School of Mathematics

Values of L-Functions and Modular Forms

Chris Skinner
Princeton University; Member, School of Mathematics
October 25, 2010

This will be an introduction to special value formulas for L-functions and especially the uses of modular forms in establishing some of them -- beginning with the values of the Riemann zeta function at negative integers and hopefully arriving at some more recent work on the Birch-Swinnerton-Dyer formula.

Splitting of Iwasawa Modules and Leopoldt Conjecture

Jean-Pierre Wintenberger
University of Strasbourg
October 20, 2010

Let p be an odd prime number and let F be a totally real field. Let F_cyc be the cyclotomic extension of F generated by the roots of unity of order a power of p . From the maximal abelian extension of F_cyc which is unramified (resp. unramified outside auxiliary primes), we get exact sequences of Iwasawa modules. We will discuss how splitting of these exact sequences are linked to Leopoldt conjecture for F and p . (JW with C. Khare)

Invariants of Graphs, Their Associated Clique Complexes and Right-Angled Coxeter Groups

Michael Davis
The Ohio State University; Member, School of Mathematics
October 19, 2010

Associated to any simplicial graph there is a right-angled Coxeter group. Invariants of the Coxeter group such as its growth series or its weighted L^2 Betti numbers can be computed from the graph's clique complex (i.e., its flag complex).

Rank Bounds for Design Matrices with Applications to Combinatorial Geometry and Locally Correctable Codes

Zeev Dvir
Institute for Advanced Study
October 19, 2010

A (q,k,t)-design matrix is an m x n matrix whose pattern of zeros/non-zeros satisfies the following design-like condition: each row has at most q non-zeros, each column has at least k non-zeros and the supports of every two columns intersect in at most t rows. We prove that for $m\geq n$, the rank of any $(q,k,t)$-design matrix over a field of characteristic zero (or sufficiently large finite characteristic) is at least $n - (qtn/2k)^2$ .

Using this result we derive the following applications: