Tidal Love numbers quantify the deformability of compact objects under external tidal fields and are key quantities in gravitational‑wave astronomy. They are essential for accurately modeling waveforms during the final orbits of an inspiral and are tightly connected to the microphysics of the compact object. At linear order, the tidal Love numbers of Schwarzschild black holes are famously zero. I will show that this property persists beyond linear order. In contrast, neutron stars exhibit a finite tidal response that encodes information about their internal structure, including their equation of state. I will present a framework for computing their tidal Love numbers beyond linear order. As I will discuss, these calculations rely on carefully matching relativistic perturbation theory of compact objects with the worldline effective field theory approach used to define their tidal deformability.

Symmetry is one of the most fundamental principles in nature, but where does it come from? Considering two distinct physical systems, 1) non-relativistic scattering of neutrons and protons in low-energy QCD and 2) relativistic scatterings of Higgs bosons in two-Higgs-doublet models, we show that the suppression, or maximization, of entanglement leads to enhanced symmetries in the underlying systems. These findings suggest a new paradigm to understand the origin of symmetry from the perspective of quantum information.

At low energies, the quark many-body system forms a unique higher-order structure of hadrons and then nuclei, but we have yet to fully understand why it happens based on QCD. Under this situation, it is also difficult to elucidate the high-density matter inside neutron stars.
The J-PARC hadron facility is challenging this grand problem through various experiments on strangeness nuclear physics and intermediate/low energy hadron physics, aiming to solve mysteries of quark confinement and its mass generation, hadron-hadron interactions (nuclear/baryon forces), high-density matter, and so on. In the seminar, the overview and future prospects of these research activities at J-PARC are presented from the experimental point of view.

Higher-spin gravity is a working model of quantum gravity in 4-dimensional de Sitter space. We discuss it at the level of cubic interactions, in a lightcone formalism originally developed for Minkowski and AdS. We use the interactions’ chiral structure to unlock a broader class of lightcone frames. This makes the formalism applicable to de Sitter, and brings out a causal property of the transformation between frames. We use this property to describe an evolution problem in a causal diamond, and especially in the largest causal diamond in de Sitter space – the static patch.

String theory generically predicts a landscape of axions. However, most studies of axion defects focus on a single-field setup. In this talk, I will discuss the nontrivial dynamics that emerge in a two-axion framework. Due to the mixing of the two axions in the potential, cosmic strings and domain walls exhibit a variety of phenomena specific to multi-axion systems. For example, strings of different axions can form “string bundles”, domain walls of one axion can induce domain walls of another, and potential bias can temporarily arise. I will also discuss the cosmological implications such as dark matter production and gravitational wave emission.

The numerical bootstrap method has been applied to solve eigenvalue problems in quantum mechanics. In this talk, I will give an overview of this method and its recent developments mainly in one-dimensional quantum mechanics. In particular, I will show that the bootstrap method can be regarded as a method for deriving eigenvalues using (an extension of) uncertainty relations. I will also show that the bootstrap method can derive exact results in solvable systems. This is a characteristic feature of the bootstrap method that is not found in other numerical analyses.

https://www-conf.kek.jp/kincha/

1967年以降、現在に至るまで、国際単位系（SI）における時間の単位である秒は、セシウム原子のマイクロ波領域の遷移周波数で定義されている。
2000年頃に我が国で発明された光格子時計をはじめとする、近年の光周波数標準の性能向上により、秒の再定義の機運が高まっている。
2030年開催の国際度量衡総会にて再定義決議の採択を目指している。この秒の再定義の現状を紹介するとともに、産総研における関連研究を紹介する。

https://www-conf.kek.jp/kincha/

「21世紀の物理学」とも称される超弦理論がこれまで人類の世界観の深化に貢献してきたことは間違いないが，我々の宇宙における素粒子標準模型やそれを超えた物理の理解により直接的に役立つのかどうかは自明ではない．
これは実験・観測の問題であると同時に，弦理論の理解そのものについての理論的な問題でもある．
本講演では，超弦理論が我々の宇宙について何を語りうるのか，そしてそのために何が必要とされているのかという大問題について，その一端を取り上げ議論したい．

Gravitational wave signals hinted at by recent pulsar timing array (PTA) observations have brought renewed interest to the scenario of metastable cosmic strings. These signals can be naturally explained by cosmic strings with lifetimes on the order of seconds. Such metastable strings are made possible by the presence of monopoles, and the PTA data suggest that the monopole mass scale is remarkably close to the energy scale of the cosmic strings. Previous analyses of gravitational wave signals from metastable strings have generally assumed a large hierarchy between these two scales. However, the observed closeness raises concerns about the validity of such assumptions—particularly regarding string formation, string decay, and the efficiency of gravitational wave emission. In this talk, I will discuss how the near-degeneracy of the monopole and string scales impacts these processes. The discussion will be based on concrete symmetry-breaking patterns that give rise to such scale configurations.

Axions are one of the candidates for the unknown dark matter. Ultralight axions form a huge number of clouds in galactic halos. When such an axion cloud passes through the Earth, it interacts electromagnetically with the geomagnetic field and generates a monochromatic electromagnetic wave whose frequency corresponding to the axion mass. Recently we modeled the axion-induced electromagnetic wave signals by solving Maxwell’s equations under the appropriate boundary conditions of the ionosphere for geomagnetic fields and showed that Earth’s natural environment can serve as a powerful probe for ultralight axion dark matter with masses ranging from 10^{-15} eV — 10^{-13} eV. Based on the derived theoretical model, we searched for axion-induced magnetic field signals within the observational data of global geomagnetic field variations (Eskdalemuir Observatory, 2012–2022). In this talk, I report on the idea of the search, the data analysis mehtod, the results of the search having several tens of axion signal candidates.