Search Talks

Novel phases can result from the interplay of electronic interactions and spin orbit coupling. In the first part, we discuss a simple Hubbard model for the pyrochlore iridates, whose phase diagram contains topological insulator (TI) and various magnetic phases. The latter host the novel topological Weyl semimetal, whose excitations behave like Weyl fermions. In the second part we study a novel spin liquid that was proposed to arise in the iridates, the 3D topological Mott insulator: a fractionalized TI where the neutral spinons acquire a topologically non-trivial band structure. The low-energy behavior is dominated by the 2D surface spinons strongly coupled to a bulk gauge field. This phase is characterized by the helical nature of the spinon surface states and the dimensional mismatch between the latter and the gauge bosons. We discuss experimental signatures as well as the possibility of dyonic excitations and a non-trivial magneto-electric response.

Many interesting physical systems in condensed matter physics may be described in the language of error-correcting codes. In this talk, we illustrate the applications of coding theoretical techniques to problems in many-body physics by reviewing our recent works. In particular, we discuss (1) the classification of quantum phases via local quantum codes, (2) thermal stability of topological order and its relation to feasibility of self-correcting quantum memory, and (3) information storage capacity of discrete spin systems.

After overviewing the fundamentals of magnetized relativistic jets production, I present the results of new global 3D general relativistic magnetohydrodynamic simulations of jet formation by black hole (BH) accretion systems. The simulations are designed to transport a large amount of magnetic flux to the center, more than the accreting gas can force into the BH. The excess magnetic flux remains outside the BH, impedes accretion, and leads to a magnetically arrested disc. We find powerful outflows. For a BH with spin parameter a = 0.5, the efficiency with which the accretion system generates outflowing energy in jets and winds is eta ~ 30%. For a = 0.99, we find eta ~ 140%, which means that more energy flows out of the BH than flows in. The only way this can happen is by extracting spin energy from the BH. Thus the a = 0.99 simulation represents an unambiguous demonstration, within an astrophysically plausible scenario, of the extraction of net energy from a spinning BH via the Penrose-Blandford-Znajek mechanism.

I will discuss how to construct a consistent effective field theory when the differing modes of the theory have the same invariant mass scale. I will sketch some phenomenological applications of the formalism relevant for the LHC.

After a short introduction to general gauge mediation, we use the operator product expansion (OPE) to explore the dynamics of the hidden sector of SUSY breaking, much like the OPE is used in e+e- scattering to hadrons in QCD. Along the way we derive consequences that the N=1 superconformal symmetry puts on three-point functions of two current superfields with an arbitrary superconformal primary operator. Using those constraints we construct a ``supermultiplet'' of OPEs. Finally, we give approximations to soft masses, which can be used even in strongly-coupled theories.  
References: arXiv:1107.1721, 1109.4940

I will present a class of models in which the dark matter particle carries flavor quantum numbers, and has renormalizable contact interactions with Standard Model fields. In particular, I will focus on models where the dark matter flavor is identified with lepton flavor in the Standard Model. The region of parameter space where the dark matter has the right abundance to be a thermal relic is accessible at current direct detection experiments. A full simulation of the signal and backgrounds, including detector effects, shows that in a significant part of parameter space these theories can be discovered above Standard Model backgrounds at the LHC. Further, flavor and charge correlations among the final state leptons might allow models of this type to be distinguished from theories where dark matter couples to leptons but does not carry flavor.

We study the constraints imposed by the existence of a single higher spin conserved current on a three dimensional conformal field theory. A single higher spin conserved current implies the existence of an infinite number of higher spin conserved currents. The correlation functions of the stress tensor and the conserved currents are then shown to be equal to those of a free field theory. Namely a theory of $N$ free bosons or free fermions. This is an extension of the Coleman-Mandula theorem to CFT's, which do not have a conventional S matrix. We also briefly discuss the case where the higher spin symmetries are ``slightly'' broken.