セミナー 2024年

Friday, January 19 2024, 16:00-18:00

鈴木勝彦, 海底資源センター

[金茶会] 海洋鉱物資源：放射光や同位体を用いた有用金属濃集プロセスの研究から環境影響評価まで

J-PARC研究棟2階会議室　リモート会場：3号館セミナーホール
https://www-conf.kek.jp/kincha/
海底鉱物資源には，長い地球の歴史で，海におけるグローバルな物質循環の中で，あるタイミングで，その場所に起きた元素濃集と言える。そこには，理由があり，その理由を科学的に明らかにすることは，海洋の物質循環を明らかするのみでなく，海底資源開発のための三要素：探査，採鉱，製錬にも大きく貢献する。本講演では，海底資源研究の最前線とその開発への応用とともに開発に向けた課題について，実際の鉱物資源をご覧に入れながら説明する。　　　　

Thursday, January 18 2024, 11:00-12:00

Xiaojun Yao, Univ. of Washington

[QCD theory seminar] When is axial gauge applicable?

Oneine (Zoom)
Axial gauge has been used in many perturbative calculations. However, it sometimes leads to puzzling results. In this talk, I will discuss a specific example in the context of heavy quark and quarkonium transport coefficients, where naive application of temporal axial gauge leads to an incorrect result. Then I will discuss the origin of the problem from both perturbative and nonperturbative aspects. Finally I will summarize the applicability condition of axial gauge and give a few examples.

Friday, January 12 2024, 16:00-17:00

Ippei Obata, KIPMU

Parity-violating scalar trispectrum from axion inflation

Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
We study a mechanism of generating the trispectrum (4-point correlation) of curvature perturbation through the dynamics of a spectator axion field and U(1) gauge field during inflation. Owing to the Chern-Simons coupling, only one helicity mode of the gauge field experiences a tachyonic instability and sources scalar perturbations. Sourced curvature perturbation exhibits parity-violating nature which can be tested through its trispectrum. We numerically compute the parity-even and parity-odd components of the sourced trispectrum. It is found that the ratio of parity-odd to parity-even mode can reach O(10%) in an exact equilateral momentum configuration. We also investigate a quasi-equilateral shape where only one of the momenta is slightly longer than the other three, and find that the parity-odd mode can reach, and more interestingly, surpass the parity-even one. This may help us to interpret a large parity-odd trispectrum signal extracted from BOSS galaxy-clustering data.

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