A SIMPLIFIED PROOF OF HESSELHOLT’S CONJECTURE ON GALOIS COHOMOLOGY OF WITT VECTORS OF ALGEBRAIC INTEGERS

2012 ◽  
Vol 86 (3) ◽  
pp. 456-460
Author(s):  
WILSON ONG
Keyword(s):  
Number Theory ◽  
Abelian Group ◽  
Residue Field ◽  
Galois Cohomology ◽  
Algebraic Integers ◽  
Original Proof ◽  
Cambridge Philos ◽  
Witt Vectors ◽  
Residue Fields ◽  
Valuation Field

AbstractLet K be a complete discrete valuation field of characteristic zero with residue field kK of characteristic p>0. Let L/K be a finite Galois extension with Galois group G=Gal(L/K) and suppose that the induced extension of residue fields kL/kK is separable. Let 𝕎n(⋅) 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), 551–557] conjectured that the pro-abelian group {H1 (G,𝕎n (𝒪L))}n≥1 is isomorphic to zero. Hogadi and Pisolkar [‘On the cohomology of Witt vectors of p-adic integers and a conjecture of Hesselholt’, J. Number Theory131(10) (2011), 1797–1807] have recently provided a proof of this conjecture. In this paper, we provide a simplified version of the original proof which avoids many of the calculations present in that version.

scholarly journals Faltings extension and Hodge-Tate filtration for abelian varieties over p-adic local fields with imperfect residue fields

2020 ◽  
pp. 1-17
Author(s):  
Tongmu He
Keyword(s):  
Abelian Varieties ◽  
Residue Field ◽  
Local Fields ◽  
Field Case ◽  
Residue Fields ◽  
Valuation Field

Abstract Let K be a complete discrete valuation field of characteristic $0$ , with not necessarily perfect residue field of characteristic $p>0$ . We define a Faltings extension of $\mathcal {O}_K$ over $\mathbb {Z}_p$ , and we construct a Hodge-Tate filtration for abelian varieties over K by generalizing Fontaine’s construction [Fon82] where he treated the perfect residue field case.

scholarly journals On valuations of K(x)

1992 ◽  
Vol 35 (3) ◽  
pp. 419-426 ◽  
Author(s):  
Sudesh K. Khanduja
Keyword(s):  
Abelian Group ◽  
Finite Index ◽  
Residue Field ◽  
Torsion Group ◽  
Closed Field ◽  
Converse Problem ◽  
Valued Field ◽  
Transcendental Extension ◽  
Residue Fields ◽  
Simple Transcendental Extension

For a valued field (K, v), let Kv denote the residue field of v and Gv its value group. One way of extending a valuation v defined on a field K to a simple transcendental extension K(x) is to choose any α in K and any μ in a totally ordered Abelian group containing Gv, and define a valuation w on K[x] by w(Σici(x – α)i) = mini (v(ci) + iμ). Clearly either Gv is a subgroup of finite index in Gw = Gv + ℤμ or Gw/Gv is not a torsion group. It can be easily shown that K(x)w is a simple transcendental extension of Kv in the former case. Conversely it is well known that for an algebraically closed field K with a valuation v, if w is an extension of v to K(x) such that either K(x)w is not algebraic over Kv or Gw/Gv is not a torsion group, then w is of the type described above. The present paper deals with the converse problem for any field K. It determines explicitly all such valuations w together with their residue fields and value groups.

scholarly journals On value groups and residue fields of some valued function fields

1994 ◽  
Vol 37 (3) ◽  
pp. 445-454
Author(s):  
Sudesh K. Khanduja
Keyword(s):  
Cyclic Group ◽  
Function Field ◽  
Function Fields ◽  
Residue Field ◽  
Torsion Group ◽  
Transcendence Degree ◽  
Manuscripta Math ◽  
Direct Sum ◽  
Residue Fields ◽  
The One

Let K = K0(x, y) be a function field of transcendence degree one over a field K0 with x, y satisfying y2 = F(x), F(x) being any polynomial over K0. Let υ0 be a valuation of K0 having a residue field k0 and υ be a prolongation of υ to K with residue field k. In the present paper, it is proved that if G0⊆G are the value groups of υ0 and υ, then either G/G0 is a torsion group or there exists an (explicitly constructible) subgroup G1 of G containing G0 with [G1:G0]<∞ together with an element γ of G such that G is the direct sum of G1 and the cyclic group ℤγ. As regards the residue fields, a method of explicitly determining k has been described in case k/k0 is a non-algebraic extension and char k0≠2. The description leads to an inequality relating the genus of K/K0 with that of k/k0: this inequality is slightly stronger than the one implied by the well-known genus inequality (cf. [Manuscripta Math.65 (1989), 357–376’, [Manuscripta Math.58 (1987), 179–214]).

