1. Cosmic transients in multi-messenger era
　2. Gravitational wave sources
　3. Gamma-ray bursts
　4. Afterglows
　5. Cosmic-ray and neutrino sources
　6. Pulsars and magnetars
　7. Fast radio bursts

私は主に古典的な立場に立って、ブラックホールなどの強重力場で おこる現象を研究してきました。今回の講演の前半では自己紹介も 兼ねて、私が重力研究を巡る状況をどのように見て、どのようにア プローチしてきたか、また今後どのような問題に取り組んでみたい かを説明します。後半では、現在すすめている研究のひとつのトピ ックをとりあげて現状を説明します（今のところアクシオン・ブラ ックホール系にするつもりです）。

It is known that infrared divergences appear in usual computations of the S-matrix in QED (or gravity) based on the Fock states. Dressed states were proposed to resolve this problem. However, we show that conventional dressed states for QED still cause IR divergences. The asymptotic symmetry in QED also suggests modifying the conventional dressed states. We propose new dressed states which are consistent with the asymptotic symmetry in QED. We conclude that S-matrix elements between the new dressed states are IR finite.

重力子やアクシオン暗黒物質探索には新しいアイデアが必要である。開放系の量子力学はその道具となり得る。 また、プランク質量スケールの重力理論研究は、宇宙論と素粒子論を結びつけるウロボロスの蛇という描像の確立のために重要である。 メゾスコピック宇宙の時間空間相関という観点からこれらの問題を眺めた時、光合成などの量子生物学との関係も興味深い。 今回は、開放系の量子力学という観点から、これらの問題を考察してみたい。

加速膨張宇宙やブラックホールとの関係に興味があり、 Eigenstate Thermalization Hypothesis (ETH) や その重力理論への応用について最近勉強を始めました。 一言で言うと、ETH やその周辺の進展は、純粋状態が どのように熱化していくのか？という問題を 明らかにしようというものです。 自分の勉強が進んだ範囲で ETH のレビューをしたいと思いますが、 遅々として進まない場合には、 別の話題に関する自分の最近の研究について話すかもしれません。

最近興味を持っている「漸近的安全性」に基づく重力の量子論へのアプローチとその時空特異点への示唆についてレビューします。 特に、重力に関する汎関数くりこみ群方程式の定式化と、簡単化したEinstein-Hilbert truncationに基づく重力定数・宇宙項の振る舞いをレビューします。

現実に実現されている量子重力理論は何か？（またそもそも重力子は存在するのか）という問は、素粒子論・宇宙論における大きな未解決問題の一つである。この問題を解決するには、現象論と量子重力理論を関連付ける必要がある。この文脈で有用であると近年明らかになってきた、S行列のユニタリー性や解析性に基づいた解析を紹介する。今後の方向性やこの解析の不満点等にも触れたい。

三つの内容について話したいと思います：
1,宇宙無毛仮説(https://journals.aps.org/prd/pdf/10.1103/PhysRevD.28.2118)のレビュー。
2, インフラトンとゲージ場結合の場合の非等方性。
3,正規直交基底でビアンキ宇宙のリッチテンソルの計算。

ブラックホールの熱力学について話します．時間があればブラックブレーンの熱力学や，これらを応用して高階微分補正によるextremal conditionの変化の計算についても話します．

周期的な電波パルスを放射するパルサーという天体が知られています。
本セミナーでは主にパルサーのモデル化と最近の観測結果をレビューします。
その上で今明らかになっていないパルサーの謎(ミリ秒パルサーの進化,制動指数のズレ,etc)について共有します。
最後に少しだけ時間をとって、最近考えている研究のアイデアについて議論したいと思います。

近年アクシオン（Axion-like particlesを含む）はダークマターとしてや加速膨張を引き起こす場として注目されている．
一方で，アクシオンのような質量項を持つスカラー場が存在すると，超放射不安定性により，回転ブラックホール周りにアクシオン雲を形成することが古くから知られている．
本講演では電磁場との結合を持つアクシオン場を考え，磁場を伴うブラックホールにおいてはアクシオン雲が電磁波の放射に伴って減衰することを示し，超放射不安定性による増幅率との比較を行う．
前半ではまず，後の比較のために回転ブラックホール時空における有質量スカラー場の超放射不安定性を簡単にレビューする．
後半では背景時空をSchwarzschildブラックホールとし，さらに背景磁場としてモノポール，一様磁場を導入し，それぞれの場合についてアクシオン－電磁場系の摂動方程式を導出する．
解析的な評価を行うために，適当な条件の下，方程式を量子力学における水素原子についての方程式と類似の物で近似する．
さらにアクシオンと電磁場の結合項が小さいという近似の下，電磁場の放射に伴うアクシオン雲の減衰率を計算する．
最後に超放射不安定性における主要モードについて，超放射不安定性による増幅率と電磁場の放射に伴う減衰率を比較する．

