tata, University of Hawaii

SUPERSYMMETRY, LHC AND DARK MATTER

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

ベービーユニバースによる自然性問題の解消

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.

Yuji Osumi, Nagoya University

宇宙の初期ゆらぎの古典性とエンタングルメント

Meeting room 1, Kenkyu honkan 1F
宇宙背景放射の温度ゆらぎなどに見られる宇宙の初期密度ゆらぎは,インフレーション期における場の量子効果によって生じたと考えられている.しかし,宇宙背景放射の温度ゆらぎは古典的なゆらぎであり,量子力学特有の性質は今のところ見つかっていない.したがって,初期ゆらぎの量子的性質はなんらかの機構によって消えると考えられる.この発表では,ゆらぎの2点間の量子相関,いわゆるエンタングルメントを調べ,それが消える条件について議論する.

Richard Hill, University of Chicago

Universal behavior in the scattering of heavy, weakly interacting dark matter on nuclear targets

Meeting room 3, Kenkyu honkan 1F
Particles that are heavy compared to the electroweak scale (M >> m_W), and that are charged under electroweak SU(2) gauge interactions display universal properties such as a characteristic fine structure in the mass spectrum induced by electroweak symmetry breaking, and an approximately universal cross section for scattering on nuclear targets. The heavy particle effective theory framework is developed to compute these properties. As illustration, the spin independent cross section for low-velocity scattering on a nucleon is evaluated in the limit M >> m_W, including complete leading-order matching onto quark and gluon operators, renormalization analysis, and systematic treatment of perturbative and hadronic-input uncertainties.

Keiko I. Nagao, KEK

Dark Matter in Inert Triplet Models

Meeting room 1, Kenkyu honkan 1F
Since the standard model (SM) does not accommodate dark matter candidate, new physics models are expected. In the inert triplet model (ITM), we introduce one triplet scalar which does not couple to the SM fermions. In this talk I plan to talk about the signature of the DM candidates in the model.

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