I don't think so. When you write
\underbrace{something}_{xyz}
it's "xyz" that appears in a smaller font, since it is typeset just
like subscripts; if you really want "xyz" to appear in normal size
type
\underbrace{something}_{\textstyle xyz}
The final result seems questionable.
Ciao
Enrico
Oops. Sorry yes my explanation was incomplete. You got what I meant. Thanks
a lot!