近年、緑黄色硫黄細菌のタンパク質内において、室温環境下でも量子コヒーレンスが保たれていることが明らかになりました。このことは量子コヒーレンスが光合成に重要な役割を果たしていることを示唆しており、現在では開放系の量子力学と密接に関わりあいながら光合成の理解が進められています。 今回は光合成のような量子生物学へ研究を広げるための準備として、緑黄色硫黄細菌に対して用いられた2次元分光法の物理と、その実験データから量子コヒーレンスをどのように読み取るのかについてレビューしたいと思います。

In the past two decades, AdS/CFT correspondence provides a new way of understanding gravity and quantum field theory. Ryu-Takayanagi conjecture connects two important concepts, extremal surfaces and entanglement entropy in these two different fields, which suggests some deep relations between quantum gravity and quantum field. In other words, the underlying degrees of freedom for gravity on asymptotical AdS space should be identified as degrees of freedom of boundary CFT. Thus, there is something that relates dynamics of spacetime, i.e. Einstein's equations with entanglement entropy of CFT. In this talk, I introduce the linear order of Einstein's equations following from the First Law of entanglement. I also demonstrate the Kinematic Space, an auxiliary de Sitter space between AdS and CFT, and reveal how dynamics of perturbation of entanglement in Kinematic Space emerges directly from the bulk linearized Einstein's equations.

昆虫はシンプルな神経系しか持たないにも関わらず、非常に優れたナビゲーション能力を持っています。ナビゲーションには太陽や風、景色など様々な手がかりが用いられますが、中でも天空の偏光パターンを利用した方向検出とそれに基づく経路積算については古くから研究されており、そのメカニズムも含めて詳細な知見が得られています。今回は、昆虫のナビゲーション戦略に関する一般的な解説と、偏光視のしくみについてご紹介したあと、私たちの研究室で得られた、ミツバチを用いた餌場学習に基づく偏光定位の解析結果についてお話します。

The QCD axion is a pseudoscalar particle introduced to solve the so-called strong CP problem in QCD, and has attracted attention also in cosmology as a candidate for dark matter, dark energy, and inflaton. In this talk, I will review the strong CP problem and various axion models as solutions to that problem. And then, I will review the predictions of axion mass and axion-photon coupling to facilitate phenomenological applications.

Cosmic inflation is an important paradigm of the early Universe which is so far developed in two equivalent ways, either by geometrical modification of Einstein's general relativity (GR) or by introducing new forms of matter beyond the standard model of particle physics. Starobinsky's R+R^2 inflation based on a geometric modification of GR is one of the most observationally favorable models of cosmic inflation based on a geometric modification of GR. In this talk, I will discuss in detail the fundamental motivations for Starobinsky inflation and present how certain logical steps in the view of its UV completion lead to the emergence of a gravity theory that is non-local in nature. Then I will establish how one can perform studies of the early Universe in the context of non-local gravity and what are the observational consequences in the scope of future CMB and gravitational waves.

I will review the concept of many-body physics with several examples and their connection to hydrodynamics. I will first review the convenientional framework of hydrodynamics and motivate the need of an lagrangian formulation based on the microscopic properties of quantum many-body systems. These quantum properties will naturally lead to contraints on the physical parameters in the effective theory of hydrodynamics. I will desribe the main idea of this formalism and present an application of this hydro EFT and its relavence to experiments.

Large excursion of the inflaton field can trigger interesting dynamics. One important example is a first order phase transition in a spectator sector which couples to the inflaton. Gravitational waves (GWs) from a first order phase transition during inflation, which is an example of an instantaneous source, has an oscillatory feature. This feature is generic for the source to happen in a universe experiencing accelerating expansion. The shape of the GW signal contains information about the evolution of the early universe following the phase transition. In particular, the slope of the infrared part of the GW spectrum is sensitive to the evolution of the Hubble parameter when the GW modes reenter the horizon after inflation, the slope of the profile of the intermediate oscillatory part depends on both the evolutions of the Hubble parameter when the modes reenter the horizon and the Hubble parameter when the modes exit the horizon during inflation, and the slope of the ultraviolet part depends on the evolutions of the Hubble parameter when the modes reenter the horizon and the Hubble parameter when the modes exit the horizon during inflation, and the details of the of the dynamics of the phase transition. We consider several examples of non-minimal models of evolution during and after the inflation, and we demonstrate that shape of the GW can be used to distinguishing them from the minimal scenario of quasi-de Sitter inflation and radiation domination after a fast reheating.

