Zeros in the Character Tables of Symmetric Groups with an $\ell$-Core Index

Abstract

Let $\mathcal{C}_n =\left [\chi_{\lambda}(\mu)\right]_{\lambda, \mu}$ be the character table for $S_n,$ where the indices $\lambda$ and $\mu$ run over the $p(n)$ many integer partitions of $n.$ In this note we study $Z_{\ell}(n),$ the number of zero entries $\chi_{\lambda}(\mu)$ in $\mathcal{C}_n,$ where $\lambda$ is an $\ell$-core partition of $n.$ For every prime $\ell\geq 5,$ we prove an asymptotic formula of the form $$ Z_{\ell}(n)\sim \alpha_{\ell}\cdot \sigma_{\ell}(n+\delta_{\ell})p(n)\gg_{\ell} n^{\frac{\ell-5}{2}}e^{\pi\sqrt{2n/3}},$$ where $\sigma_{\ell}(n)$ is a twisted Legendre symbol divisor function, $\delta_{\ell}:=(\ell^2-1)/24,$ and $1/\alpha_{\ell}>0$ is a normalization of the Dirichlet $L$-value $L\left(\left(\frac{\cdot}{\ell}\right),\frac{\ell-1}{2}\right).$ For primes $\ell$ and $n>\ell^6/24,$ we show that $\chi_{\lambda}(\mu)=0$ whenever $\lambda$ and $\mu$ are both $\ell$-cores. Furthermore, if $Z^*_{\ell}(n)$ is the number of zero entries indexed by two $\ell$-cores, then for $\ell\geq 5$ we obtain the asymptotic $$ Z^*_{\ell}(n)\sim \alpha_{\ell}^2 \cdot \sigma_{\ell}( n+\delta_{\ell})^2 \gg_{\ell} n^{\ell-3}. $$