AbstractVarieties, if they are at all complicated, are expected to have very few rational points. This might mean “there are only finitely many rational points” or “the rational points are contained in a proper closed subvariety.” Statements like these are extremely difficult to prove in any degree of generality, with Faltings’ finiteness theorem for rational points on high-genus curves a ...
Abstract Sheaves on non-reduced curves can appear in moduli spaces of 1-dimensional semistable sheaves over a surface, and moduli spaces of Higgs bundles as well. We estimate the dimension of the stack M_X(nC, \chi) of pure sheaves supported at the non-reduced curve nC (n ≥ 2) with C an integral curve on X. We prove that the Hilbert-Chow morphism h_{L,\chi} : M_X^H(L, \chi) -> |L| sending each...