This set of Physics notes seems to employ the standard LaTeX math font. However, in Eq. (2.29) the calligraphic D looks like the one from the eulervm package instead of the standard one:
What math font is this? If it is the standard math font how does one get this calligraphic D instead of the standard one?
It's a mixture of standard \mathcal and Euler Script:
\documentclass{article}
\usepackage{amsmath}
\usepackage[mathscr]{euscript}
\begin{document}
[
\langle\mathcal{O}\rangle=\int\mathscr{D}g\mathcal{O}[g]e^{-\mathcal{S}[g]}
]
\end{document}
(Sorry, but I just can't write the Euler constant upright.)