As on-shell methods of scattering amplitudes have become powerful tools to bootstrap scattering amplitudes, similar bootstrap philosophy as well as tools has also been extended to the study of cosmological correlators. In the talk, I will review relevant tools and ideas in on-shell methods of scattering amplitudes, and try to connect them to the study of cosmological correlators.

Axions are prominent cold dark matter candidates and may form gravitationally bound clumps, called “axion stars”.
Such massive objects can cause an amplification of brightness of a background source star when it passes close to a line-of-sight to that star, called gravitational microlensing events.
Therefore, the abundance of axion stars can be constrained by observations of microlensing events such as the EROS-2 survey and the Subaru Hyper Suprime-Cam observation.
We compute the expected number of microlensing events of stars composed of the ordinary QCD axion and string axions and derive microlensing constraints on these including an effect of the extended structure.
In this talk, I will mainly review the basics of axion stars and explain microlensing constraints on axion stars that possess extended structures.

Usual calculation for quantum field theory relies on Lagrangian under a certain symmetry. Then, one can obtain amplitudes by taking Feynman rules and diagrams. In contrast, a method called scattering amplitudes (also called on-shell amplitudes) directly provides the amplitudes from symmetries without relying on Lagrangian. For example, calculations of gluon n-point scattering amplitudes can be greatly reduced in this method. This approach is expected to extract some essences in quantum field theory, which are not obvious in the usual Feynman methods. Basically, conventional scattering amplitudes are methods for the massless theory. From 2017, this method has been generalized to involve any-spin massive particles by Nima Arkani-Hamed's group. In this talk, first, I will provide a brief review of the massless and massive scattering amplitudes. Next, I will introduce the scattering amplitude calculations connected with electroweak symmetry breaking, which are related to masses, vev, and longitudinal waves. In particular, we do not use the standard model Lagrangian. We derived (strictly speaking, we re-derived) several equations for electroweak symmetry breaking that are supposed to be inherent in field theory. Also, in such a bottom-up approach, we present the systematic derivation of independent three-point and four-point contact terms. This talk is based on arXiv:1909.10551 and arXiv:2008.09652.

Holographic dualities relate gravitational theories in higher dimensions to (non-gravitational or gravitational) theories in lower dimensions.
Usually, the spacetime on which the lower-dimensional theory is defined is identified as some boundary of the higher dimensional spacetime.
Therefore, important features (such as causality) of the boundary theory are encoded in whether there exist causal shortcuts in the bulk or not.
For example, in the AdS/CFT correspondence, it is known as the Gao-Wald theorem that causal shortcuts are forbidden in the bulk when considering sending information from boundary to boundary.
This implies that the causal structure of AdS is compatible with causality in CFT, and provides a nontrivial check of AdS/CFT.
In this talk, we focus on the causal structures of a holographic model called double holography.
Double holography plays a crucial role in recent studies of Hawking radiation and information paradox.
For example, the famous island formula is proven in double holography.
I will show that, the description which is considered as the physical description must include superluminal effects and hence nonlocal interactions, for it to be consistent with other descriptions.
I will also discuss some consequences and features of this nonlocality as well as its possible origin.

The black hole singularity plays a crucial role in formulating Hawking’s information paradox. The global spacetime analysis may be reconciled with unitarity by imposing a final state boundary condition on the spacelike singularity. Motivated by the final state proposal, we explore the effect of final state projection in two-dimensional conformal field theories in our recent paper arXiv:2112.08433. We calculate the time evolution under postselection by employing the real part of pseudo-entropy to estimate the amount of quantum entanglement averaged over histories between the initial and final states. We find that this quantity possesses a Page curve-like behavior.

We discuss the scale invariance approach for extending the standard model of particle physics. The dynamical chiral symmetry breaking of the hidden quantum chromodynamics sector in the model generates the Planck scale, the right-handed neutrino mass, and electroweak scale through the vacuum expected value of the real scalar field which transmits the energy scale of the hidden sector to the visible sectors. We treat this scalar field as the inflaton to achieve inflation. The inflation model predicts a small tensor-scalar ratio ($r \sim 10^{-3} $) like Higgs-inflation or Starobinsky inflation. The dynamical chiral symmetry breaking leads to dark pions, the dark matter candidates in our model. We also discuss the inflaton decay scenario for dark matter production.