Kerning with parentheses

Question

Given the MWE below, one can see that the spacing around the parentheses is rather awkward. The opening parenthesis is too close to \cos and \sin, and too far away from the \omega. The closing parenthesis is too far away from \varphi. Is there a way to reduce/add some kerning?

\documentclass{standalone}

\usepackage[charter]{mathdesign}

\begin{document}
$ \mathrm{e}^{\,\mathrm{j}(\omega t + \varphi)} =\cos (\omega t + \varphi) + \mathrm{j}\sin (\omega t + \varphi) $
\end{document}

Update: of cource one can use \kern to add kerning, but I'm looking for a more general way.

Answer 1

If you wanted to automatically add some extra kerning to a glyph in text mode, then I'd tell you to look into microtype's \SetExtraKerning command. Unfortunately, that doesn't work in math mode. I think your best option is using the \mkern command made specifically to be used in math mode. Here's how it looks

\documentclass{standalone}
\usepackage[charter]{mathdesign}
\newcommand{\leftpar}{\mkern3mu(\mkern-3mu}
\newcommand{\rightpar}{\mkern-3mu)\mkern3mu}
\begin{document}
$ \mathrm{e}^{\,\mathrm{j} \leftpar \omega t + \varphi \rightpar} =\cos \leftpar\omega t + \varphi\rightpar + \mathrm{j}\sin \leftpar\omega t + \varphi\rightpar $
\end{document}

Where mu stands for math units and it's defined as 1/18 of em.