arXiv subjects

Maria Montanucci

Publications and source records attributed to Maria Montanucci.

At least 37 records · Page 2Linked to original sources

arXiv2020

A bound for the number of points of space curves over finite fields

For a non-degenerate irreducible curve $C$ of degree $d$ in $\mathbb{P}^3$ over $\mathbb{F}_q$, we prove that the number $N_q(C)$ of $\mathbb{F}_q$-rational points of $C$ satisfies the inequality $N_q(C) \leq (d-2)q+1$. Our result improves the previous bound $N_q(C) \leq (d-1)q+1$ obtained by Homma in 2012 and leads to a natural conjecture generalizing Sziklai's bound for the number of points of plane curves over finite fields.

math.AG↗

arXiv2020

Weierstrass semigroups on the Skabelund maximal curve

In 2017, D. Skabelund constructed a maximal curve over $\mathbb{F}_{q^4}$ as a cyclic cover of the Suzuki curve. In this paper we explicitly determine the structure of the Weierstrass semigroup at any point $P$ of the Skabelund curve. We show that its Weierstrass points are precisely the $\mathbb{F}_{q^4}$-rational points. Also we show that among the Weierstrass points, two types of Weierstrass semigroup occur: one for the $\mathbb{F}_q$-rational points, one for the remaining $\mathbb{F}_{q^4}$-rational points. For each of these two types its Apéry set is computed as well as a set of generators.

math.AG↗

arXiv2020

Locally recoverable codes from automorphism groups of function fields of genus $g \geq 1$

A Locally Recoverable Code is a code such that the value of any single coordinate of a codeword can be recovered from the values of a small subset of other coordinates. When we have $δ$ non overlapping subsets of cardinality $r_i$ that can be used to recover the missing coordinate we say that a linear code $\mathcal{C}$ with length $n$, dimension $k$, minimum distance $d$ has $(r_1,\ldots, r_δ)$-locality and denote it by $[n, k, d; r_1, r_2,\dots, r_δ].$ In this paper we provide a new upper bound for the minimum distance of these codes. Working with a finite number of subgroups of cardinality $r_i+1$ of the automorphism group of a function field $\mathcal{F}| \mathbb{F}_q$ of genus $g \geq 1$, we propose a construction of $[n, k, d; r_1, r_2,\dots, r_δ]$-codes and apply the results to some well known families of function fields.

math.AG↗

arXiv2019

On certain self-orthogonal AG codes with applications to Quantum error-correcting codes

In this paper a construction of quantum codes from self-orthogonal algebraic geometry codes is provided. Our method is based on the CSS construction as well as on some peculiar properties of the underlying algebraic curves, named Swiss curves. Several classes of well-known algebraic curves with many rational points turn out to be Swiss curves. Examples are given by Castle curves, GK curves, generalized GK curves and the Abdon-Bezerra-Quoos maximal curves. Applications of our method to these curves are provided. Our construction extends a previous one due to Hernando, McGuire, Monserrat, and Moyano-Fernandez.

math.AG↗

arXiv2019

MRD-codes arising from the trinomial $x^q+x^{q^3}+cx^{q^5}\in\mathbb{F}_{q^6}[x]$

In [10], the existence of $\mathbb{F}_q$-linear MRD-codes of $\mathbb{F}_q^{6\times 6}$, with dimension $12$, minimum distance $5$ and left idealiser isomorphic to $\mathbb{F}_{q^6}$, defined by a trinomial of $\mathbb{F}_{q^6}[x]$, when $q$ is odd and $q\equiv 0,\pm 1\pmod 5$, has been proved. In this paper we show that this family produces $\mathbb{F}_q$-linear MRD-codes of $\mathbb{F}_q^{6\times 6}$, with the same properties, also in the remaining $q$ odd cases, but not in the $q$ even case. These MRD-codes are not equivalent to the previously known MRD-codes. We also prove that the corresponding maximum scattered $\mathbb{F}_q$-linear sets of $\mathrm{PG}(1,q^6)$ are not $\mathrm{P}Γ\mathrm{L}(2,q^6)$-equivalent to any previously known scattered linear set.

math.CO↗

arXiv2019

New examples of maximal curves with low genus

We investigate the Jacobian decomposition of some algebraic curves over finite fields with genus $4$, $5$ and $10$. As a corollary, explicit equations for curves that are either maximal or minimal over the finite field with $p^2$ elements are obtained for infinitely many $p$'s. Lists of small $p$'s for which maximality holds are provided. In some cases we describe the automorphism group of the curve.

math.AG↗

arXiv2019

Large automorphism groups of ordinary curves in characteristic $2$

Let $\mathcal{X}$ be a (projective, non-singular, irreducible) curve of even genus $g(\mathcal{X}) \geq 2$ defined over an algebraically closed field $K$ of characteristic $p$. If the $p$-rank $γ(\mathcal{X})$ equals $g(\mathcal{X})$, then $\mathcal{X}$ is ordinary. In this paper, we deal with large automorphism groups $G$ of ordinary curves. Under the hypotheses that $p = 2$, $g(\mathcal{X})$ is even and $G$ is solvable, we prove that $|G| < 35(g(\mathcal{X}) +1)^{3/2}$.

