Talks

For stationary black holes it is universally agreed that entropy is proportional to horizon area. It is not so clear what the relationship is for dynamical black holes. In such spacetimes the event horizon is teleologically defined while the apparent horizon is non-unique. Thus even if one believes that entropy continues to be well-defined and proportional to horizon area, there are many possible areas to choose from. In this work I will review some recent work that I have done with M. Heller, G. Plewa and M.Spalinski that examines this issue from the perspective of the fluid-gravity correspondence. In this quasi-equilibrium regime the slowly evolving black brane horizons on the gravity side are dual to a perturbed fluid flow. The fluid manifestations of the various horizon definitions can be compared and the blackbrane mechanics is dual to hydro-thermodynamics. In particular, the uncertainty as to which is the "correct" horizon can be interpreted as dual to the inherent freedom in defining an entropy current.

We suggest the existence of a fundamental connection between baryonic and dark matter. This is motivated by both the stability of these two types of matter as well as the observed similarity of their present-day densities. A unified genesis of baryonic and dark matter arises naturally in models in which proton stability is ensured by promoting the baryon number to a local symmetry. This is illustrated in a specific class of SUSY models using the Affleck-Dine mechanism. The dark matter candidate in these scenarios is charged under the baryon gauge symmetry and is required to have a mass at the weak scale. We discuss the collider constraints from B-factories, LEP, Tevatron, and LHC, as well as direct detection bounds. A baryonic dark force is shown to be consistent with all data for mediators as light as the GeV scale.

I'll discuss how to systematically construct a (d+2)-dimensional solution of the vacuum Einstein equations that is dual to a (d+1)-dimensional fluid satisfying the incompressible Navier-Stokes equations with specific higher-derivative corrections. The solution takes the form of a non-relativistic gradient expansion that is in direct correspondence with the hydrodynamic expansion of the dual fluid. The dual fluid has nevertheless an underlying description in terms of relativistic hydrodynamics, with the unusual property of having a vanishing equilibrium energy density. Using the gravitational results, as well as an interesting and exact constraint on its stress tensor, we identify the transport coefficients of the dual fluid. A simple Lagrangian model is sufficient to realise its key properties.

DEAP-3600 is a dark matter experiment using 3600 kg of liquid argon for direct WIMP search, with a target sensitivity to the spin-independent WIMP-nucleon cross-section of 10^{-46} cm^2. The detector is currently under construction at SNOLAB, located 2 km underground in Sudbury. In this single-phase liquid argon experiment, discrimination of beta/gamma backgrounds from the WIMP-induced nuclear recoil signal will be achieved by analyzing the pulse shape of scintillation light. A prototype 7-kg liquid argon detector has been taking data at SNOLAB since 2007 and has allowed extensive background studies, including significant radon and surface contamination reduction. The status of the experiment and of background reduction studies will be presented.

We describe a model of composite dark matter, bound by an asymptotically free gauge interaction. This leads to a novel relic history and to an enhancement of the present-day dark matter annihilation cross section. Potential indirect detection signals are discussed.

Many explanations have been proposed for the origin of dark matter and the creation of the baryon asymmetry, but very few of them address both cosmological puzzles at once. At the same time, the observed energy densities of dark matter and baryons are within a factor of five of each other hinting at a possible common origin. In this talk I will present a novel mechanism that generates both densities at once, with the dark matter species carrying a net baryon number. This gives rise to new and unusual dark matter signals such as the destruction of nucleons by dark matter scattering. I will describe some of these signals, and discuss how they might be detected in current and upcoming experiments and astrophysical observations.

I discuss the challenges for building models of ~10 GeV dark matter that can accommodate the numerous astrophysical constraints that threaten to exclude them, as well as direct detection constraints. A U(1)xU(1) hidden sector model with isospin violation, inelastic couplings, and annihilation into invisible products is suggested. I will also discuss similar but simpler models that could simultaneously explain excess 511 keV gamma rays from the galactic center and direct detection of light dark matter.