Fakultät für Physik




String Field Theory – Overview


About the lecture

Time and place

Thursday, 12-14 (c.t.) in A 318
Friday, 10-12 (c.t.) in A 348

String theory is usually formulated in the worldsheet formalism, which describes a single string (first-quantization). While this approach is intuitive and could be pushed far due to the exceptional properties of 2d theories, it becomes cumbersome for some questions or even fails at a more fundamental level. These motivations led to the development of string field theory (SFT), a description of string theory using the field theory formalism (second-quantization). As a field theory, SFT provides a rigorous and constructive formulation of string theory and gives access to non-perturbative, thermal and dynamical effects. In particular, it gives hope to address the important question of the string landscape.

SFT is still an active topic of research and many questions remain open. The goal of this course is to provide an introduction to the construction of the bosonic SFT and to several applications, while also covering some more advanced and recent developments (including superstring field theory).


  • worldvolume / spacetime descriptions
  • introduction to string theory and CFT
  • free string field theory
  • off-shell amplitudes
  • bosonic string field theory
  • applications (analytic solutions, tachyon condensation, consistency conditions)
  • superstring field theory
  • quantum effects and renormalization


  • QFT (renormalization is useful but not necessary).
  • Knowledge in worldsheet string theory and CFT are recommended but the motivated student can follow the course without; a summary will be provided at the beginning and the lecture notes more details.


Lecture notes (containing additional details) will be made available.

A selected set of standard references are:

  • Closed Superstring Field Theory and its Applications – De Lacroix, Erbin, Kashyap, Sen, Verma (1703.06410)
  • D-Branes, Tachyons, and String Field Theory – Taylor, Zwiebach (hep-th/0311017)
  • Tachyon Dynamics in Open String Theory – Sen (hep-th/0410103)
  • A Review on Tachyon Condensation in Open String Field Theories – Ohmori (hep-th/0102085)
  • Closed String Field Theory: Quantum Action and the BV Master Equation – Zwiebach (hep-th/9206084)
  • String field theory – Thorn
  • A First Course in String Theory – Zwiebach (book)

Note: All of these references (except the last one) focus on specific aspects and assume a solid knowledge of string theory and/or CFT.

Verantwortlich für den Inhalt: Harold Erbin