Sera Cremonini, Umut Gursoy, Phillip Szepietowski
We examine the structure of the shear viscosity to entropy density ratio $\etas$ in holographic theories of gravity coupled to a scalar field, in the presence of higher derivative corrections. Thanks to a non-trivial scalar field profile, eta/s in this setup generically runs as a function of temperature. In particular, its temperature behavior is dictated by the shape of the scalar potential and of the scalar couplings to the higher derivative terms. We consider a number of dilatonic setups, but focus mostly on phenomenological models that are QCD-like. We determine the geometric conditions needed to identify local and global minima for $\etas$ as a function of temperature, which translate to restrictions on the signs and ranges of the higher derivative couplings. Finally, such restrictions lead to an holographic argument for the existence of a global minimum for $\etas$ in these models, at or above the deconfinement transition.
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http://arxiv.org/abs/1206.3581
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