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This Week at Physics

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Events on Friday, October 17th, 2014

Special Astronomy Talk
"The Structure of the Faintest Dwarf Galaxies"
Time: 12:00 pm
Place: 4421 Sterling Hall
Speaker: Ken Freeman, ANU College of Physical and Mathematical Sciences
Abstract: The faintest dwarf galaxies are very baryon-depleted and have large
M/L ratios. Their gravitational fields are dominated by their dark halos.
If the dark halos have cores of near-constant surface density, and the
baryons have isotropic kinematics and are close to isothermal as observed,
then the density distribution of the baryons is expect to have a simple
analytic form which we can use to measure the central densities of their
dark halos. The observed density distributions of the faintest dwarf
spheroidal and dwarf irregular galaxies appear to follow this expected
distribution.

The core radii and central densities of the dark halos of rotationally
dominated late-type spirals scale with their absolute magnitudes: the
densities decrease with luminosity and the core radii increase, with
the central surface densities of the halos being almost independent of
lumiosity. I will talk about the consequences of these scaling laws and
some other correlations for the epoch of formation of the dwarfs, the
sizes of their dark halos and the existence of dark dwarfs.
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Physics Department Colloquium
Quantum thermalization, many-body Anderson localization, and the entanglement frontier
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: David Huse, Princeton University
Abstract: Progress in physics and quantum information science motivates much recent study of the behavior of extensively-entangled many-body quantum systems fully isolated from their environment, and thus undergoing unitary time evolution. What does it mean for such a system to go to thermal equilibrium? I will explain the Eigenstate Thermalization Hypothesis (ETH), which posits that each individual exact eigenstate of the system's Hamiltonian is at thermal equilibrium, and which appears to be true for most (but not all) quantum many-body systems. Prominent among the systems that do not obey this hypothesis are quantum systems that are many-body Anderson localized and thus do not constitute a reservoir that can thermalize itself. When the ETH is true, one can do standard statistical mechanics using the `single-eigenstate ensembles', which are the limit of the microcanonical ensemble where the `energy window' contains only a single many-body eigenstate. These eigenstate ensembles are more powerful than the traditional statistical mechanical ensembles, in that they can also "see" the quantum phase transition in to the localized phase, as well as a rich new world of phases and quantum phase transitions within the localized phase.
Host: Vavilov
Poster: http://www.physics.wisc.edu/twap/posters/2014/3401.pdf
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