C. A. Rosen

Heavy ions and string theory

Abstract We review a selection of recent developments in the application of ideas of string theory to heavy ion physics. Our topics divide naturally into equilibrium and non-equilibrium phenomena. On the non-equilibrium side, we discuss generalizations of Bjorken flow, numerical simulations of black hole formation in asymptotically anti-de Sitter geometries, equilibration in the dual field theory, and hard probes. On the equilibrium side, we summarize improved holographic QCD, extraction of transport coefficients, inclusion of chemical potentials, and approaches to the phase diagram. We close with some possible directions for future research.

A holographic critical point

We numerically construct a family of ve-dimensional black holes exhibiting a line of rst-order phase transitions terminating at a critical point at nite chemical potential and temperature. These black holes are constructed so that the equation of state and baryon susceptibilities approximately match QCD lattice data at vanishing chemical potential. The critical endpoint in the particular model we consider has temperature 143 MeV and chemical potential 783 MeV. Critical exponents are calculated, with results that are consistent with mean-eld scaling relations.

Dynamic critical phenomena at a holographic critical point

We study time-dependent perturbations to a family of five-dimensional black hole spacetimes constructed as a holographic model of the QCD phase diagram. We use the results to calculate two transport coefficients, the bulk viscosity and conductivity, as well as the associated baryon diffusion constant, throughout the phase diagram. Near the critical point in the T-mu plane, the transport coefficients remain finite, although their derivatives diverge, and the diffusion goes to zero. This provides further evidence that large-N_c gauge theories suppress convective transport. We also find a divergence in the low-temperature bulk viscosity, outside the region expected to match QCD, and compare the results to the transport behavior of known R-charged black holes.

A holographic model for QCD in the Veneziano limit at finite temperature and density

A bstractA holographic model of QCD in the limit of large number of colors, Nc, and massless fermion flavors, Nf , but constant ratio xf = Nf/Nc is analyzed at finite temperature and chemical potential. The five dimensional gravity model contains three bulk fields: a scalar dilaton sourcing TrF2, a scalar tachyon dual to

Fermi surfaces in N=4 Super-Yang-Mills theory

\overline{q}q

Gravitational collapse and thermalization in the hard wall model

and a 4-vector dual to the baryon current

Fermi Surfaces in Maximal Gauged Supergravity

\overline{q}

Thermalization in a holographic confining gauge theory

γμq. The main result is the μ, T phase diagram of the holographic theory. A first order deconfining transition along Th(μ) and a chiral transition at Tχ(μ) > Th(μ) are found. The chiral transition is of second order for small μ and becomes of first order at larger μ. The two regimes are separated by a tricritical point. The dependence of thermodynamical quantities including the speed of sound and susceptibilities on the chemical potential and temperature is computed. A new quantum critical regime is found at zero temperature and finite chemical potential. It is controlled by an AdS2 × R3 geometry and displays semi-local criticality.

Charged Schrodinger black holes

We investigate and classify Fermi surface behavior for a set of fermionic modes in a family of backgrounds holographically dual to N=4 Super-Yang-Mills theory at zero temperature with two distinct chemical potentials. We numerically solve fluctuation equations for every spin-1/2 field in five-dimensional maximally supersymmetric gauged supergravity not mixing with gravitini. Different modes manifest two, one or zero Fermi surface singularities, all associated to non-Fermi liquids, and we calculate dispersion relations and widths of excitations. We study two limits where the zero-temperature entropy vanishes. In one limit, a Fermi surface approaches a marginal Fermi liquid, which we demonstrate analytically, and conductivity calculations show a hard gap with the current dual to the active gauge field superconducting, while the other is insulating. In the other limit, conductivities reveal a soft gap with the roles of the gauge fields reversed.

Fermi surface behavior in the ABJM M2-brane theory

A bstractWe study a simple example of holographic thermalization in a confining field theory: the homogeneous injection of energy in the hard wall model. Working in an amplitude expansion, we find black brane formation for sufficiently fast energy injection and a scattering wave solution for sufficiently slow injection. We comment on our expectations for more sophisticated holographic QCD models.