Talks

Many of the most interesting electronic behaviors arise in materials with strong electron-electron correlations. Many of these same materials are disordered either intrinsically or due to doping. The combination of disorder and interactions generally gives rise to a feature in the density of states at the Fermi level, with two of the most influential examples being the Altshuler-Aronov anomaly and the Efros-Shklovskii Coulomb gap. Experiments on strongly correlated materials and recent numerical results on the Anderson-Hubbard model, however, show behavior which is inconsistent with both of these frameworks. This talk will present some of the features of the zero bias anomaly in strongly correlated systems, both in the case of a purely on-site interaction and in the presence of nearest-neighbor interactions, and it will describe the physical origin of some of these features.

It is a generic feature of strongly correlated electronic systems that several mechanisms (broadly represented by interactions) compete with each other. This competition often leads to the phenomenon of frustration. In strongly correlated systems such as doped Mott insulators kinetic energy and Coulomb repulsion frustrate the tendency of doped holes to phase separate. The result is the onset of a set of novel phases, which we dubbed Electronic Liquid Crystal (ELC) states, with varying degrees of complexity. Much like classical liquid crystals, electronic liquid crystal phases break translation and rotational invariance to varying degrees. In this talk I will focus on the experimental evidence and theory of two these phases, stripes and nematics, in several different systems including two-dimensional electron gases in large magnetic fields, ruthenate oxides, heavy fermions, and cuprate and pnictide superconductors.

Using the framework of deconstruction, we construct simple, weakly-coupled supersymmetric models that explain the Standard Model flavor hierarchy and produce a flavorful soft spectrum compatible with precision limits. Electroweak symmetry breaking is fully natural/ the mu-term is dynamically generated with no B mu-problem and the Higgs mass is easily raised above LEP limits without reliance on large radiative corrections. These models possess the distinctive spectrum of superpartners characteristic of 'effective supersymmetry': the third generation superpartners tend to be light, while the rest of the scalars are heavy.

I will describe the current state of our attempts to characterize the nature of the Dark Energy, the name given to the unknown phenomenology that is driving the observed accelerating cosmic expansion. There is a historical analogy between our current situation and the days of confusion before the advent of quantum mechanics. But while quantum physics emerged in a single academic generation, I fear that our attaining a deeper understanding of Dark Energy may not be as rapid. I will outline some steps we can take to try to avoid an extended period of sophisticated confusion and intellectual stagnation.

We use a field theoretic generalization of the Wigner-Weisskopf method to study the stability of the Bunch-Davies vacuum state for a massless, conformally coupled interacting test field in de Sitter space. A simple example of the impact of vacuum decay upon a non-gaussian correlation is discussed. Single particle excitations also decay into two particle states, leading to particle production that hastens the exiting of modes from the de Sitter horizon resulting in the production of \emph{entangled superhorizon pairs} with a population consistent with unitary evolution. We find a non-perturbative, self-consistent "screening" mechanism that shuts off vacuum decay asymptotically, leading to a stationary vacuum state in a manner not unlike the approach to a fixed point in the space of states.

After reviewing the basics of Coleman deLuccia tunneling, especially in the thin-wall limit, I discuss an (almost) exact tunneling solution in a piecewise linear and quadratic potential. A comparison with the exact solution for a piecewise linear potential demonstrates the dependence of the tunneling rate on the exact shape of the potential. Finally, I will mention applications when determining initial conditions for inflation in the landscape. Based on arXiv:1102.4742 [hep-th].