## 2018年度のセミナー

Date/Place | Jun. 8th (Fri.) 13:30-14:30 / H711 |
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Name | Takeo Moroi (Univ. of Tokyo) |

Title | Stability of Electroweak Vacuum in the Standard Model and Beyond (Slides) |

Abstract | I will discuss recent progresses of the calculation of the decay rate of the electroweak vacuum in the standard model. I will also discuss how extra fermions may affect the stability of the electroweak vacuum. |

Date/Place | May. 29th (Tue.) 15:30-16:30 / H711 |
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Name | Shoji Hashimoto (KEK) |

Title | Quark-hadron duality and lattice QCD |

Abstract | Quark-hadron duality is a basic assumption which many perturbative QCD calculations rely on. There are plausible arguments about why it is valid, but only at a qualitative level. We propose a set of quantities for which quantitative and non-perturbative calculation is possible using lattice QCD. A well-known example is related to the R-ratio of e+e- scattering. A primary target of the method discussed in this talk is the inclusive decays of B mesons. We discuss on how one can calculate its decay rate or some related quantities. |

Date/Place | May. 23th (Wed.)(Informal) 12:10-1:10 / H711 |
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Name | Janusz Rosiek (University of Warsaw) |

Title | Decay of Higgs boson to photons in the Standard Model Effective Field Theory (Slides) |

Abstract | Potential effects of yet undiscovered New Physics can be universally parametrized in terms of the so-called SM Effective Field Theory, defined as the Standard Model extended with all gauge-invariant operators of higher dimensions constructed of the SM fields. I will discuss a consistent setup for the perturbative calculations in such a complicated (non-renormalizable) model, including derivation of the Feynman rules in terms of the physical fields and quantization of the theory in the R_xi gauges. Then, as an application I will present the calculation of the radiative decay of Higgs boson into 2 photons in SMEFT. |

Date/Place | May. 22th (Tue.) 15:30-16:30 / H711 |
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Name | Toshifumi Noumi (Kobe Univ.) |

Title | Weak Gravity Conjecture and Infrared Consistency (Slides) |

Abstract | As is captured by the word “string landscape,” an almost infinite number of low-energy effective theories may be described in the string theory framework. However, recent studies have revealed that there exist a certain class of consistent-looking IR effective theories which are not realized in string theory, or more generally in a consistent UV theory of quantum gravity. Such theories are said to live in the “swampland” and clarifying the boundaries of landscape and swampland is an important issue in both the theoretical and phenomenological contexts. In the first half of this talk, I will review a typical example for such a criterion called the Weak Gravity Conjecture and its phenomenological implications. In the latter half, I will discuss its possible connection to other QFT principles such as unitarity. In particular, I will introduce our new proposal which we call the Tower Weak Gravity Conjecture based on the recent work arXiv:1802.04287. |

Date/Place | May. 15th (Tue.) 15:30-16:30 / H711 |
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Name | Tatsuma Nishioka (Univ. of Tokyo) |

Title | OPE for Conformal Defects and Holography |

Abstract | We study the operator product expansion(OPE) for scalar conformal defects of any codimension in CFT. The OPE for defects is decomposed into “defect OPE blocks”, the irreducible representations of the conformal group, each of which packages the contribution from a primary operator and its descendants. We use the shadow formalism to deduce an integral representation of the defect OPE blocks. They are shown to obey a set of constraint equations that can be regarded as equations of motion for a scalar field propagating on the moduli space of the defects. By employing the Radon transform between the AdS space and the moduli space, we obtain a formula of constructing an AdS scalar field from the defect OPE block for a conformal defect of any codimension in a scalar representation of the conformal group, which turns out to be the Euclidean version of the HKLL formula. We also introduce a duality between conformal defects of different codimensions and prove the equivalence between the defect OPE block for codimension-two defects and the OPE block for a pair of local operators. |

