## Upcoming Seminars

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 |

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

Title | Weak Gravity Conjecture and Infrared Consistency |

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. |