Two sample ‘t Hooft-Feynman graphs. One can be drawn on a sphere, the other a torus. The powers of $latex N$ count this in a $latex 1/N$ expansion.
Black Holes and a Return to 2D Gravity! – Part II
Black Holes and a Return to 2D Gravity! – Part II
Two sample ‘t Hooft-Feynman graphs. One can be drawn on a sphere, the other a torus. The powers of $latex N$ count this in a $latex 1/N$ expansion.