Further results for classical and universal characters twisted by roots of unity

We revisit factorizations of classical characters under various specializations, some old and some new. We first show that all characters of classical families of groups twisted by odd powers of an even primitive root of unity factorize into products of characters of smaller groups. Motivated by conjectures of Wagh and Prasad (Manuscr. Math. 2020), we then observe that certain specializations of Schur polynomials factor into products of two characters of other groups. We next show, via a detour through hook Schur polynomials, that certain Schur polynomials indexed by staircase shapes factorize into linear pieces. Lastly, we consider classical and universal characters specialized at roots of unity. One of our results, in parallel with Schur polynomials, is that universal characters take values only in ${0, \pm 1, \pm 2}$ at roots of unity.

💡 Research Summary

The paper investigates factorization phenomena for classical and universal characters of the classical Lie groups when the variables are twisted by roots of unity, focusing on odd powers of an even primitive root. The authors first prove that for any even order t and a primitive t‑th root ω, the characters of GL(n), SO(2n+1), Sp(2n) and O(2n) evaluated at (x, ωx, …, ω^{t‑1}x) are non‑zero precisely when the t‑core of the indexing partition λ is empty. In that case the character splits into a product of characters indexed by the t‑quotient λ(i). Explicitly for GL(tn) one has
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