\usepackage{fontspec}
\setmainfont{Linux Libertine O}

\newcommand{\DUtitletitle}[1]{%
    {\begin{center}\textbf{\textsc{#1}}\end{center}}
 }

\setmonofont{Latin Modern Mono Light}
\newfontfamily\TitleFont
  {EB Garamond}
  [ Mapping=tex-text ]

\newfontfamily\AltFont[Mapping=tex-text]{Linux Libertine O}