Improved lower-bound conjecture for Hilbert–Kunz multiplicities

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Let (A,m,k)(A,\mathfrak{m}, k) be a formally unmixed non-regular local ring of dimension d≥1d \geq 1 with algebraically closed residue field. Let m≥1m \geq 1 be an integer, and let Ap,dA_{p,d} be the simple singularity defined above. Improved lower-bound conjecture. If d=2m−1d=2m-1, then either

A^≅Ap,d\widehat{A}\cong A_{p,d}

or

eHK⁡(A)>2m2m−1.\operatorname{e_{HK}}(A)>\frac{2^m}{2^m-1}.

If d=2md=2m, then either

A^≅Ap,d\widehat{A}\cong A_{p,d}

or

eHK⁡(A)>2m+12m.\operatorname{e_{HK}}(A)>\frac{2^m+1}{2^m}.

This strengthens the proposed universal lower bounds suggested by the known formulas in characteristic two. It is presented as an improvement of the preceding conjecture and remains open in general.

References

Primary source

Jack Jeffries, Yusuke Nakajima, Ilya Smirnov, Kei-ichi Watanabe and Ken-ichi Yoshida, “Lower bounds on Hilbert–Kunz multiplicities and maximal F-signatures”, arXiv:2002.06166 (2022).

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