by houserichichi » Sun Jul 30, 2006 12:01 am
String Theories
Type
Spacetime dimensions
Details
Bosonic
26
Only bosons, no fermions means only forces, no matter, with both open and closed strings; major flaw: a particle with imaginary mass, called the tachyon, representing an instability in the theory.
I
10
Supersymmetry between forces and matter, with both open and closed strings, no tachyon, group symmetry is SO(32)
IIA
10
Supersymmetry between forces and matter, with closed strings and open strings bound to D-branes, no tachyon, massless fermions spin both ways (nonchiral)
IIB
10
Supersymmetry between forces and matter, with closed strings and open strings bound to D-branes, no tachyon, massless fermions only spin one way (chiral)
HO
10
Supersymmetry between forces and matter, with closed strings only, no tachyon, heterotic, meaning right moving and left moving strings differ, group symmetry is SO(32)
HE
10
Supersymmetry between forces and matter, with closed strings only, no tachyon, heterotic, meaning right moving and left moving strings differ, group symmetry is E8×E8
****************(taken directly out of a wiki)
11 dimensional spacetime is M-theory; a generalization of the five string theories into one.