Complex deformations of Bjorken flow

Through a complex shift of the time coordinate, a modification of Bjorken flow is introduced which interpolates between a glasma-like stress tensor at forward rapidities and Bjorken-like hydrodynamics around mid-rapidity. A Landau-like full-stopping regime is found at early times and rapidities not too large. Approximate agreement with BRAHMS data on the rapidity distribution of produced particles at top RHIC energies can be achieved if the complex shift of the time coordinate is comparable to the inverse of the saturation scale. The form of the stress tensor follows essentially from symmetry considerations, and it can be expressed in closed form.Comment: 14 pages, 4 figures. v2: Minor error corrected, conclusions unchange

Counter-examples to the correlated stability conjecture

We demonstrate explicit counter-examples to the Correlated Stability Conjecture (CSC), which claims that the horizon of a black brane is unstable precisely if that horizon has a thermodynamic instability, meaning that its matrix of susceptibilities has a negative eigenvalue. These examples involve phase transitions near the horizon. Ways to restrict or revise the CSC are suggested. One of our examples shows that N=1* gauge theory has a second order chiral symmetry breaking phase transition at a temperature well above the confinement scale.Comment: 18 pages, 5 figures. v2: minor improvements, reference adde

Universality of the diffusion wake in the gauge-string duality

As a particle moves through a fluid, it may generate a laminar wake behind it. In the gauge-string duality, we show that such a diffusion wake is created by a heavy quark moving through a thermal plasma and that it has a universal strength when compared to the total drag force exerted on the quark by the plasma. The universality extends over all asymptotically anti-de Sitter supergravity constructions with arbitrary scalar matter. We discuss how these results relate to the linearized hydrodynamic approximation and how they bear on our understanding of di-hadron correlators in heavy ion collisions.Comment: 36 pages, 4 figure

Using string theory to study the quark-gluon plasma: progress and perils

I outline some of the progress over the past few years in applying ideas from string theory to study the quark-gluon plasma, including the computation of the drag force on heavy quarks and estimates of total multiplicity from black hole formation. I also indicate some of the main perils of the string theory approach.Comment: 8 pages, 5 figures, contribution to the proceedings of Quark Matter 2009. v2: Slightly shortene