Consider the following:
\documentclass[12pt,a4paper,oneside]{book}
\usepackage{amsfonts, graphicx, verbatim, mathtools,amssymb, amsthm, mathrsfs,amsmath}
\usepackage{multicol}
\begin{document}
\begin{multicols}{2}
\begin{itemize}
\item $\hat{\sigma}\triangleq \max \lbrace\sigma_1^2, \sigma_2^2, \sigma_4^2\rbrace$
\item $\hat{q}(z) \triangleq \max \lbrace q_1(z), q_2(z), q_4(z)\rbrace$
\item $\hat{\psi}_p(z)\triangleq [1+\hat{q}(z)]^p-1-p\hat{q}(z)$
\item $\zeta(z) \triangleq \max \lbrace\hat{\psi}_p(z), \check{\psi}_p(z) \rbrace$
\item$\kappa\triangleq \min\lbrace \mu+\rho+\xi, \mu+\alpha+\theta+\gamma-\eta, \eta \rbrace$
\item $\check{q}(z) \triangleq \min \lbrace q_1(z), q_2(z), q_4(z)\rbrace$
\item$\check{\psi}_p(z)\triangleq [1+\check{q}(z)]^p-1-p\check{q}(z)$
\item $\mho_p\triangleq \int_M \zeta(z)\nu(dz)$
\end{itemize}
\end{multicols}
\end{document}
How can I push the right hand side bullet points a little closer to the left ones?
