Phase Diagram of the Two-Flavor Schwinger Model at Zero Temperature.

We examine the phase structure of the two-flavor Schwinger model as a function of the θ angle and the two masses, m_{1} and m_{2}. In particular, we find interesting effects at θ=π: along the SU(2)-invariant line m_{1}=m_{2}=m, in the regime where m is much smaller than the charge g, the theory undergoes logarithmic renormalization group flow of the Berezinskii-Kosterlitz-Thouless type. As a result, dimensional transmutation takes place, leading to a nonperturbatively small mass gap ∼e^{-Ag^{2}/m^{2}}. The SU(2)-invariant line lies within a region of the phase diagram where the charge conjugation symmetry is spontaneously broken and whose boundaries we determine numerically. Our numerical results are obtained using the Hamiltonian lattice gauge formulation that includes the mass shift m_{lat}=m-g^{2}a/4 dictated by the discrete chiral symmetry.

Superconductors from superstrings.

We establish that in a large class of strongly coupled (3+1)-dimensional N=1 quiver conformal field theories with gravity duals, adding a chemical potential for the R charge leads to the existence of superfluid states in which a chiral primary operator of the schematic form O=lambdalambda+W condenses. Here lambda is a gluino and W is the superpotential. Our argument is based on the construction of a consistent truncation of type IIB supergravity that includes a U(1) gauge field and a complex scalar.

Thermodynamics and bulk viscosity of approximate black hole duals to finite temperature quantum chromodynamics.

We consider classes of translationally invariant black hole solutions whose equations of state closely resemble that of QCD at zero chemical potential. We use these backgrounds to compute the ratio zeta/s of bulk viscosity to entropy density. For a class of black holes that exhibits a first-order transition, we observe a sharp rise in zeta/s near Tc. For constructions that exhibit a smooth crossover, like QCD does, the rise in zeta/s is more modest. We conjecture that divergences in zeta/s for black hole horizons are related to extrema of the entropy density as a function of temperature.

Sonic booms and diffusion wakes generated by a heavy quark in thermal gauge-string duality.

We evaluate the Poynting vector generated by a heavy quark moving through a thermal state of N=4 gauge theory using the gauge-string duality. A significant diffusion wake is observed as well as a Mach cone. We discuss the ratio of the energy going into sound modes to the energy coming in from the wake.