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Régis Blache

Publications and source records attributed to Régis Blache.

12 recordsLinked to original sources
arXiv2026

Generic ordinarity for abelian coverings of the projective line

We show that abelian coverings of the projective line of order prime to $p$ are generically $μ$-ordinary in characteristic $p$. The images of the irreducible components of Hurwitz spaces of abelian coverings of the projective line by the Torelli morphism lie in some Shimura varieties. The stratification by Newton polygons of these varieties is known, and we show that the generic Newton polygon for the Hurwitz space coincides with the generic (or $μ$-ordinary) Newton polygon of the smallest Shimura variety that contains its image. In order to do this, we compute the generic Newton polygons for $L$-functions associated to multiplicative character sums over the projective line.

math.AG↗
arXiv2025

Ruled surfaces over finite fields, and some codes over them

In the first part of this article, we consider ruled surfaces defined over a finite field; we introduce invariants for them, and describe some explicit contructions that illustrate possible behaviour of these invariants. In the second part, we consider evaluation codes on some such surfaces; we first estimate their parameters, then we construct asymptotically good families of such codes, and we show that their asymptotic parameters are better than the ones of the corresponding product codes. We also consider local properties of these codes.

cs.IT↗
arXiv2023

Classification of singular del Pezzo surfaces over finite fields

In this article, we consider weak del Pezzo surfaces defined over a finite field, and their associated, singular, anticanonical models. We first define arithmetic types for such surfaces, by considering the Frobenius actions on their Picard groups; this extends the classification of Swinnerton-Dyer and Manin for ordinary del Pezzo surfaces. We also show that some invariants of the surfaces only depend on the above type.Then we study an inverse Galois problem for singular del Pezzo surfaces having degree $3\leq d\leq 6$: we describe which types can occur over a given finite field (of odd characteristic when $3\leq d\leq 4$).

math.AG↗
arXiv2023

Construction of good codes from weak Del Pezzo surfaces

We construct algebraic geometric codes from weak del Pezzo surfaces. The codes are associated to the anti-canonical class of the anti-canonical model and to the set of rational points of these models. Since we consider weak Del Pezzo surfaces, the anti canonical model is not smooth any more. This complicates the computation of the parameters of the codes; in particular we need to distinguish the Cartier divisors from the Weil ones.

math.AG↗
arXiv2019

Anticanonical codes from del Pezzo surfaces with Picard rank one

We construct algebraic geometric codes from del Pezzo surfaces and focus on the ones having Picard rank one and the codes associated to the anticanonical class. We give explicit constructions of del Pezzo surfaces of degree 4, 5 and 6, compute the parameters of the associated anticanonical codes and study their isomorphisms arising from the automorphisms of the surface. We obtain codes with excellent parameters and some of them turn out to beat the best known codes listed on the database codetable.

math.AG↗
arXiv2015

Valuations of exponential sums and Artin-Schreier curves

Let $p$ denote an odd prime. In this paper, we are concerned with the $p$-divisibility of additive exponential sums associated to one variable polynomials over a finite field of characteristic $p$, and with (the very close question of) determining the Newton polygons of some families of Artin-Schreier curves, i.e. $p$-cyclic coverings of the projective line in characteristic $p$. We first give a lower bound on the $p$-divisibility of exponential sums associated to polynomials of fixed degree. Then we show that an Artin-Schreier curve defined over a finite field of characteristic $p$ cannot be supersingular when its genus $g$ has the form $(p-1)\left(i(p^n-1)-1\right)/2$ for some $1\leq i\leq p-1$ and $n\geq 1$ such that $n(p-1)>2$. We also determine the first vertex of the generic Newton polygon of the family of $p$-rank $0$ Artin-Schreier curves of fixed genus, and the associated Hasse polynomial.

math.NT↗
arXiv2012

Congruences for L-functions of additive exponential sums

We give a congruence for L-functions coming from affine additive exponential sums over a finite field. Precisely, we give a congruence for certain operators coming from Dwork's theory. This congruence is very similar to the congruence of Manin for the characteristic polynomial of the action of Frobenius on the Jacobian of a curve defined over a finite field.

math.NT↗
arXiv2008

p-Density, exponential sums and Artin-Schreier curves

In this paper we define the $p$-density of a finite subset $D\subset\ma{N}^r$, and show that it gives a good lower bound for the $p$-adic valuation of exponential sums over finite fields of characteristic $p$. We also give an application: when $r=1$, the $p$-density is the first slope of the generic Newton polygon of the family of Artin-Schreier curves associated to polynomials with their exponents in $D$.

math.NT↗
arXiv2006

Newton stratification for polynomials: the open stratum

In this paper we consider the Newton polygons of $L$-functions coming from additive exponential sums associated to a polynomial over a finite field $\F_q$. These polygons define a stratification of the space of polynomials of fixed degree. We determine the open stratum: we give the generic Newton polygon for polynomials of degree $d\geq 2$ when the characteristic $p$ is greater than 3d, and the Hasse polynomial, i.e. the equation defining the hypersurface complementary to the open stratum.

math.AG↗