math.AG↗

arXiv2019

Large automorphism groups of ordinary curves of even genus in odd characteristic

Let $\mathcal{X}$ be a (projective, non-singular, geometrically irreducible) curve of even genus $g(\mathcal{X}) \geq 2$ defined over an algebraically closed field $K$ of odd characteristic $p$. If the $p$-rank $γ(\mathcal{X})$ equals $g(\mathcal{X})$, then $\mathcal{X}$ is \emph{ordinary}. In this paper, we deal with \emph{large} automorphism groups $G$ of ordinary curves of even genus. We prove that $|G| < 821.37g(\mathcal{X})^{7/4}$. The proof of our result is based on the classification of automorphism groups of curves of even genus in positive characteristic, see \cite{giulietti-korchmaros-2017}. According to this classification, for the exceptional cases ${\rm Aut}(\mathcal{X}) \cong {\rm Alt}_7$ and ${\rm Aut}(\mathcal{X}) \cong \rm{M}_{11}$ we show that the classical Hurwitz bound $|{\rm Aut}(\mathcal{X})| < 84(g(\mathcal{X})-1)$ holds, unless $p=3$, $g(\mathcal{X})=26$ and ${\rm Aut}(\mathcal{X}) \cong \rm{M}_{11}$; an example for the latter case being given by the modular curve $X(11)$ in characteristic $3$.

math.AG↗

arXiv2019

Bent functions from triples of permutation polynomials

We provide constructions of bent functions using triples of permutations. This approach is due to Mesnager. In general, involutions have been mostly considered in such a machinery; we provide some other suitable triples of permutations, using monomials, binomials, trinomials, and quadrinomials.

math.CO↗

arXiv2019

Towards the full classification of exceptional scattered polynomials

Let $f(X) \in \mathbb{F}_{q^r}[X]$ be a $q$-polynomial. If the $\mathbb{F}_q$-subspace $U=\{(x^{q^t},f(x)) \mid x \in \mathbb{F}_{q^n}\}$ defines a maximum scattered linear set, then we call $f(X)$ a scattered polynomial of index $t$. The asymptotic behaviour of scattered polynomials of index $t$ is an interesting open problem. In this sense, exceptional scattered polynomials of index $t$ are those for which $U$ is a maximum scattered linear set in ${\rm PG}(1,q^{mr})$ for infinitely many $m$. The complete classifications of exceptional scattered monic polynomials of index $0$ (for $q>5$) and of index 1 were obtained by Bartoli and Zhou. In this paper we complete the classifications of exceptional scattered monic polynomials of index $0$ for $q \leq 4$. Also, some partial classifications are obtained for arbitrary $t$. As a consequence, the complete classification of exceptional scattered monic polynomials of index $2$ is given.

math.CO↗

arXiv2019

A class of linear sets in PG(1,q^5)

The maximum scattered linear sets in $PG(1,q^n)$ have been completely classified for $n \le 4$ by Csajbók-Zanella and Lavrauw-Van de Voorde. Here a wide class of linear sets in $PG(1,q^5)$ is studied which depends on two parameters. Conditions for the existence, in this class, of possible new maximum scattered linear sets in $PG(1,q^5)$ are exhibited.

math.CO↗

arXiv2019

AG codes from the second generalization of the GK maximal curve

The second generalized GK maximal curves $\mathcal{GK}_{2,n}$ are maximal curves over finite fields with $q^{2n}$ elements, where $q$ is a prime power and $n \geq 3$ an odd integer, constructed by Beelen and Montanucci. In this paper we determine the structure of the Weierstrass semigroup $H(P)$ where $P$ is an arbitrary $\mathbb{F}_{q^2}$-rational point of $\mathcal{GK}_{2,n}$. We show that these points are Weierstrass points and the Frobenius dimension of $\mathcal{GK}_{2,n}$ is computed. A new proof of the fact that the first and the second generalized GK curves are not isomorphic for any $n \geq 5$ is obtained. AG codes and AG quantum codes from the curve $\mathcal{GK}_{2,n}$ are constructed; in some cases, they have better parameters with respect to those already known.

math.AG↗

arXiv2018

Weierstrass semigroups at every point of the Suzuki curve

In this article we explicitly determine the structure of the Weierstrass semigroups $H(P)$ for any point $P$ of the Suzuki curve $\mathcal{S}_q$. As the point $P$ varies, exactly two possibilities arise for $H(P)$: one for the $\mathbb{F}_q$-rational points (already known in the literature), and one for all remaining points. For this last case a minimal set of generators of $H(P)$ is also provided. As an application, we construct dual one-point codes from an $\mathbb{F}_{q^4}\setminus\fq$-point whose parameters are better in some cases than the ones constructed in a similar way from an $\fq$-rational point.

