Semihomogenous vector bundles, Q-twisted sheaves, duality, and linear systems on abelian varieties

In this paper we point out the natural relation between Q-twisted objects of the derived category of abelian varieties, cohomological rank functions, and semihomogeneous vector bundles. We apply this to two basic classes of corresponding objects via the Fourier-Mukai-Poincar\'e transform: positive twists of the ideal sheaf of one point, and evaluation complexes of ample semihomogeneous vector bundles. This leads to Q^ 0- graded section modules associated to line bundles on abelian varieties (containing the usual section rings), built by means of semihomogeneous vector bundles. We prove a duality relation between such section modules associated to dual polarizations. Other applications include formulas relating the thresholds of relevant cohomological rank functions appearing in this context. As a consequence we produce non-trivial obstructions to surjectivity of multiplication maps of global sections of certain line bundles.