The exact motivic formula conjecture for the cusp singularity

Let (X,p)(X,p) be the cusp singularity x2=y3x^2=y^3. For each d0d\geq 0, let NQd,X,pmot(t)\mathit{NQ}_{d,X,p}^\mathrm{mot}(t) denote the normalized local motivic quotient series, and let (a;q)n(a;q)_n and (a;q)(a;q)_\infty denote the finite and infinite qq-Pochhammer symbols. Define polynomials cj(q)c_j(q) by

j=0dcj(q)tj=(t;q)d.\sum_{j=0}^d c_j(q)t^j=(-t;q)_d.

The exact motivic formula conjecture.

NQd,X,pmot(t)=j=0dL(j+12)+j(dj)cj(L)t2j,\mathit{NQ}_{d,X,p}^\mathrm{mot}(t)=\sum_{j=0}^d \mathbb{L}^{\binom{j+1}{2}+j(d-j)}c_j(\mathbb{L})t^{2j},

and

Z^X,pmot(t)=1(L1t;L1)n=0Ln2t2n(L1;L1)n.\widehat{Z}_{X,p}^\mathrm{mot}(t)=\frac{1}{(\mathbb{L}^{-1}t;\mathbb{L}^{-1})_\infty}\sum_{n=0}^\infty\frac{\mathbb{L}^{-n^2}t^{2n}}{(\mathbb{L}^{-1};\mathbb{L}^{-1})_n}.

These formulas would give the first explicit motivic zeta-series formula for the cusp and imply the cusp case of the Cohen–Lenstra conjecture. The displayed identities are conjectural, despite consistency checks through d30d\leq 30.

Sources & referencesView supporting material

Primary source

Yifeng Huang and Ruofan Jiang, “Punctual Quot schemes and Cohen–Lenstra series of the cusp singularity”, arXiv:2305.06411 (2023).

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