Natsumi Nagata, The University of Tokyo
A supersymmetric two-field relaxion model
Meeting room 1, Kenkyu honkan 1F
We discuss a supersymmetric version of a two-field relaxion model that naturalizes supersymmetric models with high SUSY-breaking. This exploits a relaxion mechanism that does not depend on QCD dynamics and where the relaxion potential barrier height is controlled by a second axion-like field. During the cosmological evolution, the relaxion rolls down with a nonzero value that breaks supersymmetry and scans the soft supersymmetric mass terms. Electroweak symmetry is broken after the soft masses become of order the supersymmetric Higgs mass term and causes the relaxion to stop rolling. This can explain the tuning in supersymmetric models, while preserving the QCD axion solution to the strong CP problem. We will also consider possible inflation models compatible with this framework.
Olcyr Sumensari, LPT Orsay
B-Physics Puzzles and Lepton Flavor Violation
Meeting room 1, Kenkyu honkan 1F
Even though the LHC searches so far did not unveil the new physics (NP)particles, the B-physics experiments at LHCb, BaBar and Belle hint towards deviations from Lepton Flavor Universality in semi-leptonic decays. In this talk I will review the status of these puzzles, and discuss the possibilities for BSM scenarios. Particular emphasis will be given to the implications for Lepton Flavor Violation in B meson decays
Mayumi Saitou, Ochanomizu University
Hydrodynamics on non-commutative space
Meeting room 3, Kenkyu honkan 1F Recently, Y. Nambu formulated a new hydrodynamics in which incompressible fluid dynamics is connected to Hamiltonian dynamics in terms of area preserving diffeomorphism. If the equations of motion of two-dimensional fluid are expressed using Poisson brackets, then it is allowed to understand a stream function plays a role of Hamiltonian. According to this standpoint, three-dimensional incompressible fluid theory can be related to the dynamics of Nambu brackets.
Recently, Y. Nambu formulated a new hydrodynamics in which incompressible fluid dynamics is connected to Hamiltonian dynamics in terms of area preserving diffeomorphism. If the equations of motion of two-dimensional fluid are expressed using Poisson brackets, then it is allowed to understand a stream function plays a role of Hamiltonian. According to this standpoint, three-dimensional incompressible fluid theory can be related to the dynamics of Nambu brackets.
In this talk, we investigate a hydrodynamics on non-commutative space based on the formulation of dynamics by Nambu. Replacing Poisson or Nambu brackets by Moyal brackets with a parameter θ, a new hydrodynamics on non-commutative space is derived. It has an additional term of O(θ2), which does not exist in the usual Navier-Stokes equation.
In hydrodynamics, to introduce Moyal brackets corresponds to a kind of quantization procedure regarding position coordinates x and y, so that it makes the position coordinates to non-commutative ones. This procedure may be a step toward finding the hydrodynamics of granular materials whose minimum size is given by θ. In order to examine the non-commutative effect, I compare the behaver of flows which have different size of θ by computer simulation. In all the discussions in this talk, incompressibility and non-relativistic flow are supposed.
Keisuke Izumi, Nagoya University
Causal Structures in Gauss-Bonnet gravity
Meeting room 3, Kenkyu honkan 1F The couplings with curvature in kinetic terms would arise as corrections from the quantum gravity theory, such as string theory. The curvature coupling in general makes the propagation to be superluminal. In the theory with superluminal modes, the causal analysis with null curves is meaningless, and thus the causal structures are nontrivial. Especially, we have to define black holes based on the fastest propagation.
The couplings with curvature in kinetic terms would arise as corrections from the quantum gravity theory, such as string theory. The curvature coupling in general makes the propagation to be superluminal. In the theory with superluminal modes, the causal analysis with null curves is meaningless, and thus the causal structures are nontrivial. Especially, we have to define black holes based on the fastest propagation.
In this talk, Gauss-Bonnet gravity will be discussed as the simplest model. We could say that in this model the kinetic term of graviton has the coupling with curvature. This model has the superluminal modes of graviton. However, we show the theorem; in stationary spacetimes, “horizon” defined by the null curve (i.e. in the usual way) becomes exactly the causal edge (i.e. the horizon in the sense of causality). Meanwhile, in dynamical spacetimes, the causal edge does not coincide with the “horizon” defined by null curves. Especially, in shrinking black hole spacetimes (by Hawking radiation), the gravitons can escape from the inside of “BH” defined by null curves.
Reference: K. Izumi, Phys.Rev. D90 (2014) no.4, 044037
Simona Murgia, University of California, Irvine
Searching for Dark Matter Shining in Gamma Rays
Seminar room, Kenkyu honkan 3F The center of the Milky Way is predicted to be the brightest source of gamma rays produced bydark matter annihilation or decay. In recent years, claims have been made of an excess consistent with a dark matter annihilation signal in the data collected by the Fermi Large Area Telescope towards the Galactic center.
