String theory provides a deeper understanding of the four dimensional phenomena that we can directly measure. In particular, gauge symmetry and parity violation follow naturally from string theory.
Consider our four dimensional world as a D3-brane embedded in 10 dimensional spacetime. All the fundamental particles such as electrons, quarks, muons and so on are the end-points of open superstrings.
The quantum states which arise from open strings beginning and ending on the 3-brane can effectively be described by gauge fields confined to the 3-brane coupling to charges which are the end points of open strings.
Supersymmetry
For consistency, a superstring has to have both bosonic and fermionic excitations which are coupled in a supersymmetric manner. There are five consistent superstring theories
It has been shown that these five superstring theories are all just different ways of looking at the same theory. |
Both heterotic and IIB closed superstrings are chiral in the sense that string excitations propagate only say clockwise and not counter-clockwise. This geometrical property ultimately translates into parity violation in our four-dimensional world.
Last updated: 06 March, 2000
