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Isoptic curves of plane curves are a live domain of study, mostly for closed, smooth, strictly convex curves. A technology-rich environment allows for a two-fold development: dynamical geometry systems enable us to perform experiments and to derive conjectures, and computer algebra systems (CAS) are the appropriate environments for an algebraic approach for determining isoptics, with its Grobner bases packages, amongst others. Closed Fermat curves in the affine plane present a specific problem: the variables of the involved polynomials represent the coordinates of points on the Fermat curve, which avoid the dense set of points with two rational coordinates (excepted 4 “trivial” points). Therefore, automated computation has to be performed over the field $$\mathbb {R}$$ of the real numbers, with which the Grobner bases packages do not work. Instead, other packages implemented in CASs have to be used. First, we present a study of the orthoptics of closed Fermat curves of even order. Then we proceed to an algebraic study of these curves using a CAS. The generalization to angles other than $$90^\circ $$ is performed afterwards, with an algebraic approach using support functions, then using numerical methods.

We study when Hurwitz curves are supersingular. Specifically, we show that the curve $H_{n,\ell}: X^nY^\ell + Y^nZ^\ell + Z^nX^\ell = 0$, with $n$ and $\ell$ relatively prime, is supersingular over the finite field $\mathbb{F}_{p}$ if and only if there exists an integer $i$ such that $p^i \equiv -1 \bmod (n^2 - n\ell + \ell^2)$. If this holds, we prove that it is also true that the curve is maximal over $\mathbb{F}_{p^{2i}}$. Further, we provide a complete table of supersingular Hurwitz curves of genus less than 5 for characteristic less than 37., 15 pages. Accepted to Involve

Orientadores: Saeed Tafazolian, Farhad Rahmati Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica e Amir Kabir University of Technology, Irã Resumo: Para uma curva algébrica C definida sobre um corpo algebricamente fechado de característica p > 0, o número a(C) é a dimensão do espaço de diferenciais holomórficos exatos em C. Calculamos o a-número para famílias infinitas de Fermat, Curvas máximas, hiperelípticas e de Hurwitz Abstract: For an algebraic curve C defined over an algebraically closed field of characteristic p > 0, the a-number a(C) is the dimension of the space of exact holomorphic differentials on C. We compute the a-number for infinite families of Fermat, Maximal, HyperElliptic and Hurwitz curves Doutorado Matemática Doutor em Matemática

Let $p$ be a prime number and let $k$ be an algebraically closed field of characteristic $p$. A $BT_1$ group scheme over $k$ is a finite commutative group scheme which arises as the kernel of $p$ on a $p$-divisible (Barsotti--Tate) group. Our main result is that every $BT_1$ scheme group over $k$ occurs as a direct factor of the $p$-torsion group scheme of the Jacobian of an explicit curve defined over $\mathbb{F}_p$. We also treat a variant with polarizations. Our main tools are the Kraft classification of $BT_1$ group schemes, a theorem of Oda, and a combinatorial description of the de Rham cohomology of Fermat curves., Comment: 13 pages. This paper is derived from arxiv:2010.15160 which has been divided and streamlined

Let K be an algebraically closed field of characteristic p ≥ 0 . A generalized Fermat curve of type ( k , n ) , where k , n ≥ 2 are integers (for p ≠ 0 we also assume that k is relatively prime to p), is a non-singular irreducible projective algebraic curve F k , n defined over K admitting a group of automorphisms H ≅ Z k n so that F k , n / H is the projective line with exactly ( n + 1 ) cone points, each one of order k. Such a group H is called a generalized Fermat group of type ( k , n ) . If ( n − 1 ) ( k − 1 ) > 2 , then F k , n has genus g n , k > 1 and it is known to be non-hyperelliptic. In this paper, we prove that every generalized Fermat curve of type ( k , n ) has a unique generalized Fermat group of type ( k , n ) if ( k − 1 ) ( n − 1 ) > 2 (for p > 0 we also assume that k − 1 is not a power of p). Generalized Fermat curves of type ( k , n ) can be described as a suitable fiber product of ( n − 1 ) classical Fermat curves of degree k. We prove that, for ( k − 1 ) ( n − 1 ) > 2 (for p > 0 we also assume that k − 1 is not a power of p), each automorphism of such a fiber product curve can be extended to an automorphism of the ambient projective space. In the case that p > 0 and k − 1 is a power of p, we use tools from the theory of complete projective intersections in order to prove that, for k and n + 1 relatively prime, every automorphism of the fiber product curve can also be extended to an automorphism of the ambient projective space. In this article we also prove that the set of fixed points of the non-trivial elements of the generalized Fermat group coincide with the hyper-osculating points of the fiber product model under the assumption that the characteristic p is either zero or p > k n − 1 .

