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Date: Fri, 7 Jun 2024 17:19:10 +0900
To: sg-l__AT__yukawa.kyoto-u.ac.jp
Subject: [Sg-l:8498] 集中講義(杉下宗太郎氏)
From: Hidenori Fukaya (Sg-l 経由) 

素粒子論グループのみなさま

6/17-19に大阪大学で行われる
杉下宗太郎氏 (京都大学)による集中講義のご案内です。
教科書で説明されているQED赤外発散の処理に
納得がいかない方におすすめです。

深谷英則　大阪大学
-------------------------------------
Title : Infrared divergences and asymptotic symmetry in QED
Lecturer : Prof. Sotaro Sugishita (Kyoto U.)

June 17（Mon) 13:30 - 15:00, 15:10 - 16:40
June 18 （Tue) 10:00 - 11:30,  13:30 - 15:00, 15:10 - 16:40
June 19  (Wed)  10:00 - 11:30,  13:30 - 15:00, 15:10-16:10 (Seminar)

Place : E204,  Department of physics, Osaka University

Course Objective:
Lectures will be given on infrared divergence problems and asymptotic
symmetries in electromagnetic theory on a 4-dimensional flat
spacetime. Electromagnetic and gravitational theories on an asymptotic
flat spacetime have an infinite-dimensional symmetry called asymptotic
symmetry, which is closely related to the behavior of the theory in
the low energy region. In this lecture, we will explain asymptotic
symmetry and infrared divergence problems in quantum electromagnetism
(QED) and explain their relationships. We also introduce the dressed
state method, which has been known for a long time as a method to
calculate the S matrix elements of QED while avoiding infrared
divergence, and show that this method is natural from the perspective
of asymptotic symmetry. We will explain that the conditions for an
appropriate dressed state can be regarded as a quantum version of a
phenomenon called the memory effect in classical electromagnetism, and
are a consequence of the superselection rule of asymptotic symmetry.

Class Plan:
1. Bremsstrahlung and memory effects in classical electromagnetic theory
2.  Asymptotic symmetry in electromagnetic theory
3. Soft photon theorem and infrared divergence in QED
4. Dress state method and asymptotic symmetry
5. Comparison with standard method and zero measure problem

Seminar (in the last slot on June 19)
Title:
Dress code for inclusive cross section in QED

Abstract:
We consider the infrared (IR) aspects of the S-matrix and inclusive
cross section in QED. One way to obtain an IR-finite cross section is
the Bloch-Nordsieck method, where we consider the inclusive cross
section by summing up soft photons. Another approach is the dressed
state formalism, which allows us to obtain IR-finite S-matrix elements
directly. The dressed state formalism is important even when
considering the inclusive cross section. When considering a
superposition of states, the interference effects among them can be
observed without decoherence only if the superposed states are
appropriately dressed.