Q-polynomial expansion for Brézin-Gross-Witten tau-function

In this paper, we prove a conjecture of Alexandrov that the generalized Brézin-Gross-Witten tau-functions are hypergeometric tau functions BKP hierarchy after re-scaling. particular, shows original BGW tau-function, which has enumerative geometric interpretations, can be represented as linear combination Schur Q-polynomials with simple coefficients.