arXiv subjects
Publications and source records attributed to Carlos Castano-Bernard.
Let X_0+(N) be the Atkin-Lehner quotient of the modular curve X_0(N) associated to the Fricke involution wN. Assume N > 3 prime and endow the real locus X+ 0 (N)(R) with the real topology. In this paper we revisit a special case of result due to Ogg on the connected components of X_0+(N)(R). Then we obtain a formula for the homology class of each connected component of X_0+(N)(R) in terms of Manin symbols.
Let E be an elliptic curve of conductor N and rank one over Q. So there is a non-constant morphism X+0(N) --> E defined over Q, where X+0(N) = X0(N)/wN and wN is the Fricke involution of the modular curve X+0(N). Under this morphism the traces of the Heegner points of X+0(N) map to rational points on E. In this paper we study the index I of the subgroup generated by all these traces on E(Q). We propose and also discuss a conjecture that says that if N is prime and I > 1, then either the number of connected components of the real locus X+0(N)(R) is greater than 1 or (less likely) the order S of the Tate-Safarevich group is non-trivial. This conjecture is backed by computations performed on each E that satisfies the above hypothesis in the range N < 129999. This paper was prepared for the proceedings of the Conference on Algorithmic Number Theory, Turku, May 8-11, 2007. We tried to make the paper as self contained as possible.
Let C be the image of a canonical embedding C of the Atkin-Lehner quotient X+0(N) associated to the Fricke involution wN. In this note we exhibit some relations among the rational points of C. For each g = 3 (resp. the first g = 4) curve C we found that there are one or more lines (resp. planes) in projectie space whose intersection with C consists entirely of rational Heegner points or the cusp point, where N is prime. We also discuss an explanation of the first non-hyperelliptic exceptional rational point.
In this paper we study a geometric coding algorithm for indefinite binary quadratic forms Q for the congruence subgroup Γ^0(N), with respect to the usual fundamental domain FN, where N is assumed prime. The cycles Q_1, . . ., Q_n that this algorithm produces are such that the the corresponding paths γ_1, . . ., γ_n in the Riemann surface X0(N)(C) have a nice behavior around the elliptic points of order 2.
Certain identities of Ramanujan may be succinctly expressed in terms of the rational function w_N(g) = w_N(f) - 1/w_N(f) on the modular curve X_0(N), where f is a certain modular unit on the Nebentypus cover X_χ(N) introduced by Ogg and Ligozat for N prime congruent to 1 (mod 4) and w_N is the Fricke involution. These correspond to levels N = 5, 13, where the genus of X_0(N) is zero. In this paper we produce some analogs of these identities for each w_N(g) such that X_0(N) has genus 1, 2, and also for each h = g + w_N(g) such that the Atkin-Lehner quotient X_0+(N) has genus 1, 2. We also found that if n is the degree of the field of definition F of the non-trivial zeros of the latter, then the degree of the normal closure of F over Q is the n-th solution of Singmaster's Problem.
Let E be an elliptic curve defined over the rationals and let N be its conductor. Assume N is prime. In this paper we give numerical evidence that suggests some conjectures on the 2-divisibility of certain sums of Heenger points on E of discriminant D dividing 4N. One of these conjectures suggests a possible link between the parity of the eigenvalue a_A(2) and the parity of the Shafarevich-Tate group of certain elliptic curves A of square conductor.