On Sharifi’s conjecture: Exceptional case

Abstract:

In the present article, we study the conjecture of Sharifi on the surjectivity of the map $\varpi _{\theta }$. Here $\theta$ is a primitive even Dirichlet character of conductor $Np$, which is exceptional in the sense of Ohta. After localizing at the prime ideal $\mathfrak {p}$ of the Iwasawa algebra related to the trivial zero of the Kubota–Leopoldt $p$-adic $L$-function $L_p(s,\theta ^{-1}\omega ^2)$, we compute the image of $\varpi _{\theta ,\mathfrak {p}}$ in a local Galois cohomology group and prove that it is an isomorphism. Also, we prove that the residual Galois representations associated to the cohomology of modular curves are decomposable after taking the same localization.