Re: Kaluza-Klein Theory and The Standard Model

Date: Thu Dec 16 05:23:50 1999
Posted By: Samuel Silverstein, faculty, physics, Stockholm University
Area of science: Physics
ID: 940887079.Ph

Message:

Judson,

Your question is a bit difficult for me to answer well, since I myself am an experimental rather than a theoretical particle physicist. To my knowledge, the most advanced theoretical work in recent years has been in the area of superstring theories.

String theories, originally developed in the 1970s, treat all of the different kinds of particles as one-dimensional "strings" vibrating in different modes in a many-dimensional space. String theories are exciting because they include a natural way to unify gravity with the other three known forces, and do not contain mathematical infinities which have plagued other attempts at unification.

Early string theories only described integer-spin bosons, and not the half-integer spin fermions (such as electrons and quarks). When fermions are added to string theories, a new symmetry appears called supersymmetry, which describes a fundamental relationship between fermions and bosons. String theories with supersymmetry are called superstring theories.

Five 10-dimensional superstring theories have been found which are mathematically consistent. A very exciting recent development has been the discovery that these five theories, although seemingly different from each other, all appear to describe the same physics! An effective 11-dimensional "M-theory" is showing some promise towards unification of these other theories, but this work is in its early stages. Theorists have also been able to describe some properties of black holes using superstring theory; perhaps the first concrete application of the theory to the "real world".

There are some websites on superstrings which do a far better job of explaining than I can. Here are some links to get you started:

John Pierre, from UCSB, has produced a very nice superstring tutorial at this site with good references and links.
More nice information can be found at The Official String Theory Web Site.
I also recommend looking at this well-written public lecture by Edward Witten, a pioneer in superstring theory.

Supersymmetry is also a hot topic for experimental physicists, as it predicts a new supersymmetric partner for each known particle. Half-integer spin quarks and leptons are paired with integer-spin "squarks" and "sleptons", while integer-spin bosons such as photons and gluons have half- integer spin partners called "photinos" and "gluinos". None of these "sparticles" predicted by supersymmetry have yet been seen experimentally, but there is hope that if they exist, they could be seen at next-generation particle accelerators such as the Large Hadron Collider (LHC) at the CERN laboratory in Geneva, Switzerland.

I hope this helps. In addition to the above links, I have also found a website with a lot of articles of varying difficulty which might interest you:

http:// web.mit.edu/redingtn/www/netadv/Xstring.html

Best Regards,
Sam

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