Seminar 2025 / セミナー情報2025
複合粒子描像に基づく高質量暗黒物質模型の検証
2025年7月11日（金） 13:30
Speaker: Takumu Yamanaka (Osaka)
Abstract:
本講演ではQCDに類似したゲージ相互作用をし、電弱量子数を持つフェルミオンを導入した複合粒子暗黒物質模型を議論する。この模型における暗黒物質はO(1-100) TeVの質量を持つ中間子様粒子(ダークパイオン)であり、近年感度が向上している暗黒物質間接探索実験で検出が期待される。暗黒物質の残存量を記述するパラメータは、暗黒物質の対消滅断面積を詳細に解析することで得られる。本講演では、ダークパイオンがより重い複合粒子へと対消滅するforbidden channelと呼ばれる過程に着目し、その残存量への寄与について議論する。
Quantum decoherence in the Caldeira-Leggett model by the real-time path integral on a computer
2025年7月18日（金） 13:30
Speaker: Hiromasa Watanabe (Keio)
Abstract:
We propose first-principle calculations of an open system based on the real-time path integral formalism, treating the environment as well as the system of interest together on a computer. We focus on the Caldeira-Leggett model, which is well known, in particular, as a model of quantum decoherence. The calculation simplifies drastically since the path integral becomes Gaussian for typical initial conditions. The relevant saddle point, which is unique and complex, can be determined by solving a linear equation with a huge but sparse coefficient matrix. The integration over the saddles can be performed analytically, and the reduced density matrix can be obtained by tracing out a large number of harmonic oscillators in the environment. In particular, we confirm the dependence of the decoherence time on the coupling constant and the temperature that has been predicted from the master equation in a certain parameter regime. We also discuss how to extend this framework to general models using the generalized Lefschetz thimble method to overcome the sign problem.