Date/Place | May. 8th (Tue.) 15:30-16:30 / H711 |
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Name | Sugumi Kannno (Osaka Univ.) |

Title | Quantum entanglement between bubble universes (Slides) |

Abstract | In de Sitter space where the universe expands exponentially, any two of mutually separated regions eventually become causally disconnected. This is most conveniently described by spanning open universe coordinates on two open charts in de Sitter space. Recently, Maldacena and Pimentel showed that the entanglement entropy of a free massive scalar field between two open charts is non-vanishing. This result shows that two causally disconnected regions in de Sitter space are entangled. I extend the calculation of Maldacena and Pimentel to the case where a bubble wall is present between the two open charts. This can be thought of as a model of pair creation of bubble universes in de Sitter space. I will discuss the effect of the bubble wall on the entanglement entropy between the bubble universes. |

Date/Place | Apr. 24th (Tue.) 15:30-16:30 / H711 |
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Name | Chen Zhang (NCTS) |

Title | Simplest Little Higgs Revisited: Hidden Mass Relation, Unitarity and Naturalness (Slides) |

Abstract | In this talk, I will present an analysis of the scalar potential of the Simplest Little Higgs (SLH) model in an approach consistent with the spirit of continuum effective field theory (CEFT). A hidden mass relation is obtained relating the pseudo-axion mass and top partner mass, serving as a crucial test of the SLH mechanism. I also propose a strategy of analyzing the fine-tuning problem consistent with the spirit of CEFT and apply it to the SLH. The scalar potential and fine-tuning analysis strategies investigated here should also be applicable to a wide class of Little Higgs and Twin Higgs models, which may reveal interesting relations as crucial tests of the related electroweak symmetry breaking mechanism and provide a new perspective on assessing their degree of fine-tuning. |

Date/Place | Apr. 17th (Tue.) 15:30-16:30 / H711 |
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Name | Yohei Ema (KEK) |

Title | Flaxion and its SUSY extension (Slides) |

Abstract | In this talk, we propose a minimal extension of the standard model which includes only one additional complex scalar field, flavon, with flavor-dependent global U(1) symmetry. It not only explains the hierarchical flavor structure in the quark and lepton sector (including neutrino sector), but also solves the strong CP problem by identifying the CP-odd component of the flavon as the QCD axion, which we call flaxion. Furthermore, the flaxion model solves the cosmological puzzles in the standard model, i.e., origin of dark matter, baryon asymmetry of the universe, and inflation. We also discuss a supersymmetric extension of this model, paying a particular attention to dynamics of an additional scalar flat direction in the early universe. |

Date/Place | Apr. 11th (Wed.) (Informal) 12:10 / H711 |
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Name | Ryo Nagai (Tohoku University) |

Title | Roles of perturbative unitarity in extended Higgs scenarios (Slides) |

Abstract | 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 the bad behavior of WW scattering amplitudes. The required conditions are called “unitarity sum rules”. The sum rules tell us nontrivial relationship between the properties of new particles/phenomena and the low-energy observables such as the 125GeV signal strengths (coupling strengths). In this talk, we discuss the implications of the unitarity sum rules and apply the sum rules to investigate physics beyond the standard model. |

Date/Place | Apr. 4th (Wed.) (Informal) 14:30-15:30 / H711 |
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Name | Ryoutaro Watanabe (Montreal U.) |

Title | Does complete set of data still prefer the B anomalies? |

Abstract | In this talk, I will show my ongoing work regarding new physics to accommodate the anomalies in b -> s mu mu and b -> c tau nu which have been standing on these days. So far, there are many papers for this topic and they concluded that U1 (singlet vector type of) leptoquark could explain the two simultaneously. In our work, we put a complete set of observables relevant for the above explanation and gives a fit analysis. As a result, we see what kind of patterns of LQ couplings are favored, which could be a guideline when one constructs a UV completed model to accommodate the B anomalies. |