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Teresa Crespo

Publications and source records attributed to Teresa Crespo.

30 records · Page 2Linked to original sources
arXiv2015

Jacobian Conjecture and Nilpotency

For K a field of characteristic 0 and d any integer number greater than or equal to 2, we prove the invertibility of polynomial endomorphisms of the affine space of dimension d over K of the form F=Id+H, where each coordinate of H is the cube of a linear form and the cube of the Jacobian matrix of H is equal to zero. Our proof uses the inversion algorithm for polynomial maps presented in our previous paper. Our current result leads us to formulate a conjecture relating the nilpotency degree of the Jacobian matrix of H with the number of necessary steps in the inversion algorithm.

math.AG↗
arXiv2015

An inversion algorithm for polynomial maps

We present an algorithmic equivalent statement to the Jacobian conjecture. Given a polynomial map F on an affine space of dimension n, our algorithm constructs n sequences of polynomials such that F is invertible if and only if the zero polynomial appears in all n sequences and moreover computes the inverse map of F. This algorithm provides a classification of polynomial automorphisms of affine spaces.

math.AC↗
arXiv2015

Induced Hopf Galois structures

For a finite Galois extension K/k and an intermediate field F such that Gal(K/F) has a normal complement in Gal(K/k), we construct and characterize Hopf Galois structures on K/k which are induced by a pair of Hopf Galois structures on K/F and F/k.

math.GR↗
arXiv2015

Galois correspondence theorem for Picard-Vessiot extensions

In this paper, we generalize the definition of the differential Galois group and the Galois correspondence theorem established previously for Picard-Vessiot extensions of real differential fields with real closed field of constants to any Picard-Vessiot extension.

math.AC↗
arXiv2014

On the Galois correspondence theorem in separable Hopf Galois theory

In this paper we present a reformulation of the Galois correspondence theorem of Hopf Galois theory in terms of groups carrying farther the description of Greither and Pareigis. We prove that the class of Hopf Galois extensions for which the Galois correspondence is bijective is larger than the class of almost classically Galois extensions but not equal to the whole class. We show as well that the image of the Galois correspondence does not determine the Hopf Galois structure.

math.GR↗
arXiv2014

From Galois to Hopf Galois: theory and practice

Hopf Galois theory expands the classical Galois theory by considering the Galois property in terms of the action of the group algebra k[G] on K/k and then replacing it by the action of a Hopf algebra. We review the case of separable extensions where the Hopf Galois property admits a group-theoretical formulation suitable for counting and classifying, and also to perform explicit computations and explicit descriptions of all the ingredients involved in a Hopf Galois structure. At the end we give just a glimpse of how this theory is used in the context of Galois module theory for wildly ramified extensions.

math.GR↗
arXiv2013

The Hopf Galois property in subfield lattices

Hopf Galois theory for finite separable field extensions was introduced by Greither and Pareigis. They showed that all Hopf Galois extensions of degree up to 5 are either Galois or almost classically Galois and they determined the Hopf Galois character of a separable extension according to the Galois group (or the degree) of its Galois closure. In this paper we study degree 6 separable extensions as well as intermediate extensions for degrees 4,5 and 6. We present an example of a non almost classically Galois Hopf Galois extension of the field of rational numbers of the smallest possible degree and new examples of Hopf Galois extensions. In the last section we prove a transitivity property of the Hopf Galois condition.

math.NT↗
arXiv2013

Real and p-adic Picard-Vessiot fields

We consider differential modules over real and p-adic differential fields such that their field of constants is real closed (respectively p-adically closed). Using Deligne's work on Tannakian categories and a result of Serre on Galois cohomology, a purely algebraic proof of the existence and unicity of real (respectively p-adic) Picard-Vessiot fields is obtained.

math.AG↗
arXiv2012

Real Picard-Vessiot theory

The existence of a Picard-Vessiot extension for a homogeneous linear differential equation has been established when the differential field over which the equation is defined has an algebraically closed field of constants. In this paper, we prove the existence of a real Picard-Vessiot extension for a homogeneous linear differential equation defined over a real differential field K with real closed field of constants. We give an adequate definition of the differential Galois group of a Picard- Vessiot extension of a real differential field with real closed field of constants and we prove a Galois correspondence theorem for such a Picard-Vessiot extension.

math.AG↗