The Introduction to Quantum Field Theory is a two-semester course. Content-wise, this is a continious 29-week long course, but for administrative purposes it is split in two:

- PHY 396 K -- Quantum Field Theory I, usually taught in the Fall, and
- PHY 396 L -- Quantum Field Theory II, usually taught in the Spring.

Physics-wise, the split is rather arbitrary, so * students seriously
interested in the Quantum Field Theory should take both halves
of the course.*

This web page is the syllabus for the whole course as taught in the academic years 2022/23 —
that is, **396K** (unique 57575) in Fall 2022, and **396L** (unique 57135) in Spring 2023 —
by **Professor Vadim Kaplunovsky**.

Both semesters of the QFT class are *planned* to be in-person, but if the covid-19 pandemic flares up
once again, the class may suddenly become hybrid or even purely-online.
I hope it does not happen, but please beware of the possibility.

In any case, I plan on mirroring all lectures via Zoom and have their recording available via Canvas. (Assuming the UT continues to support this option.) So if you are sick, — and especially if you are running a high fever, — don't come to the class but watch the lecture's recording when you feel better.

And just to be safe, get yourself fully vaccinated (3 or 4 shots, including 1 or 2 boosters). UT Health Services offer free vaccinations to all the students.

The formal pre-requisites for the QFT (I) class is graduate standing and the PHY 389 K class
(graduate Quantum Mechanics (I)).
However, what I care about is your knowledge rather than your status or grades.
**If** you have the pre-requisite knowledge — however you have learned it
— I'll sign the paperwork to let you into my class even if you are
an undergraduate student.

Understanding Quantum Field Theory requires serious knowledge of quantum mechanics
at graduate or *advanced* undergraduate level.
Besides the QM basics — like knowing how to solve the hydrogen atom —
you must be familiar with the multi-oscillator systems, the rotational symmetry
and the angular momenta as its generators, the identical particles, the perturbation
theory, and the basics of scattering theory.
For the UT undergraduate students, you should complete the undergraduate QM sequence
of 373 + 362K + 362L classes before taking the QFT class.
For students who have learned their QM elsewhere, you need either 120 hours of undergraduate
QM classes (not counting the inroductory *Modern Physics* class), or basic
undergraduate QM followed by a gradute-level QM class.
In any case, read J. J. Sakirai's book Modern Quantum Mechanics
in the summer; if you understand everything in it, you are ready for my QFT class,
but if the book looks all Japanese to you, you should beef up your Quantum Mechanics
before taking Quantum Field Theory.

Besides QM, you would need good undergraduate-level knowledge of Classical Mechanics
(especially the Lagrangian and the Hamiltonian formalisms),
Classical Electrodynamics (the vector potential **A**, the gauge transforms, the EM stress-energy tensor, etc.),
and basic special relativity
(the Lorentz transforms, the 4–vectors, and the tensors).
Make sure you are familiar with both 3D and 4D index notations, so expressions like
**F**_{μν}**F**^{μν} do not confuse you or slow you down.
You do not need general relativity for the QFT classes.
In terms of the UT undergraduate classes, the 336 + 352K + 352L classes should give you
adequate background.
If you have not taken the 352L class, read the Griffith's textbook during the summer and focus
on chapters/sections 7, 8, 9.1-2, 10.1, and 12.

The undegraduate-level Statistical Mechanics would be very useful for the second semester
of QFT (**396L**), but you would not need it for the first semester (**396K**).

On the Math side, you would need basic complex analysis, especially the contour integrals and how to calculate them from the residues. In terms of UT undergraduate classes, the M 361 class (not to be confused with M 361K) should be good enough. If you have not taken this class (or its equivalent elsewhere), get a textbook and read it during the summer; focus on the applications rather then the proofs.

Finally, if you have time, learn a bit of continuous group theory. This is not a pre-requisite, as I shall explain in class the basics of continuous groups, their generators, and their representations from scratch. But it would help if you already know something when I do.

For the QFT (II) class, the pre-requisite is QFT (I).

I presume most of QFT (II) students in Spring 2023 would have taken *my* QFT (I) class in Fall 2022,
so I know exactly what you have learned.
(Or rather, what you should have learned.)
But if you have taken your QFT (I) class from another professor — here at UT or at another University, —
please contact me in the Fall to see how well you are prepared for the QFT (II) class.
Or if you are out of twon in the Fall, see me during the first week of the Spring semester.

Please beware that the graduate classes take a lot more time and effort than the undergraduate classes you are used to. And my QFT class is rather hard even by the standards of advanced graduate classes. So if you are going to take the QFT class, do not take more than one other hard class in the same semester!

- Bosonic Fields:
- Classical field theory; relativistic fields; identical bosons and quantum fields; Klein–Gordon propagator and relativistic causality; quantum electromagnetic fields and photons.
- Fermionic fields:
- Lorentz symmetry and spinor fields; Dirac equation and its solutions; second quantization of fermions and particle-hole formalism; quantum Dirac field; Weyl and Majorana spinor fields.
- Symmetries in QFT:
- Continuous symmetries and conserved currents; spontaneous symmetry breaking and Goldstone bosons; local (gauge) symmetry and QED; Higgs mechanism and superconductivity; non-abelian gauge symmetries and the Yang-Mills theory; discrete symmetries.
- Interacting Fields and Feynman Rules:
- Perturbation theory; correlation functions and Feynman diagrams; S-matrix and cross-sections; Feynman rules for the QED, QCD, and other important firld theories.
- Quantum Electrodynamics:
- Some elementary processes; radiative corrections; infrared and ultraviolet divergencies; renormalization of fields and of the electric charge; Ward identities.
- Functional Methods:
- Path integrals in quantum mechanics; "path" integrals for classical fields and functional quantization; functional quantization of QED; QFT and statistical mechanics; quantum symmetries and conservation laws.
- Renormalization Theory:
- Systematics of renormalization; `integration out' and the Wilsonian renormalization; `running' of the coupling constants and the renormalization group.
- Non-Abelian Gauge Theories:
- Non-abelian gauge symmetries and the Yang-Mills theory; interactions of gauge bosons and Feynman rules; Fadde'ev-Popov ghosts and BRST; renormalization of the YM theories and the asymptotic freedom; chiral gauge symmetries; the Standard Model; confinement and other non-perturbative effects.

In the first semester (the 396 K class) I shall focus on:

- quantization of bosonic and fermionic fields;
- the symmetries (including the Higgs mechanism and the non-abelian gauge symmetries at the semi-classical level);
- perturbation theory and the Feynman graphs;
- elementary processes in QED.

- loop diagrams and renormalization;
- QED beyond the tree level;
- functional methods;
- QCD and other non-abelian gauge theories.

The primary textbook for both semesters of QFT is An Introduction to Quantum Field Theory by Michael Peskin and Daniel Schroeder. The UT library has a digital copy. To a large extent, the course is based on this book and should follow it fairly closely, but don't expect a 100% match.

Since both the course and the main textbook are introductory in nature, many questions would be left an-answered. The best reference book for finding the answers is The Quantum Theory of Fields by Steven Weinberg. The first two volumes of this three-volume series are based on a two-year course Dr. Weinberg used to teach here at UT — but of course they also contain much additional material. To a first approximation, Dr. Weinberg's book teaches you everything you ever wanted to know about QFT and more — which is unfortunately way too much for a one-year intoductory course. (Weinberg's volume 3 is about supersymmetry, a fascinating subject I used to teach, but I won't cover it in this class.)

Besides the textbooks, I wrote a bunch of supplementary notes (and I might write a few more). All these supplemantary notes are linked to this page.

The homeworks are absolutely essential for understanding the course material.
Often, due to the time pressure, I will explain the general theory
in class and leave the examples for the homework assignment.
It is extremely important for you to work them out by yourselves;
otherwise, you might think you understand the class material but you would not!
*Be warned: The homeworks will be very hard.*

I shall post homework assignments each week on this page. The solutions will be linked to the same page after the due date of each assignment.

*The homeworks are assigned on the honor system:*
I shall not collect or grade the homeworks, but you should endeavor
to finish them on time and check each other's solutions.

There will be separate final grades for each semester. Each grade is based on two take-home tests, one in the middle of the semester, the other at the end; the mid-term test contributes half of the grade and the end-term test the other half. There will be no in-class final exams.

- Fall 2022 mid-term exam will be given to students on October 18 and due October 25.
- Fall 2022 final exam will be given to students on December 1 (last regular lecture) and due on December 8.
- Spring 2023 mid-term exam will be given to students in the first half of March and due a week later.
- Spring 2023 final exam will be given to students On April 20 (last regular lecture) and due on April 27.

I shall try using Canvas to schedule Zoom sessions for all the lectures; this way, the lectures would be recorded and you would find the records on Canvas. Apart from that (and the mandatory posting of this syllabus to Canvas), I shall not use Canvas for anything else. In particular, all homeworks and exams will be posted to the homework page rather than to Canvas, and the exam grades shall be emailed directly to the students.

The QFT class is rather intense: there are going to be **4 hours of regular lectures each week**
as well as *extra lectures roughly every other week*.

Assuming UT continues to provide technical support, all lectures should be mirrored online via Zoom and their recording available to the students via Canvas.

- Fall 2022 semester:
- Tuesdays and Thursdays, 3:30 to 5:30 PM, in room ETC 2.132.
- Note: 4 hours each week.
- URL for the Zoom mirror: https://utexas.zoom.us/j/91065515147.
- Tuesday 8/23 class is canceled, first real class of the semester is on Thursday 8/25.

- Spring 2023 semester:
- Tuesdays and Thursdays, 3:30 to 5:30, in room PMA 5.126.
- Again, 4 hours each week.
- URL for the Zoom mirror: https://utexas.zoom.us/j/97008748254.
- First week's classes on
**1/10**and**1/12**are canceled due to family emergency. The first real class is on Tuesday 1/17.

The canceled classes will be made up.

Besides the regular lectures, I shall give a few extra lectures — roughly, every other week — about subjects that are somewhat ouside the main focus of the course but are interesting for their own sake, such as vortices or grand unified theories. The students are strongly encoraged to attend the supplementary lectures, but there is no penalty for missing them. The issues covered by supplementary lectures will not be necessary to understand the regular lectures and will not appear on exams.

I have a longish list of possible subject for the extra lectures, so at the start of each semester I shall poll the students for their preferences. I shall announce the final list of subjects — and the specific schedule — during the second week of the semester.

Should any regular lecture(s) be canceled because of some emergency, I shall make them up. The make-up lectures will use the same time slot, room, and Zoom link as the extra lectures, but unlike the extra lectures, the make-up lectures will be about the regular class material, and all the sudents should attend them.

Here are tentative schedules:

- Fall 2022 semester:
- Fridays, 4 to 5 PM, in room PMA 5.112, roughly every other week.
- URL for the Zoom mirror: https://utexas.zoom.us/j/98252371320.
- Schedule:
- Make-up lecture on
**8/26**:*Classical field theory.* - Make-up lecture on
**9/2**:*Identical bosons*. - Extra lecture on
**9/23**:*vortices and other topological defects*. - Extra lecture on
**10/7**:*Conformal symmetry*. - Extra lecture on
**10/14**:*Spinor fields in different dimensions*. - Likbez lecture on
**10/28**:*Scattering in QM*. - Extra lecture on
**11/11**:*Resonances, unstable particles, and bound states*. - Extra lecture on
**11/18**:*Chiral symmetry, its spontaneous breakdown, and the sigma models*.

- Make-up lecture on

- Spring 2023 semester:
- Fridays, 4 to 5 PM, in room PMA 5.112, roughly every other week.
- URL for the Zoom sessions: https://utexas.zoom.us/j/99205222399.
- Tentative subjects and schedule:
- Make-up lecture on
**1/20**:*Optical theorem*. - Make-up lecture on
**1/27**:*Deriving the LSZ formula*and*Intro to counterterm perturbation theory*. - Extra lecture on
**2/1**(Tuesday!):*Vacuum energy and effective potentials*. - Make-up lecture on
**2/3**:*super-renormalizable, renormalizable, and non-renormalizable theories*. - Make-up lecture on
**2/10**:*Ward–Takahashi identities*. - Make-up lecture on
**2/17**,*QED odds and ends*. - Extra lecture on
**2/24**:*Grand Unified Theories*. - Extra lecture on
**3/24**:*Lattice gauge theory*. - Extra lecture on
**3/31**:*Wilson loops*. - Extra lecture on
**4/7**:*Instantons and topology in the YM theory*. - Extra lecture on
**4/14**:*Instantons in QCD, the angle, and the strong CP problem*.

- Make-up lecture on

For students' convenience, I shall keep a log of lectures and their subjects on this page. Since the pace of the course may change according to the students' understanding, I will not make a complete schedule at the beginning of the class. Instead, I will simply log every lecture after I give it. This way, if you miss a lecture, you will know what you should read in the textbook and other students' notes.

- Instructor:
- Professor Vadim Kaplunovsky.
- E-mail:
- vadim@physics.utexas.edu.

Please use email for all questions which allow short answers (a few lines), especially*simple*homework questions, administrivia, or typos in my notes. The questions which take more elaborate answers should be asked in person or via zoom; you may ask them via email, but the anwer would have to wait till next class or office hour. - Office:
- PMA 9.314 A, phone (512) 471–4918.
- Office hour:
- Thursday, 2 to 3 PM.

Last Modified: February 14, 2023. Vadim Kaplunovsky

vadim@physics.utexas.edu