Quantum Field Theory

Prof. Mathias Scheurer

The lecture will start already in the first week of the semester, i.e., the first class will take place on Wednesday, April 10, 2024. The exercise classes will start in the second week (i.e., the first sheet will be due on Wednesday, April 17, 2024 and discussed on Friday, April 19, 2024).

Note the locations have changed:

• Wednesday, 08:00 - 09:30, Lecture Hall 57.06, Pfaffenwaldring 57
• Friday, 09:45 - 11:15, Lecture Hall 57.06, Pfaffenwaldring 57

• The lecture and the tutorials will be given in English.
• The registration for the exercise groups will be open from Friday April 12, 2024, 13:30. To register, you need the Lecture Key given in the first lecture. Note that the registration is only possible from within the university network.
• If you assign a password at the registration, you can request your current scores here.

Recordings of the lectures can be accessed via ILIAS. The recordings should be seen as a service to those of you who cannot come on a specific date (e.g., due sickness etc.) or want to recap later. However, I highly recommend attending as many lectures as possible, to take advantage of the interactive nature of the classroom and learn with/from your peers. 

There will be an individual 30 mins oral exam at the end of the course. You can choose which chapter the first few questions will be about, but should expect that any topic covered in the lecture can be part of the exam.

There are two possible exam dates you can choose: August 6, 2024 or October 11, 2024. The specific time window of your personal exam will be announced at least two weeks in advance. You will receive an email in early July asking you to sign up for one of the two possible dates.

To be able to take the oral exam, you have to pass the exercise class (see below). Students who have already obtained a suitable certificate from another lecturer must have it recognized by July 1, 2024 by sending it via E-Mail to Prof. Scheurer.

1. Altland & Simons, Condensed Matter Field Theory.
2. Piers Coleman, Introduction to Many-Body Physics.
3. Bruus & Flensberg, Many-Body Quantum Theory in Condensed Matter Physics.
4. Sachdev, Quantum Phase Transitions.
5. Abrikosov, Gorkov, & Dzylaoshinski, Methods of Quantum Field Theory in Statistical Physics.
6. Zinn-Justin, Quantum Field Theory and Critical Phenomena.
7. Wen, Quantum Field Theory of Many-Body Systems.
8. Peskin & Schroeder, An Introduction to Quantum Field Theory.
9. Ryder, Quantum Field Theory.

• The many-body path integral. The challenge of many-body quantum mechanics. Warm-up: the path integral of a single particle. Coherent states and Grassmann variables. Many-body field integrals. Matsubara sums. Free particles.

• Perturbation theory and diagrammatics. The idea of asymptotics. Interacting electrons. Random-phase approximation. Lindhard function. Screening. Self-energy.

• Hubbard-Stratonovich transformation. General idea. Different channels. Application: interacting electrons.

• Superconductivity. Phonon-induced electron-electron interaction. Field-theory of superconductivity. Higgs mechanism. Electromagnetism response of superconductors.

• Disordered electrons. Disorder ensembles. Replica theory. Finite lifetime of electrons.

• Quantum magnetism. Field theory for Ising model. Path integral for single spin and Wess-Zumino-Witten terms. Continuum field theory for Heisenberg ferromagnets and antiferromagnets. Spin liquids and emergent gauge fields.

• Particle physics. Review of relativistic quantum mechanics. Klein-Gordon and Dirac field theories. Standard model of particle physics.

The weekly exercises class will involve:
(1) Handing in solutions for those exercises labeled as "written"; these will be marked and discussed in the next tutorial. The deadline is Wednesday at 5:00 PM of the week where the problem set will be discussed. Please upload your solutions on ILIAS before the deadline.
(2) Virtual presentations: at the beginning of every tutorial, you can indicate on a list which parts of the exercises labeled as "oral" you have prepared and are willing to present. While everyone will get points for the parts signed up for, only one person will have to present it.

If any question on the exercise lists is not clear enough, please feel free to contact joao.sobral@itp3.uni-stuttgart.de for clarifications.

In order to pass the exercises, you need at least 50% of the points in (1) and 66% of the points in (2); furthermore, every student is required to present at least twice on the blackboard.

To visualize content of the lecture I will sometimes use Wolfram Mathematica. The files shown in the lecture will also be made available to you via ILIAS. While you are encouraged to play with them on your own computer, the ability to write code is not required for the assessment of the lecture. You can display the Mathematica files on your computer using the Wolfram Player for Notebooks.

You will have to
1) give a ~12 mins black-board presentation (+ 8 mins of discussions) on your part of the chapter (see list shared via email) and participate actively in the discussions. Think more of being in charge of guiding our discussion of the chapter, when it is your turn, rather than giving a formal talk. To this end, we will have two meetings
– part 1 - 5 on Thu, 13.6.24, 3:45 PM - 5:45 PM, in seminar room 5.331
– part 6-10 on Thu, 20.6.24, 3:45 PM - 5:45 PM, in seminar room 5.331
and you have to attend both – I advice that everybody has read all sections by the time of these discussions to be able to follow since

2) in the oral exam, besides the regular questions for the course, you should expect questions concerning any of the parts 1-10, including but not limited to the part you presented. This will make the full process fair to everyone.