To fzero :
The question of earth2 is in fact, how to obtain 7.A.17 from 7.A.12 and 7.A.22 (appendix of the first volume), because you have a curious overall term y_1......y_M
A closed string can separate in 2 closed strings, inversely, 2 closed strings can fusion in one closed string. Idem for open strings. 2 open strings may fusion in one closed string. See : (http://en.wikipedia.org/wiki/File:Stringinteractions.svg)
For Marcus, Spin(4,1)/Spin(3,1) should be dS4, the de-Sitter space of dimension 4
The gauge ambiguity comes certainly that we do not use the most fundamental objects. For instance, the ambiguity A_\mu \to A_\mu + \partial_\mu \phi, can be solved, for a simple topology (See Aharonov-Bohm...
The problem is, considering massless gauge bosons in 3+1 dimensions, A_\mu has 4 components, and there are only 2 physical degrees of freedom. The little group ISO(2) does not transform A_\mu like a Lorentz vector (because of the "translation" part), so one has to connect A_\mu to a conserved...
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I think it is because S-Duality maps string theories with coupling g, with string theories with coupling 1/g. So, beginning with a string theory with g>1, we can find another string theory with g' = 1/g <1, and we may apply the condition g'N>>1, that is N/g >>1
The example that Susskind takes is the simplified case of massless photons in 4 dimensions. A massless photon in 4 dimensions has only 2 polarizations (so are a_i/a_i^+ and b_i/b_i^+, which are the anihilation/creation operators, for different excitation of energy i, corresponding to the 2...
Black holes have an entropy, but they evaporate. At the end of the evaporation, the entropy is greater than the entropy at the beginning of the evaporation. I am looking for an example of a quantitative result for the entropy of the black hole after evaporation (or the entropy difference...