11.10
Theory of Double Beta Decay (Lecture 2)
报告人：
Dr. Frank Deppisch, UCL
时 间：
星期一 2025-11-10 13:00 - 15:00
地 点：
Tsung-Dao Lee Institute/N6F-N600-Lecture Room
Tencent Meeting：
https://meeting.tencent.com/dm/mtKqFev48yqs
ID: 209806028 (no password）
摘 要：
This two-lecture series provides a theoretical introduction to neutrinoless double beta (0νββ) decay. The primary motivation for studying this decay lies in its unique potential to probe fundamental symmetries of the Standard Model (SM). Specifically, it is the main probe of the potential Majorana nature of neutrinos and its discovery would show that total lepton number is violated, with profound implications for our understanding of mass generation. After establishing the context within neutrino physics, we will calculate the two-neutrino double beta decay rate, separating the phase space factor from the nuclear matrix element. We will then focus on 0νββ decay as the crucial observable of interest where we will first explore the standard mechanism of light Majorana neutrino exchange but this is not the only possibility; other beyond-the-SM physics, such as heavy sterile neutrinos, could also mediate the decay. We will conclude by examining the theoretical challenges and opportunities in probing double beta decay at current and future experiments.
报告如有变动，请查看：
https://tdli.sjtu.edu.cn/event/4517
11.12
Scattering amplitudes in gauge theories
报告人：
Dr. Kaoru Hagiwara, KEK
时间：
星期三 2025-11-12 13:30 - 15:00
地 点：
Tsung-Dao Lee Institute/N6F-N600-Lecture Room
Tencent Meeting：
https://meeting.tencent.com/dm/Df0Y6oLKIRm1
ID: 689553664
摘 要：
In quantum field theories, scattering amplitudes are calculated perturbatively by using the plane wave solustion of the equation of motion of participating particles and its Green's functions (propagators). In gauge theories, Green's functions for the gauge particles are found only after gauge fixing. The most popular method is covariant gauge fixing, including Feynman, Landau and R_\xi gauges. The common feature among all covariant gauges is to constrain the total derivative of gauge fields, \del_mu A(x)^\mu. Accordingly, all four helicity components of virtual gauge bosons are allowed to propagate (three in Landau gauge) in each Feynman diagram, leading to subtle cancellation among interfering diagrams to obtain physically observable scattering amplitudes.
In this seriese of four lectures, I will introudce the Feynman Diagram (FD) gauge, in which the scalar component of the helicity states of virtual gauge bosons are not allowed to propagate (in case of massless gauge bosons of QED and QCD), or replaced by the Goldstone boson (in case of massive weak bosons). We have modified the helicity amplitude calculation code (HELAS) inside MadGraph that allows us to obtain arbitrary tree-level scattering amplitudes in the FD gauge, for the SM and BSM models with SMEFT operators. No subtle cancellation among interfering amplitudes remain, and we can understand how individual diagrams interfer.
It is clear that the FD gauge allows us to obtain physical amplitudes for each individual Feynman diagram. We do not yet know why this is the case. I would like to explain my own thoughts on the problem, and how it can contribute to the radiative correction frameworks of the SM, QCD and the EW theory.
