报告人：Ota Atsuhisa 助理教授 重庆大学

题 目: Mode analysis of hydrodynamical Nambu-Goldstone modes（流体动力学Nambu-Goldstone模式的模式分析）

时 间：2025年1月8日（周三）上午10:00

地 点：理工楼1226

腾讯ID: 525 753 662

联系人：Navid Abbasi、郭文帝

报告摘要:

We conduct a mode analysis of a general U(1)-charged first-order relativistic hydrodynamics within the framework of the effective field theory of dissipative fluids in a Minkowski background. The most general quadratic action for collective excitations around hydrodynamic solutions -- specifically, the Nambu-Goldstone (NG) modes associated with the symmetry-breaking pattern induced by external fields -- is derived. It is found that the hydrodynamical frame invariants write the first-order dispersion relations in the low energy limit. In thermodynamical viscous fluids realized by integrating out fast modes, unitarity and local KMS symmetry for its underlying UV theory are guaranteed. Then, we find that first-order hydrodynamics are stable if the null energy condition is satisfied. As the NG modes nonlinearly realize the diffeomorphism symmetries, our mode analysis is valid in any coordinate systems, including Lorentz-transformed references. We also comment on the causal structure for the diffusive modes based on the retarded Green functions for the stochastic NG mode.

我们对一般U(1)电荷的一阶相对论流体力学进行了模式分析，该分析是在闵可夫斯基背景下的耗散流体有效场论框架内进行的。推导了围绕流体力学解的集体激发的最一般的二次作用量—特别是由外部场引起的对称性破缺模式相关的Nambu-Goldstone（NG）模式。研究发现，在低能极限下，流体力学框架不变量写出了第一阶色散关系。通过积分掉快速模式实现热力学粘性流体时，其底层紫外理论的幺正性和局部KMS对称性得到保证。随后，我们发现如果满足零能条件，一阶流体力学是稳定的。由于NG模式非线性地实现了微分同胚对称性，我们的模式分析在任何坐标系中都是有效的，包括洛伦兹变换参考系。此外，我们还基于随机NG模式的延迟格林函数讨论了扩散模式的因果结构。

报告人简介:

Prof. Atsuhisa Ota is an associate professor at Chongqing University. He received his PhD from Tokyo Institute of Technology in 2017 and has worked at Tokyo Institute of Technology, University of Cambridge, Ohio University, and the HKUST Jockey Club Institute for Advanced Study as a postdoctoral fellow before joining Chongqing University in 2023. He was a member of Dark Energy Spectroscopic Instrument (DESI) at 2020-2021. His research covers different aspects of cosmology, such as the cosmic microwave background spectral distortions, cosmological large- scale structure, and gravitational waves. In addition, he is interested in a theoretical aspects of relativistic hydrodynamics.

太田敦久是重庆大学的副教授。他于2017年获得东京工业大学博士学位，在加入重庆大学之前，曾作为博士后研究员在东京工业大学、剑桥大学、俄亥俄大学和HKUST赛马会高级研究所工作。2020年至2021年期间，他是暗能量光谱仪器（DESI）的成员。他的研究涵盖了宇宙学的不同方面，如宇宙微波背景辐射的频谱畸变、大尺度结构和引力波。此外，他还对相对论流体力学的理论方面感兴趣。