Preface
This book grew up from lectures delivered within the Elite Master Program
“Theoretical and Mathematical Physics” from the Ludwig-Maximilians-Universität
during the winter semesters 2017–2018 and 2018–2019.
The main focus of this book is the closed bosonic string field theory (SFT). While
there are many resources available for the open bosonic SFT, a single review [2] has
been written since the final construction of the bosonic closed SFT by Zwiebach [5].
For this reason, it makes sense to provide a modern and extensive study. Moreover,
the usual approach to open SFT focuses on the cubic theory, which is so special
that it is difficult to generalize the techniques to other SFTs. Finally, closed strings
are arguably more fundamental than open strings because they are always present
since they describe gravity, which further motivates my choice. However, the reader
should not take this focus as denying the major achievements and the beauty of
the open SFT; reading this book should provide most of the tools needed to feel
comfortable also with this theory.
While part of the original goal of SFT is to provide a non-perturbative definition
of string theory and to address important questions such as classifying consistent
string backgrounds or understanding dualities, no progress on this front has been
achieved so far. Hence, there is still much to understand, and the recent surge
of developments provides a new chance to deepen our understanding of closed
SFT. For example, several consistency properties of string theory have been
proven rigorously using SFT. Moreover, the recent construction of the open–closed
superstring field theory [3] together with earlier works [1, 4–6] shows that all types
of string theories can be recast as a SFT. This is why, I believe, it is a good time to
provide a complete book on SFT.
The goal of this book is to offer a self-contained description of SFT and all the
tools necessary to build it. The emphasis is on describing the concepts behind SFT
and to make the reader build intuitions on what it means. For this reason, there are
relatively few applications.
The reader is assumed to have some knowledge of QFT and a basic knowledge
of CFT and string theory (classical string, Nambu–Goto action, light-cone and oldcovariant quantizations).
v
This book grew up from lectures delivered within the Elite Master Program
“Theoretical and Mathematical Physics” from the Ludwig-Maximilians-Universität
during the winter semesters 2017–2018 and 2018–2019.
The main focus of this book is the closed bosonic string field theory (SFT). While
there are many resources available for the open bosonic SFT, a single review [2] has
been written since the final construction of the bosonic closed SFT by Zwiebach [5].
For this reason, it makes sense to provide a modern and extensive study. Moreover,
the usual approach to open SFT focuses on the cubic theory, which is so special
that it is difficult to generalize the techniques to other SFTs. Finally, closed strings
are arguably more fundamental than open strings because they are always present
since they describe gravity, which further motivates my choice. However, the reader
should not take this focus as denying the major achievements and the beauty of
the open SFT; reading this book should provide most of the tools needed to feel
comfortable also with this theory.
While part of the original goal of SFT is to provide a non-perturbative definition
of string theory and to address important questions such as classifying consistent
string backgrounds or understanding dualities, no progress on this front has been
achieved so far. Hence, there is still much to understand, and the recent surge
of developments provides a new chance to deepen our understanding of closed
SFT. For example, several consistency properties of string theory have been
proven rigorously using SFT. Moreover, the recent construction of the open–closed
superstring field theory [3] together with earlier works [1, 4–6] shows that all types
of string theories can be recast as a SFT. This is why, I believe, it is a good time to
provide a complete book on SFT.
The goal of this book is to offer a self-contained description of SFT and all the
tools necessary to build it. The emphasis is on describing the concepts behind SFT
and to make the reader build intuitions on what it means. For this reason, there are
relatively few applications.
The reader is assumed to have some knowledge of QFT and a basic knowledge
of CFT and string theory (classical string, Nambu–Goto action, light-cone and oldcovariant quantizations).
v