Among quantum field theories, conformal field theories (CFTs) are special, because they are conformally invariant for a particular value of the interaction. Even more special are so-called "Pure" CFTs, which are CFTs for all values of the coupling. A famous example for a pure CFT is N=4 SYM in 3+1 dimensions, which has the property that its entropy density at infinite coupling is exactly 3/4 of the Stefan-Boltzmann limit. In this talk I will present other examples of pure CFTs in 2+1 dimensions which can be solved exactly in the large N limit for all values of the coupling. I show that for a large class of CFTs (not only pure CFTs), the strong/weak ratio for the entropy density is a simple fraction bounded from below by 4/5. I entertain the hypothesis for CFTs at infinite coupling, the degrees of freedom contributing to the entropy density are fractional.
Paul Ramatschke / University of Colorado Boulder
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