Seminar Information

Date: | June 16 ,2017 16:20~ |

Room: | 405 |

Speaker: | 横井直人さん（東北大学金属材料研究所） |

Title: | A Holographic Dual Approach to Ferromagnets |

We propose a dual description for ferromagnetic systems based on the holographic duality. Our holographic dual model to a 3-dimensional ferromagnetic system is a (4+1)-dimensional gravitational theory with an SU(2) gauge field and a triplet scalar field, and thermal effects are represented by introducing black holes as background geometry in the dual gravitational theory. This holographic model reproduces the behavior of the mean field theory near the critical temperature, and, at low temperatures, the resulting thermodynamical quantities also incorporate the contributions from spin wave excitations and conduction electrons.

(Based on Phys. Rev. D93, 026002 (2016).)

Date: | Jun 2 ,2017 16:20~ |

Room: | 405 |

Speaker: | 岡田宣親さん（アラバマ大学） |

Title: | Inflection-point U(1)_X Higgs Inflation |

Inflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field with its value during inflation below the Planck mass (Φ_I~< M_{Pl}). In order for a renormalization group (RG) improved effective λΦ^4 potential to develop an inflection-point, the running quartic coupling λ(Φ) must exhibit a minimum with an almost vanishing value in its RG evolution, namely λ(Φ_I)-~0 and β_λ(Φ_I)?0, where β_λ is the beta-function of the quartic coupling. In this paper, we consider the inflection-point inflation in the context of the minimal gauged U(1)_X extended Standard Model (SM), which is a generalization of the minimal U(1)_{B-L} model, and is constructed as a linear combination of the SM U(1)_Y and U(1)_{B-L} gauge symmetries. We identify the U(1)_X Higgs field with the inflaton field. For a successful inflection-point inflation to be consistent with the current cosmological observations, the mass ratios among the U(1)_X gauge boson, the right-handed neutrinos and the U(1)_X Higgs boson are fixed. Our scenario can be tested in the future collider experiments such as the High-Luminosity LHC and the SHiP experiments. In addition, the inflection-point inflation provides a unique prediction for the running of the spectral index α-~ -0.0027, which can be tested in the near future.

(Reference: Phys.Rev. D95 (2017) no.3, 035035; Phys.Rev. D95 (2017) no.5, 055030)

Date: | May 26 ,2017 16:20~ |

Room: | 405 |

Speaker: | 河井伸介さん（成均館大学） |

Title: | Gravitational wave leptogenesis |

The gravitational Chern-Simons term coupled to an evolving axion is known to generate lepton number through the gravitational anomaly. We examine this leptogenesis scenario in the presence of the Gauss-Bonnet term over and above the gravitational Chern-Simons term. We find that the lepton production can be exponentially enhanced. The Gauss-Bonnet term creates CP-violating instability of gravitational waves that may appear transiently after inflation, and during the period of instability elliptically polarized gravitational waves are exponentially amplified at sub-horizon scales. This instability does not affect the spectrum of the cosmic microwave background as it occurs at much shorter length scales. In a typical scenario based on natural inflation, the observed baryon asymmetry of the Universe corresponds to the UV cutoff scale at 10^14-16 GeV.

[based on arXiv:1702.07689]

Date: | Apr. 28 ,2017 16:20~ |

Room: | 405 |

Speaker: | 小島武夫先生（山形大学工学部） |

Title: | A bosonization of U_q(sl(M|N) |

Bosonization is a powerful method to study representation theory of infinite-dimensional algebras and its application to mathematical physics, such as calculation of correlation functions of exactly solvable models. For level k = 1, bosonization has been constructed for the quantum affine algebra U_q(g) in many cases. Bosonization of an arbitrary level k ∈ C is completely different from those of level k = 1. For level k ∈ C, bosonization has been constructed only for U_q(slb(N)) and U_q(sl(M|1)). In this talk we give a bosonization of the quantum affine superalgebra Uq(sl(M|N)) (M, N = 1, 2, 3, ・ ・ ・) for an arbitrary level k. For the level k 6= -M +N we give screening operators that commute with Uq(sl(M|N)) and propose a realization of the vertex operator. This talk is based on arXiv:1701.03645.