|All Roads Lead to String Theory (Polchinski)|
Prior to the First Superstring Revolution
|Early History|| S-Matrix Theory|
|Bosonic String Theory|| Worldsheet|
Bosonic String Theory
String Perturbation Theory
|Supersymmetric Revolution|| Supersymmetry|
|First Superstring Revolution|| GSO Projection|
Type II String Theory
Type IIB String Theory
Type IIA String Theory
Type I String Theory
Type H String Theory
Type HO String Theory
Type HE String Theory
|Second Superstring Revolution|| T-Duality|
Horava-Witten String Theory
N=4 Super-Yang-Mills Theory
BFSS Matrix Theory
Matrix String Theory
Twistor String Theory
String Field Theory
Pure Spinor Formalism
After the Revolutions
|Phenomenology|| String Theory Landscape|
Minimal Supersymmetric Standard Model
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String Perturbation Theory (or Perturbative String Theory) is a method for calculating the S-Matrix of a String Theory vacuum - the asymptotic scattering behavior of weakly coupled strings moving on that geometric background - as a sum over string histories of different topologies, analogous to the sum over Feynman diagrams employed in perturbative quantum field theory.
Also as in QFT, these scattering amplitudes only describe transitions from a state in the distant past to a state in the distant future. For the finite-time evolution of strings, one needs a more advanced formalism like String Field Theory.
BasicsEdit this section
Schematically, the scattering amplitude to start with strings in a state and to finish with strings in a state is
where stands for a Measure on the Moduli Space of a particular topological class of Riemann Surfaces, is the action of a particular history from that class, and is a set of Vertex Operators encoding the initial state or final state .