scholarly journals NOTES ON EXTREMAL AND TAME VALUED FIELDS

2016 ◽  
Vol 81 (2) ◽  
pp. 400-416
Author(s):  
SYLVY ANSCOMBE ◽  
FRANZ-VIKTOR KUHLMANN
Keyword(s):  
Approximation Property ◽  
Elementary Theory ◽  
Residue Field ◽  
Axiom System ◽  
Complete Characterization ◽  
Valued Fields ◽  
Mixed Characteristic ◽  
Valued Field ◽  
Residue Fields

AbstractWe extend the characterization of extremal valued fields given in [2] to the missing case of valued fields of mixed characteristic with perfect residue field. This leads to a complete characterization of the tame valued fields that are extremal. The key to the proof is a model theoretic result about tame valued fields in mixed characteristic. Further, we prove that in an extremal valued field of finitep-degree, the images of all additive polynomials have the optimal approximation property. This fact can be used to improve the axiom system that is suggested in [8] for the elementary theory of Laurent series fields over finite fields. Finally we give examples that demonstrate the problems we are facing when we try to characterize the extremal valued fields with imperfect residue fields. To this end, we describe several ways of constructing extremal valued fields; in particular, we show that in every ℵ1saturated valued field the valuation is a composition of extremal valuations of rank 1.

scholarly journals Splitting properties of the reduction of semi-abelian varieties

2016 ◽  
Vol 12 (08) ◽  
pp. 2241-2264
Author(s):  
Alan Hertgen
Keyword(s):  
Abelian Variety ◽  
Abelian Varieties ◽  
Residue Field ◽  
Characteristic Exponent ◽  
Jacobian Variety ◽  
Ring Of Integers ◽  
Identity Component ◽  
Genus Formula ◽  
Valuation Field

Let [Formula: see text] be a complete discrete valuation field. Let [Formula: see text] be its ring of integers. Let [Formula: see text] be its residue field which we assume to be algebraically closed of characteristic exponent [Formula: see text]. Let [Formula: see text] be a semi-abelian variety. Let [Formula: see text] be its Néron model. The special fiber [Formula: see text] is an extension of the identity component [Formula: see text] by the group of components [Formula: see text]. We say that [Formula: see text] has split reduction if this extension is split. Whereas [Formula: see text] has always split reduction if [Formula: see text] we prove that it is no longer the case if [Formula: see text] even if [Formula: see text] is tamely ramified. If [Formula: see text] is the Jacobian variety of a smooth proper and geometrically connected curve [Formula: see text] of genus [Formula: see text], we prove that for any tamely ramified extension [Formula: see text] of degree greater than a constant, depending on [Formula: see text] only, [Formula: see text] has split reduction. This answers some questions of Liu and Lorenzini.

scholarly journals Perpendicularity in an Abelian Group

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Pentti Haukkanen ◽  
Mika Mattila ◽  
Jorma K. Merikoski ◽  
Timo Tossavainen
Keyword(s):  
Number Theory ◽  
Abelian Group

We give a set of axioms to establish a perpendicularity relation in an Abelian group and then study the existence of perpendicularities in(ℤn,+)and(ℚ+,·)and in certain other groups. Our approach provides a justification for the use of the symbol⊥denoting relative primeness in number theory and extends the domain of this convention to some degree. Related to that, we also consider parallelism from an axiomatic perspective.

scholarly journals The different and differentials of local fields with imperfect residue fields

1997 ◽  
Vol 40 (2) ◽  
pp. 353-365 ◽  
Author(s):  
Bart de Smit
Keyword(s):  
Galois Extension ◽  
Correction Term ◽  
Residue Field ◽  
Field Extension ◽  
Local Fields ◽  
Valuation Rings ◽  
Complete Field ◽  
Residue Fields ◽  
Residue Characteristic ◽  
Module Of Differentials

Let K be a complete field with respect to a discrete valuation and let L be a finite Galois extension of K. If the residue field extension is separable then the different of L/K can be expressed in terms of the ramification groups by a well-known formula of Hilbert. We will identify the necessary correction term in the general case, and we give inequalities for ramification groups of subextensions L′/K in terms of those of L/K. A question of Krasner in this context is settled with a counterexample. These ramification phenomena can be related to the structure of the module of differentials of the extension of valuation rings. For the case that [L: K] = p2, where p is the residue characteristic, this module is shown to determine the correction term in Hilbert's formula.

scholarly journals Existentially closed models of the theory of artinian local rings

1999 ◽  
Vol 64 (2) ◽  
pp. 825-845 ◽  
Author(s):  
Hans Schoutens
Keyword(s):  
Residue Field ◽  
Local Rings ◽  
Model Companion ◽  
Closed Model ◽  
Gorenstein Rings ◽  
Existentially Closed ◽  
Finite Set ◽  
Residue Fields

AbstractThe class of all Artinian local rings of length at most l is ∀2-elementary, axiomatised by a finite set of axioms τtl. We show that its existentially closed models are Gorenstein. of length exactly l and their residue fields are algebraically closed, and, conversely, every existentially closed model is of this form. The theory oτl of all Artinian local Gorenstein rings of length l with algebraically closed residue field is model complete and the theory τtl is companionable, with model-companion oτl.

Sign in / Sign up

Export Citation Format

Share Document