We construct the minimal regular model of the Fermat curve of odd squarefree composite exponent $N$ over the $N$-th cyclotomic integers. As an application, we compute upper and lower bounds for the arithmetic self-intersection of the dualizing sheaf of this model., 42 pages, 7 figures

It is well known that the Gauss map for a complex plane curve is birational, whereas the Gauss map in positive characteristic is not always birational. Let $q$ be a power of a prime integer. We study a certain plane curve of degree $q^2+q+1$ for which the Gauss map is inseparable with inseparable degree $q$. As a special case, we show a relation between the dual curve of the Fermat curve of degree $q^2+q+1$ and the Ballico-Hefez curve., Comment: 12 pages

The Heisenberg curve is defined to be the curve corresponding to an extension of the projective line by the Heisenberg group modulo $n$, ramified above three points. This curve is related to the Fermat curve and its group of automorphisms is studied. Also we give an explicit equation for the curve $C_3$., 13 pages

We give a precise description of the homology group of the Fermat curve as a cyclic module over a group ring. As an application, we prove the freeness of the profinite homology of the Fermat tower. This allows us to define measures, an equivalent of Anderson’s adelic beta functions, in a manner similar to Ihara’s definition of ℓ-adic universal power series for Jacobi sums. We give a simple proof of the interpolation property using a motivic decomposition of the Fermat curve.

In his paper, "The group of automorphisms of the Fermat curve" (see [7]), Tzermias proved that the automorphism group of the projective Fermat curves in characteristic 0 is the semidirect product of the direct sum of 2 copies of the cyclic group of order n and the symmetric group on 3 letters. In this paper we present an alternative proof of this fact accessible to someone with basic knowledge of Riemann surfaces and group theory. Also we include the geometric correspondence of the action. Resumen. Pavlos Tzermias en su artículo "The group of automorphisms of the Fermat curve" (ver [7]), prueba que el grupo de automorfismos de las curvas de Fermat proyectivas en característica 0 es el producto semidirecto de la suma directa de 2 copias del grupo cíclico de orden n y el grupo simétrico de 3 letras. En este artículo se presenta una prueba alternativa de este hecho accesible para alguien con conocimientos básicos en superficies de Riemann y teoría de grupos. Además, se incluye la correspondencia geométrica de la acción.

Let C denote the Fermat curve over Q of prime exponent l. The Jacobian Jac(C) of C splits over Q as the product of Jacobians Jac(C_k), 0< k < l-1, where C_k are curves obtained as quotients of C by certain subgroups of automorphisms of C. It is well known that Jac(C_k) is the power of an absolutely simple abelian variety B_k with complex multiplication. We call degenerate those pairs (l,k) for which B_k has degenerate CM type. For a non-degenerate pair (l,k), we compute the Sato-Tate group of Jac(C_k), prove the generalized Sato-Tate Conjecture for it, and give an explicit method to compute the moments and measures of the involved distributions. Regardless of (l,k) being degenerate or not, we also obtain Frobenius equidistribution results for primes of certain residue degrees in the l-th cyclotomic field. Key to our results is a detailed study of the rank of certain generalized Demjanenko matrices., 28 pages, minor edits to reflect referee's comments, to appear in the Canadian Journal of Mathematics

Let k , n ≥ 2 be integers. A generalized Fermat curve of type ( k , n ) is a compact Riemann surface S that admits a subgroup of conformal automorphisms H ≤ Aut ( S ) isomorphic to Z k n , such that the quotient surface S / H is biholomorphic to the Riemann sphere C ˆ and has n + 1 branch points, each one of order k. There exists a good algebraic model for these objects, which makes them easier to study. Using tools from algebraic topology and integration theory on Riemann surfaces, we find a set of generators for the first homology group of a generalized Fermat curve. Finally, with this information, we find a set of generators for the period lattice of the associated Jacobian variety.