math.CO↗

arXiv2018

On subfields of the second generalization of the GK maximal function field

The second generalized GK function fields $K_n$ are a recently found family of maximal function fields over the finite field with $q^{2n}$ elements, where $q$ is a prime power and $n \ge 1$ an odd integer. In this paper we construct many new maximal function fields by determining various Galois subfields of $K_n$. In case $\gcd(q+1,n)=1$ and either $q$ is even or $q \equiv 1 \pmod{4},$ we find a complete list of Galois subfields of $K_n.$ Our construction adds several previously unknown genera to the genus spectrum of maximal curves.

math.AG↗

arXiv2018

Large odd prime power order automorphism groups of algebraic curves in any characteristic

Let $\mathcal{X}$ be a (projective, geometrically irreducible, nonsingular) algebraic curve of genus $g \ge 2$ defined over an algebraically closed field $\mathbb{K}$ of odd characteristic $p\ge 0$, and let $\rm{Aut}(\mathcal{X})$ be the group of all automorphisms of $\mathcal{X}$ which fix $\mathbb{K}$ element-wise. For any a subgroup $G$ of $\rm{Aut}(\mathcal{X})$ whose order is a power of an odd prime $d$ other than $p$, the bound proven by Zomorrodian for Riemann surfaces is $|G|\leq 9(g-1)$ where the extremal case can only be obtained for $d=3$. We prove Zomorrodian's result for any $\mathbb{K}$. The essential part of our paper is devoted to extremal $3$-Zomorrodian curves $\mathcal{X}$. Two cases are distinguished according as the quotient curve $\mathcal{X}/Z$ for a central subgroup $Z$ of $\rm{Aut}(\mathcal{X})$ of order $3$ is either elliptic, or not. For elliptic type extremal $3$-Zomorrodian curves $\mathcal{X}$, we completely determine the two possibilities for the abstract structure of $G$ using deeper results on finite $3$-groups. We also show infinite families of extremal $3$-Zomorrodian curves for both types, elliptic or non-elliptic. Our paper does not adapt methods from the theory of Riemann surfaces, nevertheless it sheds a new light on the connection between Riemann surfaces and their automorphism groups.

math.AG↗

arXiv2018

A new family of maximal curves

In this article we construct for any prime power $q$ and odd $n \ge 5$, a new $\mathbb{F}_{q^{2n}}$-maximal curve $\mathcal X_n$. Like the Garcia--G\" uneri--Stichtenoth maximal curves, our curves generalize the Giulietti--Korchmáros maximal curve, though in a different way. We compute the full automorphism group of $\mathcal X_n$, yielding that it has precisely $q(q^2-1)(q^n+1)$ automorphisms. Further, we show that unless $q=2$, the curve $\mathcal{X}_n$ is not a Galois subcover of the Hermitian curve. Finally, we find new values of the genus spectrum of $\mathbb{F}_{q^{2n}}$-maximal curves, by considering some Galois subcovers of $\mathcal X_n$.

math.AG↗

arXiv2018

The complete list of genera of quotients of the $\mathbb{F}_{q^2}$-maximal Hermitian curve for $q\equiv1\pmod{4}$

Let $\mathbb{F}_{q^2}$ be the finite field with $q^2$ elements. Most of the known $\mathbb{F}_{q^2}$-maximal curves arise as quotient curves of the $\mathbb{F}_{q^2}$-maximal Hermitian curve $\mathcal{H}_{q}$. After a seminal paper by Garcia, Stichtenoth and Xing, many papers have provided genera of quotients of $\mathcal{H}_q$, but their complete determination is a challenging open problem. In this paper we determine completely the spectrum of genera of quotients of $\mathcal{H}_q$ for any $q\equiv1\pmod4$.

math.AG↗

arXiv2018

On the classification problem for the genera of quotients of the Hermitian curve

In this paper we characterize the genera of those quotient curves $\mathcal{H}_q/G$ of the $\mathbb{F}_{q^2}$-maximal Hermitian curve $\mathcal{H}_q$ for which $G$ is contained in the maximal subgroup $\mathcal{M}_1$ of ${\rm Aut}(\mathcal{H}_q)$ fixing a self-polar triangle, or $q$ is even and $G$ is contained in the maximal subgroup $\mathcal{M}_2$ of ${\rm Aut}(\mathcal{H}_q)$ fixing a pole-polar pair $(P,\ell)$ with respect to the unitary polarity associated to $\mathcal{H}_q(\mathbb{F}_{q^2})$. In this way several new values for the genus of a maximal curve over a finite field are obtained. Together with what is known in the literature, our results leave just two open cases to provide the complete list of genera of Galois subcovers of the Hermitian curve; namely, the open cases in [Bassa-Ma-Xing-Yeo, J. Combin. Theory Ser. A, 2013] when $G$ fixes a point $P \in \mathcal{H}_q(\mathbb{F}_{q^2})$ and $q$ is even, and the open cases in [Montanucci-Zini, Comm. Algebra, 2018] when $G\leq\mathcal{M}_2$ and $q$ is odd.

math.AG↗