Semiregularity conjecture for twisted coherent sheaves

Let π:MS\pi:{{{{{{{{\mathcal M}}}}}}}}\rightarrow S be a deformation of a smooth complex projective variety M0M_0 over a smooth germ (S,0)(S,0), and write Ms=π1(s)M_s=\pi^{-1}(s). Let B{{{{{{{{\mathcal B}}}}}}}} be a semiregular rank-rr coherent sheaf on M0M_0, twisted by a cocycle with coefficients in μr\mu_r. Assume that, for every pp, the class chp(B)ch_p({{{{{{{{\mathcal B}}}}}}}}) extends to a horizontal section of R2pπQR^{2p}\pi_*\mathbb Q lying in the direct summand RpπΩπpR^p\pi_*\Omega^p_\pi under the Hodge decomposition. Semiregularity conjecture. The sheaf B{{{{{{{{\mathcal B}}}}}}}} extends to a twisted coherent sheaf over π1(U)\pi^{-1}(U) for some open analytic neighborhood UU of 00 in SS. This is a twisted-sheaf analogue of a semiregularity theorem; the source says that it should follow from existing work, so the status of this formulation is left open here.

Sources & referencesView supporting material

Primary source

Eyal Markman, “Cycles on abelian 2n-folds of Weil type from secant sheaves on abelian n-folds”, arXiv:2502.03415 (2025).

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