## Events - Daily

**February 25, 2013**>>

Monday,
February 25 |
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Christina Marchetti (Syracuse U.) "Phase separation and jamming of dense active matter" Recent experiments on confluent layers of epithelial cells and vibrated granular media have motivated interest in the behavior of active systems at high density, where the interplay of steric repulsion and activity can yield active glassy or jammed states. In this talk I will discuss the behavior of dense collections of self-propelled particles in two dimensions. Two specific results will be highlighted: (i) the suppression of motility due to steric repulsion yields macroscopic phase separation in the absence of any aligning or attractive interaction; and (ii) confinement yields jammed active states where the dynamics is dominated by spatio-temporal heterogeneities reminiscent of glassy systems. Joseph Henry Room · 12:00 p.m.– 1:00 p.m. |

Condensed Matter Seminar - Juerg Froehlich, ETH Zurich & IAS, Princeton - Gauge Theory and Topological Phases of Matter We study a general class of systems of condensed matter including electron liquids and atom gases. Thanks to the U(1)- and SU(2)- gauge invariance of the quantum theory of such systems, one may study their response to coupling the electric current to a vector potential and the spin current to an SU(2)- gauge field. Response equations are found by determining their effective actions (or free energies) as functionals of the U(1)-vector potential and SU(2)-gauge field (and of the metric of the sample). The physical interpretation of these fields is explained. Using only general principles – gauge invariance, cluster properties of connected (current) Green functions in systems with a mobility gap, power counting – the form of the effective actions is determined. This leads to a “gauge theory of phases of matter” complementary to the well-known Landau theory. Applications to systems exhibiting the quantum Hall and the spin Hall effect, to 3D topological insulators, and to the primordial plasma in the universe are discussed. PCTS Seminar Room · 1:15 p.m.– 2:30 p.m. |

High Energy Theory Seminar - IAS - Piljin Yi, Korea Institute for Advanced Study - “Wall-Crossing & Quiver Invariants” Bloomberg Lecture Hall - Institute for Advanced Study · 2:30 p.m.– 4:00 p.m. |