[Tex/LaTex] \colon like symbol with circles instead of dots

Question

This is what i want to write:

And this is my attempt:

:X^{\mu}(z,‎\bar{z}) X^{\nu_{n}}(z^{\prime},‎\bar{z}^{\prime}):

Actually I don't know the command I must write for

.

Answer 1

The fdsymbol font provides a suitable \smallcirc symbol, but it needs to be scaled.

\documentclass{article}
\usepackage{amsmath}

\DeclareFontFamily{U}{FdSymbolA}{}
\DeclareFontShape{U}{FdSymbolA}{m}{n}{
    <-> s*[.28] FdSymbolA-Regular
}{}
\DeclareSymbolFont{fdsymbol}{U}{FdSymbolA}{m}{n}
\DeclareMathSymbol{\smallcirc}{\mathord}{fdsymbol}{"60}

\makeatletter
\newcommand{\hollowcolon}{\mathpalette\hollow@colon\relax}
\newcommand{\hollow@colon}[2]{%
  \mspace{1mu}%
  \vbox{%
    \hbox{$\m@th#1\smallcirc$}
    \nointerlineskip
    \kern.45ex
    \hbox{$\m@th#1\smallcirc$}
    \kern-.06ex
  }%
  \mspace{1mu}%
}
\makeatother

\newcommand{\hcolondel}[1]{%
  \mathopen{\hollowcolon}#1\mathclose{\hollowcolon}%
}
\newcommand{\colondel}[1]{%
  \mathopen{:}#1\mathclose{:}%
}

\begin{document}
\begin{gather*}
\hcolondel{X^{\mu}(z,\bar{z}) X^{\nu_{n}}(z^{\prime},\bar{z}^{\prime})}_{a+\hcolondel{Z}}
\\
\colondel{X^{\mu}(z,\bar{z}) X^{\nu_{n}}(z^{\prime},\bar{z}^{\prime})}_{a+\colondel{Z}}
\end{gather*}

\end{document}