When I write $\chi_V$ the subscript outputs too high for my taste. Is there a way I can set the vertical position of subscripts for the whole document?
Many thanks
When I write $\chi_V$ the subscript outputs too high for my taste. Is there a way I can set the vertical position of subscripts for the whole document?
Many thanks
I interpret the objective of your posting as wishing to modify (specifically, increase) the math subscript offset for all subscripts in the entire document.
If this interpretation is correct, the following LuaLaTeX-based solution may be of interest to you. It works by modifying the "primitive" length parameter \Umathsubshiftdown. For a document set in 10pt ("10 point") font size, the default value of this parameter is 1.5pt; in the example below, I suggest using a value of 2.5pt.

% !TEX TS-program = lualatex
\documentclass{article}
\begin{document}
$\chi_V \ a_i$ --- default
% change the parameter "\Umathsubshiftdown"
\Umathsubshiftdown\textstyle=2.5pt
\Umathsubshiftdown\displaystyle=2.5pt
$\chi_V \ a_i$ --- modified \texttt{\textbackslash Umathsubshiftdown}
\end{document}
\chiwith a superscript? If not, then you could do\let\oldchi\chi\renewcommand{\chi}{\oldchi^{}}; this inserts a blank superscript, shifting the subscript down slightly which might suit you better. – Werner Apr 09 '15 at 21:55\chi? – Werner Apr 09 '15 at 22:25