Math kerning in Beamer with XeLaTeX vs. PDFLaTeX

Question

Consider this minimal example:

\documentclass{beamer}

\usefonttheme[onlymath]{serif}

\begin{document}
  $fft$
\end{document}

With PDFLaTeX, it turns out as expected:

If I compile with XeLaTeX, however, the kerning is very different:

If I use the article class, it is always the first variant. If I use beamer with the lmodern package in XeLaTeX (which I am not supposed to do, as I understand), it also turns out right again.

How can this different behavior be explained, and what is the correct way to make sure that I always get the first variant? I am using Debian stretch with TeX Live package version 2016.20170123-5.

(Note: I know that I should use \mathit to name multi-letter variables.)

Weirdly, on an older installation with Debian jessie and TeX Live 2014.20141024-2+deb8u1, also get the second variant with PDFLaTeX and lmodern, but I do not get the first variant with XeLaTeX and lmodern.

See https://github.com/josephwright/beamer/issues/375#issuecomment-285613180 — Ulrike Fischer, May 15 '18 at 13:17
Possible duplicate of https://tex.stackexchange.com/questions/132835/fontspec-mathspec-ruins-my-parentheses-with-beamer ??? — samcarter_is_at_topanswers.xyz, May 15 '18 at 13:44
I'm not sure if it's a duplicate, as I cannot reproduce the other thread. For me, it produces the bad result with and without fontspec. — Sören Schulze, May 16 '18 at 09:57

score 1 · Accepted Answer · answered May 15 '18 at 13:16

1

Workaround:

\documentclass{beamer}

\usefonttheme{professionalfonts}
\usefonttheme[onlymath]{serif}

\begin{document}
  $fft$
\end{document}

answered May 15 '18 at 13:16

samcarter_is_at_topanswers.xyz

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Math kerning in Beamer with XeLaTeX vs. PDFLaTeX

1 Answers1