Algebraic construction of quasi-split algebraic tori

The main purpose of this work is to give a constructive proof for a particular case of the no-name lemma. Let [Formula: see text] be a finite group, [Formula: see text] a field that is equipped with a faithful [Formula: see text]-action, and [Formula: see text] a sign permutation [Formula: see text]-lattice (see the Introduction for the definition). Then [Formula: see text] acts naturally on the group algebra [Formula: see text] of [Formula: see text] over [Formula: see text], and hence also on the quotient field [Formula: see text]. A well-known variant of the no-name lemma asserts that the invariant sub-field [Formula: see text] is a purely transcendental extension of [Formula: see text]. In other words, there exist [Formula: see text] which are algebraically independent over [Formula: see text] such that [Formula: see text]. In this paper, we give an explicit construction of suitable elements [Formula: see text].

An abelian subextension of the dyadic division field of a hyperelliptic Jacobian

Given a field k of characteristic different from 2 and an integer d ≥ 3, let J be the Jacobian of the “generic” hyperelliptic curve given by $\begin{array}{} \displaystyle y^2 = \prod_{i = 1}^d (x - \alpha_i) \end{array}$ , where the αi’s are transcendental and independent over k; it is defined over the transcendental extension K/k generated by the symmetric functions of the αi’s. We investigate certain subfields of the field K∞ obtained by adjoining all points of 2-power order of J(K̄). In particular, we explicitly describe the maximal abelian subextension of K∞ / K(J[2]) and show that it is contained in K(J[8]) (resp. K(J[16])) if g ≥ 2 (resp. if g = 1). On the way we obtain an explicit description of the abelian subextension K(J[4]), and we describe the action of a particular automorphism in Gal(K∞ / K) on these subfields.

Existence Of Coefficient Subring for Transcendental Extension Ring

As a consequence of Cohen's structure Theorem for complete local rings that every _nite commutative ring R of characteristic pn contains a unique special primary subring R0 satisfying R/J(R) = R0/pR0: Cohen called R0 the coe_cient subring of R. In this paper we will study the case when the ring is a transcendental extension local artinian duo ring R; we proved that even in this case R will has a commutative coe_cient subring.

On the degree of irrationality in Noether’s problem

Noether’s problem asks whether, for a given field [Formula: see text] and finite group [Formula: see text], the fixed field [Formula: see text] is a purely transcendental extension of [Formula: see text], where [Formula: see text] acts on the [Formula: see text] by [Formula: see text]. The field [Formula: see text] is naturally the function field for a quotient variety [Formula: see text]. We study the degree of irrationality [Formula: see text] of [Formula: see text] for an abelian group [Formula: see text], which is defined to be the minimal degree of a dominant rational map from [Formula: see text] to projective space. In particular, we give bounds for [Formula: see text] in terms of the arithmetic of cyclotomic extensions [Formula: see text].

ON LIFTINGS OF POWERS OF IRREDUCIBLE POLYNOMIALS

Let v be a henselian valuation of arbitrary rank of a field K with valuation ring Rv having maximal ideal Mv. Using the canonical homomorphism from Rv onto Rv/Mv, one can lift any monic irreducible polynomial with coefficients in Rv/Mv to yield monic irreducible polynomials over Rv. Popescu and Zaharescu extended this approach and introduced the notion of lifting with respect to a residually transcendental prolongation w of v to a simple transcendental extension K(x) of K. As it is well known, the residue field of such a prolongation w is [Formula: see text], where [Formula: see text] is the residue field of the unique prolongation of v to a finite simple extension L of K and Y is transcendental over [Formula: see text] (see [V. Alexandru, N. Popescu and A. Zaharescu, A theorem of characterization of residual transcendental extension of a valuation, J. Math. Kyoto Univ.28 (1988) 579–592]). It is known that a lifting of an irreducible polynomial belonging to [Formula: see text] with respect to w, is irreducible over K. In this paper, we give some sufficient conditions to ensure that a given polynomial in K[x] satisfying these conditions which is a lifting of a power of some irreducible polynomial belonging to [Formula: see text] with respect to w, is irreducible over K. Our results extend Eisenstein–Dumas and generalized Schönemann irreducibility criteria.

ON IRREDUCIBLE FACTORS OF POLYNOMIALS OVER COMPLETE FIELDS

Let (K, v) be a complete rank-1 valued field. In this paper, we extend classical Hensel's Lemma to residually transcendental prolongations of v to a simple transcendental extension K(x) and apply it to prove a generalization of Dedekind's theorem regarding splitting of primes in algebraic number fields. We also deduce an irreducibility criterion for polynomials over rank-1 valued fields which extends already known generalizations of Schönemann Irreducibility Criterion for such fields. A refinement of Generalized Akira criterion proved in Khanduja and Khassa [Manuscripta Math.134(1–2) (2010) 215–224] is also obtained as a corollary of the main result.

Generalized Hensel's lemma

Let (K, v) be a complete, rank-1 valued field with valuation ring Rv, and residue field kv. Let vx be the Gaussian extension of the valuation v to a simple transcendental extension K(x) defined by The classical Hensel's lemma asserts that if polynomials F(x), G0(x), H0(x) in Rv[x] are such that (i) vx(F(x) – G0(x)H0(x)) > 0, (ii) the leading coefficient of G0(x) has v-valuation zero, (iii) there are polynomials A(x), B(x) belonging to the valuation ring of vx satisfying vx(A(x)G0(x) + B(x)H0(x) – 1) > 0, then there exist G(x), H(x) in K[x] such that (a) F(x) = G(x)H(x), (b) deg G(x) = deg G0(x), (c) vx(G(x)–G0(x)) > 0, vx(H(x) – H0(x)) > 0. In this paper, our goal is to prove an analogous result when vx is replaced by any prolongation w of v to K(x), with the residue field of wa transcendental extension of kv.