Monotonicity conjecture for the regularity of graph-power edge ideals

Let GG be a simple graph on vertex set V(G)=[n]V(G)=[n], let R=k[x1,,xn]R=\Bbbk[x_1,\ldots,x_n], and let I(Gd)I(G^d) be the edge ideal of the dd-th power of GG, where dd is a positive integer. The Castelnuovo–Mumford regularity is denoted by reg\operatorname{reg}. Monotonicity conjecture. For every simple graph GG and every positive integer dd,

reg(R/I(Gd))reg(R/I(Gd+1)).\operatorname{reg}\left(R/I(G^d)\right)\geq \operatorname{reg}\left(R/I(G^{d+1})\right).

The conjecture proposes that the regularity of edge ideals of successive graph powers is weakly decreasing. The paper proves this behavior for powers of forests and computes the regularity for powers of cycles, while the assertion for arbitrary simple graphs is suggested based on computations.

Sources & referencesView supporting material

Primary source

My Hanh Pham and Thanh Vu, “Regularity of edge ideals of powers of graphs”, arXiv:2502.05126 (2025).

Additional references

3 papers in this index state this conjecture (2004–2025). The statement above is taken from the most recent of them; the others are arXiv:2107.10781, arXiv:math/0406024.

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