Type  Spacetime Dimensions  bosons  fermions  open strings  closed strings  tachyon  chiral  SUSY  group of symmetry 
Bosonic  26  x  x  x  x  
I  10  x  x  x  x  x  SO(32)  
IIA  10  x  x  bound to odd Dbranes (1,3,5,7)  x  nonchiral  x  
IIB  10  x  x  bound to even Dbranes (0,2,4,6,8)  x  x  x  
HO  10  x  x  x  x  SO(32)  
HE

10  x  x  x  x 
E_{8 x }E_{8} 
elementary particles : excitation or resonant oscillation modes of elementary strings (tiny vibrating object).
average size of a string: Planck length, which is about 10^{35} m.
supersymmetry (SUSY): for every particle that transmit force (boson) there is a particle that make up matter (fermion).
Superstring: Strings (bosonic string) with supersymmetry.
chiral : massless fermions only spin one way. (leftright asymmetric)
nonchiral: massless fermions spin both ways.(leftright symmetric)
heterotic(H): right moving and left moving strings differ.(leftmoving in D=26 dimensions, rightmoving in D=10 dimensions and 16 dimensions compactified).
compactification: get from 10 spacetime dimension down to 4 spacetime dimension and six compact dimensions of CalabiYau space.
ten spacetime dimensions : nine space dimensions and one time dimension.
The M theory or theory of everything: The five superstring theories are related by dualities transformation and they are each a case (different aspect ) of the M theory in eleven dimensions.
Duality: simmetry and transformation that changes one theory into the another.
TDuality  Large and small distance scales can be exchanged  IIA and IIB  HO and HE 
SDuality  Strong and week coupling strengths can be exchanged  IIB and IIB  HO and I 
In string theory coupling constants are dynamical scalar fields (dilaton).
Coupling Constants for the fundamental forces in Standard Model  
Strong  1 
Electromagnetic  1/137 
Weak  10^{6} 
Gravity  10^{39} 
higher dimensional objects in String theories:  
pbranes  
zerobrane  points 
onebrane  string 
twobrane  membrane 
Dbrane  Dirichlet boundary conditions: ends of open strings attached to Dbranes D0brane: point D1brane:string (a line) D2brane:membrane (plane) D25brane:space in bosonic string theory

NSbrane 