In a recent study of how the output voltage of a Hall plate is affected by the shape of the plate and the size of its contacts, U. Ausserlechner has come up with a remarkable double integral that can be viewed as a generalisation of the classical elliptic ‘arithmetic–geometric mean (AGM)’ integral. Here we discuss transformation properties of the integral, which were experimentally observed by Ausserlechner, as well as its analytical and arithmetic features including connections with modular forms.

We provide a comprehensive study of the function $h=h(q)$ defined by

$$\begin{eqnarray}h=q\mathop{\prod }_{j=1}^{\infty }\frac{(1-q^{12j-1})(1-q^{12j-11})}{(1-q^{12j-5})(1-q^{12j-7})}\end{eqnarray}$$

$k=k(q)$

$$\begin{eqnarray}k=q\mathop{\prod }_{j=1}^{\infty }\frac{(1-q^{10j-1})(1-q^{10j-2})(1-q^{10j-8})(1-q^{10j-9})}{(1-q^{10j-3})(1-q^{10j-4})(1-q^{10j-6})(1-q^{10j-7})}.\end{eqnarray}$$

We employ a modular method to establish the new result that two types of Eisenstein series to the tredecic base may be parametrised in terms of the eta quotients ${\it\eta}^{13}({\it\tau})/{\it\eta}(13{\it\tau})$ and ${\it\eta}^{2}(13{\it\tau})/{\it\eta}^{2}({\it\tau})$. The method can also be used to give short and simple proofs for the analogous cubic, quintic and septic theories.

We construct linear maps from the spaces of quasimodular forms for a discrete subgroup Γ of SL(2,ℝ) to some cohomology spaces of the group Γ and prove that these maps are equivariant with respect to appropriate Hecke operator actions. The results are obtained by using the fact that there is a correspondence between quasimodular forms and certain finite sequences of modular forms.

Modular forms for a discrete subgroup Γ of SL(2,ℝ) can be identified with holomorphic sections of line bundles over the modular curve U corresponding to Γ, and quasimodular forms generalize modular forms. We construct vector bundles over U whose sections can be identified with quasimodular forms for Γ.

Soient $p$ un nombre premier et $\mathcal{C}$ la courbe de Hecke $p$-adique de $\mathrm{GL}_2$ de niveau moderé $1$ introduite par Coleman et Mazur. Nous montrons que $\mathcal{C}$ est lisse en ses points Eisenstein critiques et nous donnons une condition nécessaire et suffisante pour que l’application poids soit étale en un tel point en terme de certaines valeurs de la fonction $\zeta$$p$-adique. Un point important est la détermination en ces points du lieu de réductibilité schématique du pseudo-caractère Galoisien porté par $\mathcal{C}$, et ce restreint à un groupe de décomposition en $p$. L’assertion de lissité découle alors de ce que les fonctions $L$ de Dirichlet ont au plus des zéros simples aux entiers.

Let $p$ be a prime number and $\mathcal{C}$ be the $p$-adic tame level $1$ eigencurve introduced by Coleman and Mazur. We prove that $\mathcal{C}$ is smooth at the evil Eisenstein points and we give necessary and sufficient conditions for etaleness of the map to the weight space at these points in terms of $p$-adic zeta values. A key step is the determination at these points of the schematic reducibility locus of the pseudo-character carried by $\mathcal{C}$ restricted to a decomposition group at $p$. Then, the smoothness appears to be a consequence of the fact that the Dirichlet $L$-functions only have simple zeros at integers.

Let Sk, l(Γ, ω, χ) be the space of mixed cusp forms of type (k, l) associated to a Fuchsian group Γ, a holomorphic map ω: ℋ → ℋ of the upper half plane into itself and a homomorphism χ: Γ → SL(2, R) such that ω and χ are equivariant. We construct a map from Sk, l(Γ, ω, χ) to the parabolic cohomology space of Γ with coefficients in some Γ-module and prove that this map is injective.