4, One-loop amplitudes /Ulnonentel strings
In quantum eld theories. Perturbation theory involves summing up
Feynman diagrams. The number of loops in a given diagram
corresponds to the order of perturbation theory.
Feynman diagrams with no external l
Why string theory ?
High energy physics phySics of elementary particles and
Tlnere are It interactions known
Gravity , electromagnetism, weak-lime, strong ne
Gravity looks different from the other 3 forces
BRST gauge. xing
The scattering amplitudes of strings are given by path integrals
OVer Matter elds X" and metric huh
Am: = Simon-.9 [OX] e-SEX.hJ '0: WV
The in-l-egral [DH is ovev all the Incl-Has on 20 Surfaces
with gems 3 and In marked Point's (punct