The presentation conjecture for the even subalgebra of the TAMA

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Let U(so(n))U(\mathfrak{so}(n)) be the universal enveloping algebra, and let O0‾\mathfrak{O}_{\overline{0}} denote the even subalgebra of the TAMA. For a sequence A=(a1,a2,a3,a4)A=(a_1,a_2,a_3,a_4) of four distinct indices, write

XA=Xa1a2Xa3a4+Xa1a3Xa4a2+Xa1a4Xa2a3,X_A=X_{a_1a_2}X_{a_3a_4}+X_{a_1a_3}X_{a_4a_2}+X_{a_1a_4}X_{a_2a_3},

where Xij=Eij−Eji∈U(so(n))X_{ij}=E_{ij}-E_{ji}\in U(\mathfrak{so}(n)). Let II be the ideal in the exact sequence

0→I→U(so(n))→O0‾→0.0\to I\to U(\mathfrak{so}(n))\to\mathfrak{O}_{\overline{0}}\to0.

For sequences A=(a1,a2,a3,a4)A=(a_1,a_2,a_3,a_4) and B=(b1,b2,b3,b4)B=(b_1,b_2,b_3,b_4) of four distinct indices, and with T\mathcal{T} defined as in the source, the presentation conjecture for the even subalgebra of the TAMA. The ideal II is generated by the elements

∑σ∈Tσ(XAXB+∑(a,b)⊂A∩BXA∖(a,b)XB∖(a,b))−12δA,B,\sum_{\sigma\in\mathcal{T}}\sigma\left(X_AX_B+\sum_{(a,b)\subset A\cap B}X_{A\setminus(a,b)}X_{B\setminus(a,b)}\right)-12\delta_{A,B},

and consequently

O0‾≅U(so(n))/⟨∑σ∈Tσ(XAXB+∑(a,b)⊂A∩BXA∖(a,b)XB∖(a,b))−12δA,B⟩.\mathfrak{O}_{\overline{0}}\cong U(\mathfrak{so}(n))\bigg/\left\langle\sum_{\sigma\in\mathcal{T}}\sigma\left(X_AX_B+\sum_{(a,b)\subset A\cap B}X_{A\setminus(a,b)}X_{B\setminus(a,b)}\right)-12\delta_{A,B}\right\rangle.

This conjecture proposes an explicit presentation of the even TAMA in terms of generators and relations; the supplied text gives no evidence that the presentation has been proved or disproved.

References

Primary source

Kieran Calvert, Marcelo De Martino and Roy Oste, “On angular momentum algebras and their relations”, arXiv:2508.18454 (2025).

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