On the distribution of positive and negative values of Hardy's $Z$-function

Abstract

We investigate the distribution of positive and negative values of Hardy's function $$ Z(t) := \zeta(1/2+it){\chi(1/2+it)}^{-1/2}, \quad \zeta(s) = \chi(s)\zeta(1-s). $$ In particular we prove that $$ \mu\bigl(I_{+}(T,T)\bigr) \;\gg T\; \qquad \hbox{and}\qquad \mu\bigl(I_{-}(T, T)\bigr) \; \gg \; T, $$ where $\mu(\cdot)$ denotes the Lebesgue measure and \begin{align*} { I}_+(T,H) &\;=\; \bigl\{T< t\le T+H\,:\, Z(t)>0\bigr\}, { I}_-(T,H) &\;=\; \bigl\{T< t\le T+H\,:\, Z(t)<0\bigr\}. \end{align*}