Conjecture on twisted L-groups and Q-groups from algebraic Wu classes

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Let (B∗,β)(B_*,\beta) be a chain bundle with algebraic Wu class v^2k(β)\widehat v_{2k}(\beta), and let ev⁡\operatorname{ev} denote evaluation on homology. Let Σ\Sigma, Σ8\Sigma_8, Λ\Lambda, Coker⁡\operatorname{Coker}, Q−Q^-, and ι1\iota_1 be the constructions defined in the source. Conjecture on twisted groups. If (B∗,β)(B_*,\beta) is (2k−1)(2k-1)-connected, then

L4k(B∗,β)≅W0(Qβ(2k))≅Σ(ev⁡(v^2k(β)))L^{4k}(B_*,\beta)\cong W_0(Q_\beta(2k))\cong\Sigma\bigl(\operatorname{ev}(\widehat v_{2k}(\beta))\bigr)

and

Q4k(B∗,β)≅Σ8(ev⁡(v^2k(β))).Q_{4k}(B_*,\beta)\cong\Sigma_8\bigl(\operatorname{ev}(\widehat v_{2k}(\beta))\bigr).

If (B∗,β)(B_*,\beta) is (2k−2)(2k-2)-connected and ev⁡(v^2k(β))=0\operatorname{ev}(\widehat v_{2k}(\beta))=0, then [vQβ(2k−1)′]=v^2k(β)[v'_{Q_\beta(2k-1)}]=\widehat v_{2k}(\beta) and

L4k−2(B∗,β)≅W0(Qβ(2k−1))≅Λ(vQβ(2k−1)′)L^{4k-2}(B_*,\beta)\cong W_0(Q_\beta(2k-1))\cong\Lambda(v'_{Q_\beta(2k-1)})

and

Q4k−2(B∗,β)≅Coker⁡(Λ(ι1)→Λ(vQβ(2k−1)′)).Q_{4k-2}(B_*,\beta)\cong\operatorname{Coker}\bigl(\Lambda(\iota_1)\to\Lambda(v'_{Q_\beta(2k-1)})\bigr).

If instead (B∗,β)(B_*,\beta) is (2k−2)(2k-2)-connected and ev⁡(v^2k(β))≠0\operatorname{ev}(\widehat v_{2k}(\beta))\neq0, then Qβ(2k−1)≅Q−⊕H2k−1(B∗)Q_\beta(2k-1)\cong Q^-\oplus H_{2k-1}(B_*) and

L4k−2(B∗,β)≅Q4k−2(B∗,β)≅W0(Qβ(2k−1))≅Λ(H2k−1(B∗))L^{4k-2}(B_*,\beta)\cong Q_{4k-2}(B_*,\beta)\cong W_0(Q_\beta(2k-1))\cong\Lambda(H_{2k-1}(B_*))

The conjecture is presented as a consequence of the preceding conjecture, the proposition computing quasi-Wu classes, and the theorem computing Witt groups; the source supplies no resolution.

References

Primary source

Diarmuid Crowley and Csaba Nagy, “The Witt groups of extended quadratic forms over Z”, arXiv:2404.09189 (2026).

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