Conjecture on the recursive coefficients in Boij–Söderberg decompositions

Let a1,,ac+1a_1,\ldots,a_{c+1} be the parameters and let aa, r1,,rεr_1,\ldots,r_\varepsilon, z1,,zεz_1,\ldots,z_\varepsilon, ysy_s, nn, and ε\varepsilon have the meanings from Theorem~. Assume

ac+1>max{a,r1z1,,rεzε}.a_{c+1} > \max\left\{a,\frac{r_1}{z_1},\ldots,\frac{r_\varepsilon}{z_\varepsilon}\right\}.

Recursive-coefficient conjecture. For ε<s<ε+c\varepsilon<s<\varepsilon+c, one has

ys=c!a1ac(ac+1i=1sn(ac+1iai)).y_s=c! \cdot a_1\cdots a_c \cdot \left(a_{c+1}-\sum_{i=1}^{s-n}(a_{c+1-i}-a_i)\right).

The conjecture gives an explicit formula for the coefficients in the second phase of the recursive algorithm. The paper reports that it holds in codimension at most 33, while the general case remains open.

Sources & referencesView supporting material

Primary source

Courtney R. Gibbons, Robert Huben and Branden Stone, “Recursive strategy for decomposing Betti tables of complete intersections”, arXiv:1708.05440 (2017).

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