I'm trying to create a diagram using \xymatrix but cannot find a way to get rid of the excess vertical space above \vdots - does anyone have any suggestions?
\documentclass[10pt,a4paper,twoside]{article}
\usepackage{amsmath, amssymb}
\usepackage{amsthm}
\input xy
\xyoption{all}
\begin{document}
\[
\xymatrix @R=1pc @C=2.5pc{
B_t(\zeta) \ar@{-}[d] \\
\vdots \ar@{-}[d] \\
B_2(\zeta) \ar@{-}[d] \\
B_1(\zeta) \ar@{-}[d] \\
F(\zeta) \ar@{-}[d] \\
F }
\]
\end{document}