Physics Department, Princeton University

Biophysics Seminar Series - Ariel Amir (Harvard) "Bacterial growth: defects, elasticity and plasticity"
Bacterial cells have rigid walls, which define their shape, and enable them to hold high internal pressure.  While much is known about cell wall chemistry, the mechanisms controlling its growth remain elusive. The processes leading to the cylindrical shape of many bacteria are only now being unraveled. Recent experiments discovered that new cell wall is added by complexes running at constant velocity around the cell circumference, reminiscent of the motion of defects in crystals. By applying a condensed matter approach to this problem and modeling these complexes as edge dislocations, we find coupling between mechanical stresses and cell wall dynamics. Moreover, I will show that the cell wall deformations can be elastic (reversible) or plastic (irreversible), depending on the timescales over which the force is applied. I will corroborate these predictions experimentally by observing the growth of a single bacterium in a microfluidic device, using the flow to control the external force.

Joseph Henry Room  ·  12:00 p.m.– 1:00 p.m.

High Energy Physcis Seminar-Olga Driga-" Collider Investigations of Early Universe Physics"
ALICE (A Large Ion Collider Experiment) is a dedicated heavy ion experiment at Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN). The goal of the experiment is to study strongly interacting matter at extreme energy densities (QCD thermodynamics). Statistical QCD predicts that, at sufficiently high densities, there will be a transition from hadronic matter to a strongly interacting plasma of deconfined quarks and gluons -- a transition which the early universe passed in the first instances after the Big Bang.

At the LHC, two beams of heavy ions collide with the speed close to the speed of light, and for a very short instances of time the plasma of quarks and gluons is created. The complex system of ALICE detectors register those "little Big Bangs" allowing to broaden the boundaries of our contemporary knowledge.

In my talk, I discuss general picture of heavy ion collisions, giving some overview and motivation for studying heavy-ion physics. Giving place to my research work, I focus on functioning and physics of one of the two ALICE electromagnetic calorimeters, EMCal. Afterwards, I discuss ALICE results on neutral meson measurements.

Jadwin A06  ·  2:00 p.m.– 3:00 p.m.

High Energy Theory Seminar - IAS - Kevin Costello, Northwestern University - “Yangians and Supersymmetric Gauge Theory”
I'll describe a new link between supersymmetric gauge theories, with gauge group G, and the Yangian for the Lie algebra of G. The main result is that a certain twisted, deformed N=1 supersymmetric gauge theory, with gauge group G, is "controlled" by the Yangian built from G, in the same way that Chern-Simons theory is controlled by the quantum group. This statement holds to all orders in perturbation theory, and there is a similar result for pure N=2 and N=4 gauge theories. This result has many concrete corollaries: as an example, I will explain how to calculate certain vacuum expectation values of Wilson operators using the representation theory of the Yangian.


Bloomberg Lecture Hall  ·  2:30 p.m.– 4:00 p.m.