The center of the Milky Way is predicted to be the brightest source of gamma rays produced bydark matter annihilation or decay. In recent years, claims have been made of an excess consistent with a dark matter annihilation signal in the data collected by the Fermi Large Area Telescope towards the Galactic center.
Although these results are intriguing, the complexity involved in modeling the foreground and background emission from conventional astrophysical sources of gamma rays makes a conclusive interpretation of these results challenging.
In this talk, I’ll present results from these searches.
Tim Tait, University of California, Irvine
Evidence for a 17 MeV Boson from Rare Excited 8Be Decays?
Meeting room 3, Kenkyu honkan 1F
I will discuss the recent experimental results from the ATOMKI group which measured the spectrum ofinternal pair conversion e+e- events in the decay of an excited state of beryllium-8 to its ground state. They observe a resonant-like structure in the invariant mass of the e+e- which is suggestiveof a new boson at 17 MeV. I’ll review the experimental results and the types of theories whichcan describe them.
Takashi Toma, Laboratoire de Physique Theorique d'Orsay
Electric Dipole Moments of Charged Leptons with Sterile Fermions
Seminar room, Kenkyu honkan 3F
We address the impact of sterile fermions on charged lepton electric dipole moments. In this work, we consider a minimal extension of the Standard Model via the addition of sterile fermions which mix with active neutrinos. Our study reveals that, in order to have a non-vanishing contribution in this framework, the minimal extension necessitates the addition of at least 2 sterile fermion states. Sterile neutrinos can give significant contributions to the charged lepton electric dipole moments if the masses of the non-degenerate sterile states are both above the electroweak scale. In addition, the Majorana nature of neutrinos is also important for the charged lepton electric dipole moments. Furthermore as a more concrete model, we consider the most minimal realisation of the Inverse Seesaw mechanism, in which the Standard Model is extended by two right-handed neutrinos and two sterile fermion states. Our study shows that the two pairs of (heavy) pseudo-Dirac mass eigenstates can give significant contributions to the electron electric dipole moment, lying close to future experimental sensitivity. In our analysis we further discuss the possibility of having a successful leptogenesis in this framework, compatible with a large electron electric dipole moment.
Masahiro Hotta, Tohoku University
Gravitational Memory Charges of Supertranslation and Superrotation on Rindler Horizons
Meeting room 1, kenkyu honkan 1F
In a Rindler-type coordinate system spanned in a region outside of a black hole horizon, we have nonvanishing classical holographic charges as soft hairs on the horizon for stationary black holes. Taking a large black hole mass limit, the spacetimes with the charges are described by asymptotic Rindler metrics. We construct a general theory of gravitational holographic charges for a 1+3-dimensional linearized gravity field in the Minkowski background with Rindler horizons. Although matter crossing a Rindler horizon causes horizon deformation and a time-dependent coordinate shift, that is, gravitational memory, the supertranslation and superrotation charges on the horizon can be defined during and after its passage through the horizon. It is generally proven that holographic states on the horizon cannot store any information about absorbed perturbative gravitational waves. However, matter crossing the horizon really excites holographic states. By using gravitational memory operators, which consist of the holographic charge operators, we suggest a resolution of the no-cloning paradox of quantum information between matter falling into the horizon and holographic charges on the horizon from the viewpoint of the contextuality of quantum measurement.
Koji Ichikawa, IPMU
Non-Sphericity/foreground effect on the dark matter halo estimation of dwarf spheroidal galaxies
Meeting room 3, Kenkyu honkan 1F
One of the most promising ways to detect dark matter is to look for its annihilation or decay products among cosmic-rays. Especially, it is found that quite strong constraints can be imposed by the gamma-ray measurements of dwarf spheroidal galaxies. However, recent studies reveal that these constraints are largely affected by the uncertainty of the dark matter halo density. In this talk, we will discuss the robustness of the dark matter halo estimation especially focusing on the effect of the non-sphericity and contamination of foreground stars.
Yohei Saito, Institute of Industrial Science, University of Tokyo
Discreteness-Induced Transition in Multi-body Reaction Systems
Meeting room 3, Kenkyu honkan 1F Qualitative change in dynamical behaviors due to finite system size attracts much attention in various interdisciplinary fields such as systems biology (stochastic chemical reactions), ecology (population dynamics), game theory, and social networks (agent dynamics). Actually, increase in multiplicative noise intensity due to smaller system size can induce qualitative transition of stationary distribution, which has been known as noise-induced transition since 1970s [1]. Although finite system size not only increases noise intensity but also emphasizes state space discreteness, the role of such discreteness of state space has been rarely studied [2]. Thus, we identify such discreteness-induced transition in a simple 1-and 3 body reaction system[3]. This model enables us to derive a sufficient condition under which the discreteness-induced transition arises. Furthermore, we find that the critical size of discreteness-induced transition can become quadratically large, if multi-body reactions are allowed.
