Non-vanishing stable instability conjecture for complex projective spaces

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Let kk be a positive integer, and let Conf⁡nCPk\operatorname{Conf}^n\mathbb{C}P^k denote the configuration space of nn ordered distinct points in complex projective kk-space. Write Hi(−;Q)H^i(-;\mathbb{Q}) for rational cohomology. The conjecture asserts that there are positive integers n0n_0, csc_s, and ctc_t such that, for

n≥i−cs2⌈k/2⌉−2,n \geq \frac{i-c_s}{2\lceil k/2\rceil-2}, Hi(Conf⁡nCPk;Q)=Hi(Conf⁡n+1CPk;Q),H^i(\operatorname{Conf}^n\mathbb{C}P^k;\mathbb{Q})=H^i(\operatorname{Conf}^{n+1}\mathbb{C}P^k;\mathbb{Q}),

while for all n≥n0n\geq n_0 and i>(2⌈k/2⌉−2)n+csi>(2\lceil k/2\rceil-2)n+c_s,

Hi(Conf⁡nCPk;Q)≈Hi+2⌈k/2⌉−2(Conf⁡n+1CPk;Q).H^i(\operatorname{Conf}^n\mathbb{C}P^k;\mathbb{Q})\approx H^{i+2\lceil k/2\rceil-2}(\operatorname{Conf}^{n+1}\mathbb{C}P^k;\mathbb{Q}).

Moreover,

H(2⌈k/2⌉−2)n+ct(Conf⁡nCPk;Q)=H(2⌈k/2⌉−2)(n+1)+ct(Conf⁡n+1CPk;Q)=QH^{(2\lceil k/2\rceil-2)n+c_t}(\operatorname{Conf}^n\mathbb{C}P^k;\mathbb{Q})=H^{(2\lceil k/2\rceil-2)(n+1)+c_t}(\operatorname{Conf}^{n+1}\mathbb{C}P^k;\mathbb{Q})=\mathbb{Q}

for all n≥n0n\geq n_0, and

H(2⌈k/2⌉−2)n+j(Conf⁡nCPk;Q)=H(2⌈k/2⌉−2)(n+1)+j(Conf⁡n+1CPk;Q)=0H^{(2\lceil k/2\rceil-2)n+j}(\operatorname{Conf}^n\mathbb{C}P^k;\mathbb{Q})=H^{(2\lceil k/2\rceil-2)(n+1)+j}(\operatorname{Conf}^{n+1}\mathbb{C}P^k;\mathbb{Q})=0

for all n≥n0n\geq n_0 and j>ctj>c_t. Non-vanishing stable instability conjecture. For every positive integer kk, the stated stable range, shifted comparison, and top non-vanishing pattern hold. This extends the computed example for CP3\mathbb{C}P^3 and is proposed as a general form of non-vanishing stable instability for configuration-space cohomology.

References

Primary source

Megan Maguire, with Appendix by Matthew Christie and Derek Francour, “Computing cohomology of configuration spaces”, arXiv:1612.06314 (2016).

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