Browsing by Author "Pastén Vásquez, Héctor"

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    On the fibres of an elliptic surface where the rank does not jump
    (2022) Caro Reyes, Jerson; Pastén Vásquez, Héctor
    For a nonconstant elliptic surface over P1 defined over Q , it is a result of Silverman [‘Heights and the specialization map for families of abelian varieties’, J. reine angew. Math. 342 (1983), 197–211] that the Mordell–Weil rank of the fibres is at least the rank of the group of sections, up to finitely many fibres. If the elliptic surface is nonisotrivial, one expects that this bound is an equality for infinitely many fibres, although no example is known unconditionally. Under the Bunyakovsky conjecture, such an example has been constructed by Neumann [‘Elliptische Kurven mit vorgeschriebenem Reduktionsverhalten. I’, Math. Nachr. 49 (1971), 107–123] and Setzer [‘Elliptic curves of prime conductor’, J. Lond. Math. Soc. (2) 10 (1975), 367–378]. In this note, we show that the Legendre elliptic surface has the desired property, conditional on the existence of infinitely many Mersenne primes.
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    Some advances in a conjecture of Watkins and an analogue over function fields
    (2023) Caro Reyes, Jerson; Pastén Vásquez, Héctor; Pontificia Universidad Católica de Chile. Facultad de Matemáticas
    Our results are divided into two main parts, both related to a conjecture by Watkins. In 2002, Watkins conjectured that the rank of an elliptic curve defined over Q is at most the 2-adic valuation of its modular degree. The first part is related to presenting some approaches to Watkins’s conjecture in its original version. We prove this conjecture for semistable elliptic curves having exactly one rational point of order 2, provided that they have an odd number of primes of non-split multiplicative reduction or no primes of split multiplicative reduction. In addition, we show that this conjecture is satisfied when E is any quadratic twist of an elliptic curve with non-trivial rational 2-torsion and prime power conductor, in particular, for the congruent number elliptic curves. In the second part, we consider the analogous problem over function fields of positive characteristic, and we prove it in several cases. More precisely, every modular semistable elliptic curve over Fq(T) after extending constant scalars and every quadratic twist of a modular elliptic curve over Fq(T) by a polynomial with sufficiently many prime factors satisfy this version of Watkins’s conjecture. Additionally, we prove the analogue of Watkins’s conjecture for a well-known family of elliptic curves with unbounded rank due to Ulmer. In addition, we include a final appendix describing joint work with Hector Pasten [16] on a generalization of the Chabauty-Coleman bound for surfaces. While this is not directly related to the core of the thesis, it is a report on work that was performed during my time as a Ph.D. student.