Are there any symbol to make a half-space in MathJax? half the size of $\text{\,}$ approx $\text{\kern 0.08333em}$ ?
If I write jointly the letter $\rho$ with the "letter C with undertext letter D" $C_D$, and then the letters $A$ and letter $v$ (as for the formula of the Drag force), the result is $\rho C_D A v$ where the letter D ends being too far from the letter C compared with the position of $\rho$, as it where one different symbol $\rho C$ instead.
To separate them I introduced a space with $\text{\,}$ ending in $\rho \,C_D A v$, but due the proximity between letters $A$ and $v$ now looks like $\rho$ is a little far away, so I have the doubt if there exist a "half-space" symbol but I didn't found anything yet that do the trick.
I tried also with $\text{\;\!}$ with the following result $\rho \;\!C_D Av$ which looks better, but following what is said here:
$\begin{array}{l} \text{\,} = 3\,\text{mu} \\ \text{\:} = 4\,\text{mu} \\ \text{\;} = 5\,\text{mu} \\ \text{\!} = -3\,\text{mu} \\ \Rightarrow \text{\;\!} = 2\,\text{mu} \neq 1.5\,\text{mu}\,\text{(half space \,)} \end{array}$
so is not exactly half-space so maybe there is a symbol through it could be improved.
Added later
I found later the following:
$\begin{array}{l} \text{\negmedspace} = -4\,\text{mu}\\ \Rightarrow \text{\;\negmedspace} = 1\,\text{mu} \neq 1.5\,\text{mu}\,\text{(half space \,)} \end{array}$
which also isn't a half-space, but introduce a spacing of $1\,\text{mu}$ so it looks better (similar with the specing between letters $A$ and $v$): $$\rho \;\negmedspace C_D A v$$
2nd added later
Following the answer by @PeterPhipps it is possible to define the horizontal spacing at will, for example at half-space through $\text{\hspace{0.08333em}}$, which ends by looking as: $$\begin{array}{l l} \text{original - no spacing} & \rho C_D A v \\ \text{standard - \, spacing} & \rho\, C_D A v \\ \text{using \hspace{0.08333em}} & \rho\hspace{0.08333em} C_D A v \\ \text{using \;\negmedspace} & \rho\;\negmedspace C_D A v \\ \text{using \;\!} & \rho\;\! C_D A v \\ \end{array}$$
Looks like all also works on LaTex, but with \hspace
there is a risk of having your formulas splitted at mid terms if a change of line happened, so instead you should use the following: \hspace*{0.08333em}