# Symbol for qft derivative

I searched a bit on the internet, but I could not find any answer. Studying quantum field theory and Dirac equation I had to write this symbol $\overset{\leftarrow}{\partial}$, but the problem is that there is so much vertical space between the arrow and the derivative symbol, so much that I cannot insert the whole of it in the middle of an argument, because it ruins the spacing between lines. I looked in physics,amsmath and other packages, but I cannot find any implementation of this symbol, so I'm asking myself if there is any somewhere, or at least how can I solve the vertical spacing problem (should I define a new symbol by myself?). Thanks

• Couldn't \vec{\partial} be used? – Bernard Sep 14 '20 at 9:49
• I'm exactly looking for something like this, but with the arrow pointing left! – Rob Tan Sep 14 '20 at 9:50
• Oops! I didn't notice \LEFTarrow. – Bernard Sep 14 '20 at 9:53
• Maybe I found a temporary solution thanks to you! With the '\vec' suggestion I checked this tex.stackexchange.com/questions/15010/… and found the answer from egreg very useful (following instead the first answer the arrow was misaligned to the symbol). I still wait anyway if someone has a complete answer, but for the moment I can work with this, so thanks for the suggestion! – Rob Tan Sep 14 '20 at 9:55

You can remove the vertical space between the (smaller) arrow and the \partial symbol.

This only works for text size, so not in subscripts or superscripts: if needed it can be made to work also in those cases.

\documentclass{article}
\usepackage{amsmath}

\usepackage{lipsum}

\newcommand{\qftder}{%
\mathord{%
\vbox{\offinterlineskip
\ialign{\hfil##\cr$\scriptscriptstyle\leftarrow$\cr$\partial$\cr}
}%
}%
}

\begin{document}

\lipsum*[1][1-3] $\qftder$ \lipsum[2][1-3]

\end{document}


• That's great! Thanks a lot egreg. I didn't understand the phrase "This only works for text size, so not in subscripts or superscripts", what do you mean with this? – Rob Tan Sep 14 '20 at 10:16
• And also another question: in your answer that I cited in the link, you define a '\cev' command that seems to be quite universal, while in this case you are defining a specific "object" that is '\qftder', am I right? Sorry for the dumbness I just want to understand the way code works – Rob Tan Sep 14 '20 at 10:18
• @Rob I hope you don't have \frac{\qftder X}{2} inside normal text or X_{\qftder Y}. – egreg Sep 14 '20 at 10:18
• @Rob You're better in searching than I. ;-) I remembered something like that and possibly \cev is what you need. – egreg Sep 14 '20 at 10:20
• @Rob I meant something like text $\frac{\qftder X}{2}$ other text – egreg Sep 14 '20 at 10:27

You have a recent dedicated package: letterswitharrows .

\documentclass{article}
\usepackage{amssymb}
\usepackage{letterswitharrows}

\begin{document}
$\arrowoverset*\partial$%

\end{document}


• That's great too thanks! – Rob Tan Sep 14 '20 at 10:19
• Just a curiosity, if you know: why in your opinion is this not implemented in 'physics' package? In quantum field theory these kind of symbols seem to be used a lot! – Rob Tan Sep 14 '20 at 10:27
• Sorry, I'm only a mathematician and I have no idea. This package, it seems, fills a gap. – Bernard Sep 14 '20 at 10:34
• Okay just if you knew. Thanks, I will try the package! – Rob Tan Sep 14 '20 at 10:35
• Note the position of the arrow takes into account the italic angle of the symbol. – Bernard Sep 14 '20 at 10:37

There is also another alternative using a rare package named halloweenmath with the command \overscriptleftarrow{...}.

\documentclass[a4paper,12pt]{article}
\usepackage{halloweenmath}
\begin{document}
Today is not halloween :-) $\overscriptleftarrow{\partial}$!
\end{document}


• Yes I saw it somewhere, I didn't know there was type of command just there! Thanks – Rob Tan Sep 15 '20 at 7:12