On the coefficients of symmetric power $L$-functions

We study the signs of the Fourier coefficients of a newform. Let $f$ be a normalized newform of weight $k$ for ${\mathrm{\Gamma }}_0(N)$. Let $a_f(n)$ be the $n$th Fourier coefficient of $f$. For any fixed positive integer $m$, we study the distribution of the signs of $\{a_f(p^m){\}}_p$, where $p$ runs over all prime numbers. We also find out the abscissas of absolute convergence of two Dirichlet series with coefficients involving the Fourier coefficients of cusp forms and the coefficients of symmetric power $L$-functions.