セミナー 2015年

Bum-Hoon Lee, CQUeST, Sogang U., Korea

Fubini Instantons in curved spacetime

Meeting Room 3, Kenkyu Honkan 1F
TBA

Masato Nozawa, University of Milan

Supersymmetry of (Euclidean) Plebanski-Demianski solution

Meeting Room 3, Kenkyu Honkan 1F,
The Plebanski-Demianski (PD) solution has played a central role in the development of black-hole physics in general relativity since it describes the most general Petrov D metric in Einstein-Maxwell-Lambda system. Recently, Houri and Yasui have found a new king of nondegenerate rank-2 Killing-Yano (KY) tensor in the self-dual Euclidean PD metric. I will discuss in detail how this makes consistent with the theorem by Houri-Oota-Yasui, according to which the local metric admitting a non-degenerate rank 2 KY tensor must fall into the Carter family. It turns out that this is closely related to the fact that the self-dual PD solution preserves half of supersymmetry, whereas the non-self-dual solution admits only one quarter of supersymmetry. I will also explore the underlying mathematical structure of Euclidean PD solution, such as conformal ambi-Kahler structure and new type of Einstein-Weyl space.

Kei Yagyu, University of Southampton

Synergy between direct and indirect searches of non-minimal Higgs sectors

Meeting Room 3, Kenkyu Honkan 1F
I would like to review on recent my phenomenological research of non-minimal Higgs sectors especially focusing on two Higgs doublet models. First, I discuss the direct search for extra Higgs bosons at collider experiments. Next, I talk about the indirect search which focuses on deviations in the coupling constants of the discovered Higgs boson. Finally, I discuss the synergy between the direct and indirect searches.

Takuya Kanazawa, RIKEN

Some remarks on topology in QCD at high temperature

Meeting Room 3, Kenkyu Honkan 1F
QCD topology relevant to anomaly at high temperature has been elusive in the past, but the situation is changing due to rapid progress in lattice simulation techniques. In this regard, it is important to understand the finite-volume effects on topology correctly. I will present a simple analytical argument to grasp physics in a finite volume at high temperature. In addition the role of (non-)analyticity in the QCD Dirac spectra will be discussed.

Dai-suke Takahashi, OIST

Classically conformal U(1)' extended standard model and Higgs vacuum stability

Seminar Room, Kenkyu Honkan 3F
We consider the minimal U(1)’ extension of the standard model (SM) with conformal invariance at the classical level, where in addition to the SM particle contents, three generations of right-handed neutrinos and a U(1)’ Higgs field are introduced. In the presence of the three right-handed neutrinos, which are responsible for the seesaw mechanism, this model is free from all the gauge and gravitational anomalies. The U(1)’ gauge symmetry is radiatively broken via the Coleman-Weinberg mechanism, by which the U(1)’ gauge boson (Z’ boson) mass as well as the Majorana mass for the right-handed neutrinos are generated. The radiative U(1)’ symmetry breaking also induces a negative mass squared for the SM Higgs doublet to trigger the electroweak symmetry breaking. In this context, we investigate a possibility to solve the SM Higgs vacuum instability problem. The model includes only three free parameters (U(1)’ charge of the SM Higgs doublet, U(1)’ gauge coupling and Z’ boson mass), for which we perform parameter scan, and identify a parameter region resolving the SM Higgs vacuum instability. We also examine naturalness of the model. The heavy states associated with the U(1)’ symmetry breaking contribute to the SM Higgs self-energy. We find an upper bound on Z’ boson mass, mZ’ \lesssim 6  TeV, in order to avoid a fine-tuning severer than 10% level. The Z’ boson in this mass range can be discovered at the LHC Run-2 in the near future.

