Seminar Calendar
for events the day of Thursday, September 29, 2011.

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More information on this calendar program is available.
Questions regarding events or the calendar should be directed to Tori Corkery.
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Thursday, September 29, 2011

BCDE Math/Physics Seminar
12:00 pm   in 464 Loomis Laboratory,  Thursday, September 29, 2011
 Del Edit Copy
Submitted by katz.
 Jeffrey Teo (UIUC Physics)Topological defects in insulators and superconductor, reminiscence of the Atiyah-Singer index theoremAbstract: The topology of defect band Hamiltonians H(k,r) are classified by K-theory. The topological indices of Hamiltonians can be expressed as integral formulae involving their valence states, such as Chern characters or Chern-Simons invariants. The analytic indices are realized as low energy excitations bound to the defects, such as zero energy bound states (aka Majorana fermions) or spectral flow (aka chiral/helical line modes).

Number Theory
1:00 pm   in 241 Altgeld Hall,  Thursday, September 29, 2011
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Submitted by berndt.
 Harold Diamond (UIUC)Monotonicity in a Beurling G-Numbers ExampleAbstract: Following Beurling, we generally require for a generalized number system that Pi(x), the weighted "prime counting" function, be increasing. Others ask that the corresponding (unweighted) function pi(x) be increasing. Here we show that the latter condition holds for an interesting example.

Group Theory/Differential Geometry
1:00 pm   in 347 Altgeld Hall,  Thursday, September 29, 2011
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Submitted by clein.
 Chris Leininger (UIUC Math)Short geodesics in moduli spaceAbstract: This talk concerns the moduli space $\mathcal M_g$ of Riemann surfaces of genus $g$ equipped with the Teichm\"uller metric. Given any sufficiently large constant $C$, there are closed geodesics in $\mathcal M_g$ of length at most $C/g$. In this talk I will discuss a coarse description for the location of these geodesics in $\mathcal M_g$, as well a polynomial upper bound, in terms of $g$, for the number of such geodesics. This is joint work with D. Margalit

Graduate Geometry and Topology Seminar
2:00 pm   in 241 Altgeld Hall,  Thursday, September 29, 2011
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Submitted by lukyane2.
 Sarah Yeakel (UIUC Math)Gerbes and Homotopy SheavesAbstract: A gerbe is a sheaf of categories with some extra conditions that occurs frequently in geometry. I'll talk about a construction on cosimplicial spaces called the totalization, work through a specific example of a totalization that leads to a presheaf with a "homotopic gluing", and hopefully discuss why this could be a less complicated way to think of gerbes. Gerbes have application in algebraic geometry, differential topology, and even gauge theory and string theory.

Mathematics Colloquium: Coble Memorial Lectures
4:00 pm   in 245 Altgeld Hall,  Thursday, September 29, 2011
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Submitted by seminar.
 Ngo Bao Chau (University of Chicago)Geometry of the Hitchin fibrationAbstract: Nigel Hitchin observed that the cotangent bundle of the moduli space of principal bundles on a Riemann surface has a structure of an algebraic completely integrable system. A deep relation between the geometry of the Hitchen fibration and the geometry of the trace formula has been discovered. This has been helpful in the proof of the fundamental lemma in the Langlands program. The Coble Memorial Lectures will be held September 27-29, 2011. Before each lecture, coffee and cookies will be served in the Common Room (321 Altgeld Hall) at 3:30 p.m.