How to put \smallsmile or \smallfrown on top of a letter

Question

I would like to have a \smallsmile on top of a letter "T". Is there a way this can be done?

Answer 1

\stackrel

For example, \stackrel can be used:

\documentclass{article}
\usepackage{MnSymbol}% for \smallsmile and \smallfrown

\begin{document}
\[
  \mathord{\stackrel{\smallsmile}{T}}
  \neq
  \mathord{\stackrel{\smallfrown}{T}}
\]
\[
  \mathord{\mathop{T}\limits^{\smallsmile}}
  \neq
  \mathord{\mathop{T}\limits^{\smallfrown}}
\]
\end{document}

Text mode accents

\documentclass{article}
\usepackage{textcomp}% \newtie, \capitalbreve
\begin{document}
\u{T}, \capitalbreve{T} vs. \newtie{T}
\end{document}

Math mode accents

At least \smallsmile could be set as \breve accent:

\documentclass{article}

\begin{document}
\[
  \breve{T}
\]
\end{document}

Answer 2

Here's a possible way:

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}

\newcommand{\adjustedaccent}[1]{%
  \mathchoice{}{}
    {\mbox{\raisebox{-.5ex}[0pt][0pt]{$\scriptstyle#1$}}}
    {\mbox{\raisebox{-.35ex}[0pt][0pt]{$\scriptscriptstyle#1$}}}
}
\newcommand\smileacc[1]{\overset{\adjustedaccent{\smallsmile}}{#1}}
\newcommand\frownacc[1]{\overset{\adjustedaccent{\smallfrown}}{#1}}

\begin{document}
\[
\smileacc{T}\neq\frownacc{T}_{\smileacc{T}}
\]
\end{document}

It would be possible to add some horizontal shift, but it must be done manually depending on the letter the accent should go over.