Shokurov's toric equality conjecture for log canonical pairs

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Let XX be a normal Q\mathbb{Q}-factorial algebraic variety with a Q\mathbb{Q}-boundary divisor D=∑diDiD=\sum d_iD_i, where 0≤di≤10\leq d_i\leq 1 and the DiD_i are prime Weil divisors. Assume that −(KX+D)-(K_X+D) is nef and that the pair (X,D)(X,D) is log canonical. Shokurov's toric equality conjecture. The estimate

∑di≤rk⁡Pic⁡(X)+dim⁡X\sum d_i\leq \operatorname{rk}\operatorname{Pic}(X)+\dim X

holds. Moreover, equality is achieved if and only if (X,⌊D⌋)(X,\lfloor D\rfloor) is toric, meaning that XX is toric and ⌊D⌋\lfloor D\rfloor is its boundary. This gives a numerical criterion for recognizing toric varieties among log canonical pairs, but the supplied text does not state whether the claim has been resolved.

References

Primary source

Ilya Karzhemanov, “On one stable birational invariant”, arXiv:1307.5605 (2013).

Additional references

3 papers in this index state this conjecture (1999–2013). The statement above is taken from the most recent of them; the others are arXiv:math/0211336, arXiv:math/9912111.

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