Let $K$ be a totally real number field. For all prime number $p\geq 5$, let us denote by $F_p$ the Fermat curve of equation $x^p+y^p+z^p=0$. Under the assumption that $2$ is totally ramified in $K$, we establish some results about the set $F_p(K)$ of points of $F_p$ rational over $K$. We obtain a criterion so that the asymptotic Fermat's Last Theorem is true over $K$, criterion related to the set of Hilbert modular cusp newforms over $K$, of parallel weight $2$ and of level the prime ideal above $2$. It is often simply testable numerically, particularly if the narrow class number of $K$ is $1$. Furthermore, using the modular method, we prove Fermat's Last Theorem effectively, over some number fields whose degrees over $\mathbb{Q}$ are $3,4,5,6$ and $8$., Comment: in French

We propose a new construction for the multiplication algorithm of D.V. and G.V. Chudnovsky in order to improve scalar algebraic complexity. In particular, we improve the Baum-Shokrollahi construction for multiplication in \(\mathbb F_{256}/\mathbb F_4\) based on the elliptic Fermat curve \(x^3+y^3=1\).

The Dickson–Guralnick–Zieve curve, briefly DGZ curve, defined over the finite field F q arises naturally from the classical Dickson invariant of the projective linear group P G L ( 3 , F q ) . The DGZ curve is an (absolutely irreducible, singular) plane curve of degree q 3 − q 2 and genus 1 2 q ( q − 1 ) ( q 3 − 2 q − 2 ) + 1 . In this paper we show that the DGZ curve has several remarkable features, those appearing most interesting are: the DGZ curve has a large automorphism group compared to its genus albeit its Hasse–Witt invariant is positive; the Fermat curve of degree q − 1 is a quotient curve of the DGZ curve; among the plane curves with the same degree and genus of the DGZ curve and defined over F q 3 , the DGZ curve is optimal with respect the number of its F q 3 -rational points.

The absolute Galois group of the cyclotomic field K = Q ( ζ p ) acts on the etale homology of the Fermat curve X of exponent p. We study a Galois cohomology group which is valuable for measuring an obstruction for K-rational points on X. We analyze a 2-nilpotent extension of K which contains the information needed for measuring this obstruction. We determine a large subquotient of this Galois cohomology group which arises from Heisenberg extensions of K. For p = 3 , we perform a Magma computation with ray class fields, group cohomology, and Galois cohomology which determines it completely.

Anderson introduced a $p$-adic version of soliton theory. He then applied it to the Jacobian variety of a cyclic quotient of a Fermat curve and showed that torsion points of certain prime order lay outside of the theta divisor. In this paper, we evolve his theory further. As an application, we get a stronger result on the intersection of the theta divisor and torsion points on the Jacobian variety for more general curves. New examples are discussed as well. A key new ingredient is a map connecting the $p$-adic loop group and the formal group.

A generalized Fermat curve of type ( k , 3 ) , where k ? 2 , is a closed Riemann surface admitting a group H ? Z k 3 as a group of conformal automorphisms so that the quotient orbifold S / H is the Riemann sphere and it has exactly 4 cone points, each one of order k. Every genus one Riemann surface is a generalized Fermat curve of type ( 2 , 3 ) and, if k ? 3 , then a generalized Fermat curve of type ( k , 3 ) is non-hyperelliptic. For each generalized Fermat curve, we compute its field of moduli and note that it is a field of definition. Moreover, for k = e 2 i π / p , where p ? 5 is a prime integer, we produce explicit algebraic models over the corresponding field of moduli. As a byproduct, we observe that the absolute Galois group Gal ( Q ? / Q ) acts faithfully at the level of non-hyperelliptic dessins d'enfants. This last fact was already known for dessins of genus 0, 1 and for hyperelliptic ones, but it seems that the non-hyperelliptic situation is not explicitly given in the existent literature.

