Remark on equicharacteristic analogue of Hesselholts conjecture on cohomology of Witt vectors

Let $L/K$ be a finite Galois extension of complete discrete valued fields of characteristic $p$. Assume that the induced residue field extension $k_L/k_K$ is separable. For an integer $ngeq 0$, let $W_n(sO_L)$ denote the ring of Witt vectors of length $n$ with coefficients in $sO_L$. We show that the proabelian group ${H^1(G,W_n(sO_L))}_{nin N}$ is zero. This is an equicharacteristic analogue of Hesselholts conjecture.

Birational invariance of the $S$-fundamental group scheme

Let $X$ and $Y$ be nonsingular projective varieties over an algebraically closed field $k$ of positive characteristic. If $X$ and $Y$ are birational, we show their $S$-fundamental group schemes are isomorphic.

The Brauer Group of a Smooth Orbifold

Let $k$ be a field and $X/k$ be a smooth quasiprojective orbifold. Let $Xto underline{X}$ be its coarse moduli space. In this paper we study the Brauer group of $X$ and compare it with the Brauer group of the smooth locus of $underline{X}$.

Products of Brauer Severi surfaces

Let ${P_i}_{1 leq i leq r}$ and ${Q_i}_{1 leq i leq r}$ be two collections of Brauer Severi surfaces (resp. conics) over a field $k$. We show that the subgroup generated by the $P_is$ in $Br(k)$ is the same as the subgroup generated by the $Q_is$ iff $Pi P_i $ is birational to $Pi Q_i$. Moreover in this case $Pi P_i$ and $Pi Q_i$ represent the same class in $M(k)$, the Grothendieck ring of $k$-varieties. The converse holds if $char(k)=0$. Some of the above implications also hold over a general noetherian base scheme.