According to the Org mode manual, the dollar sign $ is treated as math delimiters in the following cases.

  • The enclosed text contains at most two line breaks.
  • The enclosed text is directly attached to the $ characters with no whitespace between.
  • The closing $ is followed by whitespace or punctuation.

For example, the dollar signs in $\alpha$-th will be escaped as \$ when it is exported to LaTeX document, just because the closing $ is not followed by a whitespace or punctuation. N.B. The hyphen character - is not treated as punctuation by Org mode.

Therefore, the safest way is to use \(...\) for inline math delimiters in Org mode.