Direct-summand conjecture for the non-standard level modules

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Let 0<∣m∣≤20<|m|\leq 2. Let U(m)U(m) be the maximal submodule from Theorem, let V(m)=VΛmV(m)=V^{\Lambda_m} when U(m)={0}U(m)=\{0\}, and write Y(m)−Y(m)_- and Y(m)+Y(m)_+ for the lowest- and highest-weight parts of the quotient Y(m)=Fib(m)/V(m)Y(m)={\mathcal F}ib(m)/V(m). Then Fib(m){\mathcal F}ib(m) is the level-mm module for the rank 2 hyperbolic subalgebra Fib{\mathcal F}ib.

Direct-summand conjecture. For 0<∣m∣≤20<|m|\leq 2, the maximal submodule U(m)U(m) is {0}\{0\}, V(m)=VΛmV(m)=V^{\Lambda_m} is a direct summand of Fib(m){\mathcal F}ib(m), and

Fib(m)=VΛm⊕Y(m)−⊕Y(m)+.{\mathcal F}ib(m)=V^{\Lambda_m}\oplus Y(m)_-\oplus Y(m)_+.

The preceding proposition proves complete reducibility of the quotient Y(m)Y(m), while the conjecture supplies the missing assertion that the maximal submodule vanishes and that the non-standard irreducible module splits off from Fib(m){\mathcal F}ib(m).

References

Primary source

Diego Penta, “Decomposition of the rank 3 Kac-Moody Lie algebra F with respect to the rank 2 hyperbolic subalgebra Fib”, arXiv:1605.06901 (2016).

Additional references

2 papers in this index state this conjecture (2013–2016). The statement above is taken from the most recent of them; the others are arXiv:1304.3971.

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