## Wednesday, March 19, 2008

### Frederik Denef: landscape building guide

All expert TRF readers (except for a few, 0-10, leading F-theory leaders in the world who know the sub-discipline better than the author anyway) are recommended to print and read
Frederik Denef's Les Houches Lectures (PDF)
about the construction of string-theoretical vacua.

On his 127 pages, Frederik discusses the structure and properties of the string vacua. While he dedicates a few pages to heterotic and type I strings, M-theory on G2 manifolds, non-geometrical, and non-critical compactifications, most of the paper is dedicated to F-theoretical flux vacua i.e. type IIB vacua with non-trivial axion-dilaton fields, orientifolds, and D-branes.

The paper may look long or contrived to many readers but what is important is that these insights are robust and pretty much inevitable. An extraterrestrial civilization would have to end up with pretty much equivalent papers about the string landscape at a certain level of the evolution of their science. Once you adopt the idea that the elementary particles are extended objects while the resulting theory should still reduce to effective field theories we have checked, you are inevitably led to strings and the whole structure of string theory follows.

Almost no page among the 127 pages of the paper is directly connected with a particular experiment. Nevertheless, all of them are tightly connected with one another as well as with other insights that are observationally rooted. You might feel that you are walking somewhere in between the clouds, 324 meters above the ground. Some people say that it is unsafe, religious, or unscientific to walk and talk 324 meters above the ground. But you have a structure to rely on. Is it possible to walk 324 meters above the ground and to talk to some of the low-lying clouds? Yes, it is. The rigid structure is called the Eiffel Tower. ;-)

String theory is analogous. The people who don't want to hear about things such as the Eiffel Tower or string theory are just far too narrow-minded and limited to be relevant for this type of engineering or science.

When you finish reading Frederik's paper, you will be able to pick, construct, and study your own string-theoretical vacua in the landscape. You will also remain doubtful about all kinds of anthropic questions but you will understand that these questions do not represent the bulk of the knowledge and skills that a theoretical physicist must have for his or, less frequently, her opinions to matter.