You can try,
\DeclareMathSizes{10}{10.5}{7}{7}
the format of the command is:
\DeclareMathSizes {t-size} {mt-size} {s-size} {ss-size}
Basically, we instruct the use of a <mt-size> as the math text size, <s-size> as the script size and <ss-size> the scriptscript size to be used in math, when <t-size> is the current text size. You can adjust the parameters to suit. You can also find more information at http://tex.loria.fr/general/new/fntguide.html
You can also scale down the helvetica font if you wish
\usepackage[scaled=0.95]{helvet}
This is probably a better solution than scaling up the maths fonts.
When using the \DeclareMathSizes the first parameter for the text font must be exactly what is used in the class declaration. For example with Beamer rather declare \documentclass[10pt]{beamer},
otherwise the command will appear as it is not working. It is also normal when you declare math sizes to provide a range of math font sizes for all the text fonts:
\DeclareMathSizes{9.8}{17}{7}{7}
\DeclareMathSizes{10.0}{17}{7}{7}
\DeclareMathSizes{10.95}{10}{7}{7} % For size 10 text
\DeclareMathSizes{11}{19}{13}{9} % For size 11 text
\DeclareMathSizes{12}{20}{14}{10} % For size 12 text
You can test the above with the minimal example below, which is somewhat reduced from that originally posted:
\documentclass[10pt]{beamer}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
%main font Helevtica
\renewcommand{\familydefault}{\sfdefault}
\usepackage{helvet}
%prevent beamer from meddling with math fonts
\usefonttheme{professionalfonts}
%following lines borrowed from cmbright.sty
\DeclareSymbolFont {operators} {OT1}{cmbr}{m}{n}
\DeclareSymbolFont {letters} {OML}{cmbrm}{m}{it}
\SetSymbolFont {letters}{bold} {OML}{cmbrm}{b}{it}
\DeclareSymbolFont {symbols} {OMS}{cmbrs}{m}{n}
\DeclareMathAlphabet{\mathit} {OT1}{cmbr}{m}{sl}
\DeclareMathAlphabet{\mathbf} {OT1}{cmbr}{bx}{n}
\DeclareMathAlphabet{\mathtt} {OT1}{cmtl}{m}{n}
\DeclareMathAlphabet{\mathbold}{OML}{cmbrm}{b}{it}
\DeclareMathSymbol{\alpha}{\mathalpha}{letters}{11}
\DeclareMathSymbol{\beta}{\mathalpha}{letters}{12}
\DeclareMathSymbol{\gamma}{\mathalpha}{letters}{13}
\DeclareMathSymbol{\delta}{\mathalpha}{letters}{14}
\DeclareMathSymbol{\epsilon}{\mathalpha}{letters}{15}
\DeclareMathSizes{9.8}{17}{7}{7}
\DeclareMathSizes{10.0}{17}{7}{7}
\DeclareMathSizes{10.95}{10}{7}{7} % For size 10 text
\DeclareMathSizes{11}{19}{13}{9} % For size 11 text
\DeclareMathSizes{12}{20}{14}{10} % For size 12 text
\begin{document}
\begin{frame}
This is a test $ a^{2}+\gamma\sigma^{\epsilon}$
\fontsize{9.8pt}{13pt}\selectfont
This is a test $ a^{2}+\gamma\sigma^{\epsilon}$
%\fontsize{10pt}{13pt}\selectfont
This is a test $ a^{2}+\gamma\sigma^{\epsilon}$
\end{frame}
\end{document}
Try this. I created a command for mathpazo U as well, because it's easier to see the difference.
\documentclass{article}
\DeclareSymbolFont{pazoletters}{OML}{zplm}{m}{it}
\DeclareMathSymbol{\pazoT}{\mathalpha}{pazoletters}{"54}
\DeclareMathSymbol{\pazoU}{\mathalpha}{pazoletters}{"55}
\begin{document}
$U \pazoU$ $T \pazoT$
\end{document}
Best Answer
Use the
sansmathpackage.Credit to Herbert.