Uniform Bounds for the Number of Rational Points of Bounded Height on Certain Elliptic Curves

Let $E$ be an elliptic curve defined over a number field $k$ and $\mathrm{\ell }$ a prime integer. When $E$ has at least one $k$-rational point of exact order $\mathrm{\ell }$, we derive a uniform upper bound $\exp (C\log B\mathrm{/}\log \log B)$ for the number of points of $E(k)$ of (exponential) height at most $B$. Here the constant $C=C(k)$ depends on the number field $k$ and is effective. For $\mathrm{\ell }=2$ this generalizes a result of Naccarato which applies for $k=\mathbb{Q}$. We follow methods previously developed by Bombieri and Zannier and further by Naccarato, with the main novelty being the application of Rosen’s result on bounding $\mathrm{\ell }$-ranks of class groups in certain extensions, which is derived using relative genus theory.