Elementary String Theory - the Large N Expansion as a String Theory
Details
Barry McFarlane will introduce the so-called Large N expansion. This expansion has been essential in the development of the AdSCFT Correspondence, where many results are derived and are valid only in the Large N limit. The talk will begin with lightning review of perturbation theory and Feynman diagrams. Then we will talk about an ingenious adaptation of Feynman diagrams as applied to gauge theories (specifically QCD) which, although still not allowing QCD to be solved from first principles, provided an invaluable tool for Statistical Physics and perturbative expansions in String Theory. This is the famous "double line" notation and t'Hooft coupling. To round out the conversation, we will show how the Large N expansion is used to compute Feynman amplitudes for open and closed strings..
Time permitting, Barry can address any questions on the topic.
Barry will largely follow this lecture of Hong Liu at MIT, the videos and lecture notes / problem sets of which can be found here:
Lecture 6: The Holographic Principle
https://ocw.mit.edu/courses/physics/8-821-string-theory-and-holographic-duality-fall-2014/lecture-notes/MIT8_821S15_Lec6.pdf
More background in this paper by Gerar t'Hooft on Large N:
Elementary String Theory - the Large N Expansion as a String Theory