Published online by Cambridge University Press: 26 April 2017
We study the $1$-level density of low-lying zeros of Dirichlet
$L$-functions attached to real primitive characters of conductor at most
$X$. Under the generalized Riemann hypothesis, we give an asymptotic expansion of this quantity in descending powers of
$\log X$, which is valid when the support of the Fourier transform of the corresponding even test function
$\unicode[STIX]{x1D719}$ is contained in
$(-2,2)$. We uncover a phase transition when the supremum
$\unicode[STIX]{x1D70E}$ of the support of
$\widehat{\unicode[STIX]{x1D719}}$ reaches
$1$, both in the main term and in the lower order terms. A new lower order term appearing at
$\unicode[STIX]{x1D70E}=1$ involves the quantity
$\widehat{\unicode[STIX]{x1D719}}(1)$, and is analogous to a lower order term which was isolated by Rudnick in the function field case.