TITLE: Nonnegativity of the quadratic Dirichlet L-function $L(\tfrac{1}{2},\chi)$ under GRH
QUESTION [7 upvotes]: I have been looking for a proof of the statement:
"Assume the Generalized Riemann Hypothesis. Let $d$ be a fundamental discriminant and $\chi_d$ the associated primitive quadratic character. Then, $$L(\tfrac{1}{2},\chi_d)\geq 0."$$
Can anyone point me in the right direction or give a reference? Thanks a lot!

REPLY [7 votes]: For real $s$, $L(s,\chi_d)$ is real, and it is certainly positive for
large $s$. It is nonzero for $s>1$ by the Euler product and $L(1,\chi_d)\ne0$.
If $L(1/2,\chi_s)<0$ what would happen for some $1/2<s<1$?