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For the study of the Mordell-Weil group of an elliptic curve ${\bf E}$ over acomplex function field of a projective curve $B$, the first author introducedthe use of differential-geometric methods arising from K\"ahler metrics on$\mathcal H \times \mathbb C$ invariant under the action of the semi-directproduct ${\rm SL}(2,\mathbb R) \ltimes \mathbb R^2$. To a properly chosengeometric model $\pi: \mathcal E \to B$ of ${\bf E}$ as an elliptic surface anda non-torsion holomorphic section $\sigma: B \to \mathcal E$ there is anassociated ``verticality'' $\eta_\sigma$ of $\sigma$ related to the locallydefined Betti map. The first-order linear differential equation satisfied by$\eta_\sigma$, expressed in terms of invariant metrics, is made use of to countthe zeros of $\eta_\sigma$, in the case when the regular locus $B^0\subset B$of $\pi: \mathcal E \to B$ admits a classifying map $f_0$ into a modular curvefor elliptic curves with level-$k$ structure, $k \ge 3$, explicitly andlinearly in terms of the degree of the ramification divisor $R_{f_0}$ of theclassifying map, and the degree of the log-canonical line bundle of $B^0$ in$B$. Our method highlights ${\rm deg}(R_{f_0})$ in the estimates, and recoversthe effective estimate obtained by a different method of Ulmer-Urz\'ua on themultiplicities of the Betti map associated to a non-torsion section, notingthat the finiteness of zeros of $\eta_\sigma$ was due toCorvaja-Demeio-Masser-Zannier. The role of $R_{f_0}$ is natural in the subjectgiven that in the case of an elliptic modular surface there is no non-torsionsection by a theorem of Shioda, for which a differential-geometric proof hadbeen given by the first author. Our approach sheds light on the study ofnon-torsion sections of certain abelian schemes.

Multiplicities of the Betti map associated to a section of an elliptic surface from a differential-geometric perspective