The status of the KSS bound and its possible violations (how perfect can a fluid be?)

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In this work we briefly review the Kovtun-Son-Starinet (KSS) computation of the ratio eta/s for quantum field theories with gravitational dual and the related conjecture that it is bound from below by 1/4 pi. We discuss the validity of the bound and the nature of its possible violations, its relevance for RHIC, its connection with phase transitions and other related issues.
© 2008 American Institute of Physics. Conference on Ten Years of AdS/CFT (2007. Buenos Aires, Argentina). This work has been partially supported by the DGICYT (Spain) under grants FPA 2004- 02602 and FPA 2005-02327 and by the Universidad Complutense/CAM, project number 910309 and BSCH-PR34/07-15875. A. D. thanks José Edelstein and the organization for their kind invitation to participate in this celebration of the tenth anniversary of the discovery of the AdS/CFT correspondence held at such a great place as Buenos Aires, and Alex Buchel and Juan Maldacena for useful comments.
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