Al-Salam–Carlitz moment Pfaffian conjecture

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Let Un(a)(x;q)U_n^{(a)}(x;q) be the Al-Salam–Carlitz polynomials, and let Gn(a;q)=∑k=0n[nk]qakG_n(a;q)=\sum_{k=0}^n\left[{{n}\atop{k}}\right]_q a^k be their moment sequence, where [nk]q=(q;q)n(q;q)k(q;q)n−k\left[{{n}\atop{k}}\right]_q=\frac{(q;q)_n}{(q;q)_k(q;q)_{n-k}}. For n≥1n\geq1, set G−1(a;q)=0G_{-1}(a;q)=0. Al-Salam–Carlitz moment Pfaffian conjecture. The identities

Pf((qi−1−qj−1)Gi+j−3(a;q))1≤i,j≤2n=an(n−1)q13⌊n/2⌋(16⌊n/2⌋2−1)−(−1)n4⌊n/2⌋2−2⌊n/2⌋⋅⌊(n−1)/2⌋∏k=1n(q;q)2k−1,\mathop{\rm Pf}\biggl((q^{i-1}-q^{j-1})G_{i+j-3}(a;q)\biggr)_{1\leq i,j\leq 2n}=a^{n(n-1)}q^{\frac13\lfloor n/2\rfloor(16\lfloor n/2\rfloor^2-1)-(-1)^n4\lfloor n/2\rfloor^2-2\lfloor n/2\rfloor\cdot\lfloor (n-1)/2\rfloor}\prod_{k=1}^{n}(q;q)_{2k-1},

and

Pf((qi−1−qj−1)Gi+j−2(a;q))1≤i,j≤2n=an(n−1)q13⌊n/2⌋(16⌊n/2⌋2−1)−(−1)n4⌊n/2⌋2∏k=1n(q;q)2k−1∑k=0nq⌊(n−2k)2/2⌋[nk]q2ak\mathop{\rm Pf}\biggl((q^{i-1}-q^{j-1})G_{i+j-2}(a;q)\biggr)_{1\leq i,j\leq 2n}=a^{n(n-1)}q^{\frac13\lfloor n/2\rfloor(16\lfloor n/2\rfloor^2-1)-(-1)^n4\lfloor n/2\rfloor^2}\prod_{k=1}^{n}(q;q)_{2k-1}\sum_{k=0}^{n}q^{\lfloor (n-2k)^2/2\rfloor}\left[{{n}\atop{k}}\right]_{q^2}a^k

would hold, where ⌊x⌋\lfloor x\rfloor is the greatest integer not exceeding xx. These are experimentally supported Pfaffian evaluations for a qq-moment sequence; their status is left open.

References

Primary source

Masao Ishikawa, Hiroyuki Tagawa and Jiang Zeng, “Pfaffian decomposition and a Pfaffian analogue of q-Catalan Hankel determinants”, arXiv:1011.5941 (2010).

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