# Contents

## Idea

String phenomenology is phenomenology in particle physics based on models that are derived or at least motivated from string theory (as effective QFTs from string vacua).

Broadly speaking, string phenomenology refers to investigations of the connection of string theory to experimentally observed physics. More restrictively it refers to constructions of string theory vacua whose effective field theory reproduces the standard model of particle physics and/or the standard model of cosmology.

String theory models natually match the general conceptual structure of the standard model of particle physics plus gravity (which is what drives the interest in string theory in the first place): for instance the standard model is a four dimensional QFT with a non-Abelian gauge symmetry, several families? of chiral fermions? and hierarchical Yukawa couplings? – and the same is true for the generic compactification of the effective QFT that describes heterotic string theory on a 6-dimensional compact space (CHSW85) as well as for 11-dimensional supergravity/M-theory compactified on a G2-manifold (AW01).

This structure alone already implies a variety of 3-body decays of the heavier fermions into the lighter ones and the existence of massive vector bosons? coupling to charged currents?, which in the observed standard model of particle physics are the W-boson, etc. (See section III of AKK12 for an exposition.)

Therefore it is not hard to find string theory compactifications that resemble the observed particle physics in broad strokes. Under some simplifying assumptions many string models have been built that very closely resemble also the fine-structure of the standard model.

A central technical issue with string model building is that of the Kaluza-Klein mechanism involved: the moduli stabilization. Historically there had been the hope that the consistency condition of moduli stabilization on string models is so strong that it strongly reduces the number of models that look like the standard model. Arguments that the number is still “not small” even with various extra assumptions lead to the term of a landscape (moduli space) of string theory models, which remains, however, poorly understood. Arguments for properties of low-energy effective QFTs that rule out a possibe string-theoretic model have been brought forward for instance in (Vafa05). A review of what is known about the space of possibilities is in (Taylor11).

While all this remains poorly understood, a noteworthy difference of string phenomenology to model building in bare QFT is that a) there is a larger framework at all in which to search for models and b) with every model automatically comes a UV-completion, which is the basic motivation for embedding the standard model of particle physics in a broader theory of quantum gravity in the first place.

## Examples

Examples of models in string phenomenology include

• G2-MSSM

• and many more that should be listed here, eventually…

## References

### Surveys

Technical surveys on particle physics string phenomenology include

• Hans Peter Nilles, String phenomenology (2004) (pdf)

• Tatsuo Kobayashi, String phenomenology (pdf)

• Washington Taylor, TASI Lectures on Supergravity and String Vacua in Various Dimensions (arXiv:1104.2051)

• Bobby Samir Acharya, Gordon Kane, Piyush Kumar, Compactified String Theories – Generic Predictions for Particle Physics (arXiv:1204.2795)

Technical surveys on cosmological string phenomenology include

### Original articles

• Bobby Acharya, Edward Witten, Chiral Fermions from Manifolds of ${G}_{2}$ Holonomy (arXiv:hep-th/0109152)

### String Phenomenology conferences

Revised on August 21, 2012 19:05:45 by Urs Schreiber (82.113.99.27)