The Stratified Strong Maximal Rank Conjecture for quadrics of bounded rank

Fix positive integers g,r,dg,r,d with r3r\geq 3 and ρ(g,r,d)0\rho(g,r,d)\geq 0, and let CC be a general curve of genus gg. For a linear series =(L,V)Gdr(C)\ell=(L,V)\in G^r_d(C), let Σk(C,)P(Sym2V)\Sigma_k(C,\ell)\subset\mathbb{P}(\operatorname{Sym}^2V) be the variety of quadric forms of rank at most kk lying in Pker(ν())\mathbb{P}\ker(\nu(\ell)), where

ν():Sym2VH0(C,L2)\nu(\ell):\operatorname{Sym}^2V\to H^0(C,L^2)

and

q(g,r,d,k)=max{1,(r+22)(rk+22)(2d+2g)}.q(g,r,d,k)=\max\left\{-1,\binom{r+2}{2}-\binom{r-k+2}{2}-(2d+2-g)\right\}.

Here 3kr+13\leq k\leq r+1, and dimension 1-1 denotes an empty locus. Stratified Strong Maximal Rank Conjecture. The degeneracy locus

Qd,kr(C)={Gdr(C)dimΣk(C,)>q(g,r,d,k)}Q^r_{d,k}(C)=\left\{\ell\in G^r_d(C)\mid \dim\Sigma_k(C,\ell)>q(g,r,d,k)\right\}

has dimension

dimQd,kr(C)=ρ(g,r,d)1(r+22)(rk+22)(2d+1g)=:β(g,r,d,k).\dim Q^r_{d,k}(C)=\rho(g,r,d)-1-\left|\binom{r+2}{2}-\binom{r-k+2}{2}-(2d+1-g)\right|=:\beta(g,r,d,k).

The conjecture refines the Strong Maximal Rank Conjecture by stratifying according to the rank of the quadrics. Under the additional assumption rd+g1r-d+g\leq 1, the source cites a result proving that Σk(C,)\Sigma_k(C,\ell) has the expected dimension for general \ell; the behavior over the degeneracy locus for all linear series remains the proposed problem.

Sources & referencesView supporting material

Primary source

Vlad Robu, “The Stratified and the Strong Maximal Rank Conjecture in P^3 and P^4”, arXiv:2605.24612 (2026).

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