[Tex/LaTex] Setting math fonts in Beamer

Question

Is it possible to only change the math font in Beamer with XeLaTeX? The only partial solution I've been about to find is to create a new command:

\renewcommand\mathfamilydefault{\rmdefault}

The above command does essentially what I want, but it also strangely inserts characters (lmr) prior to maths. For example,

\mathfamilydefault{${x}_{ij} = -d_{k}/d_{0}$},

yields:

Answer 1

there is no need for using that macro inside your text. It is an internal definition and has the value lmr

\documentclass{beamer}
\renewcommand\mathfamilydefault{\rmdefault}

\begin{document}
\begin{frame}{foo}
${x}_{ij} = -d_{k}/d_{0}$
\end{frame}
\end{document}