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Makoto Sakagaito

Publications and source records attributed to Makoto Sakagaito.

8 recordsLinked to original sources

Gersten-type conjecture for henselian local rings of normal crossing varieties

Let $n\geq 0$ and $r>0$ be integers. Let $\mathcal{O}_{X, x}^{h}$ be the henselization of the local ring $\mathcal{O}_{X, x}$ of a scheme $X$ at a point $x\in X$. For a normal crossing variety $Y$ over the spectrum of a field $k$ of positive characteristic $p>0$, K$.$Sato defined an étale logarithmic Hodge-Witt sheaf $λ^{n}_{Y, r}$ on the étale site $Y_{\mathrm{\acute{e}t}}$ which agrees with $W_{r}Ω^{n}_{Y, \log}$ in the case where $Y$ is smooth over $\operatorname{Spec}(k)$. In this paper, we prove the Gersten-type conjecture for étale sheaves which satisfy some properties over $\mathcal{O}_{Y, y}^{h}$. For example, $λ_{Y, r}^{n}$ and $μ_{l}^{\otimes n}$ satisfy these properties where $μ_{l}$ is the étale sheaf of $l$-th roots of unity for an integer $l$ which is prime to the characteristic of $Y$. Let $B$ be a discrete valuation ring of mixed characteristic $(0, p)$ and $\mathfrak{X}$ a semistable family over $\operatorname{Spec}(B)$. Suppose that $B$ contains $p$-th roots of unity. As an application of the Gersten-type conjecture for $λ^{n}_{r}$, we prove the relative version of the Gersten-type conjecture for the $p$-adic étale Tate twist $\mathfrak{T}_{1}(n)$ over $\mathcal{O}_{\mathfrak{X}, x}^{h}$. Moreover, we prove a generalization of Artin's theorem about the Brauer groups.

math.AG↗

On a generalized Brauer group in mixed characteristic cases, II

As an extension of an author's previous paper, we prove the Gersten-type conjecture for the mod $p$ étale motivic cohomology over a local ring of mixed characteristic $(0, p)$. We also prove the $\mathbb{P}^{1}$-homotopy invariance for the generalized Brauer group which is a genelization of a result due to Saltman in mixed characteristic cases.

math.NT↗

On étale hypercohomology of henselian regular local rings with values in $p$-adic étale Tate twists

Let $R$ be the henselization of a local ring of a semistable family over the spectrum of a discrete valuation ring of mixed characteristic $(0, p)$ and $k$ the residue field of $R$. In this paper, we prove an isomorphism of étale hypercohomology groups $\operatorname{H}^{n+1}_{\mathrm{\acute{e}t}}(R, \mathfrak{T}_{r}(n)) \simeq \operatorname{H}^{1}_{\mathrm{\acute{e}t}}(k, W_{r}Ω_{\log}^{n})$ for any integers $n\geq 0$ and $r>0$ where $\mathfrak{T}_{r}(n)$ is the $p$-adic Tate twist and $W_{r}Ω_{\log}^{n}$ is the logarithmic Hodge-Witt sheaf. As an application, we prove the local-global principle for Galois cohomology groups over function fields of curves over an excellent henselian discrete valuation ring of mixed characteristic.

math.NT↗

On a generalized Brauer group in mixed characteristic cases

We define a generalization of the Brauer group $\operatorname{H}_\mathrm{B}^{n}(X)$ for an equi-dimensional scheme $X$ and $n>0$. In the case where $X$ is the spectrum of a local ring of a smooth algebra over a discrete valuation ring, $\operatorname{H}_\mathrm{B}^{n}(X)$ agrees with the étale motivic cohomology $\operatorname{H}^{n+1}_{\mathrm{\acute{e}t}}\left(X, \mathbb{Z}(n-1)\right)$. We prove (a part of) the Gersten-type conjecture for the generalized Brauer group for a local ring of a smooth algebra over a mixed characteristic discrete valuation ring and an isomorphism $ \operatorname{H}_\mathrm{B}^{n}\left( R \right) \simeq \operatorname{H}_\mathrm{B}^{n}\left( k \right) $ for a henselian local ring $R$ of a smooth algebra over a mixed characteristic discrete valuation ring and the residue field $k$. As an application, we show local-global principles for Galois cohomology groups over function fields of smooth curves over a mixed characteristic excellent henselian discrete valuation ring.

math.NT↗

On Problems about a generalization of the Brauer group

In this paper, we define a generalization of the Brauer groups by using Bloch's cycle complex on etale site. We prove the Gersten conjecture of generalized Brauer group on some cases. As an application we prove the Gersten conjecture of the logarithmic Hodge-Witt cohomology for a two dimensional regular local ring which is smooth over a spectrum of some discrete valuation ring of characteristic $p>0$. Moreover we consider a generalization of Artin's theorem on Brauer groups.

math.NT↗