You need the latex file to use `\usepackage[utf8x]{inputenc}` rather than the default `\usepackage[utf8]{inputenc}`.  This works with standard (pdf)latex.

For org export to generate this you have to set the variable `org-latex-inputenc-alist` accordingly.  For example:

    (setq org-latex-inputenc-alist '(("utf8" . "utf8x")))

For the variable to be defined, you may need to `(require 'ox-latex)` first. 


Unfortunately, this does support only a limited set of math letters. Much more can be supported by including `\usepackage[mathletters]{ucs}`. This has to appear before the `inputenc` stuff, so you can't just use a `#+latex_header:`.  A way to do that is to add it at head  of `org-latex-default-packages-alist`.

    (setq org-latex-default-packages-alist (cons '("mathletters" "ucs" nil) org-latex-default-packages-alist))

Note that `ucs` documentation (usually available through `texdoc ucs`) warns about the `mathletters` option:

>  This option is disabled by default, because using math greek in a normal text does not look good.

If you want those settings to apply only to the current file rather than globally, you can define them as [file local variables][1]. Add the following near the end of the file:

    # Local Variables:
    # org-latex-inputenc-alist: (("utf8" . "utf8x"))
    # eval: (setq org-latex-default-packages-alist (cons '("mathletters" "ucs" nil) org-latex-default-packages-alist))
    # End:

`eval` is a pseudo variable allowing to execute lisp code when the file is loaded.


  [1]: https://www.gnu.org/software/emacs/manual/html_node/emacs/Specifying-File-Variables.html#Specifying-File-Variables