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

Abstract

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.

Comments: 10 pages, 5figs, Invited talk at "10 years of AdS/CFT Correspondence", Buenos Aires, Dec. 2007, honoring Juan Maldacena