报告如有变动，请查看：
https://tdli.sjtu.edu.cn/event/4497
11.12
飞秒激光成丝现象原理与应用
报告人：
Dr. Weiwei Liu（刘伟伟）,Nankai University
时 间：
星期三 2025-11-12 15:00 - 16:00
地 点：
Room 300, No.5, New Buildings of Sciences
摘 要：
高功率超快激光在透明介质传输中不产生明显的发散，其传输距离可以远远超越衍射极限，同时会产生等离子通道。该通道通常称为“光丝”，这一过程即为成丝现象。成丝现象的应用包括激光超精细加工、超快激光新脉冲产生、大气污染探测、人工干预天气甚至空间通信等。本报告将简要介绍飞秒激光成丝现象原理与应用。
报告如有变动，请查看：
https://www.physics.sjtu.edu.cn/index_report_colloquium/3934.html
11.13
Investigation the Muon Content of Very-High Energy Cosmic Ray Air Shower at LHAASO
报告人：
Dr. Cunfeng Feng（冯存锋）,Shandong University
时 间：
星期四 2025-11-13 11:00 - 12:00
地 点：
Tsung-Dao Lee Institute/N6F-N600-Lecture Room
Tencent Meeting：
https://meeting.tencent.com/dm/aZgfbjAzpLym
ID: 758794234 Password：123456
摘 要：
The muon content of cosmic ray air showers is sensitive to both the hadronic interactions within the shower and the primary cosmic ray nuclei composition. The large high altitude air shower observatory (LHAASO) has comprehensively measured the information of the air showers of very high energy cosmic rays. A cosmic ray mass independent energy reconstruction method has been proposed by combining the muon content and the electromagnetic particles of the air shower. The mean logarithmic mass of the cosmic ray also has been estimated based on the muon content of the air shower. Also, the attenuation length of muon content in the air shower has measured and compared with expectations of several hadronic interaction models. The fluctuation of the muon content of the air shower has been used to estimate the variance of logarithmic mass of the cosmic ray. This talk will show all the aforementioned air shower studies.
报告如有变动，请查看：
https://tdli.sjtu.edu.cn/event/4548
11.14
声子晶体中由损耗诱导的趋肤效应
报告人：
Dr. Weiyin Deng (邓伟胤) ，Wuhan University
时 间：
星期五 2025-11-14 10:30 - 11:30
地 点：
Room 203, No.5, New Buildings of Sciences
摘 要：
近年来，非厄米物理引起了广泛的关注，成为凝聚态物理、光学和声学等领域的研究热点。非厄米趋肤效应是指体态以趋肤模的形式坍缩到开放边界的物理现象，是非厄米物理特有的性质。本报告主要介绍课题组在由损耗诱导声场趋肤方面的一些进展，包括在二维奇异点声子晶体中观测到边缘依赖的趋肤效应，在三维奇异线声子晶体中发现了表面依赖的趋肤效应，边缘趋肤和角趋肤共存的混合阶趋肤效应，以及拓扑边界态的趋肤效应。这些工作既能增加人们对非厄米物理的认识，也会促进非厄米调控的功能性声学器件的设计。
报告如有变动，请查看：
https://mp.weixin.qq.com/s/Od244tiusajYATih33VFtw
11.14
Composite Dark Matter with Forbidden Annihilation
报告人：
Dr. Takumu Yamanaka, The University of Osaka
时 间：
星期五 2025-11-14 15:00 - 16:00
地 点：
Tsung-Dao Lee Institute/N6F-N600 - Lecture Room
Tencent Meeting：
https://meeting.tencent.com/dm/ti77iypOtuur
ID: 563505654
摘 要：
Approximately a quarter of the energy density of the Universe consists of Dark Matter (DM). A new stable particle in an extension of the Standard Model is a good candidate for DM, and thermal freeze-out scenario is one of the most attractive scenarios for the production of particle DM. Indirect detection experiments of DM started to be sensitive to the annihilation of DM whose mass is O(1-100) TeV. Assuming thermal freeze-out scenario, heavier thermal relic DM requires a larger coupling to be consistent with the observed relic abundance. One natural way to accommodate such a large coupling is to assume that DM is a composite particles from new strong dynamics.
In this seminar, I will introduce a DM model based on QCD-like SU(N) gauge theory with electroweakly interacting dark quarks. In particular, we focus on meson-like particles (dark pions) arising from chiral symmetry breaking in the new QCD-like sector. The lightest G-parity odd dark pion is stable and can be a good candidate for DM.
We investigate mass spectra of dark pions and annihilation channels of DM which mainly contribute to the relic abundance. We find that the mass term of the dark quarks affects the mass spectrum, and masses of DM and heavier G-parity even dark pions tend to be degenerate. In this case, annihilation processes which are kinematically forbidden in zero-temperature contribute to the relic abundance of DM in our setup. Taking such forbidden annihilation processes into account, we find that the DM model realizes heavy DM whose mass is O(1-100) TeV. I will also discuss the Sommerfeld effect on annihilation of dark pions.
报告如有变动，请查看：
https://tdli.sjtu.edu.cn/event/4549
图文编辑：叶丹
责任编辑：张小丽
