Bounds on the number of lifts of a Brauer character in a p-solvable group

Abstract

The Fong-Swan theorem shows that for a $p$-solvable group $G$ and Brauer character $\phi \in \ibrg$, there is an ordinary character $\chi \in \irrg$ such that $\chi^0 = \phi$, where $^0$ denotes restriction to the $p$-regular elements of $G$. This still holds in the generality of $\pi$-separable groups \cite{bpi}, where $\ibrg$ is replaced by $\ipig$. For $\phi \in \ipig$, let $L_{\phi} = \{\chi \in \irrg \mid \chi^0 = \phi \}$. In this paper we give a lower bound for the size of $L_{\phi}$ in terms of the structure of the normal nucleus of $\phi$ and, if $G$ is assumed to be odd and $\pi = \{p' \}$, we give an upper bound for $L_{\phi}$ in terms of the vertex subgroup for $\phi$.