Physics 234A: String Theory I

Fall 2015

Basic Info

Time: Mon and Fri, 1:10pm - 2:30pm (lectures);
discussions TBA.
Place: 402 Le Conte Hall

Instructor: Petr Hořava (email:
Office: 401 Le Conte Hall.

This course will give a thorough introduction to modern string theory.

In the past two decades or so, string theory has become the dominant theoretical framework for addressing questions about the fundamental structure of matter in our Universe. It has produced many new ideas and insights in other fields of physics, ranging from particle phenomenology to quantum gravity, cosmology, and more recently even to condensed matter systems. Some of this surprising power of string theory is logically explained by the fact that string theory represents a natural extension or completion of the language of quantum many-body systems and quantum field theory, which makes it relevant in all those diverse areas where the methods of many-body physics play an important role. Basics of string theory should now be in every theorist's vocabulary, regardless of the specific field of physics.

Our main goal in this semester will be two-fold. On one hand, we will develop some practical understanding of the basic elements and techniques of string theory. On the other hand, we will also focus on understanding the "big picture" -- how string theory produces new ideas and techniques relevant to other areas of physics besides particle phenomenology and quantum gravity. In that part of the semester, we will particularly discuss some recent interactions of string theory with condensed matter (via the AdS/CFT duality, but also stimulating the development of topological insulators), and with inflationary cosmology (which we will frame in the language of the effective field theory of inflation).

Throughout the semester, I will also point out some of the open questions and puzzles of our field. String theory is a live and rapidly developing field, which promises that many interesting surprises are still to come, especially in the cross-disciplinary areas of condensed matter, cosmology, and perhaps others (AMO physics? Nonequilibrium systems? Quantum computing?). Anticipating such future developments is one of the most exciting challenges in string theory today.

Specifically, in this semester we will cover the following six areas:

I. Introduction: Why strings?
II. The bosonic string.
III. Superstrings, heterotic strings, supergravity.
IV. D-branes.
V. M-theory and string dualities.
VI. Applications in condensed matter & inflationary cosmology.

The style will be somewhat similar to the style of my course taught in Fall 2008, Fall 2009, and Fall 2011. However, as the field is evolving, we will take a novel, fresh look at some of the basic questions and applications of string theory in the context relevant for current research. The main textbook is going to be

K. Becker, M. Becker and J.H. Schwarz, String Theory and M-Theory. A Modern Introduction (Cambridge University Press, 2006).

we will occasionally use other resources, including the two volumes of Joe Polchinski's book, the classic two volumes of Green-Schwarz-Witten, or the newer book by Elias Kiritsis (String Theory in a Nutshell), and sometimes even review papers from the arXiv. We will also take a closer look at the new exciting book

D. Baumann and L. McAllister, Inflation and String Theory (Cambridge University Press, 2015),

just published by CUP in April.


In order to make Physics 234A accessible to a wide audience of students from varying areas of physics and cosmology, I will develop the material from first principles, such that the course can be taken without any prior knowledge of quantum field theory (for example, it could be taken concurrently with -- or even before -- 232A). Some basic understanding of quantum mechanics and relativity is however assumed.

Homework Assignments

Homework assignments will be posted on this website weekly (or sometimes biweekly). The assignments will be due at the day/time TBD.

Most homeworks will be assigned from the list of Homework problems in Becker&Becker&Schwarz ([BBS]), unless stated explicitly otherwise. Occasionally, the assignment will contain also solved Exercises from [BBS]; if so, the students are encouraged to solve the problem before they look at the solution in [BBS].