Cycle depth formula conjecture for square-free powers

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Let CnC_n be a cycle of length nn, let I(Cn)I(C_n) be its edge ideal in the corresponding polynomial ring R=K[x∣x∈V(Cn)]R=\mathbb{K}[x\mid x\in V(C_n)], and let ν(Cn)\nu(C_n) denote its matching number. Cycle depth conjecture. For the indicated values of kk,

depth(R/I(Cn)[k])={⌈n3⌉+k−1if k=2,…,⌈n3⌉,2k−1if k=⌈n3⌉+1,…,ν(Cn).\mathrm{depth}(R/I(C_n)^{[k]})=\begin{cases}\left\lceil\frac{n}{3}\right\rceil+k-1 & \text{if } k=2,\ldots,\left\lceil\frac{n}{3}\right\rceil,\\ 2k-1 & \text{if } k=\left\lceil\frac{n}{3}\right\rceil+1,\ldots,\nu(C_n).\end{cases}

The cases k=1k=1, k=2k=2, and k=ν(Cn)k=\nu(C_n) are known in the source, and the case k=ν(Cn)−1k=\nu(C_n)-1 is established for cycles of even length; the conjecture was verified computationally up to n=15n=15, while the remaining cases are open.

References

Primary source

Kanoy Kumar Das, Amit Roy and Kamalesh Saha, “Square-free powers of Cohen-Macaulay forests, cycles, and whiskered cycles”, arXiv:2409.06021 (2024).

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