Homological stability conjecture for spaces of polynomial maps

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Let XX be the variety and PP the data defining the spaces of maps Mor⁡d,P(A1,X)\operatorname{Mor}_{d,P}(\mathbb A^1,X), let K‾\overline K be an algebraic closure of the relevant base field, and let PConf⁡m\operatorname{PConf}_m denote the ordered configuration space of mm points. Assume

d⩾k−1⩾2,n>2k(k−1).d\geqslant k-1\geqslant 2,\qquad n>2^k(k-1).

Homological stability conjecture. The cohomology group

Hci+2d(n−k)(Mor⁡d,P(A1,X)K‾,Qℓ)H^{i+2d(n-k)}_c\left(\operatorname{Mor}_{d,P}(\mathbb A^1,X)_{\overline K},\mathbb Q_{\ell}\right)

is isomorphic to

⨁m⩾0(Hci+m(n−1)(PConf⁡m,Qℓ)⊗Hcn−1(XK‾,Qℓ)⊗m⊗sgn⁡n−1)Sm\bigoplus_{m\geqslant 0}\left(H^{i+m(n-1)}_c\left(\operatorname{PConf}_m,\mathbb Q_{\ell}\right)\otimes H^{n-1}_c\left(X_{\overline K},\mathbb Q_{\ell}\right)^{\otimes m}\otimes \operatorname{sgn}^{n-1}\right)^{S_m}

for

i>−4(⌊dk−1⌋(n2k−k+1)−1).i>-4\left(\left\lfloor\frac{d}{k-1}\right\rfloor\left(\frac{n}{2^k}-k+1\right)-1\right).

This conjecture predicts that the spectral sequence associated with the cohomology of these spaces degenerates on the first page for sufficiently large parameters, yielding a stable description of the cohomology. It is motivated by the role of homological stability in geometric approaches to analytic number theory; the source gives no resolution, so the conjecture remains open.

References

Primary source

Tim Browning and W. Sawin, “A geometric version of the circle method”, arXiv:1711.10451 (2020).

Additional references

4 papers in this index state this conjecture (2007–2017). The statement above is taken from the most recent of them; the others are arXiv:1209.2773, arXiv:1012.1433, arXiv:0709.2173.

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