CARMA SEMINAR Speaker: Wilson Ong, Department of Mathematics, Australian National University Title: A simplified proof of Hesselholts conjecture on Galois cohomology of Witt vectors of algebraic integers Location: Room V129, Mathematics Building (Callaghan Campus) The University of Newcastle Time and Date: 4:00 pm, Thu, 23rd Feb 2012 Abstract: Let $K$ be a complete discrete valuation field of characteristic zero with residue field $k_K$ of characteristic $p > 0$. Let $L/K$ be a finite Galois extension with Galois group $G = \text{Gal}(L/K)$ and suppose that the induced extension of residue fields $k_L/k_K$ is separable. Let $W_n(.)$ denote the ring of $p$-typical Witt vectors of length $n$. Hesselholt [Galois cohomology of Witt vectors of algebraic integers, Math. Proc. Cambridge Philos. Soc. 137(3) (2004), 551557] conjectured that the pro-abelian group ${H^1(G,W_n(O_L))}_{n>0}$ is isomorphic to zero. Hogadi and Pisolkar [On the cohomology of Witt vectors of $p$-adic integers and a conjecture of Hesselholt, J. Number Theory 131(10) (2011), 17971807] have recently provided a proof of this conjecture. In this talk, we present a simplified version of the original proof which avoids many of the calculations present in that version. [Permanent link]