R markdown won't compile a piece of LaTeX code - r

Question

I have the following piece of code, which I would like to run I R markdown. I have tried to run it in a LaTeX compiler, which works absolutely fine. But when I add it into R markdown it won't compile the piece of code.
---
title: "Titre"
date: Fecha
output:
pdf_document:
keep_tex: true
includes:
in_header: mystyle.sty
---
\begin{table}[!htbp] \centering
\caption{}
\label{}
\begin{tabular}{#{\extracolsep{5pt}}lD{.}{.}{-3} }
\\[-1.8ex]\hline
\hline \\[-1.8ex]
& \multicolumn{1}{c}{\textit{Dependent variable:}} \\
\cline{2-2}
\\[-1.8ex] & \multicolumn{1}{c}{mpg} \\
\hline \\[-1.8ex]
cyl & -2.876^{***} \\
& (0.322) \\
& \\
Constant & 37.885^{***} \\
& (2.074) \\
& \\
\hline \\[-1.8ex]
Observations & \multicolumn{1}{c}{32} \\
R$^{2}$ & \multicolumn{1}{c}{0.726} \\
Adjusted R$^{2}$ & \multicolumn{1}{c}{0.717} \\
Residual Std. Error & \multicolumn{1}{c}{3.206 (df = 30)} \\
F Statistic & \multicolumn{1}{c}{79.561$^{***}$ (df = 1; 30)} \\
\hline
\hline \\[-1.8ex]
\textit{Note:} & \multicolumn{1}{r}{$^{*}$p$<$0.1; $^{**}$p$<$0.05; $^{***}$p$<$0.01} \\
\end{tabular}
\end{table}
The file mystyle.sty contains the following
\usepackage{dcolumn}
\newcolumntype{d}[1]{D{.}{.}{#1}}
\usepackage{booktabs}
\newcommand{\mc}[1]{\multicolumn{1}{c}{#1}} % handy shortcut macro
\usepackage{verbatim}
Are there someone who can explain why R markdown can't compile what's above?

Answer 1

By adding the table code line by line and recompiling each time, I isolated the problem to the lines with carets, e.g. the line that reads cyl & -2.876^{***} \\.
I was able to compile the document by enclosing the superscripted part in two $ signs, i.e.
cyl & -2.876$$^{***}$$ \\
(I don't know why you need two, rather than just one, $.)
This compiles just fine:
---
title: "Titre"
date: Fecha
output:
pdf_document:
keep_tex: true
includes:
in_header: mystyle.sty
---
\begin{table}[!htbp] \centering
\begin{tabular}{#{\extracolsep{5pt}}lD{.}{.}{-3} }
\\[-1.8ex]\hline
\hline \\[-1.8ex]
& \multicolumn{1}{c}{\textit{Dependent variable:}} \\
\cline{2-2}
\\[-1.8ex] & \multicolumn{1}{c}{mpg} \\
\hline \\[-1.8ex]
cyl & -2.876$$^{***}$$ \\
& (0.322) \\
& \\
Constant & 37.885$$^{***}$$ \\
& (2.074) \\
& \\
\hline \\[-1.8ex]
Observations & \multicolumn{1}{c}{32} \\
R$^{2}$ & \multicolumn{1}{c}{0.726} \\
Adjusted R$^{2}$ & \multicolumn{1}{c}{0.717} \\
Residual Std. Error & \multicolumn{1}{c}{3.206 (df = 30)} \\
F Statistic & \multicolumn{1}{c}{79.561$^{***}$ (df = 1; 30)} \\
\hline
\hline \\[-1.8ex]
\textit{Note:} & \multicolumn{1}{r}{$^{*}$p$<$0.1; $^{**}$p$<$0.05; $^{***}$p$<$0.01} \\
\end{tabular}
\end{table}