Hyungjin Kim, KAIST
Diphoton Excess and Electric Dipole Moments
Meeting room 1, Kenkyu honkan 1F
We examine the implication of the recently observed diphoton excess for the electric dipole moments of the neutron and electron. The excess can be due to a spin zero resonance which couples to photons and gluons through the loops of massive vector-like fermions. In this case, the resulting neutron electric dipole moment can be comparable to the present experimental bound if the CP-violating angle alpha in the underlying new physics is of O(10^-1). An electron EDM comparable to the present bound can be achieved through a mixing between the 750 GeV resonance and the Standard Model Higgs boson, if the mixing angle itself for an approximately pseudoscalar resonance, or the mixing angle times the CP-violating angle alpha for an approximately scalar resonance, is of O(10^-3). For the case that the 750 GeV resonance corresponds to a composite pseudo-Nambu-Goldstone boson formed by a QCD-like hypercolor dynamics confining at Lambda_HC, the resulting neutron EDM can be estimated with alpha ~ (750GeV/Lambda_HC)2theta_HC, where theta_HC is the hypercolor vacuum angle.
Masaki Yamada, Tohoku Univ
Thermalization process and DM production in the reheating era
Meeting room3, Kenkyu honkan 1F
We estimate dark matter density for the Universe with a reheating temperature smaller than the mass of dark matter, assuming dark matter to be a weakly interacting massive particle. During the reheating process, an inflaton decays and releases high-energy particles, which are scattered inelastically by the thermal plasma and emit many particles. Dark matters are produced through these inelastic scattering processes and pair creation processes by high-energy particles. We properly take account of the Landau-Pomeranchuk-Migdal effect on inelastic processes and show that the resultant energy density of dark matter is much larger than that estimated in the literature and can be consistent with that observed when the mass of dark matter is larger than O(100) GeV.
Daisuke Kawai, Kyoto University
Chaotic strings in a near Penrose limit of AdS5×T1,1
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
We study chaotic motions of a classical string in a near Penrose limit of AdS5×T1,1. It is known that chaotic solutions appear on R×T 1,1, depending on initial conditions. It may be interesting to ask whether the chaos persists even in Penrose limits or not. In this talk, we would like to introduce basic tools for studying classical chaos first ,and then we would like to show our results. We revealed that sub-leading corrections in a Penrose limit provide an unstable separatrix, so that chaotic motions are generated as a consequence of collapsed Kolmogorov-Arnold-Moser (KAM) tori. Our analysis is based on deriving a reduced system composed of two degrees of freedom by supposing a winding string ansatz. Then, we provide support for the existence of chaos by computing Poincare sections.
Masamichi Miyaji, Yukawa Institute for Theoretical Physics
Chaos from Information Metric
Meeting Room 1 Kenkyu Honkan 1F, slides (kek.jp only)
We show that rapid growth of information metric of Thermofield double stateis directly related to commutator of simple operators. Following holographic proposal for information metric, we compute information metric of thermofield double state for marginal deformation, by evaluating volume of maximal volume codimension 1 surface, and confirm that information metric increases exponentially with time. Our result implies thermofield double state of chaotic system is sensitive to change of outer environment. We note that our holographic calculation of information metric is consistent with the expected decay of two point function of spacial Wilson loops on great circle.
Yohei Ema, Univ. of Tokyo
Fate of Electroweak Vacuum during Preheating
Meeting room 1, Kenkyu honkan 1F
Our electroweak vacuum may be metastable in light of the current experimental data of the Higgs/top quark mass. From the viewpoint of cosmology, an interesting consequence is that high-scale inflation has a tension with the metastability.In order to overcome this problem, Higgs-inflaton/-curvature couplings are often introduced to stabilize Higgs during inflation. However, after inflation, the mass term induced by the additional coupling oscillates during the preheating era, and it can potentially destabilize the electroweak vacuum via resonant production of Higgs. In this talk, we study whether the Higgs-inflaton/-curvature coupling can save the electroweak vacuum by taking account of Higgs production during the preheating stage. In particular, we put upper bounds on the Higgs-inflaton/-curvature coupling.
Atsushi Naruko, Tokyo Institute of Technology
Gravitational scalar-tensor theory
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
We consider a new form of theories of gravity in which the action is written in terms of the Ricci scalar and its first and second derivatives. Despite the higher derivative nature of the action, the theory is free from ghost under an appropriate choice of the functional form of the Lagrangian. This model possesses 2 + 2 physical degrees of freedom, namely 2 scalar degrees and 2 tensor degrees. We also discuss the correspondence between these theories and generalized bi-Galileon theories.
Ryo Nagai 長井遼, Nagoya Univ.
Unitarity sum rules for WW scattering and their implications
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only) One of the important roles of the SM Higgs boson is to keep WW scattering
One of the important roles of the SM Higgs boson is to keep WW scattering
amplitudes perturbatively unitary in high energy limit. However, once the Higgs
coupling deviates from the SM prediction, the perturbative unitarity might be
broken down at the certain energy scale. In order to maintain the perturbative
unitarity with anomalous higgs coupling in high energy limit, we need new particle(s)
whose couplings are tuned to cancel a bad behavior of WW scattering amplitudes.
The required conditions are called “unitarity sum rules”. We revisit the unitarity sum
rules and apply them to investigate the model independent property of perturbative
extra spin-0,1 particles.
Ryosuke Sato, Weizmann Inst. & KEK
Self-consistent Calculation of the Sommerfeld Enhancement
Seminar hall, 4 go-kan 1F
The annihilation cross section of the dark matter is one of the most important quantity for the phenomenology of the dark matter. If the dark matter couples with a light force carrier, non-perturbative resummation is required in non-relativistic regime due to so-called Sommerfeld enhancement. A commonly used formula of this cross section is a product of the hard (short-range) scattering cross section and the enhancement factor which is calculated by dark matter two-body wave function. However, it is known that this formula violates the unitarity bound for small velocity if there is zero energy bound state. In this talk, I will discuss the calculation of the dark matter annihilation cross section in non-relativistic quantum mechanics. In our framework, both short-range and long-range effect is treated in a non-perturbative way, and the cross section satisfies the unitarity bound.
Hiroyuki Kitamoto, Kyoto U.
Generalization of Stochastic approach for Infrared effects
Meeting Room 1, Kenkyu Honkan 1F
We extend investigations of infrared dynamics in accelerating universes. In the presence of massless and minimally coupled scalar fields, physical quantities may acquire growing time dependences through quantum fluctuations at super-horizon scales. From a semiclassical viewpoint, it was proposed that these infrared effects can be described by a Langevin equation. In de Sitter space, the stochastic approach has been proved to be equivalent to the leading power resummation of the growing time dependences. In this study, we make the resummation derivation of the Langevin equation in a general accelerating universe. The resulting Langevin equation contains a white noise term and the coefficient of each term is modified by the slow-roll parameter. Furthermore we show that the semiclassical description of the scalar fields leads to the same stochastic equation as far as we adopt an appropriate time coordinate.
The above investigations are performed in models whose nonlinear terms are given by potentials. Therefore the stochastic approach should be extended in another direction, i.e. in models with derivative interactions. If time allows, I also talk about this direction of generalization.
Yuta Hamada, Kyoto U.
Reheating-era leptogenesis
Meeting Room 1, Kenkyu Honkan 1F
