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Zeros in Tables of Characters for the Groups $S_n$ and $A_n$. II
V. A. Belonogov Institute of Mathematics and Mechanics, Ural Branch of the Russian Academy of Sciences
Abstract:
Let
$P(n)$ be the set of all partitions of a natural number
$n$. In the representation theory of symmetric groups, for every partition
$\alpha\in P(n)$, the partition
$h(\alpha)\in P(n)$ is defined so as to produce a certain set of zeros in the character table for
$S_n$. Previously, the analog
$f(\alpha)$ of
$h(\alpha)$ was obtained pointing out an extra set of zeros in the table mentioned. Namely,
$h(\alpha)$ is greatest (under the lexicographic ordering
$\le$) of the partitions
$\beta$ of
$n$ such that
$\chi^\alpha(g_\beta)\ne0$, and
$f(\alpha)$ is greatest of the partitions
$\gamma$ of
$n$ that are opposite in sign to
$h(\alpha)$ and are such that
$\chi^\alpha(g_\gamma)\ne0$, where
$\chi^\alpha$ is an irreducible character of
$S_n$, indexed by
$\alpha$, and
$g_\beta$ is an element in the conjugacy class of
$S_n$, indexed by
$\beta$. For
$\alpha\in P(n)$, under some natural restrictions, here, we construct new partitions
$h'(\alpha)$ and
$f'(\alpha)$ of
$n$ possessing the following properties.
(A) Let
$\alpha\in P(n)$ and
$n\geqslant 3$. Then
$h'(\alpha)$ is identical is sign to
$h(\alpha)$,
$\chi^\alpha(g_{h'(\alpha)})\ne0$, but
$\chi^\alpha(g_\gamma)=0$ for all
$\gamma\in P(n)$ such that the sign of
$\gamma$ coincides with one of
$h(\alpha)$,
and
$h'(\alpha)<\gamma<h(\alpha)$.
(B) Let
$\alpha\in P(n)$,
$\alpha\ne\alpha'$, and
$n\geqslant4$. Then
$f'(\alpha)$ is identical in sign to
$f(\alpha)$,
$\chi^\alpha(g_{f'(\alpha)})\ne0$, but
$\chi^\alpha(g_\gamma)=0$ for all
$\gamma\in P(n)$ such that the sign of
$\gamma$ coincides with one of
$f(\alpha)$, and
$f'(\alpha)<\gamma<f(\alpha)$. The results obtained are then applied to study pairs of semiproportional irreducible characters in
$A_n$.
Keywords:
symmetric group, alternating group, character table of a group.
UDC:
512.54 Received: 07.02.2005