Canonical Projective Embeddings of the Deligne-Lusztig Curves Associated to 2 A 2 , 2 B 2 and 2 G 2 Daniel M. Kane May 15, 2015 Abstract The Deligne-Lusztig varieties associated to the Coxeter classes of the algebraic groups 2 A 2 , 2 B 2 and 2 G 2 are affine algebraic curves. We produce explicit projective models of the closures of these curves. Furthermore for d the Coxeter number of these groups, we find polynomials for each of these models that cut out the F q -points, the F q d -points and the F q d+1 - points, and demonstrate a relation satisfied by these polynomials. Introduction There are four kinds of finite groups of Lie type of rank 1. The associated Deligne-Lusztig varieties for the Coxeter classes of these groups all give affine algebraic curves. The completions of these curves have several applications in- cluding the representation theory of the associated group ([1, 5]), coding theory ([4]) and the construction of potentially interesting covers of P 1 ([3]). In this paper, we consider these curves associated to the groups G = 2 A 2 , 2 B 2 and 2 G 2 . The remaining curve is associated to G = A 1 and is P 1 , but we do not cover this case as it is easy and doesn’t follow many of the patterns found in the analysis of the other three cases. For each of these curves, we explicitly construct an embedding C ,→ P(W ) where W is a representation of G of dimension 3,5, or 14 respectively, and provide an explicit system of equations cutting out C. The curve associated to 2 A 2 is the Fermat curve. The curve associated to B 2 is also well-known though not immediately isomorphic to our embedding. Embeddings of the curve associated to 2 G 2 were not known until recently. In [6], they constructed an explicit curve with the correct genus, symmetry group and number of points. Later, in [2], Eid and Duursma use this description to independently arrive at the embedding we produce in this paper. ∗ University of California, San Diego, Department of Mathematics / Department of Computer Science and Engineering, 9500 Gilman Drive #0404, La Jolla, CA 92093 dakane@ucsd.edu

We describe the action of the full automorphisms group on the Fermat curve of degree N. For N prime, we obtain the group algebra decomposition of the corresponding Jacobian variety.

In this paper, we study the algebraic points of degree $4$ over $\mathbb{Q}$ on the Fermat curve $F_5/\mathbb{Q}$ of equation $x^5+y^5+z^5=0$. A geometrical description of these points has been given in 1997 by Klassen and Tzermias. Using their result, as well as Bruin's work about diophantine equations of signature $(5,5,2)$, we give here an algebraic description of these points. In particular, we prove there is only one Galois extension of $\mathbb{Q}$ of degree $4$ that arises as the field of definition of a non-trivial point of $F_5$.

Let G be an abelian automorphism group of a complex algebraic curve of genus g ≥ 2 with gonality d, and let |G| be its order. We prove that except for the Fermat curve of degree d + 1, and if G is cyclic. Furthermore, if |G| > 2g − 2 + 2d and C admits a unique finite cover f: C → ℙ1 of degree d, then f is a Galois cover.

In this paper we will examine the affine algebraic curves defined on the complement of Fermat curves of degree five or higher in the affine plane. In particular we will bound the height of integral points over an affine curve outside of an exceptional set.

We give an explicit description of the F_{q^i}-rational points on the Fermat curve u^{q-1}+v^{q-1}+w^{q-1}=0 for each i=1,2,3. As a consequence, we observe that for any such point (u,v,w), the product uvw is a cube in F_{q^i}. We also describe the F_{q^2}-rational points on the Fermat surface u^{q-1}+v^{q-1}+w^{q-1}+x^{q-1}=0, and show that the product of the coordinates of any such points is a square., 8 pages