I am writing a two-column document and I have a problem with a section which produces an underfull box. What is the correct way (or some better ways) to typeset such a section so to have a beautiful output? This can be regarded as a general question as to what someone must do in such a case.
\documentclass{article}
\usepackage[top=0.7in, bottom=1.2in, left=0.8in, right=0.8in]{geometry}
\usepackage{parskip}
\setlength{\parindent}{0cm}
\usepackage{amsmath}
\usepackage{unicode-math}
\usepackage{fontspec}
\usepackage[greek,english]{babel}
\usepackage[fontsize=8pt]{scrextend}
\usepackage{multicol}
\setmainfont[Ligatures=TeX, Extension=.otf, UprightFont=*, BoldFont=*Bold, ItalicFont=*It, BoldItalicFont=*BoldIt, Mapping=tex-text]{GFSArtemisia}
\setsansfont[Mapping=tex-text]{GFSArtemisia.otf}
\setmathfont{latinmodern-math.otf}
\setmathfont[range=\varnothing]{Asana-Math.otf}
\setmathfont[range=\int]{latinmodern-math.otf}
\begin{document}
\selectlanguage{greek}
\begin{multicols*}{2}
\section{ΑΝΤΙΣΤΡΟΦΟΣ ΜΕΤΑΣΧΗΜΑΤΙΣΜΟΣ Ζ}
\end{multicols*}
\end{document}