Exceptional zero formulae for anticyclotomic p-adic L-functions of elliptic curves in the ramified case

Abstract

Iwasawa theory of modular forms over anticyclotomic ${\mathbb{Z}}_p$-extensions of imaginary quadratic fields has been studied by several authors, starting from the works of Bertolini-Darmon and Iovita-Spiess, under the crucial assumption that the prime $p$ is unramified in $K$. We start in this article the systematic study of anticyclotomic $p$-adic $L$-functions when $p$ is ramified in $K$. In particular, when $f$ is a weight $2$ modular form attached to an elliptic curve $E/\mathbb{Q}$ having multiplicative reduction at $p$, and $p$ is ramified in $K$, we show an analogue of the exceptional zeroes phenomenon investigated by Bertolini-Darmon in the setting when $p$ is inert in $K$. More precisely, we consider situations in which the $p$-adic $L$-function $L_p(E/K)$ of $E$ over the anticyclotomic ${\mathbb{Z}}_p$-extension of $K$ does not vanish identically but, by sign reasons, has a zero at certain characters $\ddot{I}‡$ of the Hilbert class field of $K$. In this case we show that the value at $\ddot{I}‡$ of the first derivative of $L_p(E/K)$ is equal to the formal group logarithm of the specialization at $p$ of a global point on the elliptic curve (actually, this global point is a twisted sum of Heegner points). This generalizes similar results of Bertolini-Darmon, available when $p$ is inert in $K$ and $\ddot{I}‡$ is the trivial character.

18 pages