Transport coefficients and universality in hot strongly coupled gauge theories
Cohen, Thomas D
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The gauge/gravity duality provides a valuable opportunity to study the behavior of relativistic fluids described by some strongly-interacting non-Abelian gauge theories. However, as yet no gravity duals are known for the field theories that are currently used to describe nature. Thus, it is particularly interesting to search for universal properties of theories with gravity duals. This dissertation discusses a broad class of theories with gravity duals, and it is shown that at high temperatures, the speed of sound squared is bounded from above by one-third of the speed of light squared. It is conjectured that this may be a universal property of theories with gravity duals. It is also shown that the temperature dependence of a number of transport coefficients takes a universal form in the high-temperature limit. In particular, in a high-temperature expansion, the power law of the leading correction away from the infinite temperature limit is universal for all of the transport coefficients, and is the same as that of the speed of sound squared.