A Note on p . adic Etale Cohomology
A Note on p . adic Etale Cohomology
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发表时间:
2021
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通讯作者:
M. Kurihara
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作者:
M. Kurihara
1o Let X be a projective smooth scheme over a complete discrete valuation ring A o2 mixed characteristics (0, p). In [2], Fontaine and Messing studied the relation between the p-adic etale cohomology o the generic fiber H(X)-H(X(R), Z) ( is an algebraic closure o2 ]) and the crystalline cohomology of the special fiber H(X). In this article, we consider not Gal(/v)-representation H(X), but H(X) itsel and study this cohomology group by using the syntomic cohomology introduced in [2]. Detailed studies containing the complete proof will appear elsewhere. We will use the 2ollowing notation" X is a projective, smooth and geometrically connected scheme over A of dimension d as above, and Y-X (resp. X) is the special fiber (resp. the generic fiber), and i" YX (resp. ]" X--X) is the canonical morphism. We assume that the residue field F of A has a finite p-base of order g (i.e. [F" F]=p0. Fontaine and Messing [2] defined the syntomic siteX and a shea S on Xn in order to link the etale cohomology to De Rham cohomology. This shea2 S is regarded as an "ideal" etale shea2 ZipS(r) on X. Namely, the group H(X, S) is expected to play a role o ,,rzt: Z/p(r))" which cannot be defined directly. In [2], a global cohomology H(X,Zp) was studied under the assumption e=ord(p)=l. Our aim in this paper is a local study o2 p-adie etale vanishing cycles i*R],Z/p%r) when e may not be 1. Put (r)=i*Rz.S e D(Y,) as in [3] where z"XXis the canonical morphism. Fontaine and Messing defined a morphism S--.i’*]’.Z/p(r) (where ]’" X,-+X,vn_,, i’" XvXv_**) in [2] 5, which induces. 3(r) -.i*Rj.Z/p(r). We study the difference between q(r) and i*Rj.Z/p(r). Theorem. If r <p--1, there exists a distinguished triangle (r) >rri*R].Z/p(r) "W9o [-r]. r-1 where W[2r,o is the logarithmic Hodge-Witt sheaf. In particular, if r >_ d(--dim X)+g(= ord [F" F]), we have a long exact sequence