Running Non-Minimal Inflation with Stabilized Inflaton Potential

Meeting Room 1, Kenkyu Honkan 1F
In the context of the Higgs model involving gauge and Yukawa interactions with the spontaneous gauge symmetry breaking, we consider $\lambda \phi^4$ inflation with non-minimal gravitational coupling, where the Higgs field is identified as inflaton. Since the inflaton quartic coupling is very small, once quantum corrections through the gauge and Yukawa interactions are taken into account, the inflaton effective potential most likely becomes unstable. In order to avoid this problem, we need to impose stability conditions on the effective inflaton potential, which lead to not only non-trivial relations among the particle mass spectrum of the model, but also correlations between the inflationary predictions and the mass spectrum. For concrete discussion, we investigate the minimal B−L extension of the Standard Model with identification of the B−L Higgs field as inflaton. The stability conditions for the inflaton effective potential fix the mass ratio among the B−L gauge boson, the right-handed neutrinos and the inflaton. This mass ratio also correlates with the inflationary predictions. In other words, if the B−L gauge boson and the right-handed neutrinos are discovered in future, their observed mass ratio provides constraints on the inflationary predictions.

Takahiro Nishinaka, Yukawa Inst.

On the superconformal Index of Argues-Douglas theories

Meeting room 1, Kenkyu honkan 1F
Argyres-Douglas (AD) theories are 4d N=2 superconformal field theories without useful Lagrangian descriptions. Therefore their superconformal indices cannot be evaluated by supersymmetric localization. In this talk, I will discuss our conjectural expression for the superconformal index of AD theories given in terms of 2d q-deformed Yang-Mills theory. Our conjecture is based on the S^1 x S^3 version of the AGT relation, and is perfectly consistent with the Higgs branch chiral rings, 2d chiral algebras, RG-flows, and the 3d reduction of AD theories.

Makoto Takamoto, The University of Tokyo

Thermal Synchrotron Radiation By Double Tearing Mode Reconnection - Application to the Crab Gamma-Ray Flares

Meeting room 1, Kenkyu honkan 1F
Recent observations have revealed the Crab shows strong gamma-ray flares through synchrotron radiation whose maximum energy is around 370MeV with time-scale around 8 hours. Surprisingly, the observed energy is beyond the maximum energy of synchrotron photons radiated by electrons accelerated in MHD magnetic field. Although there are already some theoretical models which considered magnetic reconnection with an incredibly large spatial scale in Crab pulsar wind nebula, the origin of the flares is still controversial. In this presentation, we propose a new theoretical explanation of the Crab gamma-ray flare. Instead of considering phenomena in pulsar wind nebulae, we consider the double tearing mode (DTM) magnetic reconnection in a pulsar wind region. We obtained the evolution of DTM using resistive relativistic magneto-hydrodynamic simulations, and computed synthetic synchrotron spectra in the explosive reconnection phase. We found the variability of the Crab nebula/pulsar system, seen as flares, can be naturally explained by the DTM explosive phase in the striped wind. Our results also indicate that, in order to explain the Crab gamma-ray flare by DTM in the wind region, the magnetization parameter \sigma should be around 10^5 and the wind Lorentz factor be around 300.

Christopher Kelly (RBRC Brookhaven National Laboratory)

Standard-model prediction for direct CP violation in K→ππ decay

Seminar Room, Kenkyu Honkan 3F
We discuss our recent publication (arXiv:1505.07863 [hep-lat]) of the first lattice QCD calculation of the complex kaon decay amplitude A_0 with physical kinematics, using a single 32^3 x 64 domain wall ensemble with G-parity spatial boundary conditions. We obtain approximate agreement with the experimental value for Re(A_0), which serves as a test of our method. Our prediction of Im(A_0) can be used to compute the direct CP violating ratio Re(ε′/ε), which we find to be ~2 sigma lower than the experimental value. This result provides a new test of the Standard Model theory of CP violation, one which can be made more accurate with increasing computer capability.

Sujoy Modak, KEK

Black Hole Information Paradox: a Door to New Physics?

Seminar Room, Kenkyu Honkan 3F
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