Make horizontal curly brace underlying parts of a equation so that I could write another formula under that part of specific equation

Question

How could I make horizontal curly brace underlying parts of a equation so that I could write another formula under that part of specific equation. PS: I do not want to add a text under the curly brace.

Here is my code:

 \[
 \tilde{Y}^I+\tilde{Y}^X =
 \biggl[\delta_Y \biggl(\Lambda_K \frac{\tilde{K}}{\mu}\biggr)^{-\rho Y} +  
    (1-\delta_Y )(\Lambda^T_l L^F)^{-\rho Y}
        \biggr]^{-1/\rho Y}-S_{YCZ} \tilde{C}^H - 
 \underbrace{\frac{S_{GCF}}{1-S_{GCF}}\tilde{C}^H}_\text{\tilde{C}^{G}} 
 \]

What I want to get:

Answer 1

You have errors in \underbrace command. Correct is:

\documentclass{article}
\usepackage{mathtools}

\begin{document}
 \[
 \tilde{Y}^I+\tilde{Y}^X = 
    \biggl[\delta_Y \biggl(\Lambda_K \frac{\tilde{K}}{\mu}\biggr)^{-\rho Y} + 
            (1-\delta_Y )(\Lambda^T_l L^F)^{-\rho Y}
           \biggr]^{-1/\rho Y}-S_{YCZ} \tilde{C}^H -
    \underbrace{\frac{S_{GCF}}{1-S_{GCF}}\tilde{C}^H}_{\tilde{C}^{G}}\,,
 \]
 \end{document}