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Half-turn symmetric alternating sign matrices and Tokuyama type factorisation for orthogonal group characters

Half turn symmetric alternating sign matrices (HTSASMs) are special variations of the well-known alternating sign matrices which have a long and fascinating history. HTSASMs are interesting combinatorial objects in their own right and have been the focus of recent study. Here we explore counting weighted HTSASMs with respect to a number of statistics to derive an orthogonal group version of Tokuyama's factorisation formula, which involves a deformation and expansion of Weyl's denominator formula multiplied by a general linear group character. Deformations of Weyl's original denominator formula to other root systems have been discovered by Okada and Simpson, and it is thus natural to ask for versions of Tokuyama's factorisation formula involving other root systems. Here we obtain such a formula involving a deformation of Weyl's denominator formula for the orthogonal group multiplied by a deformation of an orthogonal group character.