For any large prime $q$, $x \leq 1$ and any real $k\geq 2$, we prove a lower bound for the following $2k$-th moment \begin{ equation*} \sum_{ \substack{ \chi \in X_q^*}} \Big| \sum_{ n\leq x} \chi(n)\lambda(n)\Big|^{ 2k}, \end{ equation*} where $X_q^*$ denotes the set of primitive Dirichlet characters modulo $q$ and $\lambda(n)$ the Fourier coefficients of a fixed modular form. The bound we obtain is sharp up to a constant factor under the generalized Riemann Hypothesis.
Categories: math.NT