This page is an introduction of minimal knowledge for high energy theory research. In short, one should learn quantum field theory (QFT). And for theoretical cosmology related research (my research direction), in addition one should learn general relativity (GR) and cosmology. These courses should be learned early.

# Why early?

If you are willing to take high energy theory as your future career, I recommend an undergraduate student to learn QFT (and/or GR) in the spring semester of the 2nd year. This is considerably earlier than one may expect. Here are the considerations why you should learn it/them early:

- One should finish QFT (and/or GR) before the 3rd year, and do research in the 3rd year. Because
- Most research projects need it/them as background knowledge.
- From experience, excellent 3rd year students can start to do excellent research in this field.
- Your research experience in the 3rd year (and at best publications) will help for your graduate school application.

- Learning is a nonlinear process. You do not have to learn step by step. Because
- For the prerequistites, you will only need the core part, instead of every bit, to proceed to QFT/GR.
- It’s a good idea to learn QFT/GR twice. For example, another time in your graduate school.
- For future research, you will have to be used to nonlinear learning. Usually, you read research papers for the 1st pass, find out what you have to learn, learn the core part of required topics, and read the paper again for the 2nd pass.
- Your experience in advanced courses and research will help you to learn in depth for other elementary courses. When I was undergraduate student, I thought my understanding of the courses are good (indeed fine for exams). But I realized that there are far more physics to understand in those “simple” courses, after start to do research. Exams cannot test your depth of understandings, though they are unfortunately still needed.

- In reality, one can learn it well at 2nd year. In 2016, a 2nd year undergraduate student ranked 1st in my QFT class (which is a postgraduate class). And many 2nd year students got A+ in my QFT/GR courses.
- Research is not the best option for everyone. There are many modes of success for undergraduate students. If another path fits you better than research, you had better to know and switch early.

# How to make it?

## Resources

Of course the university courses are the most important resources. One should take quantum mechanics and classical mechanics (at least the relevant parts) before learning QFT (and/or GR). Here are some helpful resources: Theoretical Minimum by Leonard Susskind (you can tune the video speed to 1.5x or 2x), Concepts in Theoretical Physics by Daniel Baumann, and the “front” part of the PSI lectures.

Also, some popular science books help for getting an general idea. For example, The Elegant Universe by Greene, and The Emperor’s New Mind by Penrose. But be reminded that you are not ready to do research after you “understand” those popular science books. They are just how the dinner tastes instead of how it is cooked. Also, physicists need to shut up and calculate eventually.

## For HKUST students

I noted that a lot of physics students at HKUST take Modern Physics (PHYS2022) in the fall term of the 1st year. This is a good start if possible. Afterward you can learn quantum mechanics and classical mechanics in the spring term of the 1st year. If you have done so and with good score, there should be no problem to learn QFT (and/or GR) in the spring term of the 2nd year.

If you are taking Modern Physics (PHYS2022) in the fall term of the 2nd year, it is still possible to take QFT (and/or GR) in the spring term of the 2nd year. It’s tougher as you have to learn QM at the same time. But some students have followed this trejectory and got good results.

# Quantum Field Theory (QFT)

## Books

Quantum Field Theory by Srednicki. This book is my favorite for general purpose.

An Introduction To Quantum Field Theory by Peskin and Schroeder. This is an excellent QFT book for particle physicist. For students interested in other directions, say cosmology, this book may be distractive by going into lots of details in particle phenomenology.

Quantum Field Theory in a Nutshell by Zee. The book is “the most accessible and comprehensive introduction”. But one have to learn the computation techniques elsewhere.

The Quantum Theory of Fields, Volume 1, Volume 2 by Weinberg. This is the “last” QFT book. Not recommended for starters but eventually one should read it (say, at the second time of learning QFT).

See also my comments in Chinese on QFT books.

## Online resources

The “core” part of the PSI lectures.

The lecture notes of David Tong is great. Videos also available at the same link (unfortunately low resolution).

The good old Coleman lectures.

## For HKUST students

Here are my lectures in 2016. It will be offered in spring 2018, 2020, … until teaching assignment changes.

# General Relativity (GR)

## Books

Gravity by Hartle.

A First Course in General Relativity by Bernard Schutz.

More in-depth books include Einstein Gravity in a Nutshell by Zee, Spacetime and Geometry by Sean Carroll, Gravitation and Cosmology by Weinberg, General Relativity by Wald, and Gravitation by Misner, Thorne and Wheeler.

## Online resources

- The “core” part of the PSI lectures.

## For HKUST students

Here are my lectures in 2017. It will be offered in spring 2019, 2021, … until teaching assignment changes.

# Cosmology

## Online resources

For sure, there are great books, such as Cosmology. But to do *early* research, one can start by reading some lecture notes and review papers. The recommendation depends on research directions. For my research direction (inflation and cosmological perturbation theory), one can read

- TASI Lectures on Cosmology by Baumann.
- Lecture Notes on Cosmology by Baumann.
- TASI Lectures on Inflation by Baumann.
- Primordial Non-Gaussianities from Inflation Models by Chen.
- Inflation, Cosmic Perturbations and Non-Gaussianities by Wang.

## For HKUST students

Here are my lectures in 2015. Now this course has been combined with an introduction to general relativity.

# See also

See also a website by Gerard ’t Hooft on “how to become a GOOD Theoretical Physicist”. This is to my knowledge the best compiled list.