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 D-branes (1,3,5,7) x   nonchiral x  
IIB 10 x x bound to even D-branes (0,2,4,6,8) x   x x  
HO 10 x x   x     x SO(32)


10 x x   x     x
E8 x E8

 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. (left-right asymmetric)

nonchiral: massless fermions spin both ways.(left-right symmetric)

heterotic(H): right moving and left moving strings differ.(left-moving in D=26 dimensions, right-moving in D=10 dimensions and 16 dimensions compactified).

compactification: get from 10 spacetime dimension down to 4 spacetime dimension and six compact dimensions of Calabi-Yau 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.

T-Duality Large and small distance scales can be exchanged IIA and IIB HO and HE
S-Duality 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









higher dimensional objects in String theories:
zero-brane points
one-brane string
two-brane membrane
D-brane Dirichlet boundary conditions:

ends of open strings attached to D-branes

D0-brane: point

D1-brane:string (a line)

D2-brane:membrane (plane)

D25-brane